Add example that illustrates subprotocol negotiation

examples/subprotocol_negotiation.py

@@ -0,0 +1,42 @@
+import asyncio
+import logging
+from http import HTTPStatus
+from picows import ws_connect, WSTransport, WSListener, \
+    ws_create_server, WSUpgradeResponse, WSUpgradeResponseWithListener, \
+    WSUpgradeRequest
+
+class OCPPServerClientListener(WSListener):
+    def on_ws_connected(self, transport: WSTransport):
+        print("New client connected, negotiated protocol: ", transport.response.headers["Sec-WebSocket-Protocol"])
+
+
+class OCPPClientListener(WSListener):
+    def on_ws_connected(self, transport: WSTransport):
+        print("Successfully connected to the server, server supports: ",
+              transport.response.headers["Sec-WebSocket-Protocol"])
+
+
+async def main():
+    def server_client_factory(request: WSUpgradeRequest):
+        if "ocpp2.1" in request.headers["Sec-WebSocket-Protocol"]:
+            return WSUpgradeResponseWithListener(WSUpgradeResponse.create_101_response(extra_headers={"Sec-WebSocket-Protocol": "ocpp2.1"}), OCPPServerClientListener())
+        else:
+            return WSUpgradeResponseWithListener(WSUpgradeResponse.create_error_response(HTTPStatus.BAD_REQUEST, b"requested websocket subprotocol is not supported"), None)
+
+    server = await ws_create_server(server_client_factory, "127.0.0.1", 27001)
+    asyncio.create_task(server.serve_forever())
+
+    # Client request support for either ocpp1.6 or ocpp2.1 protocol
+    (transport, client) = await ws_connect(OCPPClientListener, "ws://127.0.0.1:27001/", extra_headers={"Sec-WebSocket-Protocol": "ocpp1.6,ocpp2.1"})
+
+    transport.disconnect()
+    await transport.wait_disconnected()
+
+    server.close()
+    await server.wait_closed()
+
+
+if __name__ == '__main__':
+    logging.basicConfig(level=logging.INFO)
+    logging.getLogger("picows").setLevel(9)
+    asyncio.run(main())