From df03cdf951ca1a0c6a8c0bde7868dbad8a26bf68 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Mangano-Tarumi?= <fmang@mg0.fr>
Date: Sun, 11 Oct 2020 16:50:50 +0200
Subject: [PATCH] Introduce ot::execute_process

---
 src/opustags.h |  6 ++++++
 src/system.cc  | 28 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/src/opustags.h b/src/opustags.h
index 14f280d..5c47702 100644
--- a/src/opustags.h
+++ b/src/opustags.h
@@ -61,6 +61,7 @@ enum class st {
 	/* System */
 	badly_encoded,
 	information_lost,
+	child_process_failed,
 	/* Ogg */
 	bad_stream,
 	end_of_stream,
@@ -162,6 +163,11 @@ private:
 	iconv_t cd; /**< conversion descriptor */
 };
 
+// Execute the process specified in args using execlp. Wait for the process to
+// exit and return st::ok on success, or st::child_process_failed if it did not
+// exit with 0.
+ot::status execute_process(std::string_view arg0, std::string_view arg1);
+
 /** \} */
 
 /***********************************************************************************************//**
diff --git a/src/system.cc b/src/system.cc
index 2d1dbbf..c4a88e4 100644
--- a/src/system.cc
+++ b/src/system.cc
@@ -14,8 +14,11 @@
 #include <errno.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 #include <unistd.h>
 
+using namespace std::string_literals;
+
 ot::status ot::partial_file::open(const char* destination)
 {
 	abort();
@@ -132,3 +135,28 @@ ot::status ot::encoding_converter::operator()(const char* in, size_t n, std::str
 		        "in string '" + std::string(in, n) + "'."};
 	return ot::st::ok;
 }
+
+ot::status ot::execute_process(std::string_view arg0, std::string_view arg1)
+{
+	pid_t pid = fork();
+	if (pid == -1) {
+		return {st::standard_error, "Could not fork: "s + strerror(errno)};
+	} else if (pid == 0) {
+		execlp(arg0.data(), arg0.data(), arg1.data(), nullptr);
+		// execvp only returns on error. Let’s not have a runaway child process and kill it.
+		fprintf(stderr, "error: execvp failed: %s\n", strerror(errno));
+		exit(1);
+	}
+
+	int status = 0;
+	if (waitpid(pid, &status, 0) == -1)
+		return {st::standard_error, "waitpid error: "s + strerror(errno)};
+	else if (!WIFEXITED(status))
+		return {st::child_process_failed,
+		        "Child process did not terminate normally: "s + strerror(errno)};
+	else if (WEXITSTATUS(status) != 0)
+		return {st::child_process_failed,
+		        "Child process exited with " + std::to_string(WEXITSTATUS(status))};
+
+	return st::ok;
+}