meta: Add GstNetControlMessageMeta

GstNetAddress can be used to store ancillary data which was received with
or is to be sent alongside the buffer data.  When used with socket sinks
and sources which understand this meta it allows sending and receiving
ancillary data such as unix credentials (See `GUnixCredentialsMessage`)
and Unix file descriptions (See `GUnixFDMessage`).

This will be useful for implementing protocols which use file-descriptor
passing in payloaders/depayloaders without having to re-implement all the
socket handling code already present in elements such as multisocketsink,
etc.  This, in turn, will be useful for implementing zero-copy video IPC.

This meta uses the platform independent `GSocketControlMessage` API
provided by GLib as a part of GIO.  As a result this new meta does not
require any new dependencies or any conditional compliation for
portablility, although it is unlikely to do anything useful on non-UNIX
platforms.

docs/libs/gstreamer-libs-sections.txt

@@ -868,6 +868,20 @@ GST_NET_ADDRESS_META_INFO
 gst_net_address_meta_api_get_type
 </SECTION>
 
+<SECTION>
+<FILE>gstnetcontrolmessagemeta</FILE>
+<TITLE>GstNetControlMessageMeta</TITLE>
+<INCLUDE>gst/net/gstnetcontrolmessagemeta.h</INCLUDE>
+GstNetControlMessageMeta
+gst_buffer_add_net_control_message_meta
+gst_buffer_get_net_control_message_meta
+gst_net_control_message_meta_get_info
+<SUBSECTION Standard>
+GST_NET_CONTROL_MESSAGE_META_API_TYPE
+GST_NET_CONTROL_MESSAGE_META_INFO
+<SUBSECTION Private>
+gst_net_control_message_meta_api_get_type
+</SECTION>
 
 <SECTION>
 <FILE>gstnetclientclock</FILE>

libs/gst/net/Makefile.am

@@ -6,12 +6,14 @@ libgstnet_@GST_API_VERSION@_include_HEADERS = \
     gstnet.h \
     gstnetaddressmeta.h \
     gstnetclientclock.h \
+    gstnetcontrolmessagemeta.h \
     gstnettimepacket.h \
     gstnettimeprovider.h
 
 libgstnet_@GST_API_VERSION@_la_SOURCES = \
     gstnetaddressmeta.c \
     gstnetclientclock.c \
+    gstnetcontrolmessagemeta.c \
     gstnettimepacket.c \
     gstnettimeprovider.c
 

libs/gst/net/gstnetcontrolmessagemeta.c

@@ -0,0 +1,125 @@
+/* GStreamer
+ * Copyright (C) <2014> William Manley <will@williammanley.net>
+ *
+ * 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.
+ */
+
+/**
+ * SECTION:gstnetcontrolmessagemeta
+ * @short_description: Network Control Message Meta
+ *
+ * #GstNetControlMessageMeta can be used to store control messages (ancillary
+ * data) which was received with or is to be sent alongside the buffer data.
+ * When used with socket sinks and sources which understand this meta it allows
+ * sending and receiving ancillary data such as unix credentials (See
+ * #GUnixCredentialsMessage) and Unix file descriptions (See #GUnixFDMessage).
+ */
+
+#include <string.h>
+
+#include "gstnetcontrolmessagemeta.h"
+
+static gboolean
+net_control_message_meta_init (GstMeta * meta, gpointer params,
+    GstBuffer * buffer)
+{
+  GstNetControlMessageMeta *nmeta = (GstNetControlMessageMeta *) meta;
+
+  nmeta->message = NULL;
+
+  return TRUE;
+}
+
+static gboolean
+net_control_message_meta_transform (GstBuffer * transbuf, GstMeta * meta,
+    GstBuffer * buffer, GQuark type, gpointer data)
+{
+  GstNetControlMessageMeta *nmeta = (GstNetControlMessageMeta *) meta;
+
+  /* we always copy no matter what transform */
+  gst_buffer_add_net_control_message_meta (transbuf, nmeta->message);
+
+  return TRUE;
+}
+
+static void
+net_control_message_meta_free (GstMeta * meta, GstBuffer * buffer)
+{
+  GstNetControlMessageMeta *nmeta = (GstNetControlMessageMeta *) meta;
+
+  if (nmeta->message)
+    g_object_unref (nmeta->message);
+  nmeta->message = NULL;
+}
+
+GType
+gst_net_control_message_meta_api_get_type (void)
+{
+  static volatile GType type;
+  static const gchar *tags[] = { "origin", NULL };
+
+  if (g_once_init_enter (&type)) {
+    GType _type =
+        gst_meta_api_type_register ("GstNetControlMessageMetaAPI", tags);
+    g_once_init_leave (&type, _type);
+  }
+  return type;
+}
+
+const GstMetaInfo *
+gst_net_control_message_meta_get_info (void)
+{
+  static const GstMetaInfo *meta_info = NULL;
+
+  if (g_once_init_enter (&meta_info)) {
+    const GstMetaInfo *mi =
+        gst_meta_register (GST_NET_CONTROL_MESSAGE_META_API_TYPE,
+        "GstNetControlMessageMeta",
+        sizeof (GstNetControlMessageMeta),
+        net_control_message_meta_init,
+        net_control_message_meta_free,
+        net_control_message_meta_transform);
+    g_once_init_leave (&meta_info, mi);
+  }
+  return meta_info;
+}
+
+/**
+ * gst_buffer_add_net_control_message_meta:
+ * @buffer: a #GstBuffer
+ * @message: a @GSocketControlMessage to attach to @buffer
+ *
+ * Attaches @message as metadata in a #GstNetControlMessageMeta to @buffer.
+ *
+ * Returns: (transfer none): a #GstNetControlMessageMeta connected to @buffer
+ */
+GstNetControlMessageMeta *
+gst_buffer_add_net_control_message_meta (GstBuffer * buffer,
+    GSocketControlMessage * message)
+{
+  GstNetControlMessageMeta *meta;
+
+  g_return_val_if_fail (GST_IS_BUFFER (buffer), NULL);
+  g_return_val_if_fail (G_IS_SOCKET_CONTROL_MESSAGE (message), NULL);
+
+  meta =
+      (GstNetControlMessageMeta *) gst_buffer_add_meta (buffer,
+      GST_NET_CONTROL_MESSAGE_META_INFO, NULL);
+
+  meta->message = g_object_ref (message);
+
+  return meta;
+}

libs/gst/net/gstnetcontrolmessagemeta.h

@@ -0,0 +1,62 @@
+/* GStreamer
+ * Copyright (C) <2014> William Manley <will@williammanley.net>
+ *
+ * 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_NET_CONTROL_MESSAGE_META_H__
+#define __GST_NET_CONTROL_MESSAGE_META_H__
+
+#include <gst/gst.h>
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+typedef struct _GstNetControlMessageMeta GstNetControlMessageMeta;
+
+/**
+ * GstNetControlMessageMeta:
+ * @meta: the parent type
+ * @addr: a #GSocketControlMessage stored as metadata
+ *
+ * Buffer metadata for GSocket control messages, AKA ancillary data attached to
+ * data sent across a socket.
+ */
+struct _GstNetControlMessageMeta {
+  GstMeta       meta;
+
+  GSocketControlMessage *message;
+};
+
+GType gst_net_control_message_meta_api_get_type (void);
+#define GST_NET_CONTROL_MESSAGE_META_API_TYPE \
+  (gst_net_control_message_meta_api_get_type())
+
+#define gst_buffer_get_net_control_message_meta(b) ((GstNetControlMessageMeta*)\
+  gst_buffer_get_meta((b),GST_NET_CONTROL_MESSAGE_META_API_TYPE))
+
+/* implementation */
+const GstMetaInfo *gst_net_control_message_meta_get_info (void);
+#define GST_NET_CONTROL_MESSAGE_META_INFO \
+  (gst_net_control_message_meta_get_info())
+
+GstNetControlMessageMeta * gst_buffer_add_net_control_message_meta (
+    GstBuffer *buffer, GSocketControlMessage *addr);
+
+G_END_DECLS
+
+#endif /* __GST_NET_CONTROL_MESSAGE_META_H__ */
+