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…ed connect connect() on an AF_UNIX socket returns 0: the connection is established inside the call. If the peer accepts, answers and closes before the client polls, the first event carries a hangup and SO_ERROR is 0. The connecting arm of us_internal_dispatch_ready_poll reported that as a failed connect (ECONNRESET), and the answer was never read. bsd_do_connect_raw now reports when connect() itself returned 0, and the socket keeps that answer as one bit. For such a socket SO_ERROR alone decides the connect, as in libuv. A connect that was in progress keeps the ECONNRESET fallback: a failed TCP connect whose error was already taken also reads as a hangup with SO_ERROR 0.
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Status How this was reproduced: a unix socket peer that accepts, sends and closes, and a client that does 20 ms of synchronous work after The tests in |
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No actionable comments were generated in the recent review. ℹ️ Recent review info
WalkthroughThe Unix-domain connect path now records whether ChangesUnix Socket Connect Handling
Suggested reviewers: Priority: Merge Risk:
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| Check name | Status | Explanation |
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Check skipped because no linked issues were found for this pull request. |
| Out of Scope Changes check | |
Check skipped because no linked issues were found for this pull request. |
| Title check | |
The title clearly summarizes the primary change: preserving a successful Unix-domain connect result when a peer closes early. |
| Description check | |
The PR description follows the required template. It has both sections, 'What does this PR do?' and 'How did you verify your code works?'. The 'Problem' and 'Fix' parts explain the change. The verific… |
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Explanation
The PR description follows the required template. It has both sections, 'What does this PR do?' and 'How did you verify your code works?'. The 'Problem' and 'Fix' parts explain the change. The verification section is detailed. It names the new test file, the pass and fail counts on main and on this branch, the CI builds, and the platforms that were not run (FreeBSD, macOS listener-before-accept case, Windows). The description is long, and the template headings are not used verbatim. The 'Problem', 'Fix', 'Background' and 'Downsides' headings replace 'What does this PR do?' in part, but the Fix section answers that question. The verification content answers the second heading. The description is mostly complete and meets the check.
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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 the new connect_returned_zero bit against every us_socket_t init site that zeroes the neighbouring flags (listen, connect, accept in loop.c, us_socket_from_fd) — all four are covered, and the TLS-over-unix path and the TCP site that discards connected match the scope the PR states.
Extended reasoning...
The change threads a one-bit "connect() returned 0" fact from bsd_do_connect_raw into us_socket_t for AF_UNIX connects and uses it in us_internal_dispatch_ready_poll to stop substituting ECONNRESET when SO_ERROR is 0; no security-sensitive surface. The inline findings (macOS semantics for an unaccepted listener close, and test weaknesses) are what a human should weigh; the struct-field init audit and sibling-site checks came up clean.
The conflict was in the imports of test/js/bun/net/socket.test.ts. Both sides' imports and tests are kept.
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Updated 4:21 AM PT - Oct 24th, 2026
✅ @robobun, your commit c4f74157fb2c132271278dac14a4bf749643173d passed in 🧪 To try this PR locally: bunx bun-pr 44452That installs a local version of the PR into your bun-44452 --bun |
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Inline comments:
Review comments at @test/js/bun/net/socket.test.ts:
- Around line 5614-5616: Add an assertion in the test using connectError to
verify that the TCP connection result has MySQL error code 1040 before comparing
it with the Unix connection result.
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The conflict was in test/js/bun/net/socket.test.ts: the imports, and the tests that both sides append at the end of the file. Both sides' imports and tests are kept.
The conflict was in test/js/bun/net/socket.test.ts: the imports, and the tests that both sides append at the end of the file. Both sides' imports and tests are kept.
The nine tests are unchanged. They sat at the end of test/js/bun/net/socket.test.ts, where many open changes add tests, and each of those that landed put this branch into conflict with main. In test/js/bun/net/unix-socket-peer-closes-first.test.ts they need no edit of a shared file.
There was a problem hiding this comment.
Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Additional findings (outside the current diff — GitHub can't attach inline comments there):
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packages/bun-usockets/src/bsd.c— nit: a future caller of the new out-param that does not pre-zero it reads an unwritten value on the two early-return paths. bsd_create_connect_socket_unix leaves *connected untouched when bsd_create_unix_socket_address fails at packages/bun-usockets/src/bsd.c:2090 or the Apple __pthread_fchdir fails at bsd.c:2096; only internal_bsd_create_connect_socket_unix (via bsd_do_connect_raw) writes it. Fix: write *connected = 0 at the top of bsd_create_connect_socket_unix so every return path of the public helper defines it, matching what bsd_do_connect_raw already does for its own callers.Why this was flagged
A caller passes an uninitialized int to bsd_create_connect_socket_unix (packages/bun-usockets/src/bsd.c:2086) and the path is rejected by bsd_create_unix_socket_address (bsd.c:2090) or, on macOS, __pthread_fchdir fails (bsd.c:2096). Both paths return LIBUS_SOCKET_ERROR without writing *connected; only bsd_do_connect_raw (bsd.c:1899) writes it, and that is reached only through internal_bsd_create_connect_socket_unix (bsd.c:2104). The one current caller, us_socket_group_connect_unix at packages/bun-usockets/src/context.c:658, initializes connected = 0 and returns on error at context.c:660-662, so no user-visible failure exists today; the header comment at packages/bun-usockets/src/internal/networking/bsd.h:245 promises only the 1 case. The repository review guidance asks that out-params be defined on every path, which these two early returns are not.
Verification: nit — triggers only for a caller that does not pre-initialize the out-param and inspects it after an error return; no such caller exists today. In packages/bun-usockets/src/bsd.c,
bsd_create_connect_socket_unix(line 2086) returnsLIBUS_SOCKET_ERRORat line 2091 and, on macOS, at line 2099 without ever touching*connected; the only write is at the top ofbsd_do_connect_raw(line ~1899).
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Not changed in this PR. The finding is correct. There is also a third such return: a failed The parameter follows the one that this path already has. If a maintainer prefers the store at the top of |
The test only compared the socket file with TCP. It passed if both transports reported the same wrong error. Since #45711 a full server is ERR_MYSQL_SERVER_ERROR with errno 1040 over TCP. The test now asserts that result, then the same result through the socket file. Also remove a wrong sentence from a comment: a flowing node:net stream does not pause its handle at 64 KiB.
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The Before #45711 the TCP result was a different, wrong code ( |
A unix socket whose peer closed first now opens, so a TLS client starts its handshake on it. Two tests assert the same result through the socket file and over TCP: open, a failed handshake, close. The handshake error is ECONNRESET for no answer and EPROTO for an answer that is not TLS. Without the fix the socket file reports connectError ECONNRESET.
The two TLS tests compared the socket file with a TCP run, and that run was not deterministic. The TCP peer closes after its FIN. The client then sends its first handshake flight, and the peer's kernel answers with a reset. On macOS the reset can arrive before the client reads the FIN, and a reset closes the socket with no handshake event: the test saw open, close. The tests now assert the events of the unix socket client only. A unix socket has no reset: the write fails at once, and the read returns what the peer sent, then the end.
Problem
Bun.connectgetsconnectErrorECONNRESET"Failed to connect",node:netgetsconnect ECONNRESET <path>. Node reads every byte.connect()on a unix socket returns 0.bsd_do_connect_rawreported that likeEINPROGRESS, sous_internal_dispatch_ready_poll(packages/bun-usockets/src/loop.c:550) read the peer's hangup withSO_ERROR0 as a failed connect.Fix
bsd_do_connect_rawreports whenconnect()itself returned 0.us_socket_group_connect_unixkeeps that in one bit ofus_socket_t.SO_ERRORalone decides, as in libuv. TCP keeps theECONNRESETfallback.test/js/bun/net/unix-socket-peer-closes-first.test.ts(11 tests, main fails 9).Background
EPOLLHUP) when its peer closes. TCP gets none for a FIN.SO_ERRORalone for every socket (opened a dead TCP socket in grpc-js, net: report the real connect errno instead of fabricated ECONNRESET/ECONNREFUSED #37093), and a socket family probe (infers the fact, adds a syscall).Downsides
Bun.SQLreportsERR_*_CONNECTION_FAILEDafterconnectionTimeout(30 s), notERR_*_CONNECTION_REFUSEDat once. TLS clients: a failed handshake, notconnectError.Notes
Repro
A peer that accepts, sends and closes (
c, _ = l.accept(); c.sendall(b"x" * 126892); c.close()on anAF_UNIXlistener). The client callsBun.connect({ unix })ornet.connect(path)and then does 20 ms of synchronous work. On mainbc7a813b1the answer is lost 200 of 200 times. With no work after the call it is a race (6 to 165 of 200). Node v26.3.0 loses 0.Bun.SQLwith the MySQL adapter andpath:is one more client of the same branch: a server atmax_connectionssends error 1040 on accept and closes, and the client reportedERR_MYSQL_CONNECTION_REFUSED.What the kernel reports (Linux 7.0, a socket that polls
EPOLLOUTonly)SO_ERRORconnect()= 0, peer accepts, sends, closesOUT|HUPconnect()= 0, peer accepts, closes, 0 bytesOUT|HUPconnect()= 0, listener closes before acceptOUT|ERR|HUPECONNRESETEINPROGRESS, refusedOUT|ERR|HUPECONNREFUSEDsend()or anSO_ERRORread took the errorOUT|HUPOUTRows 1, 2 and 5 look the same at the verdict. What tells them apart is what
connect()returned.recv()andsend()both take the pending error.Result against Node (the peer acts while the client does 60 ms of work after the connect call)
connect, data,end,closeerrorconnectECONNRESETshutdown(RDWR), closesconnect, data,end,closeerrorconnectECONNRESETerrorconnectECONNRESETconnect; peer sends 5, closes unreadconnect,errorwriteEPIPEerrorconnectECONNRESETTests
The tests have their own file,
test/js/bun/net/unix-socket-peer-closes-first.test.ts. They were at the end ofsocket.test.tsat first. Many open changes add tests there, and each one that landed put this branch into conflict with main (four times). The tests did not change when they moved. The peer runs on a Worker thread, and the connecting thread blocks inAtomics.waituntil the peer has closed, so the hangup is always the first event. No sleep decides the order.Bun.connectandnet.connectwith an answer of 0, 5 and 126892 bytes: open, data, end, close.Bun.SQL(mysql) against a stand-in that sends error 1040 and closes:ERR_MYSQL_SERVER_ERRORwith errno 1040 over TCP, and the same through the socket file. The test asserts the exact code and errno since3367a09ddb. It compared the two transports only while the TCP result was still a wrong code (before sql: fixes for problems found after the consolidation (#45304) #45711). Without this PR the socket file reportsERR_MYSQL_CONNECTION_REFUSED"Failed to connect".Bun.connectwithtls: true, for no answer and for a 5-byte answer that is not TLS:open, a failedhandshake(ECONNRESETorEPROTO),close. Added on Oct 24 after a review asked for the TLS variant. The first version also compared with a TCP run, and that run was not deterministic. The TCP peer closes after its FIN, the client's first handshake flight then draws a reset, and on macOS the reset can arrive before the client reads the FIN. A reset closes the socket with nohandshakeevent (loop.cdoes that by design). This happened once, on macOS aarch64 in build 131745.c4f74157fbremoved the TCP run.ECONNRESET.Debug build of the merge base: 7 fail, 2 pass. This branch: 9 pass. With the two TLS tests, on Oct 24 with the sources of main
7d240c1dd5: 9 fail, 2 pass. This branch: 11 pass, 15 runs of 15. CI builds 122886 and 125931 pass them on Linux (glibc, musl, ASAN) and on macOS x64 and aarch64, where the loop is kqueue (both builds ran them fromsocket.test.ts, before the move). Builds 128916 and 129830 ran them from their own file: 7 pass and 2 skip on macOS x64 and aarch64, where the 2 are the Linux guards. Build 129830 had the exactBun.SQLassertion. Build 131670 ran the two TLS tests on macOS x64: 9 pass and 2 skip for the file. Build 131745 ran them on macOS aarch64: the unix runs passed there too. Build 131825 ran the final form of the file on every lane and is green (181 of 181 jobs). macOS aarch64 had 9 pass and 2 skip with no retry, and the macOS x64 job that ran the file passed. The block is skipped on Windows.Also run on a debug build of this branch: the rest of
socket.test.ts(one failure, it needswww.example.com),socket-syscall-fault.test.ts,net-syscall-fault.test.ts,sql-connect-error-reporting.test.ts,fetch.unix.test.ts,websocket-unix.test.ts,unix-socket-unlink.test.ts,unix-socket-long-path.test.ts,node-net-server.test.ts,node-net-allowHalfOpen.test.js,valkey/reliability/connection-failures.test.ts, grpc-jstest-server.test.ts(the file that failed on #37093), and 36 upstreamtest-net-*,test-pipe-*,test-http-unix-socket*,test-tls-connect-pipefiles.node-net.test.tshas the same failures as the merge base on this machine (no IPv6 loopback, no public DNS, and timeouts under host load).Measurements (linux x64, clang 23, merge base
faac63e6d4)sizeof(us_socket_t)80 to 80,offsetof(group)32 to 32. The bit is bit 7 of byte 22, which was free. Checked again on main6c1eb067e3, after tls: consolidate the open TLS fixes (both engines, node:tls, node:https, WebSocket, SQL) #44618 changed the bit fields of the struct: the numbers and the bit position are the same. On main91e7e3b140, WebSocket: real closing handshake, one failure path,wsrewritten on native transports (consolidates the open WebSocket PRs) #45223 has added a bit before it. The bit is now bit 0 of byte 23. That byte had 3 free bits, and the two sizes are the same. On main7d240c1dd5, usockets: fail the connection when send() reports too many bytes #46452 has addedsend_rejectedto that byte. With this PR the byte has 1 free bit left, and the two sizes are the same.bun: text 80705377 to 80705619 bytes (llvm-size). The file size does not change.bsd_create_connect_socket_unix219 to 247 bytes,us_socket_group_connect_unix503 to 537,us_internal_dispatch_ready_poll4235 to 4251. The TCP connect functions andus_socket_from_fdkeep their size.us_socket_group_connect_unix246 to 265, 20 conditional branches before and after, the same calls (onemi_malloc,socket,connect,epoll_ctl).us_socket_group_connectfor TCP: 743 to 743.us_internal_dispatch_ready_poll: 936 to 940 instructions and one more conditional branch, both in the block that runs only when the first event of a connect has an error or hangup flag.LD_PRELOADcounter, 1000 connects, release builds): clean unix connect 9 to 9, clean TCP connect 10 to 10. A unix connect whose peer answered and closed: 7 to 10 (tworecv, oneepoll_ctl), because the answer is now read.Visible changes for other clients of a socket file (a peer that accepts and closes with no data before the first poll)
fetch(url, { unix })Bun.SQLmysql, postgresERR_*_CONNECTION_REFUSEDat onceERR_*_CONNECTION_FAILEDafter the pool's retries (up toconnectionTimeout, 30 s by default), as over TCPnode:httpconnect ECONNRESETwrite EPIPE(node:write EPIPE)WebSocketoverws+unix://Bun.connect({ unix, tls })connectErrorECONNRESET, the promise rejectsopen,handshakewithECONNRESET,close, as for a TCP peer that ends with a FINtls.connect({ path })errorconnect ECONNRESETconnect,errorread ECONNRESET,close(node:connect,end,errorECONNRESET"Client network socket disconnected before secure TLS connection was established",close)A path with no listener behind it, or no file, still fails at once:
connect()itself fails there. If the peer sent bytes that are not TLS before it closed, both TLS clients report the protocol error (EPROTO,ERR_SSL_WRONG_VERSION_NUMBER), as over TCP and as node does. TheBun.SQLrow was run again on Oct 19 against main91e7e3b140, after #45304 and #45711 changed the SQL clients: the same codes, and the same 9 attempts in 5.4 s for aconnectionTimeoutof 5 through the socket file and over TCP.Self-review
Five concerns came out of a review of the diff.
Bun.SQLchanges from "refused" to a retried "connection failed". Addressed: Downsides and the table above.ECONNRESETfallback for every socket and keep no bit. Rejected: the review ran that form. It passes the tree on Linux, but a refused TCP connect then reportsconnectas soon as something writes to the connecting handle, because thesend()takes the error.loop.cdescribes an error that something else consumed as a normal case. Rejected: the fallback is older than this PR, and the comment says why it stays.int *connectedparameter touch lines that net: report the real connect errno #39579 and node:http: half-close from the drain gate when socket.end() waited for buffered bytes #44244 also change. Not a change to make here: whichever lands second takes a small rebase (keep both bits, keep both parameters).Not changed
SO_ERROR0 on a TCP connect still reportsECONNRESET. The two TCP creation sites do not store the bit.loop.chunk of net: report the real connect errno instead of fabricated ECONNRESET/ECONNREFUSED #37093 (itsgetpeernameandMSG_PEEKprobes still failed a 0-byte answer on macOS).node:tlswords a handshake that ends because the peer of a socket file closed first:read ECONNRESETand noendevent. Node emitsendand the same code with another message (table above).Not run
SO_ERROR0 on the client and changes fromconnect ECONNRESETto open, end, close. The two guard tests for that case run on Linux only._WIN32arm ofbsd_do_connect_raw. An earlier version of this text said that a unix path is a named pipe on Windows. That is true only for a pipe name (\\.\pipe\...): any other path takesus_socket_group_connect_unixthere too. Read fromeventing/libuv.c, not run: the poll callback takes the error and eof flags from the libuv status, and a peer's close is an event with status 0, so the first event of a connect has neither flag and the changed branch is not reached by this scenario.no test proof · iteration 4 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/net/unix-socket-peer-closes-first.test.ts