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Propagate contextvars.Context through anyio streams without modifying SessionMessage (#2298)

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Marcelo Trylesinski 2026-03-31 12:49:38 -04:00 • committed by GitHub
commit e6235d1667
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1 changed files with 310 additions and 94 deletions
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23
src/mcp/client/sse.py
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@ -7,11 +7,11 @@ from urllib.parse import parse_qs, urljoin, urlparse
import anyio
import httpx
from anyio.abc import TaskStatus
from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
from httpx_sse import aconnect_sse
from httpx_sse._exceptions import SSEError
from mcp import types
from mcp.shared._context_streams import create_context_streams
from mcp.shared._httpx_utils import McpHttpClientFactory, create_mcp_http_client
from mcp.shared.message import SessionMessage
@ -51,12 +51,6 @@ async def sse_client(
auth: Optional HTTPX authentication handler.
on_session_created: Optional callback invoked with the session ID when received.
"""
read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
read_stream_writer: MemoryObjectSendStream[SessionMessage | Exception]
write_stream: MemoryObjectSendStream[SessionMessage]
write_stream_reader: MemoryObjectReceiveStream[SessionMessage]
logger.debug(f"Connecting to SSE endpoint: {remove_request_params(url)}")
async with httpx_client_factory(
headers=headers, auth=auth, timeout=httpx.Timeout(timeout, read=sse_read_timeout)
@ -65,8 +59,8 @@ async def sse_client(
event_source.response.raise_for_status()
logger.debug("SSE connection established")
read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
read_stream_writer, read_stream = create_context_streams[SessionMessage | Exception](0)
write_stream, write_stream_reader = create_context_streams[SessionMessage](0)
async def sse_reader(task_status: TaskStatus[str] = anyio.TASK_STATUS_IGNORED):
try:
@ -124,7 +118,8 @@ async def sse_client(
async def post_writer(endpoint_url: str):
try:
async with write_stream_reader, write_stream:
async for session_message in write_stream_reader:
async def _send_message(session_message: SessionMessage) -> None:
logger.debug(f"Sending client message: {session_message}")
response = await client.post(
endpoint_url,
@ -136,6 +131,14 @@ async def sse_client(
)
response.raise_for_status()
logger.debug(f"Client message sent successfully: {response.status_code}")
async for session_message in write_stream_reader:
sender_ctx = write_stream_reader.last_context
if sender_ctx is not None:
async with anyio.create_task_group() as tg:
sender_ctx.run(tg.start_soon, _send_message, session_message)
else:
await _send_message(session_message) # pragma: no cover
except Exception: # pragma: lax no cover
logger.exception("Error in post_writer")