[player] Better fix for resuming playback af long pause (issue #766)

The fix in commit 3928ab6 broke resuming from an underrun, since it meant that
pb_resume() would flush the input buffer. With this fix it is possible to call
input_resume(), which will not flush the buffer if the source is already open.

Also renamed some functions in player.c for consistency.

src/input.c

@@ -113,7 +113,7 @@ struct input_arg
 {
   uint32_t item_id;
   int seek_ms;
-  struct input_metadata *metadata;
+  bool resume;
 };
 
 /* --- Globals --- */
@@ -462,6 +462,16 @@ start(void *arg, int *retval)
   // If we are asked to start the item that is currently open we can just seek
   if (input_now_reading.open && cmdarg->item_id == input_now_reading.item_id)
     {
+      // When we resume we don't want to flush & seek, since that has either
+      // already been done, or it is not desired because we just filled the
+      // buffer after an underrun.
+      if (cmdarg->resume)
+	{
+	  DPRINTF(E_DBG, L_PLAYER, "Resuming input read loop for item '%s' (item id %" PRIu32 ")\n", input_now_reading.path, input_now_reading.item_id);
+	  *retval = cmdarg->seek_ms;
+	  return COMMAND_END;
+	}
+
       flush(&flags);
 
       ret = seek(&input_now_reading, cmdarg->seek_ms);
@@ -763,6 +773,19 @@ input_seek(uint32_t item_id, int seek_ms)
 
   cmdarg.item_id = item_id;
   cmdarg.seek_ms = seek_ms;
+  cmdarg.resume  = false;
+
+  return commands_exec_sync(cmdbase, start, NULL, &cmdarg);
+}
+
+int
+input_resume(uint32_t item_id, int seek_ms)
+{
+  struct input_arg cmdarg;
+
+  cmdarg.item_id = item_id;
+  cmdarg.seek_ms = seek_ms;
+  cmdarg.resume  = true;
 
   return commands_exec_sync(cmdbase, start, NULL, &cmdarg);
 }
@@ -776,6 +799,7 @@ input_start(uint32_t item_id)
 
   cmdarg->item_id = item_id;
   cmdarg->seek_ms = 0;
+  cmdarg->resume  = false;
 
   commands_exec_async(cmdbase, start, cmdarg);
 }

src/input.h

@@ -196,6 +196,17 @@ input_buffer_full_cb(input_cb cb);
 int
 input_seek(uint32_t item_id, int seek_ms);
 
+/*
+ * Same as input_seek(), except if the item is already being read we don't do
+ * anything (no flush & seek)
+ *
+ * @in  item_id  Queue item id to start playing
+ * @in  seek_ms  Position to start playing
+ * @return       Actual seek position if seekable, 0 otherwise, -1 on error
+ */
+int
+input_resume(uint32_t item_id, int seek_ms);
+
 /*
  * Same as input_seek(), just non-blocking and does not offer seek.
  *

src/player.c

@@ -612,19 +612,8 @@ source_stop(void)
   input_stop();
 }
 
-static void
-source_start(struct player_source *ps)
-{
-  if (!ps)
-    return;
-
-  DPRINTF(E_DBG, L_PLAYER, "Opening next track: '%s' (id=%d)\n", ps->path, ps->item_id);
-
-  input_start(ps->item_id);
-}
-
 static int
-source_restart(struct player_source *ps)
+source_start(struct player_source *ps)
 {
   short flags;
 
@@ -638,6 +627,32 @@ source_restart(struct player_source *ps)
   return input_seek(ps->item_id, (int)ps->seek_ms);
 }
 
+static void
+source_next(struct player_source *ps)
+{
+  if (!ps)
+    return;
+
+  DPRINTF(E_DBG, L_PLAYER, "Opening next track: '%s' (id=%d)\n", ps->path, ps->item_id);
+
+  input_start(ps->item_id);
+}
+
+static int
+source_restart(void)
+{
+  if (!pb_session.playing_now)
+    {
+      DPRINTF(E_LOG, L_PLAYER, "Bug! source_restart called, but playing_now is null\n");
+      return -1;
+    }
+
+  DPRINTF(E_DBG, L_PLAYER, "Restarting track: '%s' (id=%d, pos=%d)\n", pb_session.playing_now->path, pb_session.playing_now->item_id, pb_session.playing_now->pos_ms);
+
+  input_resume(pb_session.playing_now->item_id, pb_session.playing_now->pos_ms);
+
+  return 0;
+}
 
 /* ------------------------ Playback session upkeep ------------------------- */
 
@@ -910,7 +925,7 @@ event_read_start_next()
   session_update_read_next(ps);
 
   // Starts the input read loop
-  source_start(pb_session.source_list);
+  source_next(pb_session.source_list);
 }
 
 static void
@@ -1604,7 +1619,7 @@ pb_session_start(struct db_queue_item *queue_item, uint32_t seek_ms)
   session_start(ps);
 
   // Sets of opening of the new source
-  while ( (ret = source_restart(ps)) < 0)
+  while ( (ret = source_start(ps)) < 0)
     {
       // Couldn't start requested item, skip to next and remove failed item from queue
       item_id = ps->item_id;
@@ -1665,7 +1680,7 @@ pb_resume(void)
 {
   int ret;
 
-  ret = source_restart(pb_session.playing_now);
+  ret = source_restart();
   if (ret < 0)
     {
       pb_abort();