Thanks to visit codestin.com
Credit goes to github.com

Skip to content

Session ID not present in memory store should return 404, not 400 #1004

New issue
New issue
Open
Open
Session ID not present in memory store should return 404, not 400#1004
@sthomson-wyn

Description

@sthomson-wyn
sthomson-wyn
opened on Jun 23, 2025

Initial Checks

Description

When a session ID is provided by a client, but it is not present in the in-memory session store for the server, the server returns a 400

python-sdk/src/mcp/server/streamable_http_manager.py

Lines 250 to 256 in d0443a1

else:
# Invalid session ID
response = Response(
"Bad Request: No valid session ID provided",
status_code=HTTPStatus.BAD_REQUEST,
)
await response(scope, receive, send)

This is a problem, because as noted in #880 sessions are not persisted between restarts

This library should return a 404, as in

python-sdk/src/mcp/server/streamable_http.py

Line 371 in d0443a1

HTTPStatus.NOT_FOUND,
So that the client can re-initialize and get a new session ID as needed (as in https://github.com/mark3labs/mcp-go/blob/8f5b048218f6d044c3322f16b8cb0b08e10bf5d0/client/transport/streamable_http.go#L257).

400 isn't applicable because the request isn't bad, but the server simply doesn't persist sessions between restarts.

Example Code



Python & MCP Python SDK


3.10.12 and 2.3.4

Metadata
Metadata
Assignees
No one assigned
    Labels
    No labels
    No labels
    Type
    No type
    Projects
    No projects
    Milestone
    No milestone
    Relationships
    None yet
    Development
    No branches or pull requests
    Issue actions