How to expose mcp_session_id to user ?

[sequoiar]

Question

for streamable http transport, we need mcp_session_id to identify different mcp client. but, seems there is No existing api to get mcp_session_id.

Additional Context

No response

[hesreallyhim]

Check out the spec, I think it belongs in the header:
https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#session-management

A server using the Streamable HTTP transport MAY assign a session ID at initialization time, by including it in an Mcp-Session-Id header on the HTTP response containing the InitializeResult.

I'm not familiar enough to know how the sdk exposes the response headers, sorry.

[zhenjunMa]

You can retrieve the raw request from the request context and then access any data you want.

app = Server("mcp-streamable-http-demo")

@app.call_tool()
def add(a: int, b: int) -> int:
    from starlette.requests import Request
    session_id = cast(Request, app.request_context.request).headers.get("mcp-session-id")
    print(session_id)
    return a + b

[Sunrisea]

You can retrieve the raw request from the request context and then access any data you want.

app = Server("mcp-streamable-http-demo")

@app.call_tool()
def add(a: int, b: int) -> int:
from starlette.requests import Request
session_id = cast(Request, app.request_context.request).headers.get("mcp-session-id")
print(session_id)
return a + b

I tried it, but I cant get session_id in this way

[maxisbey]

Now tracked in #2098.