Make sure to consume HTTP error response bodies

[GreenStage]

Addresses #1172

Motivation and Context

Fix the errors in Cloudflare workers when multiple requests go inflight without reading response bodies, which are breaking my SDK client flows :(

How Has This Been Tested?

Unit tests and manually tested with Cloudflare workers

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/sdk@1173

commit: 17754cb

[mattzcarey]

feels weird cancelling the body before checking if response is okay. I'm not super clued up on this I just want to check line 620 will still work as expected.

[felixweinberger]

Good question.

I think both .ok and .status should still be available on the response objects after cancellation and unaffected by it.

Tried it out with this script:

(async () => {
        // Fetch something that returns a body
        const response = await fetch('https://httpbin.org/json');

        console.log('Before cancel:');
        console.log('  status:', response.status);
        console.log('  ok:', response.ok);
        console.log('  headers.content-type:', response.headers.get('content-type'));

        // Cancel the body stream
        await response.body?.cancel();
        console.log('\nBody cancelled.\n');

        console.log('After cancel:');
        console.log('  status:', response.status);
        console.log('  ok:', response.ok);
        console.log('  headers.content-type:', response.headers.get('content-type'));

        // Try to read the body now - this should fail
        console.log('\nTrying to read body after cancel:');
        try {
          const text = await response.text();
          console.log('  text:', text.substring(0, 50));
        } catch (e) {
          console.log('  ERROR:', e.message);
        }
      })();

Which gave the following output:

Before cancel:
 status: 200
 ok: true
 headers.content-type: application/json

Body cancelled.

After cancel:
 status: 200
 ok: true
 headers.content-type: application/json

Trying to read body after cancel:
 ERROR: Body is unusable: Body has already been read

So this looks good to me.

We could put 2 cancels, one inside the 405 check and then one at the end of the function, but this seems fine.

[mattzcarey]

awesome. This line I have been meaning to add for ages

[mattzcarey]

great

[mattzcarey]

this is a script and not part of the sdk. can remove changes to this :)

[mattzcarey]

One question but strong approval when answered

[mattzcarey]

The context for this is that Cloudflare Durable Objects have a 6 simultaneous connection limit which is often reached by MCP clients. This should help us use the full amount with active requests.

[felixweinberger]

@mattzcarey pushed some small clean-ups to this branch, feel free to accept and merge if you're happy with it

[mattzcarey]

I think I need a review from the auth team @pcarleton :)