René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Client hangs forever","articleBody":"### Initial Checks\n\n- [x] I confirm that I'm using the latest version of MCP Python SDK\n- [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue\n\n### Description\n\nClient hangs forever when `sse_read_timeout` is specified unless `read_timeout_seconds` in `session.call_tool` is also populated.\n\n### Example Code\n\n```Python\nimport threading\nimport time\nimport asyncio\nfrom typing import Literal\nfrom datetime import timedelta\n\nfrom mcp import ClientSession\nfrom mcp.client.streamable_http import streamablehttp_client\nfrom mcp.types import ImageContent as MCPImageContent\n\n\ndef start_comprehensive_mcp_server(transport: Literal[\"sse\", \"streamable-http\"], port=int):\n    from mcp.server import FastMCP\n\n    mcp = FastMCP(\"Comprehensive MCP Server\", port=port)\n\n    @mcp.tool(description=\"Tool that will timeout\")\n    def timeout_tool() -\u003e str:\n        time.sleep(10)\n        return \"This tool has timed out\"\n\n    @mcp.tool(description=\"Calculator tool which performs calculations\")\n    def calculator(x: int, y: int) -\u003e int:\n        return x + y\n\n    mcp.run(transport=transport)\n\n\n# Start server\nserver_thread = threading.Thread(\n    target=start_comprehensive_mcp_server, \n    kwargs={\"transport\": \"streamable-http\", \"port\": 8001}, \n    daemon=True\n)\nserver_thread.start()\ntime.sleep(3)\nprint(\"SERVER STARTED\", flush=True)\n\n\nasync def test_raw_mcp():\n    print(\"CREATING RAW MCP CONNECTION...\", flush=True)\n    \n    async with streamablehttp_client(\n        url=\"http://127.0.0.1:8001/mcp\",\n        sse_read_timeout=2,  # 2 second timeout\n    ) as (read_stream, write_stream, get_session_id):\n        print(\"TRANSPORT CONNECTED\", flush=True)\n        \n        async with ClientSession(read_stream, write_stream) as session:\n            print(\"SESSION CREATED\", flush=True)\n            \n            await session.initialize()\n            print(\"SESSION INITIALIZED\", flush=True)\n            \n            print(\"CALLING TOOL (with 2s timeout)...\", flush=True)\n            try:\n                result = await session.call_tool(\n                    \"timeout_tool\", \n                    arguments={},\n                    # read_timeout_seconds=timedelta(seconds=5), # This needs to be provided or the client will hang forever\n                )\n                print(f\"TOOL RESULT: {result}\", flush=True)\n            except Exception as e:\n                print(f\"TOOL CALL EXCEPTION: {type(e).__name__}: {e}\", flush=True)\n            \n            print(\"DONE\", flush=True)\n\n\nprint(\"RUNNING TEST...\", flush=True)\nasyncio.run(test_raw_mcp())\nprint(\"TEST COMPLETE\", flush=True)\n```\n\n### Python \u0026 MCP Python SDK\n\n```Text\n1.24.0\n```","author":{"url":"https://github.com/afarntrog","@type":"Person","name":"afarntrog"},"datePublished":"2025-12-15T20:29:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/1789/python-sdk/issues/1789"}