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…ion' listener throws and nothing handles it Bun counts an error that nothing handles and ends the run when the turn of the loop is over. Before that, uWS read the request of the connection whose listener had thrown, and the server answered it. The landing frame of the connection filter now reads the unhandled error counter of the VM before and after the listeners. When the counter moved, it stops HTTP parsing on the socket and closes it. A connection whose error a listener handles stays open, as in Node.js.
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Updated 5:01 PM PT - Oct 20th, 2026
✅ @robobun, your commit fac31d0fc8c51f492b74f0656a89830a930b73c4 passed in 🧪 To try this PR locally: bunx bun-pr 45876That installs a local version of the PR into your bun-45876 --bun |
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Status: reproduced on main 017b243 and on 1.4.2 (release builds, linux x64) with the server in the description and a peer in another process. The peer of a listener that throws reads the full response (100 bytes), then the server exits 1. Node.js v26.3.0 reads 0 bytes, and Bun 1.3.14 reads no body. Fix: #45876 (this PR). |
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
WalkthroughUnhandled errors in HTTP connection listeners now cause the connection to be refused, unless Bun’s test runner handles the error. New fixtures and tests cover HTTP and HTTPS connections, runtime modes, and test-runner recovery. ChangesNode HTTP connection listener errors
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to
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Review comments at
@test/js/node/http/node-http-connection-listener-throw.test.ts:
- Line 72: Update the cases in the listener-throw test so each completes within
Bun’s 5-second default timeout, accounting for the fixture’s stall-reporting
delay; then remove the explicit timeout override. Preserve the cases’ existing
coverage while reducing their runtime.
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src/jsc/bindings/node/JSNodeHTTPServerSocket.cppsrc/runtime/server/server_body.rstest/js/node/http/node-http-connection-listener-throw-fixture.jstest/js/node/http/node-http-connection-listener-throw.test.tstest/leaksan.supp
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline findings, I also checked two things in the new landing frame and ruled them out: the socket pointer is still valid after the listener runs, since uSockets only frees closed sockets in loop_post (us_internal_free_closed_sockets) and Bun__NodeHTTP__refuseConnection re-checks us_socket_is_closed first; and a throw from process.nextTick / queueMicrotask is counted before the counter comparison, because the EventLoop::enter_scope guard in on_connection_callback drains microtasks on drop even when the call returns Err.
Extended reasoning...
The change adds an out-of-line landing frame around the node:http 'connection' callback in src/runtime/server/server_body.rs that compares the VM's unhandled_error_counter before and after the listener and, if it moved, calls a new C++ extern in src/jsc/bindings/node/JSNodeHTTPServerSocket.cpp that stops HTTP parsing and closes the uWS socket; plus a new fixture-driven test matrix and a leaksan.supp entry. No auth, crypto or input-parsing surface is touched. Inline findings already flag the TLS spill-close interaction in the new refuse path and the per-test timeout, so a human should weigh those; the socket-lifetime and microtask-ordering concerns were checked against uSockets' deferred free and the event-loop scope guard and are not issues.
…listener's error to bun test The frame that closes a connection after a listener's error read the server again when the listeners were done. Under bun test the report of the error starts the next test inside that frame, and that test can close, collect and free the server. The frame now takes the VM before the listeners and reads nothing of the server after them. bun test takes every error of its main VM as the failure of a test, so the connection stays there, as on main. The close failed the next test. The frame is now run_connection_listeners, because on_connection is the field that holds the JS callback. test/leaksan.supp is as on main again. The Worker rows ask LeakSanitizer for 100 frames, and an existing line then matches the leak of the request pool. The fixture counts the runs of the request listener. New rows: a peer that does not read, TLS 1.2 under --hot, a Worker with a nextTick throw, an immediate that keeps the loop turning, a listener that closes the socket before it throws, and a bun test run.
The listeners of a connection can free the server: bun test starts the next test from inside the report of their error. The dispatch and its frame now take the server as a raw pointer and hold no reference to it while the listeners run. on_connection_callback copies the callback and the global out of a borrow that ends before the call. The second half of the bun test case is not run on Windows. Its wait runs inside the open callback of the connection that it waits for, and it timed out there in CI.
Problem
'connection'or'secureConnection'listener, Node.js exits at the throw. Since 1.4.0 Bun answers that connection in full and then exits.src/jsc/VirtualMachine.rs:2151). uWS reads the request before the run ends (packages/bun-usockets/src/loop.c:579).socket.getPeerCertificate()throws on Bun (node:httpsRequest socket is not a TLSSocket #16834), and the unchecked peer is answered.Fix
NewServer::run_connection_listeners(src/runtime/server/server_body.rs) readsunhandled_error_counterbefore and after the listeners. If it moved,Bun__NodeHTTP__refuseConnectionstops HTTP parsing and closes the socket.bun testtakes every error, so it stays there too.test/js/node/http/node-http-connection-listener-throw.test.ts(16 of 25 cases fail on main),test/js/node/http*. Self-reviewed: 47 concerns raised, 39 addressed, 2 rejected (they keep anasyncpass here), 6 in Notes.Background
node:httpemits both events from it.unhandled_error_countercounts errors that nothing takes. The run loop stops when it is not 0.--hotor--watch. Considered:try/catchinonServerConnection, which cannot tell whether something took the error.Downsides
asynclistener that rejects,tlsandhttp2servers, a throwing'request'listener.socket.destroy()before the throw refuses on main too.node:domainerror handler and inbun repl, this PR resets a connection that main and Node.js answer..text+256 B.Notes
Repro. The server below, and a peer in another process that sends
GET /when it connects.200 OKhead with no body. The request listener does not run'connection'when the connection opens (onServerConnection) came with node:http/https/http2: raise Node v26.3.0 compat to ~94%, sync the upstream suites, and fix the Windows/macOS transport-layer teardown bugs they exposed #32488, first released in 1.4.0 (git log -S, no bisect by build). Before it, the event was emitted from the dispatch of the first request.process.nextTickorqueueMicrotaskthrow with the body too (81 bytes, the request listener runs).Who meets this. No issue reports it (3 searches of the tracker). The throw that nobody intends is a listener that is correct on Node.js and fails on Bun: the socket of a
node:httpsserver is not atls.TLSSocket(#16834, #37255). 3 of 3 runs for each row:TypeError: socket.getPeerCertificate is not a function, exit 1What reads the request after the error is counted, on main.
TCP_DEFER_ACCEPT. The kernel hands over the connection when the request is there, and the accept frame reads it right after the open dispatch (loop.c:579). node:http: skip TCP_DEFER_ACCEPT so server.setTimeout fires on time for silent clients #36074 removes that flag.Finished. The read that completes the handshake also holds the request.global.setTimeoutto be ignored, allowing execution to continue #22546, bun run: end the entry's top-level await when a fatal error ends the run #42686),--hotand--watch.setsockoptshim that refusesTCP_DEFER_ACCEPT, which is the state of macOS and Windows).Measurements. linux-x64, release builds from one toolchain, main 017b243 against this PR. The fixture of the test is the driver:
<runtime> node-http-connection-listener-throw-fixture.js <case>.nextTick,queueMicrotask) by door (http,https,https-secureConnection), cells served, 3 runs a cellasynclistener and anasynclistener withawait nullworker:httpandworker:http-nextTick, bytes the peer readshttps-secureConnection-writes-big-unread, runs of the request listener, 8 runs--hot, a listener that throws for each peer: first peer, second peer, processbun test: a listener throws in test A. Test A, its peer, the next testnode --test: fails, answered, passesgdbinstruction steps over 3 connections, a call counts as one): 109 to 94. The thunk runs 4 times per connection (accept, open, and two close events). Its 3 early returns go from 16 to 6 instructions each, becauserun_connection_listenersis out of line. The open event goes from 61 to 76. Calls 3 to 3. Conditional branches 14 to 15.size -A:.text+256 B..rodata,.bun_builtins,.data,.bss+0 B. The stripped file has the same size. Host functions +0.recvfrom,sendto,shutdown,closeon main,closewith this PR).Still answered after this PR, on purpose. Node.js sends nothing in each case, unless a line says otherwise.
asynclistener that rejects. A rejected promise is reported at the end of the loop turn, after the request is read. A pass inside this frame was built and reviewed for this PR, and it is not in it. With the pass before the listeners, an'unhandledRejection'listener runs inside the open filter, and one that callsserver.close()gets'connection'for a closed socket. With the pass only after them, a connection is closed for a promise that another callback rejected. Run the ticks and microtasks that 'unhandledRejection' listeners queue #45597, Report unhandled rejections made in the event loop's last turn #45582 and Handle an error before the event loop sleeps, not at its next wake #45599 change when rejections are reported, so this waits for them.net.ts:tls.createServerwith a'secureConnection'listener (6 bytes of payload),http2.createSecureServerwith'secureConnection'or'session'(67 bytes), and the same withallowHTTP1and an HTTP/1.1 peer (100 bytes). Under--hotalso anetserver, h2c, and anhttp.Serverthat gets its sockets throughemit("connection").net.tsreports the error and keeps the socket (node:net: route throws from 'data'/'connection' listeners to uncaughtException and keep the socket alive #35347). Not in this PR.'request'listener that throws: 89 bytes, a200 OKhead with no body. That is node:http: send nothing on destroy() before the headers go out, and a 500 (not an empty 200) for a throwing listener #39366.setImmediate(fail)): 100 bytes on main and with this PR. On Linux the request is read right after the open dispatch, before the immediate runs.'uncaughtException'listener throws or callsprocess.exit(): the peer reads the 503 head of a stopping VM (36 bytes).'connection'listener skips'secureConnection', where Node.js emits it. That is node:https: emit 'connection' at TCP accept, before the TLS handshake #46167.socket.destroy()on an https socket that still has unsent data, a request that arrives later still runs the request listener (5 of 6 runs on main, 6 of 6 with this PR, 0 of 6 on Node.js).Other differences to know.
node:domainis a shim on main (Missing functionality of 'domain' API: control of async unhandled exceptions #6045, domain: implement node:domain on AsyncLocalStorage and port the upstream domain suite (+40 upstream tests) #31828). Withdomain.add(server)ordomain.run()around the server and an'error'handler on the domain, Node.js answers the peer and exits 0. Main answers and exits 1. This PR resets the peer and exits 1.bun repl: the session survives the error and installs no handler, so the counter moves.node -iand main answer the peer, and this PR resets it.bun test: the runner takes the error as the failure of the test that runs, and the connection stays, as on main and undernode --test. A Worker insidebun testkeeps the close. Without this rule the reset fails the next test (read ECONNRESET), and a test that passes on main fails.'secureConnection'listener that throws: Node.js answers the first peer, because its Worker ends behind the read that holds the request. This PR closes it. The test pins that row as Bun only.'connection'rows match Node.js in the bytes that the peer reads. Node.js emits'connection'before the TLS handshake and Bun after it (node:https: emit 'connection' at TCP accept, before the TLS handshake #46167 moves it).reportError()inside a listener counts an error, so the connection is closed. Node.js exits there.'uncaughtException'listener, a capture callback or aBun.ModuleGraphonErrortakes does not move the counter.socket.destroy()and then throws, under--hot: the peer reads about 2.6 MB in 8 of 10 runs. On main it reads all 4 MB in 7 of 10 runs, because the request is parsed on the destroyed socket and the end of that parse flushes the rest (packages/bun-uws/src/HttpContext.h:826). Node.js cuts at about 2.6 MB ondestroy()alone.Questions for the maintainer.
unhandled_error_counter, the field that ends the run. hot/watch: keep driving timers and surviving errors after an unhandled error #38206 stops that counter under--hotand--watch(read from its diff, not run): the three watcher rows are then answered again. A count of the reports that nothing took, bumped where the VM decides that, does not depend on hot/watch: keep driving timers and surviving errors after an unhandled error #38206 or domain: route fs callback throws to uncaughtException, unblocking 4 tests (domain 88%→96%) #34661, and it also sees a Worker whose handler throws. It is a new field on the VM, so it is not in this PR.--hotand--watch: is a connection whose listener failed closed (this PR) or answered (hot/watch: keep driving timers and surviving errors after an unhandled error #38206)?uncaught_exception(domain: route fs callback throws to uncaughtException, unblocking 4 tests (domain 88%→96%) #34661), and this frame is then reached only in a Worker, under--hot,--watchandbun test.Open PRs that touch the same lines. #46167 and the draft #35538 change the call in the filter thunk. The frame goes around
on_connection_callback, for each dispatch of a connection.Self-review. The first local shape ended the main run inside the callback through a hook on the VM. The review measured that the close alone stops every refused peer, and that half was removed. The second review ran on this commit plus a commit with two rejected-promise passes for
asynclisteners. Its result:bun testthe report of the error starts the next test inside the frame, and that test can free the server: a use after free. The caseunder bun testends with SIGSEGV on a release build with that frame (3 of 3 runs). The frame now takes the VM first and reads nothing of the server after the listeners.bun testthe close failed the next test and one test that passes on main. The runner now counts as what takes the error.test/leaksan.suppis gone. The Worker rows ask LeakSanitizer for 100 frames, and an existing line then matches the leak of Bun.serve: free a Worker's RequestContext pools when its VM is torn down #37513.stopHTTPParsing()the request listener runs in 8 of 8 runs), TLS 1.2 under--hot, a Worker with anextTickthrow, an immediate that keeps the loop turning, a listener that closes the socket before it throws, and abun testrun.asyncpass in this PR, because the process survives the error under--hotand a pending top-level await. The reasons in the first item weigh more.net.tsservers and the destroyed https socket. Put to the maintainer: the three questions above.Tests.
--hot,--watch, the Worker https row). One test runsbun teston a file.socket.destroy()refuses it, a listener that closes the socket before it throws changes nothing, andbun testkeeps the connection.node-http.test.tsis exempt from LeakSanitizer in CI.test/js/node/httpandtest/js/node/http2(51 files) andbun-serve-propagate-errors: 1858 pass, 1 fail. The one isnode-http-uaf.test.ts, a 2000 request fixture at its 60 s limit. It reaches that limit on a debug build of main in the same container too.test-http-*andtest-https-*files under 6 jobs: 6 of 450 fail, all client timing tests on a debug build.test-http-client-close-with-default-agent.jspasses alone.test-http-abort-queued.jsandtest-http-outgoing-end-cork.jspass 2 of 3 runs alone, and 5 of 5 in release builds of main and of this PR.test-http-agent-keepalive.js,test-http-client-timeout-option.jsandtest-https-timeout.jswait 1 ms to 100 ms for an event that a debug build delivers later.under bun testcase timed out on Windows in that run (every attempt on aarch64, once on x64). Its second half waits inside the open callback of the connection that it waits for, which is the re-entry of event loop: never re-enter from inside a dispatch callback (de-block expect().resolves and HTMLRewriter.transform, then assert) #33261. That half is now skipped on Windows.us_internal_loop_postdefers the free only on the epoll and kqueue backends). uSockets reads the socket after the open dispatch on main too, so this PR adds no new kind of read there. It is not measured.no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/http/node-http-connection-listener-throw.test.ts