The Miniflare unit tests flake fairly often on Windows (and occasionally on other OSes). The errors are a bit difficult to debug because Ava only renders "Fetch failed" and not the cause that contains the actual useful info.

Errors

The patch to the concordance library exposes the cause for these errors, such as:

Caused by: Error: write ECONNABORTED␊
miniflare:test:ci:         at afterWriteDispatched (node:internal/stream_base_commons:161:15)␊
miniflare:test:ci:         at writeGeneric (node:internal/stream_base_commons:152:3)␊
miniflare:test:ci:         at Socket._writeGeneric (node:net:958:11)␊
miniflare:test:ci:         at Socket._write (node:net:970:8)␊
miniflare:test:ci:         at writeOrBuffer (node:internal/streams/writable:572:12)␊
miniflare:test:ci:         at _write (node:internal/streams/writable:501:10)␊
miniflare:test:ci:         at Writable.write (node:internal/streams/writable:510:10)␊
miniflare:test:ci:         at AsyncWriter.end (D:\\a\\workers-sdk\\workers-sdk\\node_modules\\.pnpm\\undici@7.14.0\\node_modules\\undici\\lib\\dispatcher\\client-h1.js:1569:14)␊
miniflare:test:ci:         at writeIterable (D:\\a\\workers-sdk\\workers-sdk\\node_modules\\.pnpm\\undici@7.14.0\\node_modules\\undici\\lib\\dispatcher\\client-h1.js:1438:12)␊

Diagnosis

This can be caused by a race condition between Undici's Keep-Alive mechanism and the Miniflare/Workerd server.

• Undici keeps the TCP connection open (Keep-Alive) after a request finishes, hoping to reuse it for the next test to save time.
• The server (Miniflare) decides to close the connection (perhaps due to an idle timeout, which happens faster on constrained Windows CI runners).
• Undici doesn't know the connection is dead yet. It attempts to write a new request to that existing socket (writeGeneric -> Socket._write).
• The OS realizes the pipe is broken during the write operation and throws ECONNABORTED.

Fix

The fix is to prevent Undici from trying to keep the connection alive.

• One way is to add a Connection: close header to the request to force undici to use a new connection for each request. But this felt a bit invasive on the request (and also this header is disallowed for HTTP.
• Instead we are configuring the Undici dispatche with reset: true which has the same effect of preventing Undici from trying to keep the connection alive. See docs here.

Extras

In addition to the main fix, this PR also quietens/silences a lot of the other miniflare tests that were dumping unnecessary and distracting logs into the test output.

• Tests
  • Tests included/updated
  • Tests not necessary because: covered by current tests
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: test flake improvements
• Wrangler V3 Backport
  • Wrangler PR:
  • Not necessary because: test flake improvement is not a bug fix

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