Initial import

mcp_python/client/stdio.py

@@ -0,0 +1,84 @@
+import sys
+from contextlib import asynccontextmanager
+
+import anyio
+import anyio.lowlevel
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
+from anyio.streams.text import TextReceiveStream
+from pydantic import BaseModel, Field
+
+from mcp_python.types import JSONRPCMessage
+
+
+class StdioServerParameters(BaseModel):
+    command: str
+    """The executable to run to start the server."""
+
+    args: list[str] = Field(default_factory=list)
+    """Command line arguments to pass to the executable."""
+
+    env: dict[str, str] = Field(default_factory=dict)
+    """
+    The environment to use when spawning the process.
+
+    The environment is NOT inherited from the parent process by default.
+    """
+
+
+@asynccontextmanager
+async def stdio_client(server: StdioServerParameters):
+    """
+    Client transport for stdio: this will connect to a server by spawning a process and communicating with it over stdin/stdout.
+    """
+    read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception]
+    read_stream_writer: MemoryObjectSendStream[JSONRPCMessage | Exception]
+
+    write_stream: MemoryObjectSendStream[JSONRPCMessage]
+    write_stream_reader: MemoryObjectReceiveStream[JSONRPCMessage]
+
+    read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
+    write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
+
+    process = await anyio.open_process(
+        [server.command, *server.args], env=server.env, stderr=sys.stderr
+    )
+
+    async def stdout_reader():
+        assert process.stdout, "Opened process is missing stdout"
+
+        try:
+            async with read_stream_writer:
+                buffer = ""
+                async for chunk in TextReceiveStream(process.stdout):
+                    lines = (buffer + chunk).split("\n")
+                    buffer = lines.pop()
+
+                    for line in lines:
+                        try:
+                            message = JSONRPCMessage.model_validate_json(line)
+                        except Exception as exc:
+                            await read_stream_writer.send(exc)
+                            continue
+
+                        await read_stream_writer.send(message)
+        except anyio.ClosedResourceError:
+            await anyio.lowlevel.checkpoint()
+
+    async def stdin_writer():
+        assert process.stdin, "Opened process is missing stdin"
+
+        try:
+            async with write_stream_reader:
+                async for message in write_stream_reader:
+                    json = message.model_dump_json(by_alias=True)
+                    await process.stdin.send((json + "\n").encode())
+        except anyio.ClosedResourceError:
+            await anyio.lowlevel.checkpoint()
+
+    async with (
+        anyio.create_task_group() as tg,
+        process,
+    ):
+        tg.start_soon(stdout_reader)
+        tg.start_soon(stdin_writer)
+        yield read_stream, write_stream