From 23049a7ff69b2f62d1696c63729dc1dc2f646961 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Mangano-Tarumi?= <fmang@mg0.fr>
Date: Sat, 8 Dec 2018 11:24:17 -0500
Subject: [PATCH] introduce ot::is_opus_stream

---
 src/ogg.cc     |  9 +++++++++
 src/opustags.h |  7 +++++++
 t/ogg.cc       | 38 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/src/ogg.cc b/src/ogg.cc
index a8fd51f..456da4a 100644
--- a/src/ogg.cc
+++ b/src/ogg.cc
@@ -14,6 +14,15 @@
 
 using namespace std::literals::string_literals;
 
+bool ot::is_opus_stream(const ogg_page& identification_header)
+{
+	if (ogg_page_bos(&identification_header) == 0)
+		return false;
+	if (identification_header.body_len < 8)
+		return false;
+	return (memcmp(identification_header.body, "OpusHead", 8) == 0);
+}
+
 ot::status ot::ogg_reader::read_page()
 {
 	while (ogg_sync_pageout(&sync, &page) != 1) {
diff --git a/src/opustags.h b/src/opustags.h
index 26c0b96..e5455bd 100644
--- a/src/opustags.h
+++ b/src/opustags.h
@@ -146,6 +146,13 @@ struct ogg_logical_stream : ogg_stream_state {
 	}
 };
 
+/**
+ * Identify the codec of a logical stream based on the first bytes of the first packet of the first
+ * page. For Opus, the first 8 bytes must be OpusHead. Any other signature is assumed to be another
+ * codec.
+ */
+bool is_opus_stream(const ogg_page& identification_header);
+
 /**
  * Ogg reader, combining a FILE input, an ogg_sync_state reading the pages.
  *
diff --git a/t/ogg.cc b/t/ogg.cc
index f1c4d4c..d1ac483 100644
--- a/t/ogg.cc
+++ b/t/ogg.cc
@@ -14,6 +14,8 @@ static void check_ref_ogg()
 	ot::status rc = reader.read_page();
 	if (rc != ot::st::ok)
 		throw failure("could not read the first page");
+	if (!ot::is_opus_stream(reader.page))
+		throw failure("failed to identify the stream as opus");
 	rc = reader.read_header_packet([](ogg_packet& p) {
 		if (p.bytes != 19)
 			throw failure("unexpected length for the first packet");
@@ -114,10 +116,44 @@ static void check_memory_ogg()
 	}
 }
 
+void check_identification()
+{
+	auto good_header = (unsigned char*)
+		"\x4f\x67\x67\x53\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x42\xf2"
+		"\xe6\xc7\x00\x00\x00\x00\x7e\xc3\x57\x2b\x01\x13";
+	auto good_body = (unsigned char*) "OpusHeadABCD";
+
+	ogg_page id;
+	id.header = good_header;
+	id.header_len = 28;
+	id.body = good_body;
+	id.body_len = 12;
+	if (!ot::is_opus_stream(id))
+		throw failure("could not identify opus header");
+
+	// Bad body
+	id.body_len = 7;
+	if (ot::is_opus_stream(id))
+		throw failure("opus header was too short to be valid");
+	id.body_len = 12;
+	id.body = (unsigned char*) "Not_OpusHead";
+	if (ot::is_opus_stream(id))
+		throw failure("was not an opus header");
+	id.body = good_body;
+
+	// Remove the BoS bit from the header.
+	id.header = (unsigned char*)
+		"\x4f\x67\x67\x53\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x42\xf2"
+		"\xe6\xc7\x00\x00\x00\x00\x7e\xc3\x57\x2b\x01\x13";
+	if (ot::is_opus_stream(id))
+		throw failure("was not the beginning of a stream");
+}
+
 int main(int argc, char **argv)
 {
-	std::cout << "1..2\n";
+	std::cout << "1..3\n";
 	run(check_ref_ogg, "check a reference ogg stream");
 	run(check_memory_ogg, "build and check a fresh stream");
+	run(check_identification, "stream identification");
 	return 0;
 }