hlsdemux2: Add preloader helper.

Add a helper that submits and handles blocking preload requests for future
PART/MAP data from live playlists. Add handling in the hlsdemux stream to submit
preload requests when hitting the end of the available segments in a live
playlist.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3883>

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux-preloader.c

@@ -0,0 +1,228 @@
+/* GStreamer
+ Copyright (C) 2022 Jan Schmidt <jan@centricular.com>
+ *
+ * gsthlsdemux-preloader.c:
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include "gsthlsdemux-preloader.h"
+
+GST_DEBUG_CATEGORY_EXTERN (gst_hls_demux2_debug);
+#define GST_CAT_DEFAULT gst_hls_demux2_debug
+
+typedef struct _GstHLSDemuxPreloadRequest GstHLSDemuxPreloadRequest;
+struct _GstHLSDemuxPreloadRequest
+{
+  GstHLSDemuxPreloader *preloader;      /* Parent preloader */
+  GstM3U8PreloadHint *hint;
+  DownloadRequest *download_request;
+};
+
+static GstHLSDemuxPreloadRequest *
+gst_hls_demux_preload_request_new (GstHLSDemuxPreloader * preloader,
+    GstM3U8PreloadHint * hint)
+{
+  GstHLSDemuxPreloadRequest *req = g_new0 (GstHLSDemuxPreloadRequest, 1);
+  req->preloader = preloader;
+  req->hint = gst_m3u8_preload_hint_ref (hint);
+
+  return req;
+};
+
+static void
+gst_hls_demux_preload_request_free (GstHLSDemuxPreloadRequest * req)
+{
+  gst_m3u8_preload_hint_unref (req->hint);
+
+  /* The download request must have been cancelled and removed by the preload helper */
+  g_assert (req->download_request == NULL);
+  g_free (req);
+};
+
+static gboolean
+gst_hls_demux_preloader_submit (GstHLSDemuxPreloader * preloader,
+    GstHLSDemuxPreloadRequest * preload_req, const gchar * referrer_uri);
+static void gst_hls_demux_preloader_cancel_request (GstHLSDemuxPreloader *
+    preloader, GstHLSDemuxPreloadRequest * req);
+
+GstHLSDemuxPreloader *
+gst_hls_demux_preloader_new (DownloadHelper * download_helper)
+{
+  GstHLSDemuxPreloader *preloader = g_new0 (GstHLSDemuxPreloader, 1);
+
+  preloader->download_helper = download_helper;
+  preloader->active_preloads = g_ptr_array_new ();
+
+  return preloader;
+}
+
+void
+gst_hls_demux_preloader_free (GstHLSDemuxPreloader * preloader)
+{
+  gst_hls_demux_preloader_cancel (preloader, M3U8_PRELOAD_HINT_ALL);
+  g_ptr_array_free (preloader->active_preloads, TRUE);
+  g_free (preloader);
+}
+
+void
+gst_hls_demux_preloader_load (GstHLSDemuxPreloader * preloader,
+    GstM3U8PreloadHint * hint, const gchar * referrer_uri)
+{
+  /* Check if we have an active preload already for this hint */
+  guint idx;
+  for (idx = 0; idx < preloader->active_preloads->len; idx++) {
+    GstHLSDemuxPreloadRequest *req =
+        g_ptr_array_index (preloader->active_preloads, idx);
+    if (hint->hint_type == req->hint->hint_type) {
+      /* We already have an active hint of this type. If this new one is different, cancel
+       * the active preload before starting this one */
+      if (gst_m3u8_preload_hint_equal (hint, req->hint)) {
+        GST_LOG ("Ignoring pre-existing preload of type %d uri: %s, range:%"
+            G_GINT64_FORMAT " size %" G_GINT64_FORMAT, hint->hint_type,
+            hint->uri, hint->offset, hint->size);
+        return;                 /* Nothing to do */
+      }
+
+      gst_hls_demux_preloader_cancel_request (preloader, req);
+      g_ptr_array_remove_index_fast (preloader->active_preloads, idx);
+      break;
+    }
+  }
+
+  /* If we get here, then there's no preload of this type. Create one */
+  GstHLSDemuxPreloadRequest *req =
+      gst_hls_demux_preload_request_new (preloader, hint);
+  /* Submit the request */
+
+  if (gst_hls_demux_preloader_submit (preloader, req, referrer_uri)) {
+    g_ptr_array_add (preloader->active_preloads, req);
+  } else {
+    /* Discard failed request */
+    gst_hls_demux_preloader_cancel_request (preloader, req);
+  }
+}
+
+void
+gst_hls_demux_preloader_cancel (GstHLSDemuxPreloader * preloader,
+    GstM3U8PreloadHintType hint_types)
+{
+  /* Go through the active downloads and remove/cancel any with the matching type */
+  guint idx;
+  for (idx = 0; idx < preloader->active_preloads->len;) {
+    GstHLSDemuxPreloadRequest *req =
+        g_ptr_array_index (preloader->active_preloads, idx);
+    if (hint_types & req->hint->hint_type) {
+      gst_hls_demux_preloader_cancel_request (preloader, req);
+      g_ptr_array_remove_index_fast (preloader->active_preloads, idx);
+      continue;                 /* Don't increment idx++, as we just removed an item */
+    }
+
+    idx++;
+  }
+}
+
+static void
+on_download_cancellation (DownloadRequest * request, DownloadRequestState state,
+    GstHLSDemuxPreloadRequest * preload_req)
+{
+}
+
+static void
+on_download_error (DownloadRequest * request, DownloadRequestState state,
+    GstHLSDemuxPreloadRequest * preload_req)
+{
+  GstM3U8PreloadHint *hint = preload_req->hint;
+  GST_DEBUG ("preload type %d uri: %s download error", hint->hint_type,
+      hint->uri);
+  GST_FIXME ("How to handle failed preload request?");
+}
+
+static void
+on_download_progress (DownloadRequest * request, DownloadRequestState state,
+    GstHLSDemuxPreloadRequest * preload_req)
+{
+  GstM3U8PreloadHint *hint = preload_req->hint;
+  GST_DEBUG ("preload type %d uri: %s download progress", hint->hint_type,
+      hint->uri);
+}
+
+static void
+on_download_complete (DownloadRequest * request, DownloadRequestState state,
+    GstHLSDemuxPreloadRequest * preload_req)
+{
+  GstM3U8PreloadHint *hint = preload_req->hint;
+  GST_DEBUG ("preload type %d uri: %s download complete", hint->hint_type,
+      hint->uri);
+}
+
+static gboolean
+gst_hls_demux_preloader_submit (GstHLSDemuxPreloader * preloader,
+    GstHLSDemuxPreloadRequest * preload_req, const gchar * referrer_uri)
+{
+  g_assert (preload_req->download_request == NULL);
+
+  DownloadRequest *download_req = download_request_new ();
+  GstM3U8PreloadHint *hint = preload_req->hint;
+
+  /* Configure our download request */
+  gint64 end = RFC8673_LAST_BYTE_POS;
+  if (hint->size > 0) {
+    end = hint->offset + hint->size - 1;
+  }
+
+  download_request_set_uri (download_req, hint->uri, hint->offset, end);
+  download_request_set_callbacks (download_req,
+      (DownloadRequestEventCallback) on_download_complete,
+      (DownloadRequestEventCallback) on_download_error,
+      (DownloadRequestEventCallback) on_download_cancellation,
+      (DownloadRequestEventCallback) on_download_progress, preload_req);
+
+  GST_DEBUG ("Submitting preload type %d uri: %s, range:%" G_GINT64_FORMAT
+      " - %" G_GINT64_FORMAT, hint->hint_type, hint->uri, hint->offset, end);
+
+  if (!downloadhelper_submit_request (preloader->download_helper,
+          referrer_uri, DOWNLOAD_FLAG_NONE, download_req, NULL)) {
+    /* Abandon the request */
+    download_request_unref (download_req);
+    return FALSE;
+  }
+
+  preload_req->download_request = download_req;
+  return TRUE;
+}
+
+static void
+gst_hls_demux_preloader_cancel_request (GstHLSDemuxPreloader * preloader,
+    GstHLSDemuxPreloadRequest * preload_req)
+{
+  if (preload_req->download_request) {
+    GstM3U8PreloadHint *hint = preload_req->hint;
+    GST_DEBUG ("Cancelling preload type %d uri: %s, range start:%"
+        G_GINT64_FORMAT " size %" G_GINT64_FORMAT, hint->hint_type, hint->uri,
+        hint->offset, hint->size);
+
+    downloadhelper_cancel_request (preloader->download_helper,
+        preload_req->download_request);
+    download_request_unref (preload_req->download_request);
+    preload_req->download_request = NULL;
+  }
+  gst_hls_demux_preload_request_free (preload_req);
+}

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux-preloader.h

@@ -0,0 +1,46 @@
+/* GStreamer
+ Copyright (C) 2022 Jan Schmidt <jan@centricular.com>
+ *
+ * gsthlsdemux-preloader.h:
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+#ifndef __GST_HLS_DEMUX_PRELOADER_H__
+#define __GST_HLS_DEMUX_PRELOADER_H__
+
+#include <glib.h>
+
+#include "m3u8.h"
+
+#include "downloadrequest.h"
+#include "downloadhelper.h"
+
+G_BEGIN_DECLS
+
+typedef struct _GstHLSDemuxPreloader GstHLSDemuxPreloader;
+
+struct _GstHLSDemuxPreloader {
+  DownloadHelper *download_helper; /* Owned by the demuxer */
+  GPtrArray *active_preloads;
+};
+
+GstHLSDemuxPreloader *gst_hls_demux_preloader_new (DownloadHelper *download_helper);
+void gst_hls_demux_preloader_free (GstHLSDemuxPreloader *preloader);
+void gst_hls_demux_preloader_load (GstHLSDemuxPreloader *preloader, GstM3U8PreloadHint *hint, const gchar *referrer_uri);
+void gst_hls_demux_preloader_cancel (GstHLSDemuxPreloader *preloader, GstM3U8PreloadHintType hint_types);
+
+G_END_DECLS
+#endif /* __GST_HLS_DEMUX_PRELOADER_H__ */

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.c

@@ -1844,6 +1844,11 @@ gst_hls_demux_stream_finalize (GObject * object)
   gst_buffer_replace (&hls_stream->pending_typefind_buffer, NULL);
   gst_buffer_replace (&hls_stream->pending_segment_data, NULL);
 
+  if (hls_stream->preloader) {
+    gst_hls_demux_preloader_free (hls_stream->preloader);
+    hls_stream->preloader = NULL;
+  }
+
   if (hls_stream->moov)
     gst_isoff_moov_box_free (hls_stream->moov);
 
@@ -2298,6 +2303,61 @@ gst_hls_demux_reset_for_lost_sync (GstHLSDemux * hlsdemux)
   }
 }
 
+static void
+gst_hls_demux_stream_update_preloads (GstHLSDemuxStream * hlsdemux_stream)
+{
+  GstHLSMediaPlaylist *playlist = hlsdemux_stream->playlist;
+  GstAdaptiveDemux *demux =
+      GST_ADAPTIVE_DEMUX2_STREAM_CAST (hlsdemux_stream)->demux;
+  GstHLSDemux *hlsdemux = GST_HLS_DEMUX_CAST (demux);
+
+  gboolean preloads_allowed = hlsdemux->llhls_enabled
+      && GST_HLS_MEDIA_PLAYLIST_IS_LIVE (playlist);
+
+  if (playlist->preload_hints == NULL || !preloads_allowed) {
+    if (hlsdemux_stream->preloader != NULL) {
+      /* Cancel any preloads, the new playlist doesn't have them */
+      gst_hls_demux_preloader_cancel (hlsdemux_stream->preloader,
+          M3U8_PRELOAD_HINT_ALL);
+    }
+    /* Nothing to preload */
+    return;
+  }
+
+  if (hlsdemux_stream->preloader == NULL) {
+    GstAdaptiveDemux *demux =
+        GST_ADAPTIVE_DEMUX2_STREAM (hlsdemux_stream)->demux;
+    hlsdemux_stream->preloader =
+        gst_hls_demux_preloader_new (demux->download_helper);
+    if (hlsdemux_stream->preloader == NULL) {
+      GST_WARNING_OBJECT (hlsdemux_stream, "Failed to create preload handler");
+      return;
+    }
+  }
+
+  /* The HLS spec says any extra preload hint of each type should be ignored */
+  GstM3U8PreloadHintType seen_types = 0;
+  guint idx;
+  for (idx = 0; idx < playlist->preload_hints->len; idx++) {
+    GstM3U8PreloadHint *hint = g_ptr_array_index (playlist->preload_hints, idx);
+    switch (hint->hint_type) {
+      case M3U8_PRELOAD_HINT_MAP:
+      case M3U8_PRELOAD_HINT_PART:
+        if (seen_types & hint->hint_type) {
+          continue;             /* Ignore preload hint type we've already seen */
+        }
+        seen_types |= hint->hint_type;
+        break;
+      default:
+        GST_FIXME_OBJECT (hlsdemux_stream, "Ignoring unknown preload type %d",
+            hint->hint_type);
+        continue;               /* Unknown hint type, ignore it */
+    }
+    gst_hls_demux_preloader_load (hlsdemux_stream->preloader, hint,
+        playlist->uri);
+  }
+}
+
 static GstFlowReturn
 gst_hls_demux_stream_update_media_playlist (GstHLSDemux * demux,
     GstHLSDemuxStream * stream, gchar ** uri, GError ** err)
@@ -2429,6 +2489,11 @@ gst_hls_demux_stream_update_media_playlist (GstHLSDemux * demux,
     stream->playlist = new_playlist;
   }
 
+  if (!GST_HLS_MEDIA_PLAYLIST_IS_LIVE (stream->playlist)) {
+    /* Make sure to cancel any preloads if a playlist isn't live after reload */
+    gst_hls_demux_stream_update_preloads (stream);
+  }
+
   if (stream->is_variant) {
     /* Update time mappings. We only use the variant stream for collecting
      * mappings since it is the reference on which rendition stream timing will
@@ -2581,6 +2646,7 @@ gst_hls_demux_stream_update_fragment_info (GstAdaptiveDemux2Stream * stream)
               stream->current_position, hlsdemux_stream->in_partial_segments,
               &seek_result)) {
         GST_INFO_OBJECT (stream, "At the end of the current media playlist");
+        gst_hls_demux_stream_update_preloads (hlsdemux_stream);
         return GST_FLOW_EOS;
       }
 
@@ -2620,6 +2686,7 @@ gst_hls_demux_stream_update_fragment_info (GstAdaptiveDemux2Stream * stream)
        * hit the live edge and need to wait for a playlist update */
       if (file->partial_only) {
         GST_INFO_OBJECT (stream, "At the end of the current media playlist");
+        gst_hls_demux_stream_update_preloads (hlsdemux_stream);
         return GST_FLOW_EOS;
       }
 

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.h

@@ -30,6 +30,8 @@
 #include "m3u8.h"
 #include "gstisoff.h"
 #include "gstadaptivedemux.h"
+#include "gsthlsdemux-preloader.h"
+
 #if defined(HAVE_OPENSSL)
 #include <openssl/evp.h>
 #elif defined(HAVE_NETTLE)
@@ -126,6 +128,9 @@ struct _GstHLSDemuxStream
   gboolean in_partial_segments;
   guint part_idx;
 
+  /* Preload helper, that manages blocking preload downloads */
+  GstHLSDemuxPreloader *preloader;
+
   /* Whether we need to typefind the next buffer */
   gboolean do_typefind;
 

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/meson.build

@@ -1,5 +1,6 @@
 hls_sources = [
   'hls/gsthlsdemux.c',
+  'hls/gsthlsdemux-preloader.c',
   'hls/gsthlsdemux-util.c',
   'hls/gsthlselement.c',
   'hls/m3u8.c',