server: close TCP listener when HTTP/3 UDP bind fails by robobun · Pull Request #32542 · oven-sh/bun

robobun · 2026-06-20T17:43:15Z

When Bun.serve with http3: true successfully binds the TCP port but the QUIC listener cannot bind the matching UDP port on the final attempt, the error path threw and called deinit() while the TCP listen socket was still linked into the uWS socket group. ~TemplatedApp then hit the head_listen_sockets == NULL assertion in debug builds; in release builds the listen socket kept polling into a freed HttpContext and segfaulted on the next accept.

What changed

Close the TCP listener unconditionally when the H3 bind fails, then either retry (port: 0 with attempts remaining) or throw. Previously the close only ran on the retry branch.

How to reproduce

const dgram = require('dgram');
const sock = dgram.createSocket('udp4');
sock.bind(0, '127.0.0.1', () => {
  const port = sock.address().port;
  Bun.serve({ port, hostname: '127.0.0.1', tls, http3: true, fetch: () => new Response('ok') });
});

Before: debug assertion group->head_listen_sockets == NULL failed; release build segfaults if anything connects to the leaked TCP port.
After: throws Failed to listen on UDP port N for HTTP/3 and the TCP port is released.

Found by Fuzzilli (fingerprint 23068b3612b07851).

When Bun.serve with http3: true successfully binds the TCP port but the QUIC listener cannot bind the matching UDP port on the final attempt, the error path threw and called deinit() while the TCP listen socket was still linked into the uWS socket group. ~TemplatedApp then hit the head_listen_sockets == NULL assertion in debug builds, and in release builds left the listen socket polling into a freed HttpContext, crashing on the next accept. Close the TCP listener unconditionally when the H3 bind fails, then either retry (port: 0 with attempts remaining) or throw.

robobun · 2026-06-20T17:43:24Z

^{Updated 10:52 AM PT - Jun 20th, 2026}

❌ @robobun, your commit 16f916e has 1 failures in Build #63658 (All Failures):

scripts/build/ci.ts - build failed on 🐧 x64 - build-rust
scripts/build/ci.ts - build failed on 🐧 x64-musl-baseline - build-cpp
scripts/build/ci.ts - build failed on 🐧 aarch64-musl - build-cpp
scripts/build/ci.ts - build failed on 🐧 x64-musl - build-rust
scripts/build/ci.ts - build failed on 🐧 aarch64-android - build-rust
scripts/build/ci.ts - build failed on 🍎 x64 - build-rust
scripts/build/ci.ts - build failed on 🐧 x64-asan - build-rust
scripts/build/ci.ts - build failed on 🐧 aarch64 - build-rust
scripts/build/ci.ts - build failed on 🐧 aarch64-musl - build-rust
scripts/build/ci.ts - build failed on 🐧 x64-musl-baseline - build-rust
scripts/build/ci.ts - build failed on 🐧 x64-baseline - build-rust
scripts/build/ci.ts - build failed on :freebsd: x64 - build-rust
scripts/build/ci.ts - build failed on :freebsd: aarch64 - build-rust
scripts/build/ci.ts - build failed on 🐧 x64-android - build-rust
scripts/build/ci.ts - build failed on 🍎 aarch64 - build-rust
scripts/build/ci.ts - build failed on 🐧 x64-musl - build-cpp

🧪 To try this PR locally:

bunx bun-pr 32542

That installs a local version of the PR into your bun-32542 executable, so you can run:

bun-32542 --bun

coderabbitai · 2026-06-20T17:47:12Z

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test/js/bun/http/serve-http3.test.ts

Walkthrough

In NewServer::listen, the H3 retry loop now unconditionally closes the TCP listener when the H3 UDP bind fails, instead of only doing so on non-final attempts. A new regression test verifies that after Bun.serve throws on a UDP-occupied port, no TCP listener remains open.

Changes

H3 UDP Bind Failure: TCP Listener Cleanup

Layer / File(s)	Summary
TCP listener cleanup on H3 bind failure + regression test `src/runtime/server/mod.rs`, `test/js/bun/http/serve-http3.test.ts`	When `h3_listener` is `None` after a UDP bind attempt, `self.listener.take()` and `close()` are now called unconditionally before the retry/throw decision. The new test binds a UDP socket to force the failure, asserts `Bun.serve` throws an "HTTP/3" error, and then confirms the TCP port is not left open by checking that a subsequent TCP connect returns `CLOSED` rather than `LEAKED`.

Possibly related PRs

oven-sh/bun#30741: Touches NewServer::listen H3 retry logic in the same src/runtime/server/mod.rs file, changing config.h3 to config.http3 gating and related retry conditions—directly adjacent to the cleanup path modified here.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically summarizes the main fix: closing the TCP listener when HTTP/3 UDP bind fails, which directly addresses the core issue in the changeset.
Description check	✅ Passed	The description includes both required template sections: 'What changed' provides context, and 'How to reproduce' demonstrates verification, though the template asks for 'How did you verify'.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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coderabbitai

Actionable comments posted: 1

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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@test/js/bun/http/serve-http3.test.ts`:
- Around line 1107-1108: The error assertion on line 1108 uses a broad substring
check for "HTTP/3" which could be satisfied by any early HTTP/3 setup error
instead of specifically testing the UDP bind failure for the port. Replace the
substring check with an assertion that matches the exact error message thrown by
the listen() function when UDP binding fails on the specific port being tested.
This ensures the test actually exercises the intended TCP-success/UDP-failure
code path rather than passing vacuously on unrelated HTTP/3 errors.

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📒 Files selected for processing (2)

src/runtime/server/mod.rs
test/js/bun/http/serve-http3.test.ts

github-actions · 2026-06-20T17:49:56Z

This PR may be a duplicate of:

server: close TCP listener when H3 UDP bind fails #32539 - Fixes the exact same bug (TCP listener not closed when H3 UDP bind fails) with the same code change hoisting listener.take().close() outside the retry check
Bun.serve: close listen socket before destroying app in deinit() #32543 - Fixes the same root cause (listen socket leak on H3 UDP bind failure) but from the deinit() side, closing the listener before destroying the uws app

🤖 Generated with Claude Code

robobun · 2026-06-20T17:51:24Z

Closing as a duplicate of #32539, which has the identical source change and was opened first.

github-actions Bot added the claude label Jun 20, 2026

coderabbitai Bot reviewed Jun 20, 2026

View reviewed changes

Comment thread test/js/bun/http/serve-http3.test.ts Resolved

test: assert exact HTTP/3 UDP bind error message

16f916e

github-actions Bot mentioned this pull request Jun 20, 2026

Bun.serve: close listen socket before destroying app in deinit() #32543

Closed

robobun closed this Jun 20, 2026

robobun deleted the farm/332ffdac/http3-listen-fail-close-tcp branch June 20, 2026 17:51

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server: close TCP listener when HTTP/3 UDP bind fails - #32542

server: close TCP listener when HTTP/3 UDP bind fails#32542
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robobun commented Jun 20, 2026

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