Fix macOS crash when accept() returns zero-length address#2389
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danlapid
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Aug 17, 2025
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Let's use #2365, it's a more polished fix and includes a test. It just needs a couple comments addressed on the test. |
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Pushed commit to use the exact code of https://github.com/capnproto/capnproto/pull/2365/files , no code changes as of yet so review comments are not yet addressed. |
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kentonv
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Aug 18, 2025
On macOS, accept() can return a valid file descriptor with addrlen=0 when a connection is aborted during the accept (e.g., during "happy eyeballs" dual-stack connection attempts). This is a bug in XNU (the macOS kernel). This commit: 1. Adds special handling for zero-length address returns on macOS 2. Adds platform-specific checks for socket connection errors 3. Implements more robust error detection in socket accept logic 4. Includes comprehensive tests for aborted socket connections The changes improve socket connection handling, particularly on macOS, by gracefully managing scenarios where connections are aborted before being fully accepted. Based on PR #2365 by Aaron O'Mullan
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kentonv
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Aug 20, 2025
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As reported in cloudflare/workerd#4623
On macOS, accept() can return a valid file descriptor with addrlen == 0 when a connection is aborted during the accept (e.g., during "happy eyeballs" dual-stack connection attempts). This was causing workerd to crash with:
Fatal uncaught kj::Exception: kj/async-io.c++:3126:
failed: expected addrlen >= sizeof(addr->sa_family) [0 >= 1]
This fix:
Fixes cloudflare/workerd#4623
🤖 Generated with Claude Code
Tried to produce a test for this but was unable to as it seems to be a race condition.
At least I was able to reproduce the issue locally and prove that this change fixes it.