webrtcsink: Add a custom signaller example in Python

This re-implements the default webrtcsink/src signalling protocol in
Python for demonstration purposes.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1569>

net/webrtc/examples/webrtcsink-custom-signaller.py

@@ -0,0 +1,206 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2018 Matthew Waters <matthew@centricular.com>
+#               2022 Nirbheek Chauhan <nirbheek@centricular.com>
+#               2024 Sebastian Dröge <sebastian@centricular.com>
+#
+# Demo application that shows how to implement a custom signaller around
+# webrtcsink from Python
+
+from websockets.version import version as wsv
+import random
+import ssl
+import websockets
+import asyncio
+import os
+import sys
+import json
+import argparse
+
+import gi
+gi.require_version('Gst', '1.0')
+from gi.repository import Gst  # NOQA
+gi.require_version('GstSdp', '1.0')
+from gi.repository import GstSdp  # NOQA
+gi.require_version('GstWebRTC', '1.0')
+from gi.repository import GstWebRTC  # NOQA
+
+# Ensure that gst-python is installed
+try:
+    from gi.overrides import Gst as _
+except ImportError:
+    print('gstreamer-python binding overrides aren\'t available, please install them')
+    raise
+
+class WebRTCClient:
+    def __init__(self, loop, server):
+        self.conn = None
+        self.pipe = None
+        self.webrtc = None
+        self.event_loop = loop
+        self.server = server
+
+        self.pipe = Gst.parse_launch('webrtcsink name=sink do-fec=false  videotestsrc is-live=true ! video/x-raw,width=800,height=600 ! sink.  audiotestsrc is-live=true ! sink.')
+        bus = self.pipe.get_bus()
+        self.event_loop.add_reader(bus.get_pollfd().fd, self.on_bus_poll_cb, bus)
+        self.webrtcsink = self.pipe.get_by_name('sink')
+        self.signaller = self.webrtcsink.get_property('signaller')
+        self.signaller.connect('start', self.signaller_on_start)
+        self.signaller.connect('stop', self.signaller_on_stop)
+        self.signaller.connect('send-session-description', self.signaller_on_send_session_description)
+        self.signaller.connect('send-ice', self.signaller_on_send_ice)
+        self.signaller.connect('end-session', self.signaller_on_end_session)
+        self.signaller.connect('consumer-added', self.signaller_on_consumer_added)
+        self.signaller.connect('consumer-removed', self.signaller_on_consumer_removed)
+        self.signaller.connect('webrtcbin-ready', self.signaller_on_webrtcbin_ready)
+        self.pipe.set_state(Gst.State.PLAYING)
+
+    async def send(self, msg):
+        assert self.conn
+        print(f'>>> {msg}')
+        await self.conn.send(json.dumps(msg))
+
+    async def connect(self):
+        print(f'connecting to {self.server}')
+        self.conn = await websockets.connect(self.server)
+        assert self.conn
+        async for message in self.conn:
+            await self.handle_json(message)
+        self.close_pipeline()
+
+    def send_soon(self, msg):
+        asyncio.run_coroutine_threadsafe(self.send(msg), self.event_loop)
+
+    def on_bus_poll_cb(self, bus):
+        def remove_bus_poll():
+            self.event_loop.remove_reader(bus.get_pollfd().fd)
+            self.event_loop.stop()
+        while bus.peek():
+            msg = bus.pop()
+            if msg.type == Gst.MessageType.ERROR:
+                err = msg.parse_error()
+                print("ERROR:", err.gerror, err.debug)
+                remove_bus_poll()
+                break
+            elif msg.type == Gst.MessageType.EOS:
+                remove_bus_poll()
+                break
+            elif msg.type == Gst.MessageType.LATENCY:
+                self.pipe.recalculate_latency()
+
+    async def handle_json(self, message):
+        try:
+            msg = json.loads(message)
+        except json.decoder.JSONDecoderError:
+            print('Failed to parse JSON message, this might be a bug')
+            raise
+        print(f'<<< {msg}')
+
+        if msg['type'] == 'welcome':
+            self.peer_id = msg['peerId']
+            print(f'Got peer ID {self.peer_id} assigned')
+            meta = self.signaller_emit_request_meta()
+            await self.send({'type': 'setPeerStatus', 'roles': ['producer'], 'meta': meta})
+        elif msg['type'] == 'sessionStarted':
+            pass
+        elif msg['type'] == 'startSession':
+            self.signaller_emit_session_requested(msg['sessionId'], msg['peerId'], None)
+        elif msg['type'] == 'endSession':
+            self.signaller_emit_session_ended(msg['sessionId'])
+        elif msg['type'] == 'peer':
+            if 'sdp' in msg:
+                sdp = msg['sdp']
+                assert sdp['type'] == 'answer'
+                self.signaller_emit_session_description(msg['sessionId'], sdp['sdp'])
+            elif 'ice' in msg:
+                ice = msg['ice']
+                self.signaller_emit_handle_ice(msg['sessionId'], ice['sdpMLineIndex'], None, ice['candidate'])
+            else:
+                print('unknown peer message')
+            pass
+        elif msg['type'] == 'error':
+            self.signaller_emit_error(f'Error message from server {msg['details']}')
+        else:
+            print('unknown message type')
+
+    def close_pipeline(self):
+        if self.pipe:
+            self.pipe.set_state(Gst.State.NULL)
+            self.pipe = None
+        self.webrtcsink = None
+        self.signaller = None
+
+    async def stop(self):
+        if self.conn:
+            await self.conn.close()
+        self.conn = None
+
+    # Signal handlers that are called from webrtcsink
+    def signaller_on_start(self, _):
+        print('starting')
+        asyncio.run_coroutine_threadsafe(self.connect(), self.event_loop)
+        return True
+
+    def signaller_on_stop(self, _):
+        print('stopping')
+        self.event_loop.stop()
+        return True
+
+    def signaller_on_send_session_description(self, _, session_id, offer):
+        sdp = offer.sdp.as_text()
+        assert offer.type == GstWebRTC.WebRTCSDPType.OFFER
+        self.send_soon({'type': 'peer', 'sessionId': session_id, 'sdp': { 'type': 'offer', 'sdp': sdp }})
+        return True
+
+    def signaller_on_send_ice(self, _, session_id, candidate, sdp_m_line_index, sdp_mid):
+        self.send_soon({'type': 'peer', 'sessionId': session_id, 'ice': {'candidate': candidate, 'sdpMLineIndex': sdp_m_line_index}})
+        return True
+
+    def signaller_on_end_session(self, _, session_id):
+        self.send_soon({'type': 'endSession', 'sessionId': session_id})
+        return True
+
+    def signaller_on_consumer_added(self, _, peer_id, webrtcbin):
+        pass
+
+    def signaller_on_consumer_removed(self, _, peer_id, webrtcbin):
+        pass
+
+    def signaller_on_webrtcbin_ready(self, _, peer_id, webrtcbin):
+        pass
+
+    # Signals we have to emit to notify webrtcsink
+    def signaller_emit_error(self, error):
+        self.signaller.emit('error', error)
+
+    def signaller_emit_request_meta(self):
+        meta = self.signaller.emit('request-meta')
+        return meta
+
+    def signaller_emit_session_requested(self, session_id, peer_id, offer):
+        self.signaller.emit('session-requested', session_id, peer_id, offer)
+
+    def signaller_emit_session_description(self, session_id, sdp):
+        res, sdp = GstSdp.SDPMessage.new_from_text(sdp)
+        answer = GstWebRTC.WebRTCSessionDescription.new(GstWebRTC.WebRTCSDPType.ANSWER, sdp)
+        self.signaller.emit('session-description', session_id, answer)
+
+    def signaller_emit_handle_ice(self, session_id, sdp_m_line_index, sdp_mid, candidate):
+        self.signaller.emit('handle-ice', session_id, sdp_m_line_index, sdp_mid, candidate)
+
+    def signaller_emit_session_ended(self, session_id):
+        return self.signaller.emit('session-ended', session_id)
+
+    def signaller_emit_shutdown(self):
+        self.signaller.emit('shutdown')
+
+if __name__ == '__main__':
+    Gst.init(None)
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--server', default='ws://127.0.0.1:8443',
+                        help='Signalling server to connect to, eg "ws://127.0.0.1:8443"')
+    args = parser.parse_args()
+    loop = asyncio.new_event_loop()
+    c = WebRTCClient(loop, args.server)
+    res = loop.run_forever()
+    sys.exit(res)