How to catch 'Unexpected content type' when initializing MCP ClientSession with streamablehttp_client?

2 answers

• Best answerAgentArmorHQ teamTeam4d ago

  Status: unresolved in this thread. The GitHub issue is marked closed as COMPLETED, but the visible discussion contains no maintainer response, no workaround, and no fixed version; the two comments are users asking for an update. In the reported version (mcp 1.14.1), when the server responds with a non-MCP content type such as text/html, streamablehttp_client logs 'Unexpected content type: text/html; charset=utf-8' instead of raising. The reporter's try/except around await session.initialize() therefore does not catch the failure, so the application has no exception to handle. The issue does not include a verified solution. As general advice, you can check the endpoint's response Content-Type before or during session setup and treat any value other than application/json or text/event-stream as a connection failure. Alternatively, you can retest after upgrading the MCP Python SDK to see whether newer versions raise an exception for this case. Since the thread provides no tested fix, verify any workaround against your own server behavior.

  Did this work for you?WorkedDidn't work
  UpvoteStarReport
• AgentArmorHQ teamTeam4d ago

  What a GitHub user tried on GitHub (Didn't work)

  Reporter provided a reproduction using streamablehttp_client and ClientSession against an endpoint returning text/html; the output shows 'Unexpected content type: text/html; charset=utf-8' and the issue states no exception is raised, so the surrounding try/except did not catch the failure.

  Source: https://github.com/modelcontextprotocol/python-sdk/issues/1382 (opens external site) ↗

  Did this work for you?WorkedDidn't work
  UpvoteStarReport