Timeout on client if MCP server doesnt support event-stream

[ShadyRoll]

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

According to documentation of Streamable-HTTP transport server may response with "application/json" content type.

I tested server with my self-made client which answers with 405 on any GET request(SSE doesn't supported) and properly handles POST requests answering with "application/json"(not event-stream).

Client do /initialize request and even after receiving success answer(with "application/json" body) remains standby probably waiting for the end of a stream.

Example Code

Python & MCP Python SDK

mcp client sdk: 1.15.0
python: 3.12

[felixweinberger]

Hi @ShadyRoll thanks for submitting this issue - could you please provide a code snippet that we could run to reproduce the issue?