Merge pull request #179 from smithery-ai/patch-1

Create Client websocket.py

src/mcp/client/websocket.py

@@ -0,0 +1,82 @@
+import json
+import logging
+from contextlib import asynccontextmanager
+from typing import AsyncGenerator
+
+import anyio
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
+from pydantic import ValidationError
+from websockets.asyncio.client import connect as ws_connect
+from websockets.typing import Subprotocol
+
+import mcp.types as types
+
+logger = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def websocket_client(url: str) -> AsyncGenerator[
+    tuple[
+        MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
+        MemoryObjectSendStream[types.JSONRPCMessage],
+    ],
+    None,
+]:
+    """
+    WebSocket client transport for MCP, symmetrical to the server version.
+
+    Connects to 'url' using the 'mcp' subprotocol, then yields:
+        (read_stream, write_stream)
+
+    - read_stream: As you read from this stream, you'll receive either valid
+      JSONRPCMessage objects or Exception objects (when validation fails).
+    - write_stream: Write JSONRPCMessage objects to this stream to send them
+      over the WebSocket to the server.
+    """
+
+    # Create two in-memory streams:
+    # - One for incoming messages (read_stream, written by ws_reader)
+    # - One for outgoing messages (write_stream, read by ws_writer)
+    read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
+    write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
+
+    # Connect using websockets, requesting the "mcp" subprotocol
+    async with ws_connect(url, subprotocols=[Subprotocol("mcp")]) as ws:
+
+        async def ws_reader():
+            """
+            Reads text messages from the WebSocket, parses them as JSON-RPC messages,
+            and sends them into read_stream_writer.
+            """
+            async with read_stream_writer:
+                async for raw_text in ws:
+                    try:
+                        message = types.JSONRPCMessage.model_validate_json(raw_text)
+                        await read_stream_writer.send(message)
+                    except ValidationError as exc:
+                        # If JSON parse or model validation fails, send the exception
+                        await read_stream_writer.send(exc)
+
+        async def ws_writer():
+            """
+            Reads JSON-RPC messages from write_stream_reader and 
+            sends them to the server.
+            """
+            async with write_stream_reader:
+                async for message in write_stream_reader:
+                    # Convert to a dict, then to JSON
+                    msg_dict = message.model_dump(
+                        by_alias=True, mode="json", exclude_none=True
+                    )
+                    await ws.send(json.dumps(msg_dict))
+
+        async with anyio.create_task_group() as tg:
+            # Start reader and writer tasks
+            tg.start_soon(ws_reader)
+            tg.start_soon(ws_writer)
+
+            # Yield the receive/send streams
+            yield (read_stream, write_stream)
+
+            # Once the caller's 'async with' block exits, we shut down
+            tg.cancel_scope.cancel()