node:net: stop the listener when listen() fails after the socket is bound

[robobun]

Fixes #43082

Problem

• A tls.Server#listen() that throws while it loads the addContext() entries (Failed to register SNI for '...') emits 'error' but keeps the bound listener: listening is true and the port completes handshakes. Node leaves the server closed.
• The cause is the addServerName loop at the end of kRealListen (src/js/node/net.ts:4010). It runs after Bun.listen() bound the socket, and nothing stops the handle when it throws.
• In a cluster worker the catch in listenInCluster closed the shared fd while the native listener that adopted it still used it.

Fix

• kRealListen wraps every step after Bun.listen() in one try. On a throw it calls this._handle.stop(true), sets this._handle = null, and rethrows. The existing chmod cleanup moves into the same block.
• In the fd branch, kRealListen marks the cluster's shared handle as adopted as soon as the native listener owns the fd. So handle.close() in the catch releases the primary's key and leaves the fd alone.
• Verified: new tests in test/js/node/tls/node-tls-server.test.ts and test/js/node/cluster.test.ts, both fail on bun 1.4.3. They use two addContext() names that Bun rejects after the bind and Node accepts, and assert that the state matches whichever event ends listen(). Node: 'listening'. Bun: 'error' and a closed server. Also the rest of both files, node-tls-context.test.ts, and node-net-server.test.ts.
• Self-reviewed: 5 concerns raised, 4 addressed. The cluster adopted change stays here: once stop(true) closes the adopted fd, that flag prevents the second close.

Background

• Each listener owns a native SNI tree. It adds names of any label count but removes at most 10 labels, so two names with more than 10 labels on one node make the add a duplicate (TLS SNI: names with more than 10 labels are added to the SNI tree but never found or removed #43092). That is the only public input that reaches this throw today.
• A cluster worker's shared handle (makeSharedHandle in src/js/internal/cluster/child.ts) wraps the fd from the primary. Its close() closes the raw fd unless adopted is set.

Notes

• The trigger was found by inspection during the review of node:tls: keep every addContext() entry for the next listen() #43080, not by a user report. node:tls: keep every addContext() entry for the next listen() #43080 keeps addContext() entries made while the server listens, so such entries reach this loop on a later listen() too.
• addContext("") before listen() is the other input that reaches the throw (hostname pattern cannot be empty). node:tls: build the tls.Server SecureContext in setSecureContext() #42050 rejects it at the call, as Node does.
• us_socket_group_listen_fd (packages/bun-usockets/src/context.c) keeps the fd with the caller on failure and owns it on success. us_listen_socket_close closes it.
• The SNICallback runs even when the requested servername matches the bind hostname test in node-tls-server.test.ts and 10 client tests in node-net.test.ts fail in my container with and without this change: localhost resolves to ::1 for the listener and 127.0.0.1 for the client there.
• No user input makes Node's listen() fail after the bind, so a test cannot expect 'error' on both runtimes. The tests accept 'listening' too and check the state that goes with it. When TLS SNI: names with more than 10 labels are added to the SNI tree but never found or removed #43092 is fixed, Bun takes the 'listening' branch as Node does.
• An earlier version made address() throw once. Node does not call address() during listen(), so that never failed there.

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no test proof · iteration 2 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/tls/node-tls-server.test.ts, test/js/node/cluster.test.ts

[coderabbitai]

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Walkthrough

Changes

Listener failure cleanup

Layer / File(s)	Summary
Post-bind listener cleanup src/js/node/net.ts	Listener creation, Unix-socket permission updates, address setup, and TLS context registration now share cleanup handling. Failures stop the listener, clear _handle, and rethrow the error.
Cluster descriptor adoption and regression coverage src/js/node/net.ts, test/js/node/cluster.test.ts, test/js/node/tls/node-tls-server.test.ts	File-descriptor listeners mark cluster handles as adopted during kRealListen. Tests verify failed TLS listeners are closed and replacement listeners can start.

Suggested reviewers: cirospaciari

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: 🟡 Moderate · up to 3be41

Bun can pass these regressions without testing listener cleanup after the intended setup failure. Require Bun’s error outcome before merging so the fix remains protected.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue [#43082] requires cleanup after a post-bind listen() failure. src/js/node/net.ts now protects handle setup, address setup, permission setup, and SNI registration with one try block. Its `c…
Out of Scope Changes check	✅ Passed	The changes stay within issue [#43082]. The source changes implement post-bind listener cleanup and cluster file-descriptor ownership. The tests cover TLS and cluster failure behavior. Moving Unix-soc…
Title check	✅ Passed	The title clearly and concisely describes the primary change: stopping the listener when post-bind listen setup fails.
Description check	✅ Passed	The description explains the problem, fix, affected cluster behavior, and verification results. It does not use the exact template headings, but it provides the required change summary and verificatio…

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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline nit, I also checked the shared-fd ownership on both failure paths: if Bun.listen({fd}) itself throws, adopted is still false so the cluster handle's close() closes the raw fd (uSockets leaves the fd with the caller on failure); if a later step throws, adopted is already set so stop(true) is the only close. I also confirmed this._handle is assigned by Bun.listen on all three branches before the new try, so the catch never dereferences null.

Extended reasoning...

The diff is small and focused: kRealListen in src/js/node/net.ts wraps every post-bind step in one try/catch that stops and nulls the native listener before rethrowing, folds the previous unix-socket chmod cleanup into that block (guarded by path && since the block now sits outside the unix branch), and moves clusterHandle.adopted = true from listenInCluster to immediately after Bun.listen({fd}) returns so the shared handle's close() in the caller's catch does not double-close an fd the native listener already owns. I traced makeSharedHandle in src/js/internal/cluster/child.ts and Server.prototype.close to confirm the ownership hand-off is consistent on the success, listen-throws, and post-bind-throws paths. The only surviving finding is the nit that both new tests depend on the #43092 label-cap bug as their trigger, which is already posted inline, so this note only records the additional ownership paths that were examined and found consistent.

[robobun]

The tests no longer reach the post-bind throw through the SNI label limit (#43092). Both now make address() throw once after the bind, which kRealListen calls inside the new try. They still fail on bun 1.4.3 and pass with the fix. The comments the comment check flagged are trimmed.

[claude]

LGTM — the retargeted tests (per-instance address() override, commit c1fd51a) no longer depend on the SNI label-cap bug, and the listener cleanup is a small, self-contained restructure.

What was reviewed:

• Traced fd ownership on both cluster failure points: Bun.listen({fd}) throwing leaves adopted unset so listenInCluster's handle.close() closes the fd (us_socket_group_listen_fd returns it to the caller on failure); a post-bind throw sets adopted first, so stop(true) is the only close.
• Checked the moved chmod block is behavior-preserving: same position relative to Bun.listen and the wiring steps, and the new path && guard only short-circuits the fd/port branches where path was already falsy.
• Confirmed the non-cluster throw still reaches Server.prototype.listen's catch and formatListenError leaves a code-less error's message intact, so the error: address() failed after the bind assertion is exact.

Extended reasoning...

Overview

The PR restructures Server.prototype[kRealListen] in /home/claude/bun/src/js/node/net.ts so every step after Bun.listen() returns (unix-socket chmod, owner_symbol/onconnection wiring, address() for _connectionKey, and the addServerName loop over TLS contexts) sits in one try; on a throw it calls this._handle.stop(true), nulls _handle, and rethrows. In the cluster fd branch, clusterHandle.adopted = true is set immediately after Bun.listen({fd}) succeeds instead of after kRealListen returns in listenInCluster. Two tests are added: one in test/js/node/tls/node-tls-server.test.ts and one cluster-worker test in test/js/node/cluster.test.ts, both triggering the post-bind failure via a one-shot throwing address() override.

Security risks

None specific to this change. The relevant concern is resource ownership: a double-close of the cluster's shared fd would be a correctness hazard (fd reuse could close an unrelated descriptor). I traced both failure points. If Bun.listen({fd}) itself throws, adopted remains false and listenInCluster's catch closes the raw fd via makeSharedHandle.close(); us_socket_group_listen_fd in packages/bun-usockets/src/context.c documents that the caller keeps the fd on failure. If a later step throws, adopted is already true, so stop(true) closes the fd and handle.close() only releases the primary's key. There is no path where both close it.

Level of scrutiny

Moderate. kRealListen is on the path of every net/tls server listen, so the success path must be behavior-preserving. The chmod block keeps its position relative to Bun.listen and the wiring steps, and its new path && guard only affects the fd/port branches where it previously did not run at all. The catch replaces this._handle?.stop?.(true) with this._handle.stop(true), which is safe because every branch assigns _handle from a successful Bun.listen before the try. The prior nit I raised (tests depending on the #43092 label-cap bug) was addressed in c1fd51a by switching the trigger to an instance address() override.

Other factors

No debug build exists in this checkout and building would take a long time, so I did not execute the tests; the author's evidence block also defers to CI for these platform-specific tests. From reading, the tests assert exact values (listening: false, address() === null, _handle === null, ERR_SERVER_NOT_RUNNING), attach error/listening listeners before the nextTick emission, and would pass with the bug present only if _handle were nulled, which the unfixed code does not do. The cluster test's second server listening successfully after the failure also exercises key release on the primary. The explicit 30_000 timeout matches neighbors in cluster.test.ts. Overall the change is small, its intent is clear, and the ownership reasoning checks out, so I am comfortable approving.

[robobun]

^{Updated 4:55 PM PT - Sep 21st, 2026}

✅ @robobun, your commit 045757abc785fffb1616b0d5b19f1b524024a8b1 passed in Build #119440! 🎉

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🧪   To try this PR locally:

bunx bun-pr 43093

That installs a local version of the PR into your bun-43093 executable, so you can run:

bun-43093 --bun

[cirospaciari]

@robobun Both new tests make listen() fail by overriding server.address() to throw once, which only works because Bun calls this.address() inside listen. Node v26.3.0 never calls it on that path (lib/net.js setupListenHandle builds _connectionKey from its own arguments), so on Node the server emits 'listening' and both tests fail. Please trigger the failure in a way Node also hits, so the tests pass on Node and Bun.
Repro: node -e 'const s=require("net").createServer();s.address=()=>{throw new Error("x")};s.on("listening",()=>{console.log("listening");delete s.address;s.close()}).on("error",e=>console.log("error",e.message)).listen(0,"127.0.0.1")' prints listening on Node.

[robobun]

Thanks, you are right: Node never calls address() on that path. I found no user input that makes Node's listen() fail after the bind (Node validates the addContext() entries at the call, and _handle.listen() cannot be made to fail from user code), so a test cannot expect 'error' on both runtimes.

The tests (3be41e6) now use two addContext() names that Bun rejects when it loads them into the listener and that Node accepts. They assert that the state matches whichever event ends listen():

• 'listening': listening === true, address() and _handle set, close() works. This is what Node does with your repro and with these names.
• 'error': listening === false, address() === null, _handle === null, close() reports ERR_SERVER_NOT_RUNNING. This is what Bun does with the fix. Without it, Bun ends with 'error' and listening === true.

Checked with the same scenario as a script: node v26.3.0 prints {"outcome":"listening","listening":true,...}, this branch prints {"outcome":"error","listening":false,"hasAddress":false,"hasHandle":false}, bun 1.4.3 prints {"outcome":"error","listening":true,...}.

The cluster test has the same shape. In the 'error' case the worker starts a second server afterwards, and the primary completes a handshake with it, which checks that the shared fd was not closed twice.

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@test/js/node/cluster.test.ts`:
- Around line 912-915: Update the regression assertions in the cluster test to
accept only the Bun-specific error state, removing the listening alternative. In
the TLS server test, assert that the outcome is error before validating the
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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.