node:net: keep the process alive while an early-unref'd/paused socket is still connecting

[Jarred-Sumner]

Fixes #37086

Repro

import net from "node:net";
const server = net.createServer(() => {});
server.listen(0, "127.0.0.1", () => {
  const s = new net.Socket();
  s.unref(); // before connect()
  s.connect(server.address().port, "127.0.0.1", () => {
    console.log("CONNECTED");
    s.destroy();
    server.close();
  });
});
server.unref();

Node and Bun 1.3.14 print CONNECTED; Bun 1.4.0 exits 0 silently before the connection completes. This is what makes every testcontainers program exit during container startup (its Ryuk client calls socket.unref() before .connect()). The same happens for s.connect(); s.unref() and s.connect(); s.pause().

Cause

In Node a pending uv_connect_t keeps the loop alive no matter what the handle's ref state is; unref()/readStop only matter once the socket is established. Bun's native socket instead had a ref_pollref_on_connect flag that made an early unref() skip taking the loop hold for the connect attempt altogether, and an unref() on a connecting handle dropped it immediately. #36619 started applying node:net's recorded unref() to the freshly created (detached) handle, which routed the common "unref before connect" case into that path.

Fix

Native (Listener.rs / socket_body.rs): the connect attempt always holds poll_ref (taken before do_connect, released by every failure path); ref()/unref() on a not-yet-established socket only record the preference and on_open applies it. pause()/resume() on a half-connected socket are likewise left for after the open (uws_sys/socket.rs) — usockets re-arms reads on open without clearing its paused bit, so a pause latched there made every later pause() a no-op and a paused stream buffered without bound once connected.

net.ts: an autoSelectFamily retry handle inherits a mid-connect pause() the same way it inherits unref(), and the read(0) that connect() queued on the next tick is left to afterConnect while still connecting, so a pause() issued mid-connect is not undone by a read queued before it (Node only issues that read from afterConnect).

Tests

test/js/node/net/node-net.test.ts:

• unref()/pause() around connect(): unref/pause before connect(), right after it, and while the native connect is actually in flight → connected then exit; ref() after unref() (both timings) keeps holding; an in-flight pause() still lets backpressure stop reads. The unref/pause cases print nothing (or hang) on 1.4.0; all match Node's output.
• unref survives an autoSelectFamily retry no longer needs its 500 ms sentinel timer (the pending connect holds the loop by itself — that sentinel was also why it failed under slow debug/ASAN builds) and gains a pause() variant, which hung before this change.

Also ran node-net-server, node-tls-connect, node-tls-server, node-http, socket-reconnect-live, double-connect, bun/net/socket.test.ts and the node parallel net pause/connect tests locally with no new failures.

[robobun]

^{Updated 12:06 AM PT - Aug 21st, 2026}

✅ @Jarred-Sumner, your commit bfbfe8e557f507aac04b12f9795dc619cb3e6d58 passed in Build #102408! 🎉

---

🧪   To try this PR locally:

bunx bun-pr 39856

That installs a local version of the PR into your bun-39856 executable, so you can run:

bun-39856 --bun

[coderabbitai]

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• src/js/node/net.ts
• src/runtime/socket/Listener.rs
• src/runtime/socket/socket_body.rs
• src/uws_sys/socket.rs
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Walkthrough

Summary

Socket reference and pause state now persist correctly through connection, handle replacement, and establishment. Tests cover connection completion, process exit, reference restoration, retry behavior, and backpressure.

Changes

Socket reference lifecycle

Layer / File(s)	Summary
Reference state model src/runtime/socket/Listener.rs, src/runtime/socket/socket_body.rs	Socket creation paths initialize user_wants_ref. ref() and unref() update established sockets immediately and defer pending changes until on_open.
Connection reference lifecycle src/runtime/socket/Listener.rs, src/runtime/socket/socket_body.rs, src/js/node/net.ts	Connecting sockets retain an event-loop reference until completion. on_open applies the requested reference state. Deferred reads and replacement handles respect connection, pause, and unref state.
Handle replacement and validation src/uws_sys/socket.rs, test/js/node/net/node-net.test.ts	Pause and resume operations apply only to established sockets. Tests cover retries, pre-connect state changes, process exit, reference restoration, and backpressure.

Suggested reviewers: robobun, cirobspaciari, dylan-conway

Merge Risk: 🔵 Low · up to bfbfe

The change improves socket lifetime and pause behavior during connection setup, but an unresolved TCP-to-TLS lifecycle issue may still keep the process alive unexpectedly after reference-state changes. The PR is mergeable with explicit owner awareness or follow-up on that behavior.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary fix for sockets that are unrefed or paused while connecting.
Description check	✅ Passed	The description explains the regression, cause, fix, verification, and test coverage, satisfying the template requirements.
Linked Issues check	✅ Passed	The implementation and tests satisfy issue #37086 by keeping pending connections alive until completion and applying unref state afterward.
Out of Scope Changes check	✅ Passed	The changes remain focused on connection lifetime, ref/unref behavior, pause handling, retries, and related regression tests.

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Actionable comments posted: 3

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Inline comments:
In `@src/runtime/socket/socket_body.rs`:
- Line 3589: Update both upgraded wrappers in upgrade_tls to initialize
user_wants_ref from this.user_wants_ref.get() instead of resetting it to true,
while preserving the existing was_reffed handling.

In `@test/js/node/net/node-net.test.ts`:
- Around line 763-767: Add a pause-before-connect case to the parameterized
tests around the existing connection scenarios, using s.pause() before
s.connect(port, "127.0.0.1"). Ensure it verifies successful connection
completion and clean process exit like the other matrix entries.
- Around line 722-728: Update both subprocess assertions in
test/js/node/net/node-net.test.ts at lines 722-728 and 755-760: change stderr
handling to "pipe", await stdout, stderr, and process exit concurrently, then
assert the expected stdout and empty stderr before asserting exitCode is 0.

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Fix all unresolved CodeRabbit comments on this PR:

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• src/js/node/net.ts
• src/runtime/node/node_net_binding.rs
• src/runtime/socket/Listener.rs
• src/runtime/socket/socket_body.rs
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[claude]

Re-reviewed after 2bcc441 — the reconnect-through-a-live-handle case I flagged is now handled by running initSocketHandle unconditionally so the JS-side ref/pause state is reapplied to the reused native handle, and no new issues turned up. Because this reworks the connect-time poll_ref lifecycle for both node:net and Bun.connect (an in-flight connect now always holds the loop, and initSocketHandle newly runs on the live-handle reconnect path), a maintainer glance at the ref/unref semantics would still be worthwhile.

Checked: js_ref/js_unref now gate the immediate poll_ref op on is_established() (semi-connect defers to on_open); connect_finish refs before do_connect and handle_connect_error's existing poll_ref.unref releases it on sync failure; the raw twin at socket_body.rs:3696 keeping user_wants_ref: true is fine since it never runs on_open and holds no poll_ref; the added !this.connecting guard on the nextTick read(0) leaves the already-open-fd path untouched.

Extended reasoning...

Overview

Fixes #37086 — an early unref()/pause() on a net.Socket was letting the process exit before the connect completed (regressed in 1.4.0 via #36619). Native side (socket_body.rs, Listener.rs) renames ref_pollref_on_connect → user_wants_ref, has connect_finish take poll_ref unconditionally for the connect attempt, makes js_ref/js_unref record the preference and only touch poll_ref once is_established(), and has on_open apply the recorded preference. JS side (net.ts) runs initSocketHandle for the live-handle reconnect too (so the JS-side kUserUnrefed/kPausedUnref reasserts ref()/unref() on the reused handle), guards the connect-time nextTick read(0) on !this.connecting, and has initSocketHandle propagate kPausedUnref alongside kUserUnrefed. Tests add an 8-case matrix around unref()/pause()/ref() before/during connect and rework the autoSelectFamily-retry test to drop its sentinel timer and cover pause().

Follow-up on prior review

My earlier finding (stale user_wants_ref = false from finishSocketEnd's bookkeeping unref() leaking into a same-handle reconnect) is addressed by moving initSocketHandle outside the !this._handle guard: on reconnect it now calls handle.ref() when neither kUserUnrefed nor kPausedUnref is set, which resets user_wants_ref to true before connect_finish runs. The author's chosen JS-side fix also preserves a user's own unref() across the same reconnect, which a native reset in detach_for_reconnect would have lost. The CodeRabbit findings (TLS-upgrade user_wants_ref inheritance, stderr piping, pause-before-connect variant) are all applied; the second upgrade_tls construction site (the raw ciphertext-tap twin at line 3696) staying true is correct — that wrapper starts IS_ACTIVE with no poll_ref and never goes through on_open, so the field is inert there.

Security risks

None. No parsing of untrusted input, no auth/crypto, no allocation-size arithmetic. The change is event-loop ref bookkeeping.

Level of scrutiny

Moderate-to-high. Ref/unref lifecycle bugs manifest as either premature exit (the bug being fixed) or processes that never exit, both of which are hard to bisect. This change also shifts Bun.connect's native .unref() semantics for a mid-connect socket (previously dropped poll_ref immediately, now defers to on_open) — that's the correct fix and restores 1.3.14 behavior, but it's a Bun-native surface change, not purely node-compat.

Other factors

Test coverage is thorough for the matrix and the author ran the adjacent suites locally. The one thing I'd want a maintainer to sanity-check is that running initSocketHandle (specifically _undestroy() / kended = false / handle.ref()) on a still-live handle mid-reconnect has no side effects on paths beyond the allowHalfOpen scenario the author verified — I traced it and it looks fine, but it's the broadest behavior change in the diff.

[robobun]

I closed #37087 in favor of this PR. One test timing from that PR is not in the unref()/pause() around connect() block here: s.unref(); s.ref(); with both calls before connect(), where the server ends the connection. The expected output is connected then closed, since the later ref() has to win over the earlier unref(). The two ref() after unref() cases here both run after connect(). The before-connect() timing could be one more row in that it.each list.

[claude]

🟡 The ref() after unref() it.each only covers 'right after connect()' and 'while the connect is in flight' — robobun's last comment (closing #37087) asked for the missing s.unref(); s.ref(); before connect() row, which exercises the distinct _handle === null path (kUserUnrefed + once('connect') handlers + initSocketHandle) rather than js_ref/js_unref on a native handle. One more row: ["before connect()", 's.unref(); s.ref(); s.resume(); s.connect(port, "127.0.0.1");'].

Extended reasoning...

What's missing

The ref() after unref() matrix at test/js/node/net/node-net.test.ts:781-784 has two rows:

it.each([
  ["right after connect()", `s.connect(port, "127.0.0.1"); s.unref(); s.ref(); s.resume();`],
  ["while the connect is in flight", `s.connect(port, "127.0.0.1"); ${inFlight("s.unref(); s.ref(); s.resume();")}`],
])("ref() after unref() %s keeps holding the loop", ...);

There is no before connect() row. The sibling matrix immediately above (lines 767-774) covers all three timings — before/after/in-flight — for both unref() and pause(), so this matrix is asymmetric.

Why it was requested

robobun's comment at 2026-08-21T06:33:41Z is the last entry in the PR timeline (after the final commit bfbfe8e) and explicitly asks for this row:

One test timing from that PR is not in the unref()/pause() around connect() block here: s.unref(); s.ref(); with both calls before connect(), where the server ends the connection. The expected output is connected then closed, since the later ref() has to win over the earlier unref(). The two ref() after unref() cases here both run after connect(). The before-connect() timing could be one more row in that it.each list.

This comment is unaddressed in the final diff.

Why the before-connect timing is a distinct code path

The two existing rows both run after connect() has been called, so _handle already exists (detached right-after, or a non-established native socket in-flight). In both cases unref()/ref() reach the native js_unref/js_ref (socket_body.rs:3225-3252), which — after this PR's change — toggle ref_pollref_on_connect on the not-yet-established handle and on_open applies it.

Before connect(), _handle is null. Socket.prototype.unref() and Socket.prototype.ref() in net.ts instead:

• toggle this[kUserUnrefed] (true then false),
• each register a once('connect', ...) handler,
• and later initSocketHandle reads the final kUserUnrefed state when the handle is created (net.ts:4273-4274 — if (self[kUserUnrefed] || self[kPausedUnref]) handle.unref?.()), then both once-handlers fire in registration order on 'connect'.

None of that JS-side bookkeeping is exercised by the after-connect / in-flight rows.

Step-by-step through the missing row

With s.unref(); s.ref(); s.resume(); s.connect(port, "127.0.0.1"); and the server calling c.end():

1. s.unref(): _handle is null → kUserUnrefed = true, once('connect', h1) registered.
2. s.ref(): _handle is null → kUserUnrefed = false, once('connect', h2) registered.
3. s.connect(...): creates _handle, calls initSocketHandle → kUserUnrefed is false and kPausedUnref is false, so handle.unref() is not called. connect_finish refs poll_ref for the connect attempt.
4. Connection opens → on_open sees ref_pollref_on_connect == true (never touched) → poll_ref stays held. 'connect' fires → h1 (unref-era) and h2 (ref-era) run in order; the last one wins.
5. Server ends → client emits 'close' → stdout is connected\nclosed\n, exit 0.

That's the expected output the existing assertion already checks — so adding the row is a one-line change.

Impact and fix

Per REVIEW.md "Cover the variant matrix, not just the repro": every sibling entry point receiving the same fix should be covered, and this timing variant was explicitly requested by a reviewer. The code path likely works correctly (the final kUserUnrefed state is what initSocketHandle reads), but leaving the row out means the pre-handle ref()-wins-over-unref() ordering has no coverage.

Add one row to the it.each at line 781:

["before connect()", `s.unref(); s.ref(); s.resume(); s.connect(port, "127.0.0.1");`],

[Jarred-Sumner]

@robobun add this in a follow-up PR

[robobun]

Added the before connect() row in #40134.

[robobun]

Follow-up PR with the s.unref(); s.ref(); before connect() row: #40134