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

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Max 2026-06-20 16:29:57 +01:00 • committed by GitHub
commit 5a3412ddc1
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1 changed files with 37 additions and 9 deletions
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30
tests/client/test_streamable_http.py
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@ -15,7 +15,12 @@ import pytest
from inline_snapshot import snapshot
from mcp.client import ClientSession
from mcp.client.streamable_http import StreamableHTTPTransport, _encode_header_value, streamable_http_client
from mcp.client.streamable_http import (
MCP_PROTOCOL_VERSION,
StreamableHTTPTransport,
_encode_header_value,
streamable_http_client,
)
from mcp.types import JSONRPCMessage, JSONRPCNotification, JSONRPCRequest, JSONRPCResponse
@ -135,8 +140,8 @@ async def test_pinned_transport_ignores_returned_session_id_and_never_opens_get_
assert all("mcp-session-id" not in r.headers for r in recorded)
def test_constructor_pin_is_not_overwritten_by_an_initialize_result() -> None:
"""A protocol_version passed at construction wins over the InitializeResult snoop."""
def test_modern_constructor_pin_is_not_overwritten_by_an_initialize_result() -> None:
"""A 2026-07-28+ pin wins over the InitializeResult snoop (no initialize is ever sent)."""
transport = StreamableHTTPTransport("http://test/mcp", protocol_version="2026-07-28")
init = JSONRPCResponse(
jsonrpc="2.0",
@ -149,3 +154,22 @@ def test_constructor_pin_is_not_overwritten_by_an_initialize_result() -> None:
)
transport._maybe_extract_protocol_version_from_message(init) # pyright: ignore[reportPrivateUsage]
assert transport.protocol_version == "2026-07-28"
def test_stateful_constructor_pin_is_ignored_and_the_negotiated_version_wins() -> None:
"""A pre-2026 pin is a session-layer concern; the transport must not stamp it on the
initialize request and must adopt the server's negotiated version for later headers."""
transport = StreamableHTTPTransport("http://test/mcp", protocol_version="2025-06-18")
assert MCP_PROTOCOL_VERSION not in transport._prepare_headers() # pyright: ignore[reportPrivateUsage]
init = JSONRPCResponse(
jsonrpc="2.0",
id=1,
result={
"protocolVersion": "2025-03-26",
"capabilities": {},
"serverInfo": {"name": "s", "version": "0"},
},
)
transport._maybe_extract_protocol_version_from_message(init) # pyright: ignore[reportPrivateUsage]
assert transport.protocol_version == "2025-03-26"
assert transport._prepare_headers()[MCP_PROTOCOL_VERSION] == "2025-03-26" # pyright: ignore[reportPrivateUsage]