Support MCP client communication with servers over Streamable HTTP transport #46

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1. Ashfaqbs

   added

   enhancementNew feature or requestNew feature or request

   on Aug 26, 2025
2. Premansh12 commented on May 25, 2026

   

   Premansh12

   on May 25, 2026

   Last edited by Premansh12

   More actions

   Thanks for the detailed write-up — this is a well-scoped gap. The SDK already ships mcp.client.streamable_http.streamablehttp_client and the server side has examples under examples/servers/simple-streamablehttp-stateless/, but there's no matching client snippet to pair with it. Here's a PR-ready fix.

   ---

   What's added

   Two new files under examples/:

   File	Role
   examples/server_streamable_http.py	FastMCP server that starts with transport="streamable-http" (mirrors fastmcp_quickstart.py)
   examples/client_streamable_http.py	Client that uses streamablehttp_client to list tools/resources/prompts and call a tool

   ---

   Key differences vs. the stdio client

   # ── STDIO (existing example) ──────────────────────────────────────────────
   from mcp import ClientSession, StdioServerParameters
   from mcp.client.stdio import stdio_client
   
   server_params = StdioServerParameters(command="uv", args=["run", "server", ...])
   
   async with stdio_client(server_params) as (read, write):
       async with ClientSession(read, write) as session:
           await session.initialize()
           ...
   
   # ── Streamable HTTP (new example) ─────────────────────────────────────────
   from mcp import ClientSession
   from mcp.client.streamable_http import streamablehttp_client
   
   SERVER_URL = "http://127.0.0.1:8000/mcp"
   
   # streamablehttp_client yields a third value: get_session_id()
   async with streamablehttp_client(SERVER_URL) as (read, write, get_session_id):
       async with ClientSession(read, write) as session:
           await session.initialize()
           session_id = get_session_id()   # mcp-session-id header value
           ...

   The ClientSession API is identical after initialize() — same list_tools(), call_tool(), read_resource(), etc. — so existing client code can be ported just by swapping the transport context manager.

   ---

   How to run

   Terminal 1 — start the server:

   uv run examples/server_streamable_http.py
   # Listening on http://127.0.0.1:8000/mcp

   Terminal 2 — run the client:

   uv run examples/client_streamable_http.py
   # Connecting to MCP server via streamable-http: http://127.0.0.1:8000/mcp
   # Session established (id=<uuid>)
   # call_tool('add', {a: 7, b: 35}) → [TextContent(type='text', text='42')]

   Or point it at any other streamable-http server:

   SERVER_URL=https://my-remote-server.example.com/mcp uv run examples/client_streamable_http.py

   ---

   Transport comparison

   	STDIO	Streamable HTTP
   Import	mcp.client.stdio	mcp.client.streamable_http
   Config	StdioServerParameters(command=…)	URL string
   Connectivity	Local subprocess only	Local or remote
   Session tracking	N/A (1:1 process)	mcp-session-id header
   Recommended for	Local dev / Claude Desktop	Production / networked deployments
   SSE streaming	❌	✅ (server-sent events per request)
   Resumability	❌	✅ (via EventStore + last-event-id)

   ---

   I'll open a PR with these two files and a short README update pointing to both the stdio and streamable-http client examples. Happy to also add an asyncio-based integration test if that would help land this faster.

   client_streamable_http.py

   server_streamable_http.py