decoder/Bridge: add flag to make initial seek errors fatal

When the client wants to seek, but the decoder has already finished
decoding the current song, the player restarts the decoder with an
initial seek at the new position.  When this initial seek fails, MPD
pretends nothing has happened and plays this song from the start.

With this new flag, a restarted decoder marks the initial seek as
"essential" and fails the decoder if that seek fails.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/895

NEWS

@@ -7,6 +7,8 @@ ver 0.21.24 (not yet released)
   - modplug: fix Windows build failure
   - wildmidi: attempt to detect WildMidi using pkg-config
   - wildmidi: fix Windows build failure
+* player
+  - don't restart current song if seeking beyond end
 * Android
   - enable the decoder plugins ModPlug and WildMidi
   - fix build failure with Android NDK r21

src/decoder/Bridge.cxx

@@ -33,6 +33,8 @@
 #include "util/ConstBuffer.hxx"
 #include "util/StringBuffer.hxx"
 
+#include <stdexcept>
+
 #include <assert.h>
 #include <string.h>
 #include <math.h>
@@ -344,6 +346,10 @@ DecoderBridge::SeekError()
 		/* d'oh, we can't seek to the sub-song start position,
 		   what now? - no idea, ignoring the problem for now. */
 		initial_seek_running = false;
+
+		if (initial_seek_essential)
+			error = std::make_exception_ptr(std::runtime_error("Decoder failed to seek"));
+
 		return;
 	}
 

src/decoder/Bridge.hxx

@@ -62,6 +62,11 @@ public:
 	 */
 	bool initial_seek_pending;
 
+	/**
+	 * Are initial seek failures fatal?
+	 */
+	const bool initial_seek_essential;
+
 	/**
 	 * Is the initial seek currently running?  During this time,
 	 * the decoder command is SEEK.  This flag is set by
@@ -107,9 +112,11 @@ public:
 	std::exception_ptr error;
 
 	DecoderBridge(DecoderControl &_dc, bool _initial_seek_pending,
+		      bool _initial_seek_essential,
 		      std::unique_ptr<Tag> _tag)
 		:dc(_dc),
 		 initial_seek_pending(_initial_seek_pending),
+		 initial_seek_essential(_initial_seek_essential),
 		 song_tag(std::move(_tag)) {}
 
 	~DecoderBridge();

src/decoder/Control.cxx

@@ -90,6 +90,7 @@ DecoderControl::IsCurrentSong(const DetachedSong &_song) const noexcept
 void
 DecoderControl::Start(std::unique_ptr<DetachedSong> _song,
 		      SongTime _start_time, SongTime _end_time,
+		      bool _initial_seek_essential,
 		      MusicBuffer &_buffer,
 		      std::shared_ptr<MusicPipe> _pipe) noexcept
 {
@@ -99,6 +100,7 @@ DecoderControl::Start(std::unique_ptr<DetachedSong> _song,
 	song = std::move(_song);
 	start_time = _start_time;
 	end_time = _end_time;
+	initial_seek_essential = _initial_seek_essential;
 	buffer = &_buffer;
 	pipe = std::move(_pipe);
 

src/decoder/Control.hxx

@@ -117,6 +117,12 @@ public:
 
 	bool seek_error;
 	bool seekable;
+
+	/**
+	 * @see #DecoderBridge::initial_seek_essential
+	 */
+	bool initial_seek_essential;
+
 	SongTime seek_time;
 
 private:
@@ -398,11 +404,14 @@ public:
 	 * owned and freed by the decoder
 	 * @param start_time see #DecoderControl
 	 * @param end_time see #DecoderControl
+	 * @param initial_seek_essential see
+	 * #DecoderBridge::initial_seek_essential
 	 * @param pipe the pipe which receives the decoded chunks (owned by
 	 * the caller)
 	 */
 	void Start(std::unique_ptr<DetachedSong> song,
 		   SongTime start_time, SongTime end_time,
+		   bool initial_seek_essential,
 		   MusicBuffer &buffer,
 		   std::shared_ptr<MusicPipe> pipe) noexcept;
 

src/decoder/Thread.cxx

@@ -461,6 +461,7 @@ decoder_run_song(DecoderControl &dc,
 		dc.start_time = dc.seek_time;
 
 	DecoderBridge bridge(dc, dc.start_time.IsPositive(),
+			     dc.initial_seek_essential,
 			     /* pass the song tag only if it's
 				authoritative, i.e. if it's a local
 				file - tags on "stream" songs are just

src/player/Thread.cxx

@@ -223,7 +223,8 @@ private:
 	 *
 	 * Caller must lock the mutex.
 	 */
-	void StartDecoder(std::shared_ptr<MusicPipe> pipe) noexcept;
+	void StartDecoder(std::shared_ptr<MusicPipe> pipe,
+			  bool initial_seek_essential) noexcept;
 
 	/**
 	 * The decoder has acknowledged the "START" command (see
@@ -364,7 +365,8 @@ public:
 };
 
 void
-Player::StartDecoder(std::shared_ptr<MusicPipe> _pipe) noexcept
+Player::StartDecoder(std::shared_ptr<MusicPipe> _pipe,
+		     bool initial_seek_essential) noexcept
 {
 	assert(queued || pc.command == PlayerCommand::SEEK);
 	assert(pc.next_song != nullptr);
@@ -376,6 +378,7 @@ Player::StartDecoder(std::shared_ptr<MusicPipe> _pipe) noexcept
 
 	dc.Start(std::make_unique<DetachedSong>(*pc.next_song),
 		 start_time, pc.next_song->GetEndTime(),
+		 initial_seek_essential,
 		 buffer, std::move(_pipe));
 }
 
@@ -633,7 +636,7 @@ Player::SeekDecoder() noexcept
 		pipe->Clear();
 
 		/* re-start the decoder */
-		StartDecoder(pipe);
+		StartDecoder(pipe, true);
 		ActivateDecoder();
 
 		pc.seeking = true;
@@ -711,7 +714,7 @@ Player::ProcessCommand() noexcept
 		pc.CommandFinished();
 
 		if (dc.IsIdle())
-			StartDecoder(std::make_shared<MusicPipe>());
+			StartDecoder(std::make_shared<MusicPipe>(), false);
 
 		break;
 
@@ -982,7 +985,7 @@ Player::Run() noexcept
 
 	const std::lock_guard<Mutex> lock(pc.mutex);
 
-	StartDecoder(pipe);
+	StartDecoder(pipe, true);
 	ActivateDecoder();
 
 	pc.state = PlayerState::PLAY;
@@ -1022,7 +1025,7 @@ Player::Run() noexcept
 
 			assert(dc.pipe == nullptr || dc.pipe == pipe);
 
-			StartDecoder(std::make_shared<MusicPipe>());
+			StartDecoder(std::make_shared<MusicPipe>(), false);
 		}
 
 		if (/* no cross-fading if MPD is going to pause at the