warn when a handler didn't complete its job

issue #16 for some reason I couldn't get it to work it looked like the options weren't properly parsed
include strerror(errno) in error messages
2025-07-06 17:47:51 +02:00 · 2016-05-02 18:09:14 +02:00 · 2016-05-02 18:09:02 +02:00 · 2016-04-08 16:15:28 +02:00 · 2016-04-08 16:14:31 +02:00 · 2016-04-08 16:02:40 +02:00
56 changed files with 3108 additions and 670 deletions
--- a/.gitignore
+++ b/.gitignore
@ -0,0 +1,3 @@
+/build
+tests/catch.h
+src/version.h
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@ -0,0 +1,78 @@
+cmake_minimum_required (VERSION 2.8.8)
+project (opustags)
+set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD_REQUIRED on)
+set(CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/modules/")
+set(CMAKE_SOURCE_DIR "${CMAKE_BINARY_DIR}/../")
+
+# ------------
+# Dependencies
+# ------------
+find_package(Ogg REQUIRED)
+include_directories(${Ogg_INCLUDE_DIR})
+link_directories(${Ogg_LIBRARY_DIRS})
+
+# --------------------
+# Global build options
+# --------------------
+if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wextra")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pedantic")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wold-style-cast")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-parameter")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14") # for MinGW-w64
+endif()
+
+# -------
+# Version
+# -------
+execute_process(COMMAND git describe --tags --abbrev=0 OUTPUT_VARIABLE VERSION_SHORT OUTPUT_STRIP_TRAILING_WHITESPACE)
+execute_process(COMMAND git describe --always --dirty --long --tags OUTPUT_VARIABLE VERSION_LONG OUTPUT_STRIP_TRAILING_WHITESPACE)
+if("${VERSION_SHORT}" STREQUAL "")
+    set(VERSION_SHORT "0.0")
+    set(VERSION_LONG "?")
+endif()
+configure_file("${CMAKE_SOURCE_DIR}/src/version.h.in" "${CMAKE_SOURCE_DIR}/src/version.h" @ONLY)
+
+# ------------
+# Source files
+# ------------
+file(GLOB_RECURSE common_sources "${CMAKE_SOURCE_DIR}/src/*.cc")
+file(GLOB_RECURSE common_headers "${CMAKE_SOURCE_DIR}/src/*.h")
+file(GLOB_RECURSE test_sources "${CMAKE_SOURCE_DIR}/tests/*.cc")
+file(GLOB_RECURSE test_headers "${CMAKE_SOURCE_DIR}/tests/*.h")
+list(REMOVE_ITEM common_sources "${CMAKE_SOURCE_DIR}/src/main.cc")
+list(REMOVE_ITEM test_sources "${CMAKE_SOURCE_DIR}/tests/main.cc")
+
+# -------------------
+# 3rd party libraries
+# -------------------
+# Catch
+set(CATCH_PATH "${CMAKE_SOURCE_DIR}/tests/catch.h")
+if (NOT EXISTS "${CATCH_PATH}")
+    message("Downloading Catch...")
+    file(DOWNLOAD "http://raw.githubusercontent.com/philsquared/Catch/master/single_include/catch.hpp" "${CATCH_PATH}")
+endif()
+
+# ------------
+# Installation
+# ------------
+install(FILES ${CMAKE_SOURCE_DIR}/doc/opustags.1 DESTINATION ${CMAKE_INSTALL_PREFIX}/man/man1)
+install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/opustags DESTINATION ${CMAKE_INSTALL_PREFIX}/bin)
+add_custom_target(uninstall COMMAND
+    rm -f "${CMAKE_INSTALL_PREFIX}/man/man1/opustags.1" &&
+    rm -f "${CMAKE_INSTALL_PREFIX}/bin/opustags" )
+
+# -------------------
+# Linking definitions
+# -------------------
+add_library(common OBJECT ${common_sources} ${common_headers})
+add_executable(opustags "${CMAKE_SOURCE_DIR}/src/main.cc" $<TARGET_OBJECTS:common>)
+add_executable(run_tests "${CMAKE_SOURCE_DIR}/tests/main.cc" $<TARGET_OBJECTS:common> ${test_sources} ${test_headers})
+target_link_libraries(opustags ${OGG_LIBRARY})
+target_link_libraries(run_tests ${OGG_LIBRARY})
+target_include_directories(common BEFORE PUBLIC "${CMAKE_SOURCE_DIR}/src")
+target_include_directories(opustags BEFORE PUBLIC "${CMAKE_SOURCE_DIR}/src")
+target_include_directories(run_tests BEFORE PUBLIC "${CMAKE_SOURCE_DIR}/src")
+target_include_directories(run_tests BEFORE PUBLIC "${CMAKE_SOURCE_DIR}/tests")
--- a/23
+++ b/23
@ -1,23 +0,0 @@
-DESTDIR=/usr/local
-MANDEST=share/man
-CFLAGS=-Wall
-LDFLAGS=-logg
-
-all: opustags
-
-opustags: opustags.c
-
-man: opustags.1
-	gzip <opustags.1 >opustags.1.gz
-
-install: opustags man
-	mkdir -p $(DESTDIR)/bin $(DESTDIR)/$(MANDEST)/man1
-	install -m 755 opustags $(DESTDIR)/bin/
-	install -m 644 opustags.1.gz $(DESTDIR)/$(MANDEST)/man1/
-
-uninstall:
-	rm -f $(DESTDIR)/bin/opustags
-	rm -f $(DESTDIR)/$(MANDEST)/man1/opustags.1.gz
-
-clean:
-	rm -f opustags opustags.1.gz
--- a/README.md
+++ b/README.md
@ -3,53 +3,43 @@ opustags

 View and edit Opus comments.

-**Please note this project is old and not actively maintained.**
-Maybe you should use something else.
-
-It was built because at the time nothing supported Opus, but now things have
-changed for the better.
-
-For alternative, check out these projects:
-
- [EasyTAG](https://wiki.gnome.org/Apps/EasyTAG)
- [Beets](http://beets.io/)
- [Picard](https://picard.musicbrainz.org/)
- [puddletag](http://docs.puddletag.net/)
- [Quod Libet](https://quodlibet.readthedocs.io/en/latest/)
- [Goggles Music Manager](https://gogglesmm.github.io/)
-
-See also these libraries if you need a lower-level access:
-
- [TagLib](http://taglib.org/)
- [mutagen](https://mutagen.readthedocs.io/en/latest/)
-
 Requirements
 ------------

 * A POSIX-compliant system,
-* libogg.
+* `libogg`.

 Installing
 ----------

+    mkdir build && cd build
+    cmake ..
    make
-    make DESTDIR=/usr/local install
+    make install

 Documentation
 -------------

    Usage: opustags --help
-           opustags [OPTIONS] FILE
-           opustags OPTIONS FILE -o FILE
+           opustags [OPTIONS] INPUT
+           opustags [OPTIONS] -o OUTPUT INPUT

    Options:
      -h, --help              print this help
-      -o, --output            write the modified tags to a file
+      -V, --version           print version
+      -o, --output FILE       write the modified tags to this file
+      -i, --in-place [SUFFIX] use a temporary file then replace the original file
      -y, --overwrite         overwrite the output file if it already exists
+          --stream ID         select stream for the next operations
+      -l, --list              display a pretty listing of all tags
+          --no-color          disable colors in --list output
      -d, --delete FIELD      delete all the fields of a specified type
      -a, --add FIELD=VALUE   add a field
      -s, --set FIELD=VALUE   delete then add a field
      -D, --delete-all        delete all the fields!
-      -S, --set-all           read the fields from stdin
+          --full              enable full file scan
+          --export            dump the tags to standard output for --import
+          --import            set the tags from scratch basing on stanard input
+      -e, --edit              spawn the $EDITOR and apply --import on the result

 See the man page, `opustags.1`, for extensive documentation.
--- a/doc/opustags.1
+++ b/doc/opustags.1
@ -0,0 +1,209 @@
+.TH opustags 1 "2016"
+.SH NAME
+opustags \- Opus comment editor
+.SH SYNOPSIS
+.B opustags \-\-help
+.br
+.B opustags
+.RI [ OPTIONS ]
+.I INPUT
+.br
+.B opustags
+.RI [ OPTIONS ]
+.B \-o
+.I OUTPUT INPUT
+.SH DESCRIPTION
+.PP
+\fBopustags\fP can read and edit the comment header of an Opus file.
+It has two modes of operation: read\-only for tag listing, and read\-write for
+tag edition.
+.PP
+Edition mode is triggered by the \fB\-\-ouput\fP and \fB\-\-in\-place\fP
+options. Otherwise, the default mode is listing.
+.PP
+Edition options are incompatible in listing mode, the same way as listing
+options are incompatible in edition mode.
+.PP
+\fIINPUT\fP can either be the name of a file or \fB\-\fP to read from standard input.
+.SS Listing
+.PP
+In listing mode, the tags are printed on standard output. Two listing formats
+are available: pretty and raw. By default, pretty listing is implied if the
+output is a terminal, and raw listing if it isn't.
+.PP
+Pretty listing is enabled with the option \fB\-\-list\fP. Colors are enabled
+unless you use the \fB\-\-no\-color\fP option.
+.PP
+Dumping with \fB\-\-export\fP outputs the raw tags in UTF-8, for automatic
+processing. You can restore exported tags with the \fB\-\-import\fP option.
+.SS Editing
+.PP
+As for the edition mode, you need to specify an output file (or \fB\-\fP for
+standard output). It must be different from the input file. You may want to
+use \fB\-\-overwrite\fP if you know what you're doing. To overwrite the input
+file, use \fB\-\-in\-place\fP.
+.PP
+Tag edition is done with the \fB\-\-add\fP, \fB\-\-delete\fP and \fB\-\-set\fP
+options. You can use these options as many times as you wish.
+.PP
+You can delete all the tags with \fB\-\-delete\-all\fP. This operation can be
+combined with \fB\-\-add\fP to set new tags without being bothered by the old
+ones.
+.PP
+If you want to process tags yourself, you can use the \fB\-\-import\fP option
+which will cause \fBopustags\fP to read tags from standard input. The format
+is the same as the one used for output with \fB\-\-export\fP.
+Note that this option implies \fB\-\-delete\-all\fP.
+Also, input is read as UTF-8.
+.PP
+You can use \fB\-\-edit\fP to spawn your \fBEDITOR\fP and edit the tags
+interactively. In read\-write mode, if no other option is specified, this one
+is implied.
+.SS Stream Selection
+.PP
+In case an Ogg file contains multiple streams, the \fB\-\-stream\fP option lets
+you specify the particular streams to modify. You can modify several streams in
+different ways by using this option more than once. Only operations specified
+after this option and relevant, and until another \fB\-\-stream\fP option is
+found.
+.PP
+	opustags \-\-stream 1 \-\-stream 2 \-\-list # BAD
+.PP
+The above command would only show the second stream. To display both streams,
+use instead:
+.PP
+	opustags \-\-stream 1,2 \-\-list
+.PP
+See also the examples at the end of this page, and the documentation of the
+\fB\-\-stream\fP option.
+.PP
+You can easily find the id's of the available streams by calling opustags with
+no options to list the tags. Usually, you'll only have one stream, id 1.
+.SH OPTIONS
+.SS General
+.TP
+.B \-h, \-\-help
+Display a brief description of the options.
+.TP
+.B \-V, \-\-version
+Display the version of opustags.
+.TP
+.B \-\-stream \fIID\fP
+Specify the stream that will be affected by the options following it. The
+special id \fBall\fP selects all the Opus streams found, and is the default
+value.
+.sp
+The identifer of a stream is determined from its position in the file. The
+first stream found will have id 1, the second 2, and so on.
+.sp
+You can select more than one stream with this option by separated id's with commas. For example: \-\-stream 1,3. Ranges are not supported.
+.sp
+In edition mode, this option should be set if the input file contains more than
+one Opus stream, otherwise a warning is generated. If in\-place modification is
+selected, this warning becomes a fatal error.
+.SS Listing
+.TP
+.B \-l, \-\-list
+Display a pretty listing of all the tags found. This is the default option in
+read\-only mode if the standard output is a terminal.
+.TP
+.B \-\-no\-color
+By default, when listing tags with \fB\-\-list\fP, colors are used. Use this
+option to disable it.
+.TP
+.B \-\-export
+Dump the tags on standard output in a format compatible with \fB\-\-import\fP.
+If only one stream is specified, the output format is compatible with other
+tools such as vorbiscomment.
+.sp
+When exporting, output is encoded in UTF\-8 in
+order not to lose information.
+.TP
+.B \-\-full
+For performance reasons, only the beginning of the input is read, because
+that's where tags are expected. If, however, you think you have an
+unconventional file and you suspect that opustags is missing some streams, you
+can use this option to force it to read the whole file.
+.sp
+This option shouldn't be needed, but if you do find files that require this
+option, please submit a bug report (see the bottom of the page).
+.SS Edition
+.TP
+.B \-o, \-\-output \fIFILE\fI
+Edition mode. The input file will be read, its tags edited, then written to the
+specified output file. If \fIFILE\fP is \fB\-\fP then the resulting Opus file
+will be written to standard output. The output file can't be the same as the
+input file, use \fB\-\-in\-place\fP instead. This option may be specified at
+most once.
+.TP
+.B \-i, \-\-in\-place \fR[\fP\fISUFFIX\fP\fR]\fP
+Use this when you want to modify the input file in\-place. This creates a
+temporary file with the specified suffix (\fI.otmp\fP by default). This implies
+\fB\-\-overwrite\fP in that if a file with the same temporary name already
+exists, it will be overwritten without warning. Of course, this overwrites the
+input file too. You cannot use this option when the input file is the standard
+input.
+.TP
+.B \-y, \-\-overwrite
+By default, opustags refuses to overwrite an already existent file. Use
+this option to allow that.
+.TP
+.B \-d, \-\-delete \fIFIELD\fP
+Delete all the tags whose field name is \fIFIELD\fP. Note that one tag key,
+like \fIARTIST\fP, may appear more than once, in which case all of those are
+deleted.
+.TP
+.B \-a, \-\-add \fIFIELD=VALUE\fP
+Add a tag. It doesn't matter if a tag of the same type already exist (think
+about the case where there are several artists).
+.TP
+.B \-s, \-\-set \fIFIELD=VALUE\fP
+This option is provided for convenience. It deletes all the fields of the same
+type that may already exist, then adds it with the wanted value. This is
+strictly equivalent to \fB\-\-delete\fP \fIFIELD\fP \fB\-\-add\fP
+\fIFIELD=VALUE\fP.
+You can combine it with \fB\-\-add\fP to add more tags with that same \fIFIELD\fP.
+.TP
+.B \-D, \-\-delete\-all
+Delete all the tags before adding any.
+.TP
+.B \-\-import
+Set the tags from scratch. All the original tags are deleted and new ones are
+read from standard input.
+.sp
+Each line must specify a \fIFIELD=VALUE\fP pair and be LF\-terminated (except
+for the last line). Invalid lines are skipped and issue a warning. Blank lines
+are ignored. Lines whose first non-blank character is \fB#\fP are ignored.
+Blank characters at the beginning of a line are also skipped.
+.sp
+Input is read as UTF\-8, disregarding the current locale of your system.
+.TP
+.B \-e, \-\-edit
+Spawn the program specified in the environment variable \fBEDITOR\fP to edit
+tags interactively. If this variable can't be read or is empty, an error
+message is displayed.
+.sp
+The expected format is the same as the one \fB\-\-import\fP expects.
+.SH EXAMPLES
+Here's how you would list all tags in a stream:
+.PP
+	opustags in.ogg
+.PP
+Here's how you would edit two streams at once, setting the title and artist of
+the first, and only the title of the second:
+.PP
+	opustags \-\-stream 1 \-\-set TITLE=X \-\-set ARTIST=Y \-\-stream 2 \-\-set TITLE=Y in.ogg \-o out.ogg
+.PP
+Here's how you would set two artists:
+.PP
+	opustags \-\-delete ARTIST \-\-add ARTIST=A \-\-add ARTIST=B in.ogg \-o out.ogg
+.PP
+Hoping that helped!
+.SH SEE ALSO
+.BR vorbiscomment (1),
+.BR sed (1)
+.SH AUTHORS
+Frédéric Mangano <fmang+opustags@mg0.fr>,
+rr\- <https://github.com/rr\->.
+.PP
+Please report issues on GitHub at <https://github.com/fmang/opustags/issues>.
--- a/modules/FindOgg.cmake
+++ b/modules/FindOgg.cmake
@ -0,0 +1,23 @@
+# Base Io build system
+# Written by Jeremy Tregunna <jeremy.tregunna@me.com>
+#
+# Find libogg.
+
+FIND_PATH(OGG_INCLUDE_DIR ogg/ogg.h)
+
+SET(OGG_NAMES ${OGG_NAMES} ogg libogg)
+FIND_LIBRARY(OGG_LIBRARY NAMES ${OGG_NAMES} PATH)
+
+IF(OGG_INCLUDE_DIR AND OGG_LIBRARY)
+	SET(OGG_FOUND TRUE)
+ENDIF(OGG_INCLUDE_DIR AND OGG_LIBRARY)
+
+IF(OGG_FOUND)
+	IF(NOT Ogg_FIND_QUIETLY)
+		MESSAGE(STATUS "Found Ogg: ${OGG_LIBRARY}")
+	ENDIF (NOT Ogg_FIND_QUIETLY)
+ELSE(OGG_FOUND)
+	IF(Ogg_FIND_REQUIRED)
+		MESSAGE(FATAL_ERROR "Could not find ogg")
+	ENDIF(Ogg_FIND_REQUIRED)
+ENDIF (OGG_FOUND)
--- a/opustags.1
+++ b/opustags.1
@ -1,108 +0,0 @@
-.TH opustags 1 "January 2013"
-.SH NAME
-opustags \- Opus comment editor
-.SH SYNOPSIS
-.B opustags --help
-.br
-.B opustags
-.RI [ OPTIONS ]
-.I INPUT
-.br
-.B opustags
-.I OPTIONS
-.B -o
-.I OUTPUT INPUT
-.SH DESCRIPTION
-.PP
-\fBopustags\fP can read and edit the comment header of an Opus file.
-It basically has two modes: read-only and read-write (for tag edition).
-.PP
-In read-only mode, only the beginning of \fIINPUT\fP is read, and the tags are
-printed on \fBstdout\fP.
-\fIINPUT\fP can either be the name of a file or \fB-\fP to read from \fBstdin\fP.
-You can use the options below to edit the tags before printing them.
-This could be useful to preview some changes before writing them.
-.PP
-As for the edition mode, you need to specify an output file (or \fB-\fP for
-\fBstdout\fP). It must be different from the input file.
-You may want to use \fB--overwrite\fP if you know what you’re doing.
-To overwrite the input file, use \fB--in-place\fP.
-.PP
-Tag edition can be made with the \fB--add\fP, \fB--delete\fP and \fB--set\fP
-options. They can be written in any order and don’t conflict with each other.
-However, they aren’t executed in any order: first the specified tags are
-deleted, then the new tags are added. “Set” operations are mere convenience
-for delete/add.
-.PP
-You can delete all the tags with \fB--delete-all\fP. This operation can be
-combined with \fB--add\fP to set new tags without being bothered by the old
-ones. Another way to do this is to use \fB--set-all\fP as explained below.
-.PP
-If you want to process tags yourself, you can use the \fB--set-all\fP option
-which will cause \fBopustags\fP to read tags from \fBstdin\fP.
-The format is the same as the one used for output; that is to say,
-newline-separated \fIFIELD=Value\fP assignment. Note that this implies
-\fB--delete-all\fP.
-.PP
-\fBWarning:\fP the Opus format specifications requires tags to be encoded in
-\fBUTF-8\fP. This tool ignores the system locale, assuming the encoding is
-set to UTF-8, and assume that tags are already encoded in UTF-8.
-.SH OPTIONS
-.TP
-.B \-h, \-\-help
-Display a brief description of the options.
-.TP
-.B \-o, \-\-output \fIFILE\fI
-Edition mode. The input file will be read, its tags edited, then written to the
-specified output file. If \fIFILE\fP is \fB-\fP then the resulting Opus file
-will be written to \fBstdout\fP. As the input file is read incrementally, the
-output file can’t be the same as the input file.
-.TP
-.B \-i, \-\-in-place \fR[\fP\fISUFFIX\fP\fR]\fP
-Use this when you want to modify the input file in-place. This creates a
-temporary file with the specified suffix (.otmp by default). This implies
-\fB--overwrite\fP in that if a file with the same temporary name already
-exists, it will be overwritten without warning. Of course, this overwrites
-the input file too. You cannot use this option when the input file is actually
-\fBstdin\fP.
-.TP
-.B \-y, \-\-overwrite
-By default, \fBopustags\fP refuses to overwrite an already existent file. Use
-this option to allow that. Note that this doesn’t allow in-place edition, the
-output file needs to be different from the input file.
-.TP
-.B \-d, \-\-delete \fIFIELD\fP
-Delete all the tags whose field name is \fIFIELD\fP (they may be several, though
-usually there is only one of each type). You can use this option as many times
-as you want.
-.TP
-.B \-a, \-\-add \fIFIELD=VALUE\fP
-Add a tag. It doesn’t matter if a tag of the same type already exist (think
-the case where there are several artists). You can use this option as many
-times as needed, with the same field names or not. When the \fB--delete\fP
-is used with the same \fIFIELD\fP, only the older tags are deleted.
-.TP
-.B \-s, \-\-set \fIFIELD=VALUE\fP
-This option is provided for convenience. It delete all the fields of the same
-type that may already exist, then adds it with the wanted value.
-This is strictly equivalent to \fB--delete\fP \fIFIELD\fP \fB--add\fP
-\fIFIELD=VALUE\fP. You can combine it with \fB--add\fP to add tags of the same
-type. As deletion occurs before adding, \fB--set\fP won’t erase the tags
-added with \fB--add\fP.
-.TP
-.B \-D, \-\-delete-all
-Delete all the tags before adding any. When this option is specified, the
-\fB--delete\fP options are ignored. Tags then can be added using \fB--add\fP
-or \fB--set\fP, which, in that case, are equivalent.
-.TP
-.B \-S, \-\-set-all
-Sets the tags from scratch. All the original tags are deleted and new ones are
-read from \fBstdin\fP. Each line must specify a \fIFIELD=VALUE\fP pair and be
-LF-terminated (except for the last line). Invalid lines are skipped and cause
-a warning to be issued. Blank lines are ignored. This mode could be useful for
-batch processing tags through an utility like \fBsed\fP.
-.SH SEE ALSO
-.BR vorbiscomment (1),
-.BR sed (1)
-.SH AUTHOR
-Frédéric Mangano <fmang@mg0.fr>
--- a/opustags.c
+++ b/opustags.c
@ -1,513 +0,0 @@
-#include <errno.h>
-#include <getopt.h>
-#include <limits.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-#include <ogg/ogg.h>
-
-#ifdef __APPLE__
-#include <libkern/OSByteOrder.h>
-#define htole32(x) OSSwapHostToLittleInt32(x)
-#define le32toh(x) OSSwapLittleToHostInt32(x)
-#endif
-
-typedef struct {
-    uint32_t vendor_length;
-    const char *vendor_string;
-    uint32_t count;
-    uint32_t *lengths;
-    const char **comment;
-} opus_tags;
-
-int parse_tags(char *data, long len, opus_tags *tags){
-    long pos;
-    if(len < 8+4+4)
-        return -1;
-    if(strncmp(data, "OpusTags", 8) != 0)
-        return -1;
-    // Vendor
-    pos = 8;
-    tags->vendor_length = le32toh(*((uint32_t*) (data + pos)));
-    tags->vendor_string = data + pos + 4;
-    pos += 4 + tags->vendor_length;
-    if(pos + 4 > len)
-        return -1;
-    // Count
-    tags->count = le32toh(*((uint32_t*) (data + pos)));
-    if(tags->count == 0)
-        return 0;
-    tags->lengths = calloc(tags->count, sizeof(uint32_t));
-    if(tags->lengths == NULL)
-        return -1;
-    tags->comment = calloc(tags->count, sizeof(char*));
-    if(tags->comment == NULL){
-        free(tags->lengths);
-        return -1;
-    }
-    pos += 4;
-    // Comment
-    uint32_t i;
-    for(i=0; i<tags->count; i++){
-        tags->lengths[i] = le32toh(*((uint32_t*) (data + pos)));
-        tags->comment[i] = data + pos + 4;
-        pos += 4 + tags->lengths[i];
-        if(pos > len)
-            return -1;
-    }
-
-    if(pos < len)
-        fprintf(stderr, "warning: %ld unused bytes at the end of the OpusTags packet\n", len - pos);
-
-    return 0;
-}
-
-int render_tags(opus_tags *tags, ogg_packet *op){
-    // Note: op->packet must be manually freed.
-    op->b_o_s = 0;
-    op->e_o_s = 0;
-    op->granulepos = 0;
-    op->packetno = 1;
-    long len = 8 + 4 + tags->vendor_length + 4;
-    uint32_t i;
-    for(i=0; i<tags->count; i++)
-        len += 4 + tags->lengths[i];
-    op->bytes = len;
-    char *data = malloc(len);
-    if(!data)
-        return -1;
-    op->packet = (unsigned char*) data;
-    uint32_t n;
-    memcpy(data, "OpusTags", 8);
-    n = htole32(tags->vendor_length);
-    memcpy(data+8, &n, 4);
-    memcpy(data+12, tags->vendor_string, tags->vendor_length);
-    data += 12 + tags->vendor_length;
-    n = htole32(tags->count);
-    memcpy(data, &n, 4);
-    data += 4;
-    for(i=0; i<tags->count; i++){
-        n = htole32(tags->lengths[i]);
-        memcpy(data, &n, 4);
-        memcpy(data+4, tags->comment[i], tags->lengths[i]);
-        data += 4 + tags->lengths[i];
-    }
-    return 0;
-}
-
-int match_field(const char *comment, uint32_t len, const char *field){
-    size_t field_len;
-    for(field_len = 0; field[field_len] != '\0' && field[field_len] != '='; field_len++);
-    if(len <= field_len)
-        return 0;
-    if(comment[field_len] != '=')
-        return 0;
-    if(strncmp(comment, field, field_len) != 0)
-        return 0;
-    return 1;
-
-}
-
-void delete_tags(opus_tags *tags, const char *field){
-    uint32_t i;
-    for(i=0; i<tags->count; i++){
-        if(match_field(tags->comment[i], tags->lengths[i], field)){
-            tags->count--;
-            tags->lengths[i] = tags->lengths[tags->count];
-            tags->comment[i] = tags->comment[tags->count];
-            // No need to resize the arrays.
-        }
-    }
-}
-
-int add_tags(opus_tags *tags, const char **tags_to_add, uint32_t count){
-    if(count == 0)
-        return 0;
-    uint32_t *lengths = realloc(tags->lengths, (tags->count + count) * sizeof(uint32_t));
-    const char **comment = realloc(tags->comment, (tags->count + count) * sizeof(char*));
-    if(lengths == NULL || comment == NULL)
-        return -1;
-    tags->lengths = lengths;
-    tags->comment = comment;
-    uint32_t i;
-    for(i=0; i<count; i++){
-        tags->lengths[tags->count + i] = strlen(tags_to_add[i]);
-        tags->comment[tags->count + i] = tags_to_add[i];
-    }
-    tags->count += count;
-    return 0;
-}
-
-void print_tags(opus_tags *tags){
-    if(tags->count == 0)
-        puts("no tags");
-    int i;
-    for(i=0; i<tags->count; i++){
-        fwrite(tags->comment[i], 1, tags->lengths[i], stdout);
-        puts("");
-    }
-}
-
-void free_tags(opus_tags *tags){
-    if(tags->count > 0){
-        free(tags->lengths);
-        free(tags->comment);
-    }
-}
-
-int write_page(ogg_page *og, FILE *stream){
-    if(fwrite(og->header, 1, og->header_len, stream) < og->header_len)
-        return -1;
-    if(fwrite(og->body, 1, og->body_len, stream) < og->body_len)
-        return -1;
-    return 0;
-}
-
-const char *version = "opustags version 1.1.1\n";
-
-const char *usage =
-    "Usage: opustags --help\n"
-    "       opustags [OPTIONS] FILE\n"
-    "       opustags OPTIONS FILE -o FILE\n";
-
-const char *help =
-    "Options:\n"
-    "  -h, --help              print this help\n"
-    "  -o, --output            write the modified tags to a file\n"
-    "  -i, --in-place [SUFFIX] use a temporary file then replace the original file\n"
-    "  -y, --overwrite         overwrite the output file if it already exists\n"
-    "  -d, --delete FIELD      delete all the fields of a specified type\n"
-    "  -a, --add FIELD=VALUE   add a field\n"
-    "  -s, --set FIELD=VALUE   delete then add a field\n"
-    "  -D, --delete-all        delete all the fields!\n"
-    "  -S, --set-all           read the fields from stdin\n";
-
-struct option options[] = {
-    {"help", no_argument, 0, 'h'},
-    {"output", required_argument, 0, 'o'},
-    {"in-place", optional_argument, 0, 'i'},
-    {"overwrite", no_argument, 0, 'y'},
-    {"delete", required_argument, 0, 'd'},
-    {"add", required_argument, 0, 'a'},
-    {"set", required_argument, 0, 's'},
-    {"delete-all", no_argument, 0, 'D'},
-    {"set-all", no_argument, 0, 'S'},
-    {NULL, 0, 0, 0}
-};
-
-int main(int argc, char **argv){
-    if(argc == 1){
-        fputs(version, stdout);
-        fputs(usage, stdout);
-        return EXIT_SUCCESS;
-    }
-    char *path_in, *path_out = NULL, *inplace = NULL;
-    const char* to_add[argc];
-    const char* to_delete[argc];
-    int count_add = 0, count_delete = 0;
-    int delete_all = 0;
-    int set_all = 0;
-    int overwrite = 0;
-    int print_help = 0;
-    int c;
-    while((c = getopt_long(argc, argv, "ho:i::yd:a:s:DS", options, NULL)) != -1){
-        switch(c){
-            case 'h':
-                print_help = 1;
-                break;
-            case 'o':
-                path_out = optarg;
-                break;
-            case 'i':
-                inplace = optarg == NULL ? ".otmp" : optarg;
-                break;
-            case 'y':
-                overwrite = 1;
-                break;
-            case 'd':
-                if(strchr(optarg, '=') != NULL){
-                    fprintf(stderr, "invalid field: '%s'\n", optarg);
-                    return EXIT_FAILURE;
-                }
-                to_delete[count_delete++] = optarg;
-                break;
-            case 'a':
-            case 's':
-                if(strchr(optarg, '=') == NULL){
-                    fprintf(stderr, "invalid comment: '%s'\n", optarg);
-                    return EXIT_FAILURE;
-                }
-                to_add[count_add++] = optarg;
-                if(c == 's')
-                    to_delete[count_delete++] = optarg;
-                break;
-            case 'S':
-                set_all = 1;
-            case 'D':
-                delete_all = 1;
-                break;
-            default:
-                return EXIT_FAILURE;
-        }
-    }
-    if(print_help){
-        puts(version);
-        puts(usage);
-        puts(help);
-        puts("See the man page for extensive documentation.");
-        return EXIT_SUCCESS;
-    }
-    if(optind != argc - 1){
-        fputs("invalid arguments\n", stderr);
-        return EXIT_FAILURE;
-    }
-    if(inplace && path_out){
-        fputs("cannot combine --in-place and --output\n", stderr);
-        return EXIT_FAILURE;
-    }
-    path_in = argv[optind];
-    if(path_out != NULL && strcmp(path_in, "-") != 0){
-        char canon_in[PATH_MAX+1], canon_out[PATH_MAX+1];
-        if(realpath(path_in, canon_in) && realpath(path_out, canon_out)){
-            if(strcmp(canon_in, canon_out) == 0){
-                fputs("error: the input and output files are the same\n", stderr);
-                return EXIT_FAILURE;
-            }
-        }
-    }
-    FILE *in;
-    if(strcmp(path_in, "-") == 0){
-        if(set_all){
-            fputs("can't open stdin for input when -S is specified\n", stderr);
-            return EXIT_FAILURE;
-        }
-        if(inplace){
-            fputs("cannot modify stdin 'in-place'\n", stderr);
-            return EXIT_FAILURE;
-        }
-        in = stdin;
-    }
-    else
-        in = fopen(path_in, "r");
-    if(!in){
-        perror("fopen");
-        return EXIT_FAILURE;
-    }
-    FILE *out = NULL;
-    if(inplace != NULL){
-        path_out = malloc(strlen(path_in) + strlen(inplace) + 1);
-        if(path_out == NULL){
-            fputs("failure to allocate memory\n", stderr);
-            fclose(in);
-            return EXIT_FAILURE;
-        }
-        strcpy(path_out, path_in);
-        strcat(path_out, inplace);
-    }
-    if(path_out != NULL){
-        if(strcmp(path_out, "-") == 0)
-            out = stdout;
-        else{
-            if(!overwrite && !inplace){
-                if(access(path_out, F_OK) == 0){
-                    fprintf(stderr, "'%s' already exists (use -y to overwrite)\n", path_out);
-                    fclose(in);
-                    return EXIT_FAILURE;
-                }
-            }
-            out = fopen(path_out, "w");
-            if(!out){
-                perror("fopen");
-                fclose(in);
-                if(inplace)
-                    free(path_out);
-                return EXIT_FAILURE;
-            }
-        }
-    }
-    ogg_sync_state oy;
-    ogg_stream_state os, enc;
-    ogg_page og;
-    ogg_packet op;
-    opus_tags tags;
-    ogg_sync_init(&oy);
-    char *buf;
-    size_t len;
-    char *error = NULL;
-    int packet_count = -1;
-    while(error == NULL){
-        // Read until we complete a page.
-        if(ogg_sync_pageout(&oy, &og) != 1){
-            if(feof(in))
-                break;
-            buf = ogg_sync_buffer(&oy, 65536);
-            if(buf == NULL){
-                error = "ogg_sync_buffer: out of memory";
-                break;
-            }
-            len = fread(buf, 1, 65536, in);
-            if(ferror(in))
-                error = strerror(errno);
-            ogg_sync_wrote(&oy, len);
-            if(ogg_sync_check(&oy) != 0)
-                error = "ogg_sync_check: internal error";
-            continue;
-        }
-        // We got a page.
-        // Short-circuit when the relevant packets have been read.
-        if(packet_count >= 2 && out){
-            if(write_page(&og, out) == -1){
-                error = "write_page: fwrite error";
-                break;
-            }
-            continue;
-        }
-        // Initialize the streams from the first page.
-        if(packet_count == -1){
-            if(ogg_stream_init(&os, ogg_page_serialno(&og)) == -1){
-                error = "ogg_stream_init: couldn't create a decoder";
-                break;
-            }
-            if(out){
-                if(ogg_stream_init(&enc, ogg_page_serialno(&og)) == -1){
-                    error = "ogg_stream_init: couldn't create an encoder";
-                    break;
-                }
-            }
-            packet_count = 0;
-        }
-        if(ogg_stream_pagein(&os, &og) == -1){
-            error = "ogg_stream_pagein: invalid page";
-            break;
-        }
-        // Read all the packets.
-        while(ogg_stream_packetout(&os, &op) == 1){
-            packet_count++;
-            if(packet_count == 1){ // Identification header
-                if(strncmp((char*) op.packet, "OpusHead", 8) != 0){
-                    error = "opustags: invalid identification header";
-                    break;
-                }
-            }
-            else if(packet_count == 2){ // Comment header
-                if(parse_tags((char*) op.packet, op.bytes, &tags) == -1){
-                    error = "opustags: invalid comment header";
-                    break;
-                }
-                if(delete_all)
-                    tags.count = 0;
-                else{
-                    int i;
-                    for(i=0; i<count_delete; i++)
-                        delete_tags(&tags, to_delete[i]);
-                }
-                char *raw_tags = NULL;
-                if(set_all){
-                    raw_tags = malloc(16384);
-                    if(raw_tags == NULL){
-                        error = "malloc: not enough memory for buffering stdin";
-                        free(raw_tags);
-                        break;
-                    }
-                    else{
-                        char *raw_comment[256];
-                        size_t raw_len = fread(raw_tags, 1, 16383, stdin);
-                        if(raw_len == 16383)
-                            fputs("warning: truncating comment to 16 KiB\n", stderr);
-                        raw_tags[raw_len] = '\0';
-                        uint32_t raw_count = 0;
-                        size_t field_len = 0;
-                        int caught_eq = 0;
-                        size_t i = 0;
-                        char *cursor = raw_tags;
-                        for(i=0; i <= raw_len && raw_count < 256; i++){
-                            if(raw_tags[i] == '\n' || raw_tags[i] == '\0'){
-                                if(field_len == 0)
-                                    continue;
-                                if(caught_eq)
-                                    raw_comment[raw_count++] = cursor;
-                                else
-                                    fputs("warning: skipping malformed tag\n", stderr);
-                                cursor = raw_tags + i + 1;
-                                field_len = 0;
-                                caught_eq = 0;
-                                raw_tags[i] = '\0';
-                                continue;
-                            }
-                            if(raw_tags[i] == '=')
-                                caught_eq = 1;
-                            field_len++;
-                        }
-                        add_tags(&tags, (const char**) raw_comment, raw_count);
-                    }
-                }
-                add_tags(&tags, to_add, count_add);
-                if(out){
-                    ogg_packet packet;
-                    render_tags(&tags, &packet);
-                    if(ogg_stream_packetin(&enc, &packet) == -1)
-                        error = "ogg_stream_packetin: internal error";
-                    free(packet.packet);
-                }
-                else
-                    print_tags(&tags);
-                free_tags(&tags);
-                if(raw_tags)
-                    free(raw_tags);
-                if(error || !out)
-                    break;
-                else
-                    continue;
-            }
-            if(out){
-                if(ogg_stream_packetin(&enc, &op) == -1){
-                    error = "ogg_stream_packetin: internal error";
-                    break;
-                }
-            }
-        }
-        if(error != NULL)
-            break;
-        if(ogg_stream_check(&os) != 0)
-            error = "ogg_stream_check: internal error (decoder)";
-        // Write the page.
-        if(out){
-            ogg_stream_flush(&enc, &og);
-            if(write_page(&og, out) == -1)
-                error = "write_page: fwrite error";
-            else if(ogg_stream_check(&enc) != 0)
-                error = "ogg_stream_check: internal error (encoder)";
-        }
-        else if(packet_count >= 2) // Read-only mode
-            break;
-    }
-    if(packet_count >= 0){
-        ogg_stream_clear(&os);
-        if(out)
-            ogg_stream_clear(&enc);
-    }
-    ogg_sync_clear(&oy);
-    fclose(in);
-    if(out)
-        fclose(out);
-    if(!error && packet_count < 2)
-        error = "opustags: invalid file";
-    if(error){
-        fprintf(stderr, "%s\n", error);
-        if(path_out != NULL && out != stdout)
-            remove(path_out);
-        if(inplace)
-            free(path_out);
-        return EXIT_FAILURE;
-    }
-    else if(inplace){
-        if(rename(path_out, path_in) == -1){
-            perror("rename");
-            free(path_out);
-            return EXIT_FAILURE;
-        }
-        free(path_out);
-    }
-    return EXIT_SUCCESS;
-}
--- a/src/actions.cc
+++ b/src/actions.cc
@ -0,0 +1,83 @@
+#include "actions.h"
+
+using namespace opustags;
+
+void opustags::list_tags(ogg::Decoder &dec, ITagsHandler &handler, bool full)
+{
+    std::map<long, int> sequence_numbers;
+    int stream_count = 0;
+    int remaining_streams = 0;
+    std::shared_ptr<ogg::Stream> s;
+    while (!handler.done()) {
+        s = dec.read_page();
+        if (s == nullptr)
+            break; // end of stream
+        switch (s->state) {
+            case ogg::HEADER_READY:
+                stream_count++;
+                sequence_numbers[s->stream.serialno] = stream_count;
+                handler.start_of_stream(stream_count, s->type);
+                if (!handler.relevant(stream_count))
+                    s->downgrade();
+                remaining_streams++;
+                break;
+            case ogg::TAGS_READY:
+                handler.list(sequence_numbers[s->stream.serialno], s->tags);
+                s->downgrade(); // no more use for it
+            default:
+                remaining_streams--;
+        }
+        if (!full && remaining_streams <= 0) {
+            break;
+            // premature exit, but calls end_of_stream anyway
+            // we want our optimization to be transparent to the TagsHandler
+        }
+    }
+    handler.end_of_file();
+}
+
+void opustags::edit_tags(
+    ogg::Decoder &in, ogg::Encoder &out, ITagsHandler &handler)
+{
+    std::map<long, int> sequence_numbers;
+    int stream_count = 0;
+    std::shared_ptr<ogg::Stream> s;
+    for (;;) {
+        s = in.read_page();
+        if (s == nullptr)
+            break; // end of stream
+        switch (s->state) {
+
+            case ogg::HEADER_READY:
+                stream_count++;
+                sequence_numbers[s->stream.serialno] = stream_count;
+                handler.start_of_stream(stream_count, s->type);
+                if (!handler.relevant(stream_count))
+                    s->downgrade(); // makes it UNKNOWN
+                if (s->type == ogg::UNKNOWN_STREAM) {
+                    out.write_raw_page(in.current_page);
+                } else {
+                    out.forward(*s);
+                }
+                break;
+
+            case ogg::TAGS_READY:
+                handler.edit(sequence_numbers[s->stream.serialno], s->tags);
+                handler.list(sequence_numbers[s->stream.serialno], s->tags);
+                out.write_tags(s->stream.serialno, s->tags);
+                break;
+
+            case ogg::DATA_READY:
+                out.forward(*s);
+                break;
+
+            case ogg::RAW_READY:
+                out.write_raw_page(in.current_page);
+                break;
+
+            default:
+                ;
+        }
+    }
+    handler.end_of_file();
+}
--- a/src/actions.h
+++ b/src/actions.h
@ -0,0 +1,33 @@
+#pragma once
+
+#include "ogg.h"
+#include "tags_handler.h"
+
+namespace opustags {
+
+    // Decode a file and call the handler's list method every time a tags
+    // header is read. Set full to true if you want to make sure every single
+    // page of the stream is read.
+    //
+    // Use:
+    //   std::ifstream in("in.ogg");
+    //   ogg::Decoder dec(in);
+    //   TagsLister lister(options);
+    //   list_tags(dec, lister);
+    //
+    void list_tags(ogg::Decoder&, ITagsHandler &, bool full = false);
+
+    // Forward the input data to the output stream, transforming tags on-the-go
+    // with the handler's edit method.
+    //
+    // Use:
+    //   std::ifstream in("in.ogg");
+    //   ogg::Decoder dec(in);
+    //   std::ofstream out("out.ogg");
+    //   std::Encoder enc(out);
+    //   TagsEditor editor(options);
+    //   edit_tags(dec, enc, editor);
+    //
+    void edit_tags(ogg::Decoder &in, ogg::Encoder &out, ITagsHandler &);
+
+}
--- a/src/log.h
+++ b/src/log.h
@ -0,0 +1,29 @@
+#pragma once
+
+namespace opustags {
+
+    enum class LogLevel {
+        LOG_NORMAL = 0,
+        LOG_VERBOSE = 1,
+        LOG_DEBUG = 2,
+        LOG_DEBUG_EXTRA = 3,
+    };
+
+    class Log
+    {
+    public:
+        Log(std::ostream &out);
+
+        LogLevel level;
+
+        Log& operator<<(LogLevel lvl);
+        template<class T> Log& operator<<(const T&);
+
+    private:
+        std::ostream &out;
+    };
+
+
+    extern Log log;
+
+}
--- a/src/main.cc
+++ b/src/main.cc
@ -0,0 +1,88 @@
+#include "actions.h"
+#include "options.h"
+#include "version.h"
+
+#include <iostream>
+#include <fstream>
+#include <cstring>
+
+static void show_usage(const bool include_help)
+{
+    static const auto usage =
+        "Usage: opustags --help\n"
+        "       opustags [OPTIONS] INPUT\n"
+        "       opustags [OPTIONS] -o OUTPUT INPUT\n";
+
+    static const auto help =
+        "Options:\n"
+        "  -h, --help              print this help\n"
+        "  -V, --version           print version\n"
+        "  -o, --output FILE       write the modified tags to this file\n"
+        "  -i, --in-place [SUFFIX] use a temporary file then replace the original file\n"
+        "  -y, --overwrite         overwrite the output file if it already exists\n"
+        "      --stream ID         select stream for the next operations\n"
+        "  -l, --list              display a pretty listing of all tags\n"
+        "      --no-color          disable colors in --list output\n"
+        "  -d, --delete FIELD      delete all the fields of a specified type\n"
+        "  -a, --add FIELD=VALUE   add a field\n"
+        "  -s, --set FIELD=VALUE   delete then add a field\n"
+        "  -D, --delete-all        delete all the fields!\n"
+        "      --full              enable full file scan\n"
+        "      --export            dump the tags to standard output for --import\n"
+        "      --import            set the tags from scratch basing on stanard input\n"
+        "  -e, --edit              spawn the $EDITOR and apply --import on the result\n";
+
+    std::cout << "opustags v" << opustags::version_short << "\n";
+    std::cout << usage;
+    if (include_help) {
+        std::cout << "\n";
+        std::cout << help;
+    }
+}
+
+static void show_version()
+{
+    std::cout << "opustags v" << opustags::version_long << "\n";
+}
+
+int main(int argc, char **argv)
+{
+    if (argc == 1) {
+        show_usage(false);
+        return EXIT_SUCCESS;
+    }
+
+    try {
+        auto options = opustags::parse_args(argc, argv);
+        if (options.show_help) {
+            show_usage(true);
+            return EXIT_SUCCESS;
+        }
+        if (options.show_version) {
+            show_version();
+            return EXIT_SUCCESS;
+        }
+
+        if (options.path_out.empty()) {
+            std::ifstream in(options.path_in);
+            opustags::ogg::Decoder dec(in);
+            list_tags(dec, options.tags_handler, options.full);
+            // TODO: report errors if user tries to edit the stream
+        } else {
+            std::ifstream in(options.path_in);
+            std::ofstream out(options.path_out);
+            opustags::ogg::Decoder dec(in);
+            opustags::ogg::Encoder enc(out);
+            edit_tags(dec, enc, options.tags_handler);
+        }
+
+    } catch (const std::exception &e) {
+        if (errno)
+            std::cerr << "fatal error: " << e.what() << " (" << strerror(errno) << ")" << std::endl;
+        else
+            std::cerr << "fatal error: " << e.what() << std::endl;
+        return EXIT_FAILURE;
+    }
+
+    return EXIT_SUCCESS;
+}
--- a/src/ogg.cc
+++ b/src/ogg.cc
@ -0,0 +1,308 @@
+#include "ogg.h"
+
+#include <stdexcept>
+#include <fstream>
+#include <sstream>
+#include <cstring>
+#include <endian.h>
+
+using namespace opustags;
+
+////////////////////////////////////////////////////////////////////////////////
+// ogg::Stream
+
+ogg::Stream::Stream(int streamno)
+{
+    state = ogg::BEGIN_OF_STREAM;
+    type = ogg::UNKNOWN_STREAM;
+    if (ogg_stream_init(&stream, streamno) != 0)
+        throw std::runtime_error("ogg_stream_init failed");
+}
+
+ogg::Stream::~Stream()
+{
+    ogg_stream_clear(&stream);
+}
+
+void ogg::Stream::flush_packets()
+{
+    ogg_packet op;
+    while (ogg_stream_packetout(&stream, &op) > 0);
+}
+
+bool ogg::Stream::page_in(ogg_page &og)
+{
+    if (state != ogg::BEGIN_OF_STREAM && type == ogg::UNKNOWN_STREAM) {
+        state = ogg::RAW_READY;
+        return true;
+    }
+    flush_packets(); // otherwise packet_out keeps returning the same packet
+    if (ogg_stream_pagein(&stream, &og) != 0)
+        throw std::runtime_error("ogg_stream_pagein failed");
+
+    if (state == ogg::BEGIN_OF_STREAM || state == ogg::HEADER_READY) {
+        // We're expecting a header, so we parse it.
+        return handle_page();
+    } else {
+        // We're past the first two headers.
+        state = ogg::DATA_READY;
+        return true;
+    }
+}
+
+// Read the first packet of the page and parses it.
+bool ogg::Stream::handle_page()
+{
+    ogg_packet op;
+    int rc = ogg_stream_packetpeek(&stream, &op);
+    if (rc < 0)
+        throw std::runtime_error("ogg_stream_packetout failed");
+    else if (rc == 0) // insufficient data
+        return false; // asking for a new page
+    // We've read the first packet successfully.
+    // The headers are supposed to contain only one packet, so this is enough
+    // for us. Still, we could ensure there are no other packets.
+    handle_packet(op);
+    return true;
+}
+
+void ogg::Stream::handle_packet(const ogg_packet &op)
+{
+    if (state == ogg::BEGIN_OF_STREAM)
+        parse_header(op);
+    else if (state == ogg::HEADER_READY)
+        parse_opustags(op);
+    // else shrug
+}
+
+void ogg::Stream::parse_header(const ogg_packet &op)
+{
+    if (op.bytes >= 8 && memcmp(op.packet, "OpusHead", 8) == 0)
+        type = OPUS_STREAM;
+    else
+        type = UNKNOWN_STREAM;
+    state = HEADER_READY;
+}
+
+// For reference:
+// https://tools.ietf.org/html/draft-ietf-codec-oggopus-14#section-5.2
+void ogg::Stream::parse_opustags(const ogg_packet &op)
+{
+    // This part is gonna be C-ish because I don't see how I'd do this in C++
+    // without being inefficient, both in volume of code and performance.
+    char *data = reinterpret_cast<char*>(op.packet);
+    long remaining = op.bytes;
+    if (remaining < 8 || memcmp(data, "OpusTags", 8) != 0)
+        throw std::runtime_error("expected OpusTags header");
+    data += 8;
+    remaining -= 8;
+
+    // Vendor string
+    if (remaining < 4)
+        throw std::runtime_error("no space for vendor string length");
+    uint32_t vendor_length = le32toh(*reinterpret_cast<uint32_t*>(data));
+    if (remaining - 4 < vendor_length)
+        throw std::runtime_error("invalid vendor string length");
+    tags.vendor = std::string(data + 4, vendor_length);
+    data += 4 + vendor_length;
+    remaining -= 4 + vendor_length;
+
+    // User comments count
+    if (remaining < 4)
+        throw std::runtime_error("no space for user comment list length");
+    long comment_count = le32toh(*reinterpret_cast<uint32_t*>(data));
+    data += 4;
+    remaining -= 4;
+
+    // Actual comments
+    // We iterate on a long type to prevent infinite looping when comment_count == UINT32_MAX.
+    for (long i = 0; i < comment_count; i++) {
+        if (remaining < 4)
+            throw std::runtime_error("no space for user comment length");
+        uint32_t comment_length = le32toh(*reinterpret_cast<uint32_t*>(data));
+        if (remaining - 4 < comment_length)
+            throw std::runtime_error("no space for comment contents");
+        tags.add(parse_tag(std::string(data + 4, comment_length)));
+        data += 4 + comment_length;
+        remaining -= 4 + comment_length;
+    }
+
+    // Extra data to keep if the least significant bit of the first byte is 1
+    if (remaining > 0 && (*data & 1) == 1 )
+        tags.extra = std::string(data, remaining);
+
+    state = TAGS_READY;
+}
+
+void ogg::Stream::downgrade()
+{
+    type = ogg::UNKNOWN_STREAM;
+    if (state != ogg::BEGIN_OF_STREAM && state != ogg::END_OF_STREAM)
+        state = RAW_READY;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// ogg::Decoder
+
+ogg::Decoder::Decoder(std::istream &in)
+    : input(in)
+{
+    if (!in)
+        throw std::runtime_error("invalid stream to decode");
+    input.exceptions(std::ifstream::badbit);
+    ogg_sync_init(&sync);
+}
+
+ogg::Decoder::~Decoder()
+{
+    ogg_sync_clear(&sync);
+}
+
+std::shared_ptr<ogg::Stream> ogg::Decoder::read_page()
+{
+    while (page_out()) {
+        int streamno = ogg_page_serialno(&current_page);
+        auto i = streams.find(streamno);
+        if (i == streams.end()) {
+            // we could check the page number to detect new streams (pageno = 0)
+            auto s = std::make_shared<Stream>(streamno);
+            i = streams.emplace(streamno, s).first;
+        }
+        if (i->second->page_in(current_page))
+            return i->second;
+    }
+    return nullptr; // end of stream
+}
+
+// Read the next page and return true on success, false on end of stream.
+bool ogg::Decoder::page_out()
+{
+    int rc;
+    for (;;) {
+        rc = ogg_sync_pageout(&sync, &current_page);
+        if (rc < 0) {
+            throw std::runtime_error("ogg_sync_pageout failed");
+        } else if (rc == 1) {
+            break; // page complete
+        } else if (!buff()) {
+            // more data required but end of file reached
+            // TODO check sync.unsynced flag in case we've got an incomplete page
+            return false;
+        }
+    }
+    return true;
+}
+
+// Read data from the stream into the sync's buffer.
+bool ogg::Decoder::buff()
+{
+    if (input.eof())
+        return false;
+    char *buf = ogg_sync_buffer(&sync, 65536);
+    if (buf == nullptr)
+        throw std::runtime_error("ogg_sync_buffer failed");
+    input.read(buf, 65536);
+    ogg_sync_wrote(&sync, input.gcount());
+    return true;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// ogg::Encoder
+
+ogg::Encoder::Encoder(std::ostream &out)
+    : output(out)
+{
+    if (!output)
+        throw std::runtime_error("invalid stream to decode");
+    output.exceptions(std::ifstream::badbit);
+}
+
+ogg::Stream& ogg::Encoder::get_stream(int streamno)
+{
+    auto i = streams.find(streamno);
+    if (i == streams.end()) {
+        auto s = std::make_shared<Stream>(streamno);
+        i = streams.emplace(streamno, s).first;
+    }
+    return *(i->second);
+}
+
+void ogg::Encoder::forward(ogg::Stream &in)
+{
+    ogg::Stream *out = &get_stream(in.stream.serialno);
+    forward_stream(in, *out);
+    flush_stream(*out);
+}
+
+void ogg::Encoder::forward_stream(ogg::Stream &in, ogg::Stream &out)
+{
+    int rc;
+    ogg_packet op;
+    for (;;) {
+        rc = ogg_stream_packetout(&in.stream, &op);
+        if (rc < 0) {
+            throw std::runtime_error("ogg_stream_packetout failed");
+        } else if (rc == 0) {
+            break;
+        } else {
+            if (ogg_stream_packetin(&out.stream, &op) != 0)
+                throw std::runtime_error("ogg_stream_packetin failed");
+        }
+    }
+}
+
+void ogg::Encoder::flush_stream(ogg::Stream &out)
+{
+    ogg_page og;
+    if (ogg_stream_flush(&out.stream, &og))
+            write_raw_page(og);
+}
+
+void ogg::Encoder::write_raw_page(const ogg_page &og)
+{
+    output.write(reinterpret_cast<const char*>(og.header), og.header_len);
+    output.write(reinterpret_cast<const char*>(og.body), og.body_len);
+}
+
+void ogg::Encoder::write_tags(int streamno, const Tags &tags)
+{
+    ogg_packet op;
+    op.b_o_s = 0;
+    op.e_o_s = 0;
+    op.granulepos = 0;
+    op.packetno = 1; // checked on a file from ffmpeg
+
+    std::string data = render_opustags(tags);
+    op.bytes = data.size();
+    op.packet = reinterpret_cast<unsigned char*>(const_cast<char*>(data.data()));
+
+    std::shared_ptr<ogg::Stream> s = streams.at(streamno); // assume it exists
+    if (ogg_stream_packetin(&s->stream, &op) != 0)
+        throw std::runtime_error("ogg_stream_packetin failed");
+    flush_stream(*s);
+}
+
+std::string ogg::Encoder::render_opustags(const Tags &tags)
+{
+    std::stringbuf s;
+    uint32_t length;
+    s.sputn("OpusTags", 8);
+    length = htole32(tags.vendor.size());
+    s.sputn(reinterpret_cast<char*>(&length), 4);
+    s.sputn(tags.vendor.data(), tags.vendor.size());
+
+    auto assocs = tags.get_all();
+    length = htole32(assocs.size());
+    s.sputn(reinterpret_cast<char*>(&length), 4);
+
+    for (const auto assoc : assocs) {
+        length = htole32(assoc.key.size() + 1 + assoc.value.size());
+        s.sputn(reinterpret_cast<char*>(&length), 4);
+        s.sputn(assoc.key.data(), assoc.key.size());
+        s.sputc('=');
+        s.sputn(assoc.value.data(), assoc.value.size());
+    }
+
+    s.sputn(tags.extra.data(), tags.extra.size());
+    return s.str();
+}
--- a/src/ogg.h
+++ b/src/ogg.h
@ -0,0 +1,129 @@
+#pragma once
+
+#include "tags.h"
+
+#include <iostream>
+#include <map>
+#include <memory>
+#include <ogg/ogg.h>
+
+namespace opustags {
+namespace ogg
+{
+    enum StreamState {
+        BEGIN_OF_STREAM,
+        HEADER_READY,
+        TAGS_READY,
+        DATA_READY,
+        RAW_READY,
+        END_OF_STREAM,
+        // Meaning of these states below, in Stream.
+    };
+
+    enum StreamType {
+        UNKNOWN_STREAM = 0,
+        OPUS_STREAM,
+    };
+
+    // An Ogg file may contain many logical bitstreams, and among them, many
+    // Opus streams. This class represents one stream, whether it is Opus or
+    // not.
+    struct Stream
+    {
+        Stream(int streamno);
+        Stream(const Stream&) = delete;
+        ~Stream();
+
+        // Called by Decoder once a page was read.
+        // Returns true if it's ready, false if it expects more data.
+        // In the latter case, Decoder::read_page will keep reading.
+        bool page_in(ogg_page&);
+
+        // Make the stream behave as if it were unknown.
+        // As a consequence, no more effort would be made in extracting data.
+        void downgrade();
+
+        StreamState state;
+        StreamType type;
+        Tags tags;
+
+        // Here are the meanings of the state variable:
+        //   BEGIN_OF_STREAM: the stream was just initialized,
+        //   HEADER_READY: the header (first packet) was found,
+        //   TAGS_READY: the tags are parsed and complete,
+        //   DATA_READY: we've read a data page whose meaning is no concern to us,
+        //   RAW_READY: we don't even know what kind of stream that is, so don't alter it,
+        //   END_OF_STREAM: no more thing to read, not even the current page.
+
+        // From the state, we decide what to do with the Decoder's current_page.
+        // The difference between DATA_READY and RAW_DATA is that the former
+        // might require a reencoding of the current page. For example, if the
+        // tags grow and span over two pages, all the following pages are gonna
+        // need a new sequence number.
+
+        // For an Opus stream, the sequence will be:
+        //   BEGIN_OF_STREAM → HEADER_READY → TAGS_READY → DATA_READY* → END_OF_STREAM
+        // For an unknown stream:
+        //   BEGIN_OF_STREAM → HEADER_READY → RAW_READY* → END_OF_STREAM
+
+        ogg_stream_state stream;
+
+    private:
+        void flush_packets();
+        bool handle_page();
+        void handle_packet(const ogg_packet&);
+        void parse_header(const ogg_packet&);
+        void parse_opustags(const ogg_packet&);
+    };
+
+    struct Decoder
+    {
+        Decoder(std::istream&);
+        Decoder(const Decoder&) = delete;
+        ~Decoder();
+
+        // Read a page, dispatch it, and return the stream it belongs to.
+        // The read page is given to Stream::page_in before this function
+        // returns.
+        // After the end of the file is reached, it returns NULL.
+        std::shared_ptr<Stream> read_page();
+
+        std::istream &input;
+
+        ogg_sync_state sync;
+        ogg_page current_page;
+        std::map<int, std::shared_ptr<Stream>> streams;
+
+    private:
+        bool page_out();
+        bool buff();
+    };
+
+    struct Encoder
+    {
+        Encoder(std::ostream&);
+
+        // Copy the input stream's current page.
+        void forward(Stream &in);
+
+        // Write the page without even ensuring its page number is correct.
+        // It would be an efficient way to copy a stream identically, and also
+        // needed for write_page.
+        void write_raw_page(const ogg_page&);
+
+        void write_tags(int streamno, const Tags&);
+
+        std::ostream &output;
+
+        // We're gonna need some ogg_stream_state for adjusting the page
+        // numbers and splitting large packets as it's gotta be done.
+        std::map<int, std::shared_ptr<Stream>> streams;
+
+    private:
+        Stream& get_stream(int streamno);
+        void forward_stream(Stream &in, Stream &out);
+        void flush_stream(Stream &out);
+        std::string render_opustags(const Tags &tags);
+    };
+}
+}
--- a/src/options.cc
+++ b/src/options.cc
@ -0,0 +1,199 @@
+#include "options.h"
+
+#include "tags_handlers/insertion_tags_handler.h"
+#include "tags_handlers/modification_tags_handler.h"
+#include "tags_handlers/external_edit_tags_handler.h"
+#include "tags_handlers/export_tags_handler.h"
+#include "tags_handlers/import_tags_handler.h"
+#include "tags_handlers/listing_tags_handler.h"
+#include "tags_handlers/removal_tags_handler.h"
+
+#include <getopt.h>
+#include <regex>
+#include <sstream>
+
+using namespace opustags;
+
+ArgumentError::ArgumentError(const std::string &message)
+    : std::runtime_error(message.c_str())
+{
+}
+
+Options::Options() :
+    show_help(false),
+    show_version(false),
+    overwrite(false),
+    full(false),
+    in_place(false)
+{
+}
+
+Options opustags::parse_args(const int argc, char **argv)
+{
+    static const auto short_def = "hVeo:i::yd:a:s:Dl";
+
+    static const option long_def[] = {
+        {"help",        no_argument,        0, 'h'},
+        {"version",     no_argument,        0, 'V'},
+        {"full",        no_argument,        0, 0},
+        {"output",      required_argument,  0, 'o'},
+        {"in-place",    optional_argument,  0, 'i'},
+        {"overwrite",   no_argument,        0, 'y'},
+        {"delete",      required_argument,  0, 'd'},
+        {"add",         required_argument,  0, 'a'},
+        {"stream",      required_argument,  0, 0},
+        {"set",         required_argument,  0, 's'},
+        {"list",        no_argument,        0, 'l'},
+        {"delete-all",  no_argument,        0, 'D'},
+        {"edit",        no_argument,        0, 'e'},
+        {"import",      no_argument,        0, 0},
+        {"export",      no_argument,        0, 0},
+
+        // TODO: parse no-colors
+
+        {nullptr, 0, 0, 0}
+    };
+
+    // TODO: use --list as default switch
+
+    Options options;
+
+    std::vector<int> current_streamnos {StreamTagsHandler::ALL_STREAMS};
+    int option_index;
+    char c;
+    optind = 0;
+
+    while ((c = getopt_long(
+        argc, argv, short_def, long_def, &option_index)) != -1) {
+
+        const std::string arg(optarg == nullptr ? "" : optarg);
+
+        switch (c) {
+            case 'h':
+                options.show_help = true;
+                break;
+
+            case 'V':
+                options.show_version = true;
+                break;
+
+            case 'o':
+                if (arg.empty())
+                    throw ArgumentError("Output path cannot be empty");
+                options.path_out = arg;
+                break;
+
+            case 'i':
+                // TODO: shouldn't we generate random file name here to which
+                // we apply the arg, rather than use the arg as a whole?
+                options.path_out = arg.empty() ? ".otmp" : arg;
+                options.in_place = true;
+                break;
+
+            case 'y':
+                options.overwrite = true;
+                break;
+
+            case 'd':
+                if (arg.find('=') != std::string::npos)
+                    throw ArgumentError("Invalid field: '" + arg + "'");
+                for (const auto streamno : current_streamnos) {
+                    options.tags_handler.add_handler(
+                        std::make_shared<RemovalTagsHandler>(streamno, arg));
+                }
+                break;
+
+            case 'a':
+            case 's':
+            {
+                std::smatch match;
+                std::regex regex("^(\\w+)=(.*)$");
+                if (!std::regex_match(arg, match, regex))
+                    throw ArgumentError("Invalid field: '" + arg + "'");
+                for (const auto streamno : current_streamnos) {
+                    if (c == 's') {
+                        options.tags_handler.add_handler(
+                            std::make_shared<ModificationTagsHandler>(
+                                streamno, match[1], match[2]));
+                    } else {
+                        options.tags_handler.add_handler(
+                            std::make_shared<InsertionTagsHandler>(
+                                streamno, match[1], match[2]));
+                    }
+                }
+                break;
+            }
+
+            case 'l':
+                for (const auto streamno : current_streamnos) {
+                    options.tags_handler.add_handler(
+                        std::make_shared<ListingTagsHandler>(
+                            streamno, std::cout));
+                }
+                break;
+
+            case 'e':
+                options.tags_handler.add_handler(
+                    std::make_shared<ExternalEditTagsHandler>());
+                break;
+
+            case 'D':
+                for (const auto streamno : current_streamnos) {
+                    options.tags_handler.add_handler(
+                        std::make_shared<RemovalTagsHandler>(streamno));
+                }
+                break;
+
+            case 0:
+            {
+                std::string long_arg = long_def[option_index].name;
+                if (long_arg == "stream") {
+                    int i;
+                    current_streamnos.clear();
+                    std::stringstream ss(optarg);
+                    while (ss >> i) {
+                        current_streamnos.push_back(i);
+                        if (ss.peek() == ',')
+                            ss.ignore();
+                    }
+                }
+                else if (long_arg == "full")
+                    options.full = true;
+                else if (long_arg == "export")
+                    options.tags_handler.add_handler(
+                        std::make_shared<ExportTagsHandler>(std::cout));
+                else if (long_arg == "import")
+                    options.tags_handler.add_handler(
+                        std::make_shared<ImportTagsHandler>(std::cin));
+                break;
+            }
+
+            default:
+                throw ArgumentError("Invalid flag");
+        }
+    }
+
+    std::vector<std::string> stray;
+    while (optind < argc)
+        stray.push_back(argv[optind++]);
+
+    if (!options.show_help && !options.show_version) {
+        if (stray.empty())
+            throw ArgumentError("Missing input path");
+
+        options.path_in = stray.at(0);
+        if (options.path_in.empty())
+            throw ArgumentError("Input path cannot be empty");
+
+        if (stray.size() > 1)
+            throw ArgumentError("Extra argument: " + stray.at(1));
+
+        if (options.path_out.empty()) {
+            options.tags_handler.add_handler(
+                std::make_shared<ListingTagsHandler>(
+                    StreamTagsHandler::ALL_STREAMS, std::cout));
+        }
+    }
+
+    return options;
+}
--- a/src/options.h
+++ b/src/options.h
@ -0,0 +1,33 @@
+#pragma once
+
+#include "tags_handlers/composite_tags_handler.h"
+
+#include <stdexcept>
+#include <map>
+#include <vector>
+
+namespace opustags
+{
+    struct Options final
+    {
+        Options();
+
+        bool show_help;
+        bool show_version;
+        bool overwrite;
+        bool full;
+
+        bool in_place;
+        std::string path_in;
+        std::string path_out;
+
+        CompositeTagsHandler tags_handler;
+    };
+
+    struct ArgumentError : std::runtime_error
+    {
+        ArgumentError(const std::string &message);
+    };
+
+    Options parse_args(const int argc, char **argv);
+}
--- a/src/tags.cc
+++ b/src/tags.cc
@ -0,0 +1,103 @@
+#include "tags.h"
+#include <algorithm>
+
+using namespace opustags;
+
+// ASCII only, but for tag keys it's good enough
+static bool iequals(const std::string &a, const std::string &b)
+{
+    if (a.size() != b.size())
+        return false;
+    for (size_t i = 0; i < a.size(); i++)
+        if (std::tolower(a[i]) != std::tolower(b[i]))
+            return false;
+    return true;
+}
+
+bool Tag::operator !=(const Tag &other_tag) const
+{
+    return !operator ==(other_tag);
+}
+
+bool Tag::operator ==(const Tag &other_tag) const
+{
+    return key == other_tag.key
+        && value == other_tag.value;
+}
+
+Tags::Tags()
+{
+}
+
+Tags::Tags(const std::vector<Tag> &tags) : tags(tags)
+{
+}
+
+const std::vector<Tag> Tags::get_all() const
+{
+    return tags;
+}
+
+std::string Tags::get(const std::string &key) const
+{
+    for (auto &tag : tags)
+        if (iequals(tag.key, key))
+            return tag.value;
+    throw std::runtime_error("Tag '" + key + "' not found.");
+}
+
+void Tags::add(const Tag &tag)
+{
+    tags.push_back(tag);
+}
+
+void Tags::add(const std::string &key, const std::string &value)
+{
+    tags.push_back({key, value});
+}
+
+void Tags::clear()
+{
+    tags.clear();
+}
+
+void Tags::remove(const std::string &key)
+{
+    std::vector<Tag> new_tags;
+    std::copy_if(
+        tags.begin(),
+        tags.end(),
+        std::back_inserter(new_tags),
+        [&](const Tag &tag) { return !iequals(tag.key, key); });
+    tags = new_tags;
+}
+
+bool Tags::contains(const std::string &key) const
+{
+    return std::count_if(
+        tags.begin(),
+        tags.end(),
+        [&](const Tag &tag) { return iequals(tag.key, key); }) > 0;
+}
+
+Tag opustags::parse_tag(const std::string &assoc)
+{
+    size_t eq = assoc.find_first_of('=');
+    if (eq == std::string::npos)
+        throw std::runtime_error("misconstructed tag");
+    std::string name = assoc.substr(0, eq);
+    std::string value = assoc.substr(eq + 1);
+    return { name, value };
+}
+
+bool Tags::operator !=(const Tags &other_tags) const
+{
+    return !operator ==(other_tags);
+}
+
+bool Tags::operator ==(const Tags &other_tags) const
+{
+    return vendor == other_tags.vendor
+        && extra == other_tags.extra
+        && get_all() == other_tags.get_all();
+}
--- a/src/tags.h
+++ b/src/tags.h
@ -0,0 +1,49 @@
+#pragma once
+
+#include <map>
+#include <vector>
+#include <utility>
+
+namespace opustags {
+
+    struct Tag final
+    {
+        bool operator !=(const Tag &other_tag) const;
+        bool operator ==(const Tag &other_tag) const;
+
+        std::string key;
+        std::string value;
+    };
+
+    // A std::map adapter that keeps the order of insertion.
+    class Tags final
+    {
+    public:
+        Tags();
+        Tags(const std::vector<Tag> &tags);
+
+        const std::vector<Tag> get_all() const;
+
+        std::string get(const std::string &key) const;
+        void add(const Tag &tag);
+        void add(const std::string &key, const std::string &value);
+        void remove(const std::string &key);
+        bool contains(const std::string &key) const;
+        void clear();
+
+        bool operator !=(const Tags &other_tags) const;
+        bool operator ==(const Tags &other_tags) const;
+
+        // Additional fields are required to match the specs:
+        // https://tools.ietf.org/html/draft-ietf-codec-oggopus-14#section-5.2
+
+        std::string vendor;
+        std::string extra;
+
+    private:
+        std::vector<Tag> tags;
+    };
+
+    Tag parse_tag(const std::string &assoc); // KEY=value
+
+}
--- a/src/tags_handler.h
+++ b/src/tags_handler.h
@ -0,0 +1,50 @@
+#pragma once
+
+#include "tags.h"
+
+namespace opustags {
+
+    // TagsHandler define various operations related to tags and stream in
+    // order to control the main loop.
+    // In its implementation, it is expected to receive an option structure.
+    class ITagsHandler
+    {
+    public:
+        // Irrelevant streams don't even need to be parsed, so we can save some
+        // effort with this method.
+        // Returns true if the stream should be parsed, false if it should be
+        // ignored (list) or copied identically (edit).
+        virtual bool relevant(const int streamno) = 0;
+
+        // The list method is called by list_tags every time it has
+        // successfully parsed an OpusTags header.
+        virtual void list(const int streamno, const Tags &) = 0;
+
+        // Transform the tags at will.
+        // Returns true if the tags were indeed modified, false if they weren't.
+        // The latter case may be used for optimization.
+        virtual bool edit(const int streamno, Tags &) = 0;
+
+        // The work is done.
+        // When listing tags, once we've caught the streams we wanted, it's no
+        // use keeping reading the file for new streams. In that case, a true
+        // return value would abort any further processing.
+        virtual bool done() = 0;
+
+        // Signals a new stream was found.
+        // The meaning of type is in ogg::StreamType, but all you should assume
+        // is that when type is null (UNKNOWN_STREAM), list or edit won't be
+        // called.
+        virtual void start_of_stream(const int streamno, const int type) {}
+
+        // Signals the end of the file (and all the streams).
+        // If after this function is called, done() returns false, it's an
+        // error. However, it would be better to raise the error inside
+        // end_of_stream().
+        // For example, if you expect to find the stream #1 and reach the
+        // end-of-stream before finding it, better tell the user that you
+        // didn't do what he expected.
+        virtual void end_of_file() {}
+    };
+
+}
--- a/src/tags_handlers/composite_tags_handler.cc
+++ b/src/tags_handlers/composite_tags_handler.cc
@ -0,0 +1,44 @@
+#include "tags_handlers/composite_tags_handler.h"
+
+using namespace opustags;
+
+void CompositeTagsHandler::add_handler(std::shared_ptr<ITagsHandler> handler)
+{
+    handlers.push_back(std::move(handler));
+}
+
+bool CompositeTagsHandler::relevant(const int streamno)
+{
+    for (const auto &handler : handlers)
+        if (handler->relevant(streamno))
+            return true;
+    return false;
+}
+
+void CompositeTagsHandler::list(const int streamno, const Tags &tags)
+{
+    for (const auto &handler : handlers)
+        handler->list(streamno, tags);
+}
+
+bool CompositeTagsHandler::edit(const int streamno, Tags &tags)
+{
+    bool modified = false;
+    for (const auto &handler : handlers)
+        modified |= handler->edit(streamno, tags);
+    return modified;
+}
+
+bool CompositeTagsHandler::done()
+{
+    for (const auto &handler : handlers)
+        if (!handler->done())
+            return false;
+    return true;
+}
+
+const std::vector<std::shared_ptr<ITagsHandler>>
+    CompositeTagsHandler::get_handlers() const
+{
+    return handlers;
+}
--- a/src/tags_handlers/composite_tags_handler.h
+++ b/src/tags_handlers/composite_tags_handler.h
@ -0,0 +1,25 @@
+#pragma once
+
+#include <memory>
+#include <vector>
+#include "tags_handler.h"
+
+namespace opustags {
+
+    class CompositeTagsHandler final : public ITagsHandler
+    {
+    public:
+        void add_handler(std::shared_ptr<ITagsHandler> handler);
+
+        bool relevant(const int streamno) override;
+        void list(const int streamno, const Tags &) override;
+        bool edit(const int streamno, Tags &) override;
+        bool done() override;
+
+        const std::vector<std::shared_ptr<ITagsHandler>> get_handlers() const;
+
+    private:
+        std::vector<std::shared_ptr<ITagsHandler>> handlers;
+    };
+
+}
--- a/src/tags_handlers/export_tags_handler.cc
+++ b/src/tags_handlers/export_tags_handler.cc
@ -0,0 +1,31 @@
+#include "tags_handlers/export_tags_handler.h"
+
+using namespace opustags;
+
+ExportTagsHandler::ExportTagsHandler(std::ostream &output_stream)
+    : output_stream(output_stream)
+{
+}
+
+bool ExportTagsHandler::relevant(const int)
+{
+    return true;
+}
+
+void ExportTagsHandler::list(const int streamno, const Tags &tags)
+{
+    output_stream << "[Stream " << streamno << "]\n";
+    for (const auto tag : tags.get_all())
+        output_stream << tag.key << "=" << tag.value << "\n";
+    output_stream << "\n";
+}
+
+bool ExportTagsHandler::edit(const int, Tags &)
+{
+    return false;
+}
+
+bool ExportTagsHandler::done()
+{
+    return false;
+}
--- a/src/tags_handlers/export_tags_handler.h
+++ b/src/tags_handlers/export_tags_handler.h
@ -0,0 +1,22 @@
+#pragma once
+
+#include <iostream>
+#include "tags_handler.h"
+
+namespace opustags {
+
+    class ExportTagsHandler : public ITagsHandler
+    {
+    public:
+        ExportTagsHandler(std::ostream &output_stream);
+
+        bool relevant(const int streamno) override;
+        void list(const int streamno, const Tags &) override;
+        bool edit(const int streamno, Tags &) override;
+        bool done() override;
+
+    private:
+        std::ostream &output_stream;
+    };
+
+}
--- a/src/tags_handlers/external_edit_tags_handler.cc
+++ b/src/tags_handlers/external_edit_tags_handler.cc
@ -0,0 +1,22 @@
+#include "tags_handlers/external_edit_tags_handler.h"
+
+using namespace opustags;
+
+bool ExternalEditTagsHandler::relevant(const int streamno)
+{
+    return false;
+}
+
+void ExternalEditTagsHandler::list(const int streamno, const Tags &)
+{
+}
+
+bool ExternalEditTagsHandler::edit(const int streamno, Tags &)
+{
+    return false;
+}
+
+bool ExternalEditTagsHandler::done()
+{
+    return true;
+}
--- a/src/tags_handlers/external_edit_tags_handler.h
+++ b/src/tags_handlers/external_edit_tags_handler.h
@ -0,0 +1,17 @@
+#pragma once
+
+#include <iostream>
+#include "tags_handler.h"
+
+namespace opustags {
+
+    class ExternalEditTagsHandler : public ITagsHandler
+    {
+    public:
+        bool relevant(const int streamno) override;
+        void list(const int streamno, const Tags &) override;
+        bool edit(const int streamno, Tags &) override;
+        bool done() override;
+    };
+
+}
--- a/src/tags_handlers/import_tags_handler.cc
+++ b/src/tags_handlers/import_tags_handler.cc
@ -0,0 +1,67 @@
+#include <regex>
+#include "tags_handlers/import_tags_handler.h"
+
+using namespace opustags;
+
+ImportTagsHandler::ImportTagsHandler(std::istream &input_stream)
+    : parsed(false), input_stream(input_stream)
+{
+}
+
+bool ImportTagsHandler::relevant(const int)
+{
+    return true;
+}
+
+void ImportTagsHandler::list(const int, const Tags &)
+{
+}
+
+bool ImportTagsHandler::edit(const int streamno, Tags &tags)
+{
+    // the reason why we do it this way is because the tests indirectly create
+    // this handler with std::cin, and we do not want the constructor to block!
+    parse_input_stream_if_needed();
+
+    const auto old_tags = tags;
+    tags.clear();
+
+    if (tag_map.find(streamno) != tag_map.end()) {
+        const auto &source_tags = tag_map.at(streamno);
+        for (const auto &source_tag : source_tags.get_all())
+            tags.add(source_tag.key, source_tag.value);
+    }
+
+    return old_tags != tags;
+}
+
+bool ImportTagsHandler::done()
+{
+    return false;
+}
+
+void ImportTagsHandler::parse_input_stream_if_needed()
+{
+    if (parsed)
+        return;
+    parsed = true;
+
+    const std::regex whitespace_regex("^\\s*$");
+    const std::regex stream_header_regex(
+        "^\\s*\\[stream\\s+(\\d+)\\]\\s*$", std::regex_constants::icase);
+    const std::regex tag_regex(
+        "^\\s*([a-z0-9]+)\\s*=\\s*(.*?)\\s*$", std::regex_constants::icase);
+
+    int current_stream_number = 1;
+    std::string line;
+    while (std::getline(input_stream, line)) {
+        std::smatch match;
+        if (std::regex_match(line, match, stream_header_regex)) {
+            current_stream_number = std::atoi(match[1].str().c_str());
+        } else if (std::regex_match(line, match, tag_regex)) {
+            tag_map[current_stream_number].add(match[1], match[2]);
+        } else if (!std::regex_match(line, match, whitespace_regex)) {
+            throw std::runtime_error("Malformed input data near line " + line);
+        }
+    }
+}
--- a/src/tags_handlers/import_tags_handler.h
+++ b/src/tags_handlers/import_tags_handler.h
@ -0,0 +1,27 @@
+#pragma once
+
+#include <iostream>
+#include <map>
+#include "tags_handler.h"
+
+namespace opustags {
+
+    class ImportTagsHandler : public ITagsHandler
+    {
+    public:
+        ImportTagsHandler(std::istream &input_stream);
+
+        bool relevant(const int streamno) override;
+        void list(const int streamno, const Tags &) override;
+        bool edit(const int streamno, Tags &) override;
+        bool done() override;
+
+    private:
+        void parse_input_stream_if_needed();
+
+        bool parsed;
+        std::istream &input_stream;
+        std::map<int, Tags> tag_map;
+    };
+
+}
--- a/src/tags_handlers/insertion_tags_handler.cc
+++ b/src/tags_handlers/insertion_tags_handler.cc
@ -0,0 +1,28 @@
+#include "tags_handlers/insertion_tags_handler.h"
+#include "tags_handlers_errors.h"
+
+using namespace opustags;
+
+InsertionTagsHandler::InsertionTagsHandler(
+    const int streamno,
+    const std::string &tag_key,
+    const std::string &tag_value)
+    : StreamTagsHandler(streamno), tag_key(tag_key), tag_value(tag_value)
+{
+}
+
+std::string InsertionTagsHandler::get_tag_key() const
+{
+    return tag_key;
+}
+
+std::string InsertionTagsHandler::get_tag_value() const
+{
+    return tag_value;
+}
+
+bool InsertionTagsHandler::edit_impl(Tags &tags)
+{
+    tags.add(tag_key, tag_value);
+    return true;
+}
--- a/src/tags_handlers/insertion_tags_handler.h
+++ b/src/tags_handlers/insertion_tags_handler.h
@ -0,0 +1,26 @@
+#pragma once
+
+#include "tags_handlers/stream_tags_handler.h"
+
+namespace opustags {
+
+    class InsertionTagsHandler : public StreamTagsHandler
+    {
+    public:
+        InsertionTagsHandler(
+            const int streamno,
+            const std::string &tag_key,
+            const std::string &tag_value);
+
+        std::string get_tag_key() const;
+        std::string get_tag_value() const;
+
+    protected:
+        bool edit_impl(Tags &) override;
+
+    private:
+        const std::string tag_key;
+        const std::string tag_value;
+    };
+
+}
--- a/src/tags_handlers/listing_tags_handler.cc
+++ b/src/tags_handlers/listing_tags_handler.cc
@ -0,0 +1,16 @@
+#include "tags_handlers/listing_tags_handler.h"
+
+using namespace opustags;
+
+ListingTagsHandler::ListingTagsHandler(
+    const int streamno,
+    std::ostream &output_stream)
+    : StreamTagsHandler(streamno), output_stream(output_stream)
+{
+}
+
+void ListingTagsHandler::list_impl(const Tags &tags)
+{
+    for (const auto &tag : tags.get_all())
+        output_stream << tag.key << "=" << tag.value << "\n";
+}
--- a/src/tags_handlers/listing_tags_handler.h
+++ b/src/tags_handlers/listing_tags_handler.h
@ -0,0 +1,20 @@
+#pragma once
+
+#include <iostream>
+#include "tags_handlers/stream_tags_handler.h"
+
+namespace opustags {
+
+    class ListingTagsHandler : public StreamTagsHandler
+    {
+    public:
+        ListingTagsHandler(const int streamno, std::ostream &output_stream);
+
+    protected:
+        void list_impl(const Tags &) override;
+
+    private:
+        std::ostream &output_stream;
+    };
+
+}
--- a/src/tags_handlers/modification_tags_handler.cc
+++ b/src/tags_handlers/modification_tags_handler.cc
@ -0,0 +1,33 @@
+#include "tags_handlers/modification_tags_handler.h"
+
+using namespace opustags;
+
+ModificationTagsHandler::ModificationTagsHandler(
+    const int streamno,
+    const std::string &tag_key,
+    const std::string &tag_value)
+    : StreamTagsHandler(streamno), tag_key(tag_key), tag_value(tag_value)
+{
+}
+
+std::string ModificationTagsHandler::get_tag_key() const
+{
+    return tag_key;
+}
+
+std::string ModificationTagsHandler::get_tag_value() const
+{
+    return tag_value;
+}
+
+bool ModificationTagsHandler::edit_impl(Tags &tags)
+{
+    if (tags.contains(tag_key)) {
+        if (tags.get(tag_key) == tag_value)
+            return false;
+        tags.remove(tag_key);
+    }
+
+    tags.add(tag_key, tag_value);
+    return true;
+}
--- a/src/tags_handlers/modification_tags_handler.h
+++ b/src/tags_handlers/modification_tags_handler.h
@ -0,0 +1,26 @@
+#pragma once
+
+#include "tags_handlers/stream_tags_handler.h"
+
+namespace opustags {
+
+    class ModificationTagsHandler : public StreamTagsHandler
+    {
+    public:
+        ModificationTagsHandler(
+            const int streamno,
+            const std::string &tag_key,
+            const std::string &tag_value);
+
+        std::string get_tag_key() const;
+        std::string get_tag_value() const;
+
+    protected:
+        bool edit_impl(Tags &) override;
+
+    private:
+        const std::string tag_key;
+        const std::string tag_value;
+    };
+
+}
--- a/src/tags_handlers/removal_tags_handler.cc
+++ b/src/tags_handlers/removal_tags_handler.cc
@ -0,0 +1,35 @@
+#include "tags_handlers/removal_tags_handler.h"
+#include "tags_handlers_errors.h"
+
+using namespace opustags;
+
+RemovalTagsHandler::RemovalTagsHandler(const int streamno)
+    : StreamTagsHandler(streamno)
+{
+}
+
+RemovalTagsHandler::RemovalTagsHandler(
+    const int streamno, const std::string &tag_key)
+    : StreamTagsHandler(streamno), tag_key(tag_key)
+{
+}
+
+std::string RemovalTagsHandler::get_tag_key() const
+{
+    return tag_key;
+}
+
+bool RemovalTagsHandler::edit_impl(Tags &tags)
+{
+    if (tag_key.empty()) {
+        const auto anything_removed = tags.get_all().size() > 0;
+        tags.clear();
+        return anything_removed;
+    } else {
+        if (!tags.contains(tag_key))
+            return false;
+
+        tags.remove(tag_key);
+        return true;
+    }
+}
--- a/src/tags_handlers/removal_tags_handler.h
+++ b/src/tags_handlers/removal_tags_handler.h
@ -0,0 +1,22 @@
+#pragma once
+
+#include "tags_handlers/stream_tags_handler.h"
+
+namespace opustags {
+
+    class RemovalTagsHandler : public StreamTagsHandler
+    {
+    public:
+        RemovalTagsHandler(const int streamno);
+        RemovalTagsHandler(const int streamno, const std::string &tag_key);
+
+        std::string get_tag_key() const;
+
+    protected:
+        bool edit_impl(Tags &) override;
+
+    private:
+        const std::string tag_key;
+    };
+
+}
--- a/src/tags_handlers/stream_tags_handler.cc
+++ b/src/tags_handlers/stream_tags_handler.cc
@ -0,0 +1,59 @@
+#include "tags_handlers/stream_tags_handler.h"
+
+#include <iostream>
+
+using namespace opustags;
+
+const int StreamTagsHandler::ALL_STREAMS = -1;
+
+StreamTagsHandler::StreamTagsHandler(const int streamno)
+    : streamno(streamno), work_finished(false)
+{
+}
+
+int StreamTagsHandler::get_streamno() const
+{
+    return streamno;
+}
+
+bool StreamTagsHandler::relevant(const int streamno)
+{
+    return streamno == this->streamno || this->streamno == ALL_STREAMS;
+}
+
+void StreamTagsHandler::list(const int streamno, const Tags &tags)
+{
+    if (!relevant(streamno))
+        return;
+    list_impl(tags);
+    work_finished = this->streamno != ALL_STREAMS;
+}
+
+bool StreamTagsHandler::edit(const int streamno, Tags &tags)
+{
+    if (!relevant(streamno))
+        return false;
+    const auto ret = edit_impl(tags);
+    work_finished = this->streamno != ALL_STREAMS;
+    return ret;
+}
+
+bool StreamTagsHandler::done()
+{
+    return work_finished;
+}
+
+void StreamTagsHandler::end_of_file()
+{
+    if (!work_finished && streamno != ALL_STREAMS)
+        std::cerr << "warning: stream " << streamno << " wasn't found" << std::endl;
+}
+
+void StreamTagsHandler::list_impl(const Tags &)
+{
+}
+
+bool StreamTagsHandler::edit_impl(Tags &)
+{
+    return false;
+}
--- a/src/tags_handlers/stream_tags_handler.h
+++ b/src/tags_handlers/stream_tags_handler.h
@ -0,0 +1,33 @@
+#pragma once
+
+#include "tags_handler.h"
+
+namespace opustags {
+
+    // Base handler that holds the stream number it's supposed to work with
+    // and performs the usual boilerplate.
+    class StreamTagsHandler : public ITagsHandler
+    {
+    public:
+        static const int ALL_STREAMS;
+
+        StreamTagsHandler(const int streamno);
+
+        int get_streamno() const;
+
+        bool relevant(const int streamno) override;
+        void list(const int streamno, const Tags &) override;
+        bool edit(const int streamno, Tags &) override;
+        bool done() override;
+        void end_of_file() override;
+
+    protected:
+        virtual void list_impl(const Tags &);
+        virtual bool edit_impl(Tags &);
+
+    private:
+        const int streamno;
+        bool work_finished;
+    };
+
+}
--- a/src/tags_handlers_errors.cc
+++ b/src/tags_handlers_errors.cc
@ -0,0 +1,13 @@
+#include "tags_handlers_errors.h"
+
+using namespace opustags;
+
+TagAlreadyExistsError::TagAlreadyExistsError(const std::string &tag_key)
+    : std::runtime_error("Tag already exists: " + tag_key)
+{
+}
+
+TagDoesNotExistError::TagDoesNotExistError(const std::string &tag_key)
+    : std::runtime_error("Tag does not exist: " + tag_key)
+{
+}
--- a/src/tags_handlers_errors.h
+++ b/src/tags_handlers_errors.h
@ -0,0 +1,17 @@
+#pragma once
+
+#include <stdexcept>
+
+namespace opustags {
+
+    struct TagAlreadyExistsError : std::runtime_error
+    {
+        TagAlreadyExistsError(const std::string &tag_key);
+    };
+
+    struct TagDoesNotExistError : std::runtime_error
+    {
+        TagDoesNotExistError(const std::string &tag_key);
+    };
+
+}
--- a/src/version.h.in
+++ b/src/version.h.in
@ -0,0 +1,10 @@
+#pragma once
+
+#include <string>
+
+namespace opustags {
+
+    static const std::string version_short = "@VERSION_SHORT@";
+    static const std::string version_long = "@VERSION_LONG@";
+
+}
--- a/tests/actions_test.cc
+++ b/tests/actions_test.cc
@ -0,0 +1,169 @@
+#include "actions.h"
+#include "catch.h"
+
+#include "ogg.h"
+#include "tags_handlers/insertion_tags_handler.h"
+#include "tags_handlers/stream_tags_handler.h"
+
+#include <fstream>
+#include <cstring>
+
+using namespace opustags;
+
+static bool same_streams(ogg::Decoder &a, ogg::Decoder &b)
+{
+    std::shared_ptr<ogg::Stream> sa, sb;
+    ogg_packet pa, pb;
+    int ra, rb;
+
+    for (;;) {
+        sa = a.read_page();
+        sb = b.read_page();
+        if (!sa && !sb)
+            break; // both reached the end at the same time
+        if (!sa || !sb)
+            return false; // one stream is shorter than the other
+        if (sa->stream.serialno != sb->stream.serialno)
+            return false;
+        for (;;) {
+            ra = ogg_stream_packetout(&sa->stream, &pa);
+            rb = ogg_stream_packetout(&sb->stream, &pb);
+            if (ra != rb)
+                return false;
+            else if (ra == 0)
+                break;
+            else if (ra < 0)
+                throw std::runtime_error("ogg_stream_packetout failed");
+            // otherwise we got a valid packet on both sides
+            if (pa.bytes != pb.bytes || pa.b_o_s != pb.b_o_s || pa.e_o_s != pb.e_o_s)
+                return false;
+            if (pa.granulepos != pb.granulepos || pa.packetno != pb.packetno)
+                return false;
+            if (memcmp(pa.packet, pb.packet, pa.bytes) != 0)
+                return false;
+        }
+    }
+    return true;
+}
+
+static bool same_files(std::istream &a, std::istream &b)
+{
+    static const size_t block = 1024;
+    char ba[block], bb[block];
+    while (a && b) {
+        a.read(ba, block);
+        b.read(bb, block);
+        if (a.gcount() != b.gcount())
+            return false;
+        if (memcmp(ba, bb, a.gcount()) != 0)
+            return false;
+    }
+    if (a || b)
+        return false; // one of them is shorter
+    return true;
+}
+
+TEST_CASE("editing an unknown stream should do nothing", "[actions]")
+{
+    std::ifstream in("../tests/samples/beep.ogg");
+    std::stringstream out;
+    ogg::Decoder dec(in);
+    ogg::Encoder enc(out);
+
+    StreamTagsHandler editor(StreamTagsHandler::ALL_STREAMS);
+    edit_tags(dec, enc, editor);
+
+    in.clear();
+    in.seekg(0, in.beg);
+    out.clear();
+    out.seekg(0, out.beg);
+    REQUIRE(same_files(in, out));
+}
+
+TEST_CASE("fake editing of an Opus stream should preserve the stream", "[actions]")
+{
+    std::ifstream in("../tests/samples/mystery-beep.ogg");
+    std::stringstream out;
+    ogg::Decoder dec(in);
+    ogg::Encoder enc(out);
+
+    StreamTagsHandler editor(StreamTagsHandler::ALL_STREAMS);
+    edit_tags(dec, enc, editor);
+
+    in.clear();
+    in.seekg(0, in.beg);
+    out.clear();
+    out.seekg(0, out.beg);
+    REQUIRE(same_files(in, out));
+}
+
+TEST_CASE("editing a specific stream", "[actions]")
+{
+    std::ifstream in("../tests/samples/mystery-beep.ogg");
+    std::stringstream out;
+
+    {
+        ogg::Decoder dec(in);
+        ogg::Encoder enc(out);
+        InsertionTagsHandler editor(3, "pwnd", "yes");
+        edit_tags(dec, enc, editor);
+    }
+
+    in.clear();
+    in.seekg(0, in.beg);
+    out.clear();
+    out.seekg(0, out.beg);
+
+    {
+        ogg::Decoder a(in);
+        ogg::Decoder b(out);
+        std::shared_ptr<ogg::Stream> s2[6];
+        for (int i = 0; i < 6; i++) {
+            // get the headers
+            a.read_page();
+            s2[i] = b.read_page();
+        }
+
+        REQUIRE(s2[0]->type == ogg::OPUS_STREAM);
+        REQUIRE(s2[1]->type == ogg::UNKNOWN_STREAM);
+        REQUIRE(s2[2]->type == ogg::OPUS_STREAM);
+        REQUIRE(!s2[0]->tags.contains("pwnd"));
+        REQUIRE(s2[2]->tags.get("pwnd") == "yes");
+
+        REQUIRE(same_streams(a, b));
+    }
+}
+
+class GetLanguages : public StreamTagsHandler {
+public:
+    GetLanguages() : StreamTagsHandler(StreamTagsHandler::ALL_STREAMS) {}
+    std::vector<std::string> languages;
+protected:
+    void list_impl(const Tags &tags) {
+        languages.push_back(tags.get("LANGUAGE"));
+    }
+};
+
+TEST_CASE("listing tags", "[actions]")
+{
+    std::ifstream in("../tests/samples/mystery-beep.ogg");
+    ogg::Decoder dec(in);
+    GetLanguages lister;
+    list_tags(dec, lister);
+
+    REQUIRE(lister.languages.size() == 2);
+    REQUIRE(lister.languages[0] == "und");
+    REQUIRE(lister.languages[1] == "und");
+}
+
+TEST_CASE("listing tags, full scan", "[actions]")
+{
+    std::ifstream in("../tests/samples/mystery-beep.ogg");
+    ogg::Decoder dec(in);
+    GetLanguages lister;
+    list_tags(dec, lister, true);
+
+    REQUIRE(lister.languages.size() == 2);
+    REQUIRE(lister.languages[0] == "und");
+    REQUIRE(lister.languages[1] == "und");
+}
--- a/tests/main.cc
+++ b/tests/main.cc
@ -0,0 +1,2 @@
+#define CATCH_CONFIG_MAIN
+#include "catch.h"
--- a/tests/ogg_test.cc
+++ b/tests/ogg_test.cc
@ -0,0 +1,148 @@
+#include "ogg.h"
+#include "catch.h"
+
+#include <fstream>
+
+using namespace opustags;
+
+TEST_CASE("decoding a single-stream Ogg Opus file", "[ogg]")
+{
+    std::ifstream src("../tests/samples/mystery.ogg");
+    ogg::Decoder dec(src);
+
+    std::shared_ptr<ogg::Stream> s = dec.read_page();
+    REQUIRE(s != nullptr);
+    REQUIRE(s->state == ogg::HEADER_READY);
+    REQUIRE(s->type == ogg::OPUS_STREAM);
+
+    std::shared_ptr<ogg::Stream> s2 = dec.read_page();
+    REQUIRE(s2 == s);
+    REQUIRE(s->state == ogg::TAGS_READY);
+    REQUIRE(s->type == ogg::OPUS_STREAM);
+    REQUIRE(s->tags.get("encoder") == "Lavc57.24.102 libopus");
+}
+
+TEST_CASE("decoding garbage", "[ogg]")
+{
+    std::ifstream src("Makefile");
+    ogg::Decoder dec(src);
+    REQUIRE_THROWS(dec.read_page());
+}
+
+TEST_CASE("decoding an Ogg Vorbis file", "[ogg]")
+{
+    std::ifstream src("../tests/samples/beep.ogg");
+    ogg::Decoder dec(src);
+
+    std::shared_ptr<ogg::Stream> s = dec.read_page();
+    REQUIRE(s != nullptr);
+    REQUIRE(s->state == ogg::HEADER_READY);
+    REQUIRE(s->type == ogg::UNKNOWN_STREAM);
+
+    s = dec.read_page();
+    REQUIRE(s != nullptr);
+    REQUIRE(s->state == ogg::RAW_READY);
+}
+
+TEST_CASE("decoding a multi-stream file", "[ogg]")
+{
+    std::ifstream src("../tests/samples/mystery-beep.ogg");
+    ogg::Decoder dec(src);
+    std::shared_ptr<ogg::Stream> first, second, third, s;
+
+    s = dec.read_page();
+    first = s;
+    REQUIRE(s != nullptr);
+    REQUIRE(s->state == ogg::HEADER_READY);
+    REQUIRE(s->type == ogg::OPUS_STREAM);
+
+    s = dec.read_page();
+    second = s;
+    REQUIRE(s != nullptr);
+    REQUIRE(s != first);
+    REQUIRE(s->state == ogg::HEADER_READY);
+    REQUIRE(s->type == ogg::UNKNOWN_STREAM);
+
+    s = dec.read_page();
+    third = s;
+    REQUIRE(s != nullptr);
+    REQUIRE(s != first);
+    REQUIRE(s != second);
+    REQUIRE(s->state == ogg::HEADER_READY);
+    REQUIRE(s->type == ogg::OPUS_STREAM);
+
+    s = dec.read_page();
+    REQUIRE(s == first);
+    REQUIRE(s->state == ogg::TAGS_READY);
+
+    s = dec.read_page();
+    REQUIRE(s == second);
+    REQUIRE(s->state == ogg::RAW_READY);
+
+    s = dec.read_page();
+    REQUIRE(s == third);
+    REQUIRE(s->state == ogg::TAGS_READY);
+}
+
+static void craft_stream(std::ostream &out, const std::string &tags_data)
+{
+    ogg::Encoder enc(out);
+    ogg_stream_state os;
+    ogg_page og;
+    ogg_packet op;
+    ogg_stream_init(&os, 0);
+
+    op.packet = reinterpret_cast<unsigned char*>(const_cast<char*>("OpusHead"));
+    op.bytes = 8;
+    op.b_o_s = 1;
+    op.e_o_s = 0;
+    op.granulepos = 0;
+    op.packetno = 0;
+    ogg_stream_packetin(&os, &op);
+    ogg_stream_flush(&os, &og);
+    enc.write_raw_page(og);
+
+    op.packet = reinterpret_cast<unsigned char*>(const_cast<char*>(tags_data.data()));
+    op.bytes = tags_data.size();
+    op.b_o_s = 0;
+    op.e_o_s = 1;
+    op.granulepos = 0;
+    op.packetno = 1;
+    ogg_stream_packetin(&os, &op);
+    ogg_stream_flush(&os, &og);
+    enc.write_raw_page(og);
+
+    ogg_stream_clear(&os);
+}
+
+const char *evil_tags =
+    "OpusTags"
+    "\x00\x00\x00\x00" "" /* vendor */
+    "\x01\x00\x00\x00" /* one comment */
+    "\xFA\x00\x00\x00" "TITLE=Evil"
+    /* ^ should be \x0A as the length of the comment is 10 */
+;
+
+TEST_CASE("decoding a malicious Ogg Opus file", "[ogg]")
+{
+    std::stringstream buf;
+    craft_stream(buf, std::string(evil_tags, 8 + 4 + 4 + 4 + 10));
+    buf.seekg(0, buf.beg);
+    ogg::Decoder dec(buf);
+
+    std::shared_ptr<ogg::Stream> s = dec.read_page();
+    REQUIRE(s != nullptr);
+    REQUIRE(s->state == ogg::HEADER_READY);
+    REQUIRE(s->type == ogg::OPUS_STREAM);
+
+    REQUIRE_THROWS(dec.read_page());
+}
+
+TEST_CASE("decoding a bad stream", "[ogg]")
+{
+    std::ifstream in("uioprheuio");
+    REQUIRE_THROWS(std::make_shared<ogg::Decoder>(in));
+}
+
+// Encoding is trickier, and might as well be done in actions_test.cc, given
+// opustags::edit_tags covers all of Encoder's regular code.
--- a/tests/options_test.cc
+++ b/tests/options_test.cc
@ -0,0 +1,205 @@
+#include "options.h"
+#include "catch.h"
+
+#include "tags_handlers/export_tags_handler.h"
+#include "tags_handlers/external_edit_tags_handler.h"
+#include "tags_handlers/import_tags_handler.h"
+#include "tags_handlers/insertion_tags_handler.h"
+#include "tags_handlers/listing_tags_handler.h"
+#include "tags_handlers/modification_tags_handler.h"
+#include "tags_handlers/removal_tags_handler.h"
+
+#include <memory>
+
+using namespace opustags;
+
+static std::unique_ptr<char[]> string_to_uptr(const std::string &str)
+{
+    auto ret = std::make_unique<char[]>(str.size() + 1);
+    for (size_t i = 0; i < str.size(); i++)
+        ret[i] = str[i];
+    ret[str.size()] = 0;
+    return ret;
+}
+
+static Options retrieve_options(
+    std::vector<std::string> args, bool fake_input_path = true)
+{
+    // need to pass non-const char*, but we got const objects. make copies
+    std::vector<std::unique_ptr<char[]>> arg_holders;
+    arg_holders.push_back(string_to_uptr("fake/path/to/program"));
+    for (size_t i = 0; i < args.size(); i++)
+        arg_holders.push_back(string_to_uptr(args[i]));
+    if (fake_input_path)
+        arg_holders.push_back(string_to_uptr("fake/path/to/input"));
+
+    auto plain_args = std::make_unique<char*[]>(arg_holders.size());
+    for (size_t i = 0; i < arg_holders.size(); i++)
+        plain_args[i] = arg_holders[i].get();
+
+    return parse_args(arg_holders.size(), plain_args.get());
+}
+
+// retrieve a specific TagsHandler from the CompositeTagsHandler in options
+template<typename T> static T *get_handler(
+    const Options &options, const size_t index)
+{
+    const auto handlers = options.tags_handler.get_handlers();
+    const auto handler = dynamic_cast<T*>(handlers.at(index).get());
+    REQUIRE(handler);
+    return handler;
+}
+
+TEST_CASE("option parsing", "[options]")
+{
+    SECTION("--help") {
+        REQUIRE(retrieve_options({"--help"}).show_help);
+        REQUIRE(retrieve_options({"-h"}).show_help);
+        REQUIRE(!retrieve_options({}).show_help);
+    }
+
+    SECTION("--version") {
+        REQUIRE(retrieve_options({"--version"}).show_version);
+        REQUIRE(retrieve_options({"-V"}).show_version);
+        REQUIRE(!retrieve_options({}).show_version);
+    }
+
+    SECTION("--overwrite") {
+        REQUIRE(retrieve_options({"--overwrite"}).overwrite);
+        REQUIRE(retrieve_options({"-y"}).overwrite);
+        REQUIRE(!retrieve_options({}).overwrite);
+    }
+
+    SECTION("--full") {
+        REQUIRE(retrieve_options({"--full"}).full);
+        REQUIRE(!retrieve_options({}).full);
+    }
+
+    SECTION("--in-place") {
+        REQUIRE(!retrieve_options({}).in_place);
+        REQUIRE(retrieve_options({}).path_out.empty());
+        REQUIRE(retrieve_options({"--in-place", "ABC"}, false).in_place);
+        REQUIRE(
+            retrieve_options({"--in-place", "ABC"}, false).path_out == ".otmp");
+        REQUIRE(retrieve_options({"--in-place"}).in_place);
+        REQUIRE(retrieve_options({"--in-place"}).path_out == ".otmp");
+        REQUIRE(retrieve_options({"--in-place=ABC"}).in_place);
+        REQUIRE(retrieve_options({"--in-place=ABC"}).path_out == "ABC");
+        REQUIRE(retrieve_options({"-i", "ABC"}, false).in_place);
+        REQUIRE(retrieve_options({"-i", "ABC"}, false).path_out == ".otmp");
+        REQUIRE(retrieve_options({"-i"}).in_place);
+        REQUIRE(retrieve_options({"-i"}).path_out == ".otmp");
+        REQUIRE(retrieve_options({"-iABC"}).in_place);
+        REQUIRE(retrieve_options({"-iABC"}).path_out == "ABC");
+    }
+
+    SECTION("input") {
+        REQUIRE_THROWS(retrieve_options({}, false));
+        REQUIRE_THROWS(retrieve_options({""}, false));
+        REQUIRE(retrieve_options({"input"}, false).path_in == "input");
+        REQUIRE_THROWS(retrieve_options({"input", "extra argument"}, false));
+    }
+
+    SECTION("--output") {
+        REQUIRE(retrieve_options({"--output", "ABC"}).path_out == "ABC");
+        REQUIRE(retrieve_options({"-o", "ABC"}).path_out == "ABC");
+        REQUIRE_THROWS(retrieve_options({"--output", ""}));
+        REQUIRE_THROWS(retrieve_options({"-o", ""}));
+    }
+
+    SECTION("--import") {
+        get_handler<ImportTagsHandler>(retrieve_options({"--import"}), 0);
+    }
+
+    SECTION("--export") {
+        get_handler<ExportTagsHandler>(retrieve_options({"--export"}), 0);
+    }
+
+    SECTION("--edit") {
+        get_handler<ExternalEditTagsHandler>(retrieve_options({"--edit"}), 0);
+        get_handler<ExternalEditTagsHandler>(retrieve_options({"-e"}), 0);
+    }
+
+    SECTION("--list") {
+        get_handler<ListingTagsHandler>(retrieve_options({"--list"}), 0);
+        get_handler<ListingTagsHandler>(retrieve_options({"-l"}), 0);
+        // TODO:
+        // test enabling / disabling colors, which should be
+        // contained inside the state of ListingTagsHandler
+        // TODO:
+        // it should be the default operation for readonly mode - test this too
+    }
+
+    SECTION("--delete-all") {
+        REQUIRE(get_handler<RemovalTagsHandler>(
+            retrieve_options({"--delete-all"}), 0)->get_tag_key().empty());
+
+        REQUIRE(get_handler<RemovalTagsHandler>(
+            retrieve_options({"-D"}), 0)->get_tag_key().empty());
+    }
+
+    SECTION("--delete") {
+        const auto opts = retrieve_options({"--delete", "A", "-d", "B"});
+        REQUIRE(get_handler<RemovalTagsHandler>(opts, 0)->get_tag_key() == "A");
+        REQUIRE(get_handler<RemovalTagsHandler>(opts, 1)->get_tag_key() == "B");
+        REQUIRE_THROWS(retrieve_options({"--delete", "invalid="}));
+    }
+
+    SECTION("--add") {
+        const auto opts = retrieve_options({"--add", "A=1", "-a", "B=2"});
+        const auto handler1 = get_handler<InsertionTagsHandler>(opts, 0);
+        const auto handler2 = get_handler<InsertionTagsHandler>(opts, 1);
+        REQUIRE(handler1->get_tag_key() == "A");
+        REQUIRE(handler1->get_tag_value() == "1");
+        REQUIRE(handler2->get_tag_key() == "B");
+        REQUIRE(handler2->get_tag_value() == "2");
+        REQUIRE_THROWS(retrieve_options({"--add", "invalid"}));
+    }
+
+    SECTION("--set") {
+        const auto opts = retrieve_options({"--set", "A=1", "-s", "B=2"});
+        const auto handler1 = get_handler<ModificationTagsHandler>(opts, 0);
+        const auto handler2 = get_handler<ModificationTagsHandler>(opts, 1);
+        REQUIRE(handler1->get_tag_key() == "A");
+        REQUIRE(handler1->get_tag_value() == "1");
+        REQUIRE(handler2->get_tag_key() == "B");
+        REQUIRE(handler2->get_tag_value() == "2");
+        REQUIRE_THROWS(retrieve_options({"--set", "invalid"}));
+    }
+
+    SECTION("--stream") {
+        // by default, use all the streams
+        REQUIRE(
+            get_handler<RemovalTagsHandler>(retrieve_options({"-d", "xyz"}), 0)
+            ->get_streamno() == StreamTagsHandler::ALL_STREAMS);
+
+        // ...unless the user supplies an option to use a specific stream
+        REQUIRE(
+            get_handler<RemovalTagsHandler>(
+                retrieve_options({"--stream", "1", "-d", "xyz"}), 0)
+            ->get_streamno() == 1);
+
+        // ...which can be combined multiple times
+        {
+            const auto opts = retrieve_options({
+                "--stream", "1",
+                "-d", "xyz",
+                "--stream", "2",
+                "-d", "abc"});
+            const auto handler1 = get_handler<RemovalTagsHandler>(opts, 0);
+            const auto handler2 = get_handler<RemovalTagsHandler>(opts, 1);
+            REQUIRE(handler1->get_streamno() == 1);
+            REQUIRE(handler2->get_streamno() == 2);
+        }
+
+        // ...or contain comma separated values
+        {
+            const auto opts = retrieve_options({
+                "--stream", "1,2", "-d", "xyz"});
+            const auto handler1 = get_handler<RemovalTagsHandler>(opts, 0);
+            const auto handler2 = get_handler<RemovalTagsHandler>(opts, 1);
+            REQUIRE(handler1->get_streamno() == 1);
+            REQUIRE(handler2->get_streamno() == 2);
+        }
+    }
+}
--- a/tests/samples/beep.ogg
+++ b/tests/samples/beep.ogg
--- a/tests/samples/mystery-beep.ogg
+++ b/tests/samples/mystery-beep.ogg
--- a/tests/samples/mystery.ogg
+++ b/tests/samples/mystery.ogg
--- a/tests/tags_handlers/composite_tags_handler_test.cc
+++ b/tests/tags_handlers/composite_tags_handler_test.cc
@ -0,0 +1,96 @@
+#include "tags_handlers/composite_tags_handler.h"
+#include "catch.h"
+
+using namespace opustags;
+
+namespace
+{
+    struct DummyTagsHandler : ITagsHandler
+    {
+        DummyTagsHandler();
+
+        bool relevant(const int streamno) override;
+        void list(const int streamno, const Tags &) override;
+        bool edit(const int streamno, Tags &) override;
+        bool done() override;
+
+        bool relevant_ret, edit_ret, done_ret, list_fired;
+    };
+}
+
+DummyTagsHandler::DummyTagsHandler()
+    : relevant_ret(true), edit_ret(true), done_ret(true), list_fired(false)
+{
+}
+
+bool DummyTagsHandler::relevant(const int)
+{
+    return relevant_ret;
+}
+
+void DummyTagsHandler::list(const int, const Tags &)
+{
+    list_fired = true;
+}
+
+bool DummyTagsHandler::edit(const int, Tags &)
+{
+    return edit_ret;
+}
+
+bool DummyTagsHandler::done()
+{
+    return done_ret;
+}
+
+TEST_CASE("composite tags handler", "[tags_handlers]")
+{
+    auto handler1 = std::make_shared<DummyTagsHandler>();
+    auto handler2 = std::make_shared<DummyTagsHandler>();
+    CompositeTagsHandler composite_handler;
+    composite_handler.add_handler(handler1);
+    composite_handler.add_handler(handler2);
+
+    SECTION("relevance") {
+        const int dummy_streamno = 1;
+        handler1->relevant_ret = true;
+        handler2->relevant_ret = true;
+        REQUIRE(composite_handler.relevant(dummy_streamno));
+        handler1->relevant_ret = false;
+        REQUIRE(composite_handler.relevant(dummy_streamno));
+        handler2->relevant_ret = false;
+        REQUIRE(!composite_handler.relevant(dummy_streamno));
+    }
+
+    SECTION("listing") {
+        const int dummy_streamno = 1;
+        Tags dummy_tags;
+        REQUIRE(!handler1->list_fired);
+        REQUIRE(!handler2->list_fired);
+        composite_handler.list(dummy_streamno, dummy_tags);
+        REQUIRE(handler1->list_fired);
+        REQUIRE(handler2->list_fired);
+    }
+
+    SECTION("editing") {
+        const int dummy_streamno = 1;
+        Tags dummy_tags;
+        handler1->edit_ret = true;
+        handler2->edit_ret = true;
+        REQUIRE(composite_handler.edit(dummy_streamno, dummy_tags));
+        handler1->edit_ret = false;
+        REQUIRE(composite_handler.edit(dummy_streamno, dummy_tags));
+        handler2->edit_ret = false;
+        REQUIRE(!composite_handler.edit(dummy_streamno, dummy_tags));
+    }
+
+    SECTION("finish") {
+        handler1->done_ret = true;
+        handler2->done_ret = true;
+        REQUIRE(composite_handler.done());
+        handler1->done_ret = false;
+        REQUIRE(!composite_handler.done());
+        handler2->done_ret = false;
+        REQUIRE(!composite_handler.done());
+    }
+}
--- a/tests/tags_handlers/export_tags_handler_test.cc
+++ b/tests/tags_handlers/export_tags_handler_test.cc
@ -0,0 +1,23 @@
+#include "tags_handlers/export_tags_handler.h"
+#include "catch.h"
+#include <sstream>
+
+using namespace opustags;
+
+TEST_CASE("export tags handler", "[tags_handlers]")
+{
+    std::stringstream ss;
+    ExportTagsHandler handler(ss);
+    handler.list(1, {{{"a", "value1"}, {"b", "value2"}}});
+    handler.list(2, {{{"c", "value3"}, {"d", "value4"}}});
+
+    REQUIRE(ss.str() == R"([Stream 1]
+a=value1
+b=value2
+
+[Stream 2]
+c=value3
+d=value4
+
+)");
+}
--- a/tests/tags_handlers/import_tags_handler_test.cc
+++ b/tests/tags_handlers/import_tags_handler_test.cc
@ -0,0 +1,142 @@
+#include "tags_handlers/import_tags_handler.h"
+#include "catch.h"
+#include <sstream>
+
+using namespace opustags;
+
+TEST_CASE("import tags handler", "[tags_handlers]")
+{
+    SECTION("tags for streams not mentioned in import get emptied")
+    {
+        Tags tags = {{{"remove", "me"}}};
+        std::stringstream ss;
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().empty());
+    }
+
+    SECTION("streams that do not exist in the input file are ignored")
+    {
+        // TODO: rather than ignoring, at least print a warning
+        // requires #6
+
+        Tags tags;
+        std::stringstream ss;
+        ss << "[Stream 5]\nkey = value\n";
+        ImportTagsHandler handler(ss);
+        REQUIRE(!handler.edit(1, tags));
+        REQUIRE(tags.get_all().empty());
+    }
+
+    SECTION("adding unique tags")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << "[Stream 1]\nkey = value\nkey2 = value2\n";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().size() == 2);
+        REQUIRE(tags.get("key") == "value");
+        REQUIRE(tags.get("key2") == "value2");
+    }
+
+    SECTION("adding tags with the same key")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << "[Stream 1]\nkey = value1\nkey = value2\n";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().size() == 2);
+        REQUIRE(tags.get_all().at(0).key == "key");
+        REQUIRE(tags.get_all().at(1).key == "key");
+        REQUIRE(tags.get_all().at(0).value == "value1");
+        REQUIRE(tags.get_all().at(1).value == "value2");
+    }
+
+    SECTION("overwriting existing tags")
+    {
+        Tags tags = {{{"remove", "me"}}};
+        std::stringstream ss;
+        ss << "[Stream 1]\nkey = value\nkey2 = value2\n";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().size() == 2);
+        REQUIRE(tags.get("key") == "value");
+        REQUIRE(tags.get("key2") == "value2");
+    }
+
+    SECTION("various whitespace issues are worked around")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << " [StrEaM  1] \n\n  key = value  \nkey2=value2\n";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().size() == 2);
+        REQUIRE(tags.get("key") == "value");
+        REQUIRE(tags.get("key2") == "value2");
+    }
+
+    SECTION("not specifying stream assumes first stream")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << "key=value";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().size() == 1);
+        REQUIRE(tags.get("key") == "value");
+    }
+
+    SECTION("multiple streams")
+    {
+        Tags tags1;
+        Tags tags2;
+        std::stringstream ss;
+        ss << "[stream 1]\nkey=value\n[stream 2]\nkey2=value2";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags1));
+        REQUIRE(handler.edit(2, tags2));
+        REQUIRE(tags1.get_all().size() == 1);
+        REQUIRE(tags2.get_all().size() == 1);
+        REQUIRE(tags1.get("key") == "value");
+        REQUIRE(tags2.get("key2") == "value2");
+    }
+
+    SECTION("sections listed twice are concatenated")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << "[stream 1]\nkey=value\n"
+            "[stream 2]\nkey=irrelevant\n"
+            "[Stream 1]\nkey2=value2";
+        ImportTagsHandler handler(ss);
+        REQUIRE(handler.edit(1, tags));
+        REQUIRE(tags.get_all().size() == 2);
+        REQUIRE(tags.get("key") == "value");
+        REQUIRE(tags.get("key2") == "value2");
+    }
+
+    SECTION("weird input throws errors - malformed section headers")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << "[stream huh]\n";
+        REQUIRE_THROWS({
+            ImportTagsHandler handler(ss);
+            handler.edit(1, tags);
+        });
+    }
+
+    SECTION("weird input throws errors - malformed lines")
+    {
+        Tags tags;
+        std::stringstream ss;
+        ss << "tag huh\n";
+        REQUIRE_THROWS({
+            ImportTagsHandler handler(ss);
+            handler.edit(1, tags);
+        });
+    }
+}
--- a/tests/tags_handlers/insertion_tags_handler_test.cc
+++ b/tests/tags_handlers/insertion_tags_handler_test.cc
@ -0,0 +1,22 @@
+#include "tags_handlers/insertion_tags_handler.h"
+#include "catch.h"
+
+using namespace opustags;
+
+TEST_CASE("insertion tags handler", "[tags_handlers]")
+{
+    Tags tags;
+    const auto streamno = 1;
+    const auto expected_tag_key = "tag_key";
+    const auto expected_tag_value = "tag_value";
+    InsertionTagsHandler handler(
+        streamno, expected_tag_key, expected_tag_value);
+
+    REQUIRE(handler.edit(streamno, tags));
+    REQUIRE(tags.get_all().size() == 1);
+    REQUIRE(tags.get(expected_tag_key) == expected_tag_value);
+
+    REQUIRE(handler.edit(streamno, tags));
+    REQUIRE(tags.get_all().size() == 2);
+    REQUIRE(tags.get(expected_tag_key) == expected_tag_value);
+}
--- a/tests/tags_handlers/listing_tags_handler_test.cc
+++ b/tests/tags_handlers/listing_tags_handler_test.cc
@ -0,0 +1,22 @@
+#include "tags_handlers/listing_tags_handler.h"
+#include "catch.h"
+#include <sstream>
+
+using namespace opustags;
+
+TEST_CASE("listing tags handler", "[tags_handlers]")
+{
+    const auto streamno = 1;
+
+    Tags tags;
+    tags.add("z", "value1");
+    tags.add("a", "value2");
+    tags.add("y", "value3");
+    tags.add("c", "value4");
+
+    std::stringstream ss;
+    ListingTagsHandler handler(streamno, ss);
+    handler.list(streamno, tags);
+
+    REQUIRE(ss.str() == "z=value1\na=value2\ny=value3\nc=value4\n");
+}
--- a/tests/tags_handlers/modification_tags_handler_test.cc
+++ b/tests/tags_handlers/modification_tags_handler_test.cc
@ -0,0 +1,33 @@
+#include "tags_handlers/modification_tags_handler.h"
+#include "catch.h"
+
+using namespace opustags;
+
+TEST_CASE("modification tags handler", "[tags_handlers]")
+{
+    const auto streamno = 1;
+    const auto first_tag_key = "tag_key";
+    const auto other_tag_key = "other_tag_key";
+    const auto dummy_value = "dummy";
+    const auto new_value = "dummy 2";
+
+    Tags tags;
+    tags.add(first_tag_key, dummy_value);
+
+    REQUIRE(tags.get_all().size() == 1);
+
+    // setting nonexistent keys adds them
+    ModificationTagsHandler handler1(streamno, other_tag_key, dummy_value);
+    REQUIRE(handler1.edit(streamno, tags));
+    REQUIRE(tags.get_all().size() == 2);
+    REQUIRE(tags.get(other_tag_key) == dummy_value);
+
+    // setting existing keys overrides their values
+    ModificationTagsHandler handler2(streamno, other_tag_key, new_value);
+    REQUIRE(handler2.edit(streamno, tags));
+    REQUIRE(tags.get_all().size() == 2);
+    REQUIRE(tags.get(other_tag_key) == new_value);
+
+    // setting existing keys reports no modifications if values are the same
+    REQUIRE(!handler2.edit(streamno, tags));
+}
--- a/tests/tags_handlers/removal_tags_handler_test.cc
+++ b/tests/tags_handlers/removal_tags_handler_test.cc
@ -0,0 +1,43 @@
+#include "tags_handlers/removal_tags_handler.h"
+#include "catch.h"
+
+using namespace opustags;
+
+TEST_CASE("removal tags handler", "[tags_handlers]")
+{
+    const auto streamno = 1;
+
+    SECTION("removing a single tag")
+    {
+        const auto expected_tag_key = "tag_key";
+        const auto other_tag_key = "other_tag_key";
+        const auto dummy_value = "dummy";
+        RemovalTagsHandler handler(streamno, expected_tag_key);
+
+        Tags tags;
+        tags.add(expected_tag_key, dummy_value);
+        tags.add(other_tag_key, dummy_value);
+
+        REQUIRE(tags.get_all().size() == 2);
+        REQUIRE(handler.edit(streamno, tags));
+        REQUIRE(tags.get_all().size() == 1);
+        REQUIRE(tags.contains(other_tag_key));
+        REQUIRE(!handler.edit(streamno, tags));
+    }
+
+    SECTION("removing all tags")
+    {
+        RemovalTagsHandler handler(streamno);
+
+        Tags tags;
+        tags.add("z", "value1");
+        tags.add("a", "value2");
+        tags.add("y", "value3");
+        tags.add("c", "value4");
+
+        REQUIRE(tags.get_all().size() == 4);
+        REQUIRE(handler.edit(streamno, tags));
+        REQUIRE(tags.get_all().size() == 0);
+        REQUIRE(!handler.edit(streamno, tags));
+    }
+}
--- a/tests/tags_handlers/stream_tags_handler_test.cc
+++ b/tests/tags_handlers/stream_tags_handler_test.cc
@ -0,0 +1,92 @@
+#include "tags_handlers/stream_tags_handler.h"
+#include "catch.h"
+
+using namespace opustags;
+
+namespace
+{
+    class DummyTagsHandler final : public StreamTagsHandler
+    {
+    public:
+        DummyTagsHandler(const int streamno);
+
+    protected:
+        void list_impl(const Tags &) override;
+        bool edit_impl(Tags &) override;
+
+    public:
+        bool list_fired, edit_fired;
+    };
+}
+
+DummyTagsHandler::DummyTagsHandler(const int streamno)
+    : StreamTagsHandler(streamno), list_fired(false), edit_fired(false)
+{
+}
+
+void DummyTagsHandler::list_impl(const Tags &)
+{
+    list_fired = true;
+}
+
+bool DummyTagsHandler::edit_impl(Tags &)
+{
+    edit_fired = true;
+    return true;
+}
+
+TEST_CASE("stream-based tags handler", "[tags_handlers]")
+{
+    SECTION("concrete stream") {
+        const auto relevant_stream_number = 1;
+        const auto irrelevant_stream_number = 2;
+        Tags dummy_tags;
+        DummyTagsHandler handler(relevant_stream_number);
+
+        SECTION("relevance") {
+            REQUIRE(!handler.relevant(irrelevant_stream_number));
+            REQUIRE(handler.relevant(relevant_stream_number));
+        }
+
+        SECTION("listing") {
+            handler.list(irrelevant_stream_number, dummy_tags);
+            REQUIRE(!handler.list_fired);
+            handler.list(relevant_stream_number, dummy_tags);
+            REQUIRE(handler.list_fired);
+        }
+
+        SECTION("Editing") {
+            REQUIRE(!handler.edit(irrelevant_stream_number, dummy_tags));
+            REQUIRE(!handler.edit_fired);
+            REQUIRE(handler.edit(relevant_stream_number, dummy_tags));
+            REQUIRE(handler.edit_fired);
+        }
+
+        SECTION("finish through listing") {
+            REQUIRE(!handler.edit(irrelevant_stream_number, dummy_tags));
+            REQUIRE(!handler.done());
+            REQUIRE(handler.edit(relevant_stream_number, dummy_tags));
+            REQUIRE(handler.done());
+        }
+
+        SECTION("finish through editing") {
+            handler.list(irrelevant_stream_number, dummy_tags);
+            REQUIRE(!handler.done());
+            handler.list(relevant_stream_number, dummy_tags);
+            REQUIRE(handler.done());
+        }
+    }
+
+    SECTION("any stream") {
+        Tags dummy_tags;
+        DummyTagsHandler handler(StreamTagsHandler::ALL_STREAMS);
+        REQUIRE(handler.relevant(1));
+        REQUIRE(handler.relevant(2));
+        REQUIRE(handler.relevant(3));
+        REQUIRE(!handler.done());
+        handler.list(1, dummy_tags);
+        REQUIRE(!handler.done());
+        handler.list(2, dummy_tags);
+        REQUIRE(!handler.done());
+    }
+}
--- a/tests/tags_test.cc
+++ b/tests/tags_test.cc
@ -0,0 +1,85 @@
+#include "tags.h"
+#include "catch.h"
+
+using namespace opustags;
+
+TEST_CASE("tag manipulation", "[tags]")
+{
+    SECTION("basic operations") {
+        Tags tags;
+        REQUIRE(!tags.contains("a"));
+        tags.add("a", "1");
+        REQUIRE(tags.get("a") == "1");
+        REQUIRE(tags.contains("a"));
+        tags.remove("a");
+        REQUIRE(!tags.contains("a"));
+        REQUIRE_THROWS(tags.get("a"));
+    }
+
+    SECTION("clearing") {
+        Tags tags;
+        tags.add("a", "1");
+        tags.add("b", "2");
+        REQUIRE(tags.get_all().size() == 2);
+        tags.clear();
+        REQUIRE(tags.get_all().empty());
+    }
+
+    SECTION("maintaing order of insertions") {
+        Tags tags;
+        tags.add("z", "1");
+        tags.add("y", "2");
+        tags.add("x", "3");
+        tags.add("y", "4");
+
+        REQUIRE(tags.get_all().size() == 4);
+        REQUIRE(tags.get_all()[0].key == "z");
+        REQUIRE(tags.get_all()[1].key == "y");
+        REQUIRE(tags.get_all()[2].key == "x");
+        REQUIRE(tags.get_all()[3].key == "y");
+
+        tags.remove("z");
+        REQUIRE(tags.get_all().size() == 3);
+        REQUIRE(tags.get_all()[0].key == "y");
+        REQUIRE(tags.get_all()[1].key == "x");
+        REQUIRE(tags.get_all()[2].key == "y");
+
+        tags.add("gamma", "5");
+        REQUIRE(tags.get_all().size() == 4);
+        REQUIRE(tags.get_all()[0].key == "y");
+        REQUIRE(tags.get_all()[1].key == "x");
+        REQUIRE(tags.get_all()[2].key == "y");
+        REQUIRE(tags.get_all()[3].key == "gamma");
+    }
+
+    SECTION("key to multiple values") {
+        // ARTIST is set once per artist.
+        // https://www.xiph.org/vorbis/doc/v-comment.html
+        Tags tags;
+        tags.add("ARTIST", "You");
+        tags.add("ARTIST", "Me");
+        REQUIRE(tags.get_all().size() == 2);
+    }
+
+    SECTION("removing multivalues should remove all of them") {
+        Tags tags;
+        tags.add("ARTIST", "You");
+        tags.add("ARTIST", "Me");
+        tags.remove("ARTIST");
+        REQUIRE(tags.get_all().empty());
+    }
+
+    SECTION("tag parsing") {
+        Tag t = parse_tag("TITLE=Foo=Bar");
+        REQUIRE(t.key == "TITLE");
+        REQUIRE(t.value == "Foo=Bar");
+    }
+
+    SECTION("case insensitiveness for keys") {
+        Tags tags;
+        tags.add("TITLE", "Boop");
+        REQUIRE(tags.get("title") == "Boop");
+        tags.remove("titLE");
+        REQUIRE(tags.get_all().empty());
+    }
+}
Author	SHA1	Message	Date
Frédéric Mangano	2ef9a825da	warn when a handler didn't complete its job issue #16 for some reason I couldn't get it to work it looked like the options weren't properly parsed	2016-05-02 18:09:14 +02:00
Frédéric Mangano	4de88d0ed2	include strerror(errno) in error messages issue #15	2016-05-02 18:09:02 +02:00
Frédéric Mangano	0624376fcc	tags handler: signal start_of_stream and end_of_file end_of_file is the old end_of_stream issue #6	2016-04-08 16:15:28 +02:00
Frédéric Mangano	52e4a8ca58	don't warn about unused parameters it gets annoying, and dropping the names of the parameters in the prototypes sounds like a terrible solution	2016-04-08 16:14:31 +02:00
Frédéric Mangano	dd0656cb07	assign sequence numbers to unknown streams too issue #14	2016-04-08 16:02:40 +02:00
Frédéric Mangano	d3b4a389bc	drop mentions of any kind of “smart reordering” that's the case when the user specifies a --set before a --delete this shouldn't happen, so we might as well not specify it I think issue #5	2016-04-07 13:29:22 +02:00
Frédéric Mangano	410708e252	list_tags: always call end_of_stream when done related to issue #6	2016-04-07 13:29:13 +02:00
Frédéric Mangano	dad987a8da	list_tags: add a test to ensure full scan works it'd require some effort to craft a file where this option matters, but at least we want to make sure the full scan code is run once so we know it doesn't crash close #11	2016-04-06 10:07:41 +02:00
Frédéric Mangano	76bf95a74c	main: do use options.full when calling list_tags	2016-04-06 10:05:53 +02:00
Frédéric Mangano	2d7f812119	harmonize header inclusion style close #7 I don't intend this patch as a piece of art, but it carries the main idea	2016-04-06 10:02:47 +02:00
Frédéric Mangano	1ff2553f5f	assign sequential numbers to streams see issue #14 I remain unsure of whether we should include unknown streams in the sequence in a distant future, if we extend the tool to support more stream types, the numbers would change to include the newly supported streams in the sequence	2016-03-30 17:38:55 +02:00
Frédéric Mangano	eb968dc513	list_tags: stop reading after the headers see #11 remains the command-line to adjust	2016-03-30 17:37:56 +02:00
Frédéric Mangano	a21331057b	ogg: emit HEADER_READY on unknown streams too	2016-03-30 17:37:56 +02:00
Frédéric Mangano	5ae31c9bc9	fix typo in man page	2016-03-30 17:37:56 +02:00
rr-	2957fa3538	Update README to match current install procedure	2016-03-17 08:04:21 +01:00
rr-	74b9cade48	Update README to match current CLI state	2016-03-17 08:03:06 +01:00
rr-	8e9204420b	Handlers: removing nonexistent tag is not an error	2016-03-17 08:00:45 +01:00
rr-	7b616aa671	Fix brace style Breaking habits is difficult	2016-03-17 07:57:36 +01:00
rr-	159340926a	Make --list work also when editing the streams	2016-03-17 07:53:19 +01:00
rr-	e1d954388e	Add --list by default (closes #9 )	2016-03-17 07:52:58 +01:00
rr-	d48573ceef	Add preliminary main() implementation	2016-03-17 07:43:42 +01:00
rr-	d8dcc38777	Options: implement --stream=1,2 (closes #8 )	2016-03-16 20:08:56 +01:00
rr-	7d20fc70b2	Tests: fix warnings about unused parameter	2016-03-16 20:01:39 +01:00
rr-	a210d1229e	Handlers: implement import tags handler	2016-03-16 20:00:28 +01:00
rr-	e60f7f84a0	Fix non deterministic argument parsing	2016-03-16 20:00:27 +01:00
rr-	a3daa0f108	Handlers: implement export tags handler	2016-03-16 20:00:27 +01:00
rr-	84a8d14ae0	Tags: add ability to compare tags	2016-03-16 20:00:27 +01:00
rr-	74904fd516	Tags: make constructible with initializer lists	2016-03-16 19:10:30 +01:00
rr-	fc2a4cb41c	Remove old C code ...which is available on master anyway	2016-03-16 17:53:33 +01:00
rr-	1c2232c197	Build: remove old Makefile	2016-03-16 17:53:10 +01:00
rr-	f26de884aa	Build: make installation targets Usage: cd build cmake .. make sudo make install	2016-03-16 17:53:10 +01:00
rr-	0d91429435	Change path to auto generated version.h This is to make it possible to zip just the src/ directory if one wishes not to use git.	2016-03-16 17:34:50 +01:00
rr-	54571e8bc3	Add git-based version (closes #12 )	2016-03-16 17:32:59 +01:00
rr-	a06f337a63	Options/handlers: add stubs regarding new manpage	2016-03-16 13:48:27 +01:00
rr-	b5d2e03a7b	Options: require output path to be non empty	2016-03-16 13:08:02 +01:00
rr-	f726eaeb91	Options: throw an error for extra arguments	2016-03-16 13:05:00 +01:00
rr-	8f5a6bb534	Options: parse input path	2016-03-16 13:02:21 +01:00
rr-	7f7766f175	Options: change in_place to contain bool This should minify conditional statements to just one, after finishing work, whether to move the path_out back to the original file.	2016-03-16 12:31:43 +01:00
Frédéric Mangano	be3984423f	man: reorganize + add a few options including --version, --full, --export, --list, --no-color	2016-03-09 16:35:33 +01:00
Frédéric Mangano	2443490b0b	update the man page to reflect the new expectations	2016-03-07 17:16:09 +01:00
Frédéric Mangano	a96cc9c222	allow inserting already present tags	2016-03-04 15:23:07 +01:00
Frédéric Mangano	cd550d8d80	move single tag parsing outside of Tags class	2016-03-04 15:21:05 +01:00
Frédéric Mangano	4cd0e34d0d	ogg: fix wrapping loop issue for comment_count since the number of remaining bytes keeps decreasing, it wouldn't cause infinite looping, but it would allow an indefinite number of comments (more than 2^32)	2016-03-04 15:02:17 +01:00
Frédéric Mangano	0e2b1fec9c	tests: make style uniform	2016-03-04 14:50:48 +01:00
Frédéric Mangano	817ba5cba6	actions: fix hardcoded serialno in test I had originally written the tests with a different sample	2016-03-03 21:19:24 +01:00
Frédéric Mangano	20663a847f	testing actions! a tough one	2016-03-03 21:14:46 +01:00
Frédéric Mangano	40bbc90786	ogg: check the validity of streams	2016-03-03 21:14:46 +01:00
Frédéric Mangano	d21517de94	ogg: test a malicious tags packet	2016-03-03 21:14:46 +01:00
Frédéric Mangano	a78906a8d4	specify TagsHandler::end_of_stream	2016-03-03 21:14:36 +01:00
rr-	32c5e2b0a6	Tags: make keys case insensitive	2016-03-03 12:30:56 +01:00
rr-	449235ed5a	Tests: add missing sample	2016-03-03 12:30:03 +01:00
rr-	661c469bd6	Tags: implement multi values, change .set to .add	2016-03-03 12:30:03 +01:00
Frédéric Mangano	7f984e1492	ogg: test multi-stream Ogg files the sample is generated with this command: ffmpeg -i mystery.ogg -i beep.ogg -c copy -map 0:0 -map 1:0 -map 0:0 -shortest mystery-beep.ogg it should be added into the CMakeLists.txt	2016-03-02 16:08:13 +01:00
Frédéric Mangano	4f1070f272	ogg: checked the packetno of the OpusTags packet	2016-03-02 15:53:21 +01:00
Frédéric Mangano	b4dc544031	ogg: test decoding garbage	2016-03-02 15:35:36 +01:00
Frédéric Mangano	5e19657d25	test: tags keys should be case insensitive	2016-03-02 15:20:15 +01:00
Frédéric Mangano	898846f1f4	ogg: test up to tags decoding and it works!	2016-03-02 15:20:05 +01:00
Frédéric Mangano	c19233236a	ogg: flush packets before paging in	2016-03-02 15:15:13 +01:00
Frédéric Mangano	84a0ce55af	proposition of logger	2016-03-02 14:44:04 +01:00
Frédéric Mangano	95ddd2e7da	some more tests for Tags it needs to be a multimap	2016-03-02 14:33:45 +01:00
Frédéric Mangano	9fd629bcc3	ogg: wrong reference magic number a fairy told me as I was commuting	2016-03-02 09:27:33 +01:00
Frédéric Mangano	53fbf533fb	ogg: fix memory issue using shared pointers	2016-03-01 16:24:47 +01:00
Frédéric Mangano	0e3dfbe381	forbid copy of ogg::Stream and ogg::Decoder realize they cause serious memory issues now adding a Stream to the vector doesn't typecheck…	2016-03-01 16:03:11 +01:00
Frédéric Mangano	8364667b4c	at least call the new opustags 2.x	2016-03-01 15:52:10 +01:00
Frédéric Mangano	4d9ee3bf88	ogg decoding test, along with an opus sample	2016-03-01 15:49:04 +01:00
Frédéric Mangano	f941464c61	ogg: Decoder and Encoder to use a reference rather than a pointer	2016-03-01 15:01:24 +01:00
Frédéric Mangano	f469d76e62	untested tags rendering routine draft	2016-03-01 14:37:09 +01:00
Frédéric Mangano	acbf99d276	first untested implementation of tags parsing	2016-03-01 14:08:27 +01:00
Frédéric Mangano	fe7f23576a	ogg: parse magic number	2016-03-01 13:29:01 +01:00
rr-	c101041bd7	StreamTagsHandler: fix done() for ALL_STREAMS	2016-02-25 10:06:49 +01:00
rr-	e5e7952b89	Improve CompositeTagsHandler::done()	2016-02-25 10:03:58 +01:00
rr-	221c314625	ModificationTagsHandler: small optimization	2016-02-24 23:13:16 +01:00
rr-	7b6ad95b35	Refactor Options to use TagsHandlers; add --stream	2016-02-24 22:14:21 +01:00
rr-	24c2dae49e	Add ability to target any stream in TagsHandlers	2016-02-24 22:14:15 +01:00
rr-	02c966bacb	Add getters to TagsHandlers for most things	2016-02-24 21:55:48 +01:00
rr-	4f5d33491b	RemovalTagsHandler: add ability to delete all tags	2016-02-24 21:38:24 +01:00
rr-	d9f123c84c	Add ListingTagsHandler	2016-02-24 21:25:59 +01:00
rr-	a67f8c1472	Change Tags to preserve order of insertion	2016-02-24 21:25:59 +01:00
rr-	d7b187ec59	Remove unused #include	2016-02-24 20:48:26 +01:00
rr-	fca4f81eac	Add ModificationTagsHandler	2016-02-24 20:32:03 +01:00
rr-	b362f6565f	Add RemovalTagsHandler	2016-02-24 20:18:10 +01:00
rr-	6832cbf3f5	Add InsertionTagsHandler + a place for errors	2016-02-24 20:13:38 +01:00
rr-	2ee7702b9d	Add StreamTagsHandler	2016-02-24 20:04:24 +01:00
rr-	aeca60d128	Add CompositeTagsHandler	2016-02-24 20:03:31 +01:00
rr-	1d8d96cdee	Use K&R brace style for SECTION macro in tests	2016-02-24 20:03:31 +01:00
rr-	094bed2b35	Make Tags just an string<->string map for now	2016-02-24 19:43:11 +01:00
rr-	b62ac98ca5	Move TagsHandler to own file, make an interface	2016-02-24 19:42:45 +01:00
Frédéric Mangano	12327e6f68	style fixes missing newlines nullptr instead of NULL bracket tweak	2016-02-24 18:15:39 +01:00
rr-	326c164e09	Restyle to K&R	2016-02-24 18:10:03 +01:00
Frédéric Mangano	a84aeaea96	implement most of ogg::Encoder	2016-02-23 14:23:27 +01:00
Frédéric Mangano	8d1ea8d32d	implement ogg::Decoder	2016-02-23 13:26:22 +01:00
Frédéric Mangano	ff17d35531	partial implementation of ogg::Stream	2016-02-23 11:21:00 +01:00
Frédéric Mangano	c2d6763e2b	implementation of list_tags and edit_tags (actions)	2016-02-23 10:41:27 +01:00
Frédéric Mangano	6baf120a94	more doc in actions.h and ogg.h example uses brief description of the states	2016-02-23 10:41:27 +01:00
Frédéric Mangano	f1109dd04f	specify the expected behavior of the main loops in particular, the TagsHandler interface also, rename the Reader/Writer classes to Decoder/Encoder for clarity	2016-02-22 18:32:54 +01:00
Frédéric Mangano	390c9268a7	use references to ogg_page instead of pointers	2016-02-20 13:55:25 +01:00
Frédéric Mangano	a8a6552f29	sample main loops for ogg manipulation linking now breaks because the ogg module isn't implemented	2016-02-20 13:35:08 +01:00
Frédéric Mangano	e198b5f9ef	first design of the Ogg decoder and encoder	2016-02-20 13:35:08 +01:00
rr-	e474ec8420	Fix libogg linkage	2016-02-20 13:35:08 +01:00
rr-	15c9f187a5	Remove dummy plugs	2016-02-20 13:35:08 +01:00
rr-	3a320a7b39	Add basic option parsing + tests	2016-02-20 13:35:08 +01:00
rr-	5cdcb5457f	Add CMake; prepare basic structure - Added Catch (downloaded automatically by cmake) for unit tests - Added basic tests/ and src/ directories - Added basic unit test example. Any changes to files other than main.cc in src/ will recompile the relevant tests as needed - Added CMakeLists that compiles the project using cmake - Moved the man page to docs/ - Moved old source file to src/ - Since libogg doesn't support cmake based builds, I've added also a module in CMakeModules that searches for it, but I haven't tested if it works yet... - Haven't really touched Makefile - I've changed it only to refer to the new file locations	2016-02-20 13:35:08 +01:00