Fixed bug GH-22981 (unix socket connect fails with EAGAIN when listen backlog is full)

[shoutoutuoadi325]

Fixes GH-22981.

php_network_connect_socket() runs the connect with the socket in
non-blocking mode so it can honour the timeout. The flip side is that
connect() to a unix domain socket returns EAGAIN as soon as the listen
backlog fills up, while a blocking connect would wait for a slot. Short
bursts of connections (PDO over a unix socket in the report) then fail
with "Resource temporarily unavailable".

Retry the connect while it keeps returning EAGAIN, bounded by the
connect timeout if one was given, matching what a blocking connect
does. Everything else (other errors, async connects, TCP) is unchanged.

gh22981.phpt runs a server with backlog=1 that starts accepting late:
connect #3 fails before the patch, all 20 succeed after. It also runs a
server that never accepts and expects the client to fail once its
connect timeout expires.

[Copilot]

🟡 Changes recommended

Unresolved issues remain in transient-error handling, timeout-bounded retries, and timeout regression coverage.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Fixes Unix-domain socket connection failures when the listen backlog is full by retrying transient connection errors.

Changes:

• Adds bounded retry handling for Unix socket connections.
• Adds GH-22981 regression coverage.
• Documents the fix in NEWS.

File summaries

File	Description
NEWS	Documents the bug fix.
main/network.c	Implements Unix socket connection retries.
ext/standard/tests/streams/gh22981.phpt	Tests delayed backlog recovery.

Review details

Suppressed comments (2)

ext/standard/tests/streams/gh22981.phpt:64

• Please add coverage for a backlog that remains full until the client timeout expires. This test only exercises eventual success—the server starts accepting after 200 ms and every client has a 5-second timeout—so it would not catch a retry loop that ignores or exceeds the supplied timeout.

for ($i = 0; $i < 20; $i++) {
    $conn = stream_socket_client('unix://' . $socketPath, $errno, $errstr, 5);

main/network.c:359

• On platforms where EWOULDBLOCK differs from EAGAIN, a non-blocking UNIX-domain connect() can report EWOULDBLOCK for this transient full-backlog condition. This guard then falls through to the hard-error path, so the fix remains platform-dependent; use the existing PHP_IS_TRANSIENT_ERROR(error) macro, which covers both values.

		if (!asynchronous && error == EAGAIN && addr->sa_family == AF_UNIX) {

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.