sip: media-pipeline: Debug pipeline graph on SIGUSR2

Ust GST_DEBUG_BIN_TO_DOT_FILE to generate a dot graph of a pipeline for
debugging purposes when SIGUSR2 is received.

Note the same signal is also used within the dummy plugin to simulate an
incoming call from an unknown number, so when testing you probably want either
the sip plugin or the dummy plugin, but not both.

plugins/sip/calls-sip-media-pipeline.c

@@ -28,6 +28,7 @@
 #include "calls-sip-media-pipeline.h"
 #include "util.h"
 
+#include <glib-unix.h>
 #include <gst/gst.h>
 #include <gio/gio.h>
 
@@ -842,11 +843,38 @@ calls_sip_media_pipeline_class_init (CallsSipMediaPipelineClass *klass)
 }
 
 
+static gboolean
+usr2_handler (CallsSipMediaPipeline *self)
+{
+  g_print ("playing: %d\n"
+           "paused: %d\n"
+           "stopped: %d\n"
+           "target map: %d\n"
+           "current state: %d\n",
+           self->element_map_playing,
+           self->element_map_paused,
+           self->element_map_stopped,
+           EL_ALL_RTP,
+           self->state);
+
+  GST_DEBUG_BIN_TO_DOT_FILE_WITH_TS (GST_BIN (self->pipeline),
+                                     GST_DEBUG_GRAPH_SHOW_ALL,
+                                     "usr2-debug");
+
+  return G_SOURCE_CONTINUE;
+}
+
+
 static void
 calls_sip_media_pipeline_init (CallsSipMediaPipeline *self)
 {
   if (!gst_is_initialized ())
     gst_init (NULL, NULL);
+
+  /* Pipeline debugging */
+  g_unix_signal_add (SIGUSR2,
+                     (GSourceFunc) usr2_handler,
+                     self);
 }