streamText hanging in a multi-turn MCP session

[kamal]

Potentially related to #127, but I observe a consistent behavior where my chat session will hang after ai-sdk streamText performs the fifth request in the "same turn". If I leave it for a while, eventually the call will continue and complete.

Initially, I thought I was being rate limited by Anthropic. To mitigate this, I added the option to disable parallel tool calls, in an effort to slow it down but that didn't help.

Now I'm suspecting if what I'm seeing is due to the Simultaneous open connections limit. I'm wondering if MCP tool calls are not cleanly releasing their connections.

I do not experience the same issue when running the dev server on my local machine.

[mattzcarey]

hey @kamal, thanks for raising this. Do you have a minimal reproduction you could share?

[kamal]

hi @mattzcarey, in my debugging, I found several spots where the MCP sdk does not close the connection, for example, when performing auto discovery of the oauth endpoints where it just throws without first canceling the body. According to the Cloudflare docs, you need to call .json(), or .text() or otherwise call response.body.cancel() to mark the connection as consumed.

I believe there are similar issues when performing a tool call. I believe SSEServerTransport doesn't seem to close properly could be related.

[mattzcarey]

Thanks @kamal for your investigation. To help fix this could you send me some code snippets of how you are connecting to the MCP servers. Is it during the onStart method on the Agent class or more adHoc. I am struggling to replicate your findings. Here is my test repo

[kamal]

@mattzcarey I'm able to replicate the issue using your test repo using my MCP server. Comparing the public MCP server you have in your test, my MCP server implements auth, has a bunch more tools. I have a particular prompt that I use to induce it to do multi-turn. If you'd like, I can share with you the MCP server, prompt and credentials privately.

[mattzcarey]

@kamal that would be very useful. I have only just joined so still building up my collection of problematic servers. Can you message me on discord or X. @mattzcarey in the Cloudflare server https://discord.com/channels/595317990191398933/@home

[kamal]

@mattzcarey 👍🏽 I've messaged you on discord