decoder/Plugin: allow scan_{file,stream}() to throw

Bug #915 is about an I/O exception thrown where none was allowed,
leading to crash via std::terminate().  However, instead of catching
and logging the error inside the decoder plugin, it should be able to
propagate the I/O error to the MPD core, so MPD can avoid trying other
decoder plugins.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/915

src/decoder/DecoderPlugin.hxx

@@ -67,18 +67,22 @@ struct DecoderPlugin {
 	void (*file_decode)(DecoderClient &client, Path path_fs);
 
 	/**
-	 * Scan metadata of a file.
+         * Scan metadata of a file.
+         *
+	 * Throws on I/O error.
 	 *
-	 * @return false if the operation has failed
+	 * @return false if the file was not recognized
 	 */
-	bool (*scan_file)(Path path_fs, TagHandler &handler) noexcept;
+	bool (*scan_file)(Path path_fs, TagHandler &handler);
 
 	/**
-	 * Scan metadata of a file.
+	 * Scan metadata of a stream.
+         *
+	 * Throws on I/O error.
 	 *
-	 * @return false if the operation has failed
+	 * @return false if the stream was not recognized
 	 */
-	bool (*scan_stream)(InputStream &is, TagHandler &handler) noexcept;
+	bool (*scan_stream)(InputStream &is, TagHandler &handler);
 
 	/**
 	 * @brief Return a "virtual" filename for subtracks in
@@ -135,7 +139,7 @@ struct DecoderPlugin {
 	 * Read the tag of a file.
 	 */
 	template<typename P>
-	bool ScanFile(P path_fs, TagHandler &handler) const noexcept {
+	bool ScanFile(P path_fs, TagHandler &handler) const {
 		return scan_file != nullptr
 			? scan_file(path_fs, handler)
 			: false;
@@ -144,7 +148,7 @@ struct DecoderPlugin {
 	/**
 	 * Read the tag of a stream.
 	 */
-	bool ScanStream(InputStream &is, TagHandler &handler) const noexcept {
+	bool ScanStream(InputStream &is, TagHandler &handler) const {
 		return scan_stream != nullptr
 			? scan_stream(is, handler)
 			: false;

src/decoder/plugins/AudiofileDecoderPlugin.cxx

@@ -241,7 +241,7 @@ audiofile_stream_decode(DecoderClient &client, InputStream &is)
 }
 
 static bool
-audiofile_scan_stream(InputStream &is, TagHandler &handler) noexcept
+audiofile_scan_stream(InputStream &is, TagHandler &handler)
 {
 	if (!is.IsSeekable() || !is.KnownSize())
 		return false;

src/decoder/plugins/DsdiffDecoderPlugin.cxx

@@ -449,7 +449,7 @@ dsdiff_stream_decode(DecoderClient &client, InputStream &is)
 }
 
 static bool
-dsdiff_scan_stream(InputStream &is, TagHandler &handler) noexcept
+dsdiff_scan_stream(InputStream &is, TagHandler &handler)
 {
 	DsdiffMetaData metadata;
 	DsdiffChunkHeader chunk_header;

src/decoder/plugins/DsfDecoderPlugin.cxx

@@ -326,7 +326,7 @@ dsf_stream_decode(DecoderClient &client, InputStream &is)
 }
 
 static bool
-dsf_scan_stream(InputStream &is, TagHandler &handler) noexcept
+dsf_scan_stream(InputStream &is, TagHandler &handler)
 {
 	/* check DSF metadata */
 	DsfMetaData metadata;

src/decoder/plugins/FaadDecoderPlugin.cxx

@@ -414,7 +414,7 @@ faad_stream_decode(DecoderClient &client, InputStream &is)
 }
 
 static bool
-faad_scan_stream(InputStream &is, TagHandler &handler) noexcept
+faad_scan_stream(InputStream &is, TagHandler &handler)
 {
 	auto result = faad_get_file_time(is);
 	if (!result.first)

src/decoder/plugins/FfmpegDecoderPlugin.cxx

@@ -646,8 +646,7 @@ ffmpeg_decode(DecoderClient &client, InputStream &input)
 }
 
 static bool
-FfmpegScanStream(AVFormatContext &format_context,
-		 TagHandler &handler) noexcept
+FfmpegScanStream(AVFormatContext &format_context, TagHandler &handler)
 {
 	const int find_result =
 		avformat_find_stream_info(&format_context, nullptr);
@@ -680,7 +679,7 @@ FfmpegScanStream(AVFormatContext &format_context,
 }
 
 static bool
-ffmpeg_scan_stream(InputStream &is, TagHandler &handler) noexcept
+ffmpeg_scan_stream(InputStream &is, TagHandler &handler)
 {
 	AvioStream stream(nullptr, is);
 	if (!stream.Open())

src/decoder/plugins/FlacDecoderPlugin.cxx

@@ -69,7 +69,7 @@ flac_write_cb(const FLAC__StreamDecoder *dec, const FLAC__Frame *frame,
 }
 
 static bool
-flac_scan_file(Path path_fs, TagHandler &handler) noexcept
+flac_scan_file(Path path_fs, TagHandler &handler)
 {
 	FlacMetadataChain chain;
 	if (!chain.Read(NarrowPath(path_fs))) {
@@ -84,7 +84,7 @@ flac_scan_file(Path path_fs, TagHandler &handler) noexcept
 }
 
 static bool
-flac_scan_stream(InputStream &is, TagHandler &handler) noexcept
+flac_scan_stream(InputStream &is, TagHandler &handler)
 {
 	FlacMetadataChain chain;
 	if (!chain.Read(is)) {
@@ -313,7 +313,7 @@ oggflac_init(gcc_unused const ConfigBlock &block)
 }
 
 static bool
-oggflac_scan_file(Path path_fs, TagHandler &handler) noexcept
+oggflac_scan_file(Path path_fs, TagHandler &handler)
 {
 	FlacMetadataChain chain;
 	if (!chain.ReadOgg(NarrowPath(path_fs))) {
@@ -328,7 +328,7 @@ oggflac_scan_file(Path path_fs, TagHandler &handler) noexcept
 }
 
 static bool
-oggflac_scan_stream(InputStream &is, TagHandler &handler) noexcept
+oggflac_scan_stream(InputStream &is, TagHandler &handler)
 {
 	FlacMetadataChain chain;
 	if (!chain.ReadOgg(is)) {

src/decoder/plugins/MadDecoderPlugin.cxx

@@ -1051,7 +1051,7 @@ MadDecoder::RunScan(TagHandler &handler) noexcept
 }
 
 static bool
-mad_decoder_scan_stream(InputStream &is, TagHandler &handler) noexcept
+mad_decoder_scan_stream(InputStream &is, TagHandler &handler)
 {
 	MadDecoder data(nullptr, is);
 	return data.RunScan(handler);

src/decoder/plugins/MpcdecDecoderPlugin.cxx

@@ -275,7 +275,7 @@ mpcdec_get_file_duration(InputStream &is)
 }
 
 static bool
-mpcdec_scan_stream(InputStream &is, TagHandler &handler) noexcept
+mpcdec_scan_stream(InputStream &is, TagHandler &handler)
 {
 	const auto duration = mpcdec_get_file_duration(is);
 	if (duration.IsNegative())

src/decoder/plugins/OpusDecoderPlugin.cxx

@@ -424,7 +424,7 @@ VisitOpusDuration(InputStream &is, OggSyncState &sync, OggStreamState &stream,
 }
 
 static bool
-mpd_opus_scan_stream(InputStream &is, TagHandler &handler) noexcept
+mpd_opus_scan_stream(InputStream &is, TagHandler &handler)
 {
 	InputStreamReader reader(is);
 	OggSyncState oy(reader);

src/decoder/plugins/SndfileDecoderPlugin.cxx

@@ -267,7 +267,7 @@ static constexpr struct {
 };
 
 static bool
-sndfile_scan_stream(InputStream &is, TagHandler &handler) noexcept
+sndfile_scan_stream(InputStream &is, TagHandler &handler)
 {
 	SF_INFO info;
 

src/decoder/plugins/VorbisDecoderPlugin.cxx

@@ -370,7 +370,7 @@ VisitVorbisDuration(InputStream &is,
 }
 
 static bool
-vorbis_scan_stream(InputStream &is, TagHandler &handler) noexcept
+vorbis_scan_stream(InputStream &is, TagHandler &handler)
 {
 	/* initialize libogg */
 

src/decoder/plugins/WavpackDecoderPlugin.cxx

@@ -614,7 +614,7 @@ wavpack_scan_file(Path path_fs, TagHandler &handler) noexcept
 }
 
 static bool
-wavpack_scan_stream(InputStream &is, TagHandler &handler) noexcept
+wavpack_scan_stream(InputStream &is, TagHandler &handler)
 {
 	WavpackInput isp(nullptr, is);