souphttpsrc: Clean up all pending operations from libsoup before unreffing our context

When we cancel connection attempts and similar things, there are still
some operations pending on our main context from the GCancellables. We
should let them all run before unreffing our context, otherwise we leak
file descriptors.

Unfortunately this requires libsoup 2.47.0 or newer as earlier versions
steal our main context from us and we can't use it for cleanup later
without assertions and funny crashes.

Based on a patch by Dmitry Shatrov <shatrov@gmail.com>.

https://bugzilla.gnome.org/show_bug.cgi?id=663944

ext/soup/gstsouphttpsrc.c

@@ -81,6 +81,15 @@
 #include "gstsouphttpsrc.h"
 #include "gstsouputils.h"
 
+/* libsoup before 2.47.0 was stealing our main context from us,
+ * so we can't reliable use it to clean up all pending resources
+ * once we're done... let's just continue leaking on old versions.
+ * https://bugzilla.gnome.org/show_bug.cgi?id=663944
+ */
+#if defined(SOUP_MINOR_VERSION) && SOUP_MINOR_VERSION >= 47
+#define LIBSOUP_DOES_NOT_STEAL_OUR_CONTEXT 1
+#endif
+
 #include <gst/tag/tag.h>
 
 GST_DEBUG_CATEGORY_STATIC (souphttpsrc_debug);
@@ -912,11 +921,23 @@ gst_soup_http_src_session_open (GstSoupHTTPSrc * src)
   return TRUE;
 }
 
+#ifdef LIBSOUP_DOES_NOT_STEAL_OUR_CONTEXT
+static gboolean
+dummy_idle_cb (gpointer data)
+{
+  return FALSE /* Idle source is removed */ ;
+}
+#endif
+
 static void
 gst_soup_http_src_session_close (GstSoupHTTPSrc * src)
 {
   GST_DEBUG_OBJECT (src, "Closing session");
 
+  if (src->loop)
+    g_main_loop_quit (src->loop);
+
+  g_mutex_lock (&src->mutex);
   if (src->session) {
     soup_session_abort (src->session);  /* This unrefs the message. */
     g_object_unref (src->session);
@@ -924,11 +945,33 @@ gst_soup_http_src_session_close (GstSoupHTTPSrc * src)
     src->msg = NULL;
   }
   if (src->loop) {
+#ifdef LIBSOUP_DOES_NOT_STEAL_OUR_CONTEXT
+    GSource *idle_source;
+
+    /* Iterating the main context to give GIO cancellables a chance
+     * to initiate cleanups. Wihout this, resources allocated by
+     * libsoup for the connection are not released and socket fd is
+     * leaked. */
+    idle_source = g_idle_source_new ();
+    /* Suppressing "idle souce without callback" warning */
+    g_source_set_callback (idle_source, dummy_idle_cb, NULL, NULL);
+    g_source_set_priority (idle_source, G_PRIORITY_LOW);
+    g_source_attach (idle_source, src->context);
+    /* Acquiring the context. Idle source guarantees that we'll not block. */
+    g_main_context_push_thread_default (src->context);
+    g_main_context_iteration (src->context, TRUE);
+    /* Ensuring that there's no unhandled pending events left. */
+    while (g_main_context_iteration (src->context, FALSE));
+    g_main_context_pop_thread_default (src->context);
+    g_source_unref (idle_source);
+#endif
+
     g_main_loop_unref (src->loop);
     g_main_context_unref (src->context);
     src->loop = NULL;
     src->context = NULL;
   }
+  g_mutex_unlock (&src->mutex);
 }
 
 static void
@@ -1565,8 +1608,11 @@ gst_soup_http_src_do_request (GstSoupHTTPSrc * src, const gchar * method,
         break;
     }
 
-    if (src->ret == GST_FLOW_CUSTOM_ERROR)
+    if (src->ret == GST_FLOW_CUSTOM_ERROR) {
+      g_main_context_push_thread_default (src->context);
       g_main_loop_run (src->loop);
+      g_main_context_pop_thread_default (src->context);
+    }
 
   } while (src->ret == GST_FLOW_CUSTOM_ERROR);
 
@@ -1575,7 +1621,9 @@ gst_soup_http_src_do_request (GstSoupHTTPSrc * src, const gchar * method,
       && src->read_position >= src->stop_position) {
     src->outbuf = NULL;
     gst_soup_http_src_session_unpause_message (src);
+    g_main_context_push_thread_default (src->context);
     g_main_loop_run (src->loop);
+    g_main_context_pop_thread_default (src->context);
 
     g_cond_signal (&src->request_finished_cond);
     /* Return OK unconditionally here, src->ret will