stream: add a generic concat implementation

This is not available to users. It can be used only though the
stream_concat_open(). It's unused yet; to be used in the following
commit.

stream/stream.h

@@ -179,6 +179,10 @@ char *mp_url_escape(void *talloc_ctx, const char *s, const char *ok);
 // stream_memory.c
 struct stream *stream_memory_open(struct mpv_global *global, void *data, int len);
 
+// stream_concat.c
+struct stream *stream_concat_open(struct mpv_global *global, struct mp_cancel *c,
+                                  struct stream **streams, int num_streams);
+
 // stream_file.c
 char *mp_file_url_to_filename(void *talloc_ctx, bstr url);
 char *mp_file_get_path(void *talloc_ctx, bstr url);

stream/stream_concat.c

@@ -0,0 +1,160 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libavutil/common.h>
+
+#include "common/common.h"
+#include "stream.h"
+
+struct priv {
+    struct stream **streams;
+    int num_streams;
+
+    int64_t size;
+
+    int cur; // streams[cur] is the stream for current stream.pos
+};
+
+static int fill_buffer(struct stream *s, char* buffer, int len)
+{
+    struct priv *p = s->priv;
+
+    while (1) {
+        int res = stream_read_partial(p->streams[p->cur], buffer, len);
+        if (res || p->cur == p->num_streams - 1)
+            return res;
+
+        p->cur += 1;
+        if (s->seekable)
+            stream_seek(p->streams[p->cur], 0);
+    }
+}
+
+static int seek(struct stream *s, int64_t newpos)
+{
+    struct priv *p = s->priv;
+
+    int64_t next_pos = 0;
+    int64_t base_pos = 0;
+
+    // Look for the last stream whose start position is <= newpos.
+    // Note that the last stream's size is essentially ignored. The last
+    // stream is allowed to have an unknown size.
+    for (int n = 0; n < p->num_streams; n++) {
+        if (next_pos > newpos)
+            break;
+
+        base_pos = next_pos;
+        p->cur = n;
+
+        int64_t size = stream_get_size(p->streams[n]);
+        if (size < 0)
+            break;
+
+        next_pos = base_pos + size;
+    }
+
+    int ok = stream_seek(p->streams[p->cur], newpos - base_pos);
+    s->pos = base_pos + stream_tell(p->streams[p->cur]);
+    return ok;
+}
+
+static int control(struct stream *s, int cmd, void *arg)
+{
+    struct priv *p = s->priv;
+    if (cmd == STREAM_CTRL_GET_SIZE && p->size >= 0) {
+        *(int64_t *)arg = p->size;
+        return 1;
+    }
+    return STREAM_UNSUPPORTED;
+}
+
+static void s_close(struct stream *s)
+{
+    struct priv *p = s->priv;
+
+    for (int n = 0; n < p->num_streams; n++)
+        free_stream(p->streams[n]);
+}
+
+static int open2(struct stream *stream, void *arg)
+{
+    struct priv *p = talloc_zero(stream, struct priv);
+    stream->priv = p;
+
+    stream->fill_buffer = fill_buffer;
+    stream->control = control;
+    stream->close = s_close;
+
+    stream->seekable = true;
+
+    struct priv *list = arg;
+    if (!list || !list->num_streams) {
+        MP_FATAL(stream, "No sub-streams.\n");
+        return STREAM_ERROR;
+    }
+
+    for (int n = 0; n < list->num_streams; n++) {
+        struct stream *sub = list->streams[n];
+
+        stream->read_chunk = MPMAX(stream->read_chunk, sub->read_chunk);
+
+        int64_t size = stream_get_size(sub);
+        if (n != list->num_streams - 1 && size < 0) {
+            MP_WARN(stream, "Sub stream %d has unknown size.\n", n);
+            stream->seekable = false;
+            p->size = -1;
+        } else if (size >= 0 && p->size >= 0) {
+            p->size += size;
+        }
+
+        if (!sub->seekable)
+            stream->seekable = false;
+
+        MP_TARRAY_APPEND(p, p->streams, p->num_streams, sub);
+    }
+
+    if (stream->seekable)
+        stream->seek = seek;
+
+    return STREAM_OK;
+}
+
+static const stream_info_t stream_info_concat = {
+    .name = "concat",
+    .open2 = open2,
+    .protocols = (const char*const[]){ "concat", NULL },
+};
+
+// Create a stream with a concatenated view on streams[]. Copies the streams
+// array. Takes over ownership of every stream passed to it (it will free them
+// if the concat stream is closed).
+// If an error happens, NULL is returned, and the streams are not freed.
+struct stream *stream_concat_open(struct mpv_global *global, struct mp_cancel *c,
+                                  struct stream **streams, int num_streams)
+{
+    // (struct priv is blatantly abused to pass in the stream list)
+    struct priv arg = {
+        .streams = streams,
+        .num_streams = num_streams,
+    };
+
+    struct stream *s = NULL;
+    stream_create_instance(&stream_info_concat, "concat://",
+                           STREAM_READ | STREAM_SILENT, c, global, &arg, &s);
+    return s;
+}

wscript_build.py

@@ -359,6 +359,7 @@ def build(ctx):
         ( "stream/stream_bluray.c",              "libbluray" ),
         ( "stream/stream_cb.c" ),
         ( "stream/stream_cdda.c",                "cdda" ),
+        ( "stream/stream_concat.c" ),
         ( "stream/stream_dvb.c",                 "dvbin" ),
         ( "stream/stream_dvdnav.c",              "dvdnav" ),
         ( "stream/stream_edl.c" ),