modelcontextprotocol/python-sdk
Watch
1
0
Fork
You've already forked python-sdk
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Ignore pre-2026 protocol_version pins at the StreamableHTTP transport (#2923)

Browse source
This commit is contained in:
Max 2026-06-20 16:29:57 +01:00 • committed by GitHub
commit 5a3412ddc1
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
2 changed files with 37 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

4
src/mcp/client/client.py
View file

@ -97,7 +97,9 @@ class Client:
Pinning to ``2026-07-28`` or later selects the stateless transport era: no initialize
handshake is sent on the wire (the session synthesizes its `InitializeResult` locally),
and for HTTP the ``MCP-Protocol-Version`` header is set from the first request.
and for HTTP the ``MCP-Protocol-Version`` header is set from the first request. A modern
pin currently requires a URL or `Transport`; the in-memory `Server`/`MCPServer` path
does not yet have a modern entry point.
Leave as ``None`` to negotiate the version via the initialize handshake.
"""

12
src/mcp/client/streamable_http.py
View file

@ -93,13 +93,14 @@ class StreamableHTTPTransport:
Args:
url: The endpoint URL.
protocol_version: Pin the MCP-Protocol-Version header from the first request
instead of waiting to snoop it from an InitializeResult. Required for
stateless 2026-07-28 sessions that never send initialize.
protocol_version: Pin the MCP-Protocol-Version header from the first request.
Only honoured for stateless 2026-07-28+ sessions that never send
initialize; for earlier (stateful) versions the header is populated
from the negotiated InitializeResult, so a pre-2026 value is ignored.
"""
self.url = url
self.session_id: str | None = None
self.protocol_version: str | None = protocol_version
self.protocol_version: str | None = protocol_version if protocol_version in MODERN_PROTOCOL_VERSIONS else None
def _per_message_headers(self, message: JSONRPCMessage) -> dict[str, str]:
"""Per-POST routing headers (Mcp-Method, Mcp-Name) for 2026-07-28+ pinned transports.
@ -158,7 +159,8 @@ class StreamableHTTPTransport:
def _maybe_extract_protocol_version_from_message(self, message: JSONRPCMessage) -> None:
"""Extract protocol version from initialization response message."""
if self.protocol_version is not None:
# Constructor pin wins over snooping the InitializeResult.
# Only a modern constructor pin reaches here (pre-2026 values are dropped
# in __init__), and a modern pin never sends initialize.
return
if isinstance(message, JSONRPCResponse) and message.result: # pragma: no branch
try: