demux: change hack for closing subtitle files early

Subtitles (and a few other file types, like playlists) are not streamed,
but fully read on opening. This means keeping the file handle or network
socket open is a waste of resources and could cause other weird
behavior. This is why there's a hack to close them after opening.

Change this hack to make the demuxer itself do this, which is less
weird. (Until recently, demuxer->stream ownership was more complex,
which is why it was done this way.)

There is some evil shit due to a huge ownership/lifetime mess of various
objects. Especially EDL (the currently only nested demuxer case)
requires being careful about mp_cancel and passing down stream pointers.

As one defensive programming measure, stop accessing the "stream"
variable in open_given_type(), even where it would still work. This
includes removing a redundant line of code, and removing the peak call,
which should not be needed anymore, as the remaining demuxers do this
mostly correctly.

demux/demux.c

@@ -2252,20 +2252,23 @@ static void demux_init_cuesheet(struct demuxer *demuxer)
     }
 }
 
-static void demux_maybe_replace_stream(struct demuxer *demuxer)
+// A demuxer can use this during opening if all data was read from the stream.
+// Calling this after opening was completed is not allowed. Also, if opening
+// failed, this must not be called (or trying another demuxer would fail).
+// Useful so that e.g. subtitles don't keep the file or socket open.
+// Replaces it with a dummy stream for dumb reasons.
+// If there's ever the situation where we can't allow the demuxer to close
+// the stream, this function could ignore the request.
+void demux_close_stream(struct demuxer *demuxer)
 {
     struct demux_internal *in = demuxer->in;
-    assert(!in->threading && demuxer == in->d_user);
+    assert(!in->threading && demuxer == in->d_thread);
 
-    if (demuxer->fully_read) {
-        MP_VERBOSE(demuxer, "assuming demuxer read all data; closing stream\n");
-        free_stream(demuxer->stream);
-        demuxer->stream = open_memory_stream(NULL, 0); // dummy
-        in->d_thread->stream = demuxer->stream;
-
-        if (demuxer->desc->control)
-            demuxer->desc->control(in->d_thread, DEMUXER_CTRL_REPLACE_STREAM, NULL);
-    }
+    MP_VERBOSE(demuxer, "demuxer read all data; closing stream\n");
+    free_stream(demuxer->stream);
+    demuxer->stream = open_memory_stream(NULL, 0); // dummy
+    demuxer->stream->cancel = demuxer->cancel;
+    in->d_user->stream = demuxer->stream;
 }
 
 static void demux_init_ccs(struct demuxer *demuxer, struct demux_opts *opts)
@@ -2335,7 +2338,6 @@ static struct demuxer *open_given_type(struct mpv_global *global,
         .events = DEMUX_EVENT_ALL,
         .duration = -1,
     };
-    demuxer->seekable = stream->seekable;
 
     struct demux_internal *in = demuxer->in = talloc_ptrtype(demuxer, in);
     *in = (struct demux_internal){
@@ -2370,12 +2372,8 @@ static struct demuxer *open_given_type(struct mpv_global *global,
            desc->name, d_level(check));
 
     // not for DVD/BD/DVB in particular
-    if (stream->seekable && (!params || !params->timeline))
-        stream_seek(stream, 0);
-
-    // Peek this much data to avoid that stream_read() run by some demuxers
-    // will flush previous peeked data.
-    stream_peek(stream, STREAM_BUFFER_SIZE);
+    if (demuxer->stream->seekable && (!params || !params->timeline))
+        stream_seek(demuxer->stream, 0);
 
     in->d_thread->params = params; // temporary during open()
     int ret = demuxer->desc->open(in->d_thread, check);
@@ -2414,8 +2412,8 @@ static struct demuxer *open_given_type(struct mpv_global *global,
                 struct demuxer_params params2 = {0};
                 params2.timeline = tl;
                 struct demuxer *sub =
-                    open_given_type(global, log, &demuxer_desc_timeline, stream,
-                                    &params2, DEMUX_CHECK_FORCE);
+                    open_given_type(global, log, &demuxer_desc_timeline,
+                                    demuxer->stream, &params2, DEMUX_CHECK_FORCE);
                 if (sub) {
                     demuxer = sub;
                 } else {
@@ -2438,6 +2436,7 @@ static const int d_force[]   = {DEMUX_CHECK_FORCE, -1};
 // If params->does_not_own_stream==false, this does _not_ free the stream if
 // opening fails. But if it succeeds, a later demux_free() call will free the
 // stream.
+// This may free the stream parameter on success.
 static struct demuxer *demux_open(struct stream *stream,
                                   struct demuxer_params *params,
                                   struct mpv_global *global)
@@ -2518,7 +2517,7 @@ struct demuxer *demux_open_url(const char *url,
     struct demuxer *d = demux_open(s, params, global);
     if (d) {
         talloc_steal(d->in, priv_cancel);
-        demux_maybe_replace_stream(d);
+        assert(d->cancel);
     } else {
         params->demuxer_failed = true;
         free_stream(s);

demux/demux.h

@@ -32,7 +32,6 @@
 
 enum demux_ctrl {
     DEMUXER_CTRL_SWITCHED_TRACKS = 1,
-    DEMUXER_CTRL_REPLACE_STREAM,
 };
 
 #define MAX_SEEK_RANGES 10
@@ -295,6 +294,7 @@ int demuxer_add_chapter(demuxer_t *demuxer, char *name,
                         double pts, uint64_t demuxer_id);
 void demux_set_stream_tags(struct demuxer *demuxer, struct sh_stream *sh,
                            struct mp_tags *tags);
+void demux_close_stream(struct demuxer *demuxer);
 
 void demux_metadata_changed(demuxer_t *demuxer);
 void demux_update(demuxer_t *demuxer);

demux/demux_cue.c

@@ -264,6 +264,8 @@ static int try_open_file(struct demuxer *demuxer, enum demux_check check)
         return -1;
     }
 
+    demux_close_stream(demuxer);
+
     mp_tags_merge(demuxer->metadata, p->f->tags);
     return 0;
 }

demux/demux_edl.c

@@ -388,6 +388,7 @@ static int try_open_file(struct demuxer *demuxer, enum demux_check check)
     if (p->data.start == NULL)
         return -1;
     bstr_eatstart0(&p->data, HEADER);
+    demux_close_stream(demuxer);
     return 0;
 }
 

demux/demux_lavf.c

@@ -1063,6 +1063,14 @@ static int demux_open_lavf(demuxer_t *demuxer, enum demux_check check)
         demuxer->seekable = true;
     }
 
+    if (demuxer->fully_read) {
+        demux_close_stream(demuxer);
+        if (priv->own_stream)
+            free_stream(priv->stream);
+        priv->own_stream = false;
+        priv->stream = demuxer->stream;
+    }
+
     return 0;
 }
 
@@ -1179,18 +1187,10 @@ static void demux_seek_lavf(demuxer_t *demuxer, double seek_pts, int flags)
 
 static int demux_lavf_control(demuxer_t *demuxer, int cmd, void *arg)
 {
-    lavf_priv_t *priv = demuxer->priv;
-
     switch (cmd) {
     case DEMUXER_CTRL_SWITCHED_TRACKS:
         select_tracks(demuxer, 0);
         return CONTROL_OK;
-    case DEMUXER_CTRL_REPLACE_STREAM:
-        if (priv->own_stream)
-            free_stream(priv->stream);
-        priv->own_stream = false;
-        priv->stream = demuxer->stream;
-        return CONTROL_OK;
     default:
         return CONTROL_UNKNOWN;
     }

demux/demux_libarchive.c

@@ -85,6 +85,7 @@ static int open_file(struct demuxer *demuxer, enum demux_check check)
     demuxer->fully_read = true;
 
     mp_archive_free(mpa);
+    demux_close_stream(demuxer);
 
     return 0;
 }

demux/demux_playlist.c

@@ -391,6 +391,8 @@ static int open_file(struct demuxer *demuxer, enum demux_check check)
     demuxer->filetype = p->format ? p->format : fmt->name;
     demuxer->fully_read = true;
     talloc_free(p);
+    if (ok)
+        demux_close_stream(demuxer);
     return ok ? 0 : -1;
 }