Document transient connection errors from TcpListener::accept by valentynkit · Pull Request #158074 · rust-lang/rust

valentynkit · 2026-06-18T10:14:44Z

TcpListener::accept can return an error that belongs to a single incoming
connection, not to the listener, for example a connection aborted by the peer
before it could be accepted (ConnectionAborted). The listener stays usable, so
a server looping over connections usually wants to log the error and keep
accepting rather than treat it as fatal. This was not documented, and the
incoming example treated every error as a failed connection.

This implements the libs-team decision in #142557: document these transient
errors instead of changing accept to retry them, since retrying would hide
errors that some callers want to observe.

Changes:

Add an # Errors section to accept describing this behavior, without
listing specific error codes since some may be more permanent than others.
Note that Interrupted errors are retried internally on Unix.
Add the same pointer to incoming and into_incoming, which are accept
in a loop.

Addresses #142557.

r? rust-lang/libs

`accept` can return an error that belongs to a single incoming connection, not to the listener itself, for example a connection aborted by the peer before it could be accepted. The listener stays usable in that case, so code serving a long-lived listener usually wants to log the error and keep accepting connections rather than treat it as fatal. This was previously undocumented. - Add an `# Errors` section to `accept` that describes this behavior without listing specific error codes. - Note that `Interrupted` errors are retried internally on Unix. - Point `incoming` and `into_incoming` at `accept` for the same details.

rustbot · 2026-06-18T10:14:49Z

Thanks for the pull request, and welcome! The Rust Project is excited to review your changes, and you should hear from @Darksonn (or someone else) some time within the next two weeks.

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Random selection from Darksonn, Mark-Simulacrum, clarfonthey, jhpratt

Darksonn

Hmm. There are a lot of different errors it can return. This only documents one case.

View changes since this review

Darksonn · 2026-06-18T10:38:41Z

+    /// # Errors
+    ///
+    /// Some errors returned by this function relate to a single incoming
+    /// connection that failed before it could be accepted, such as one aborted
+    /// by the peer ([`ConnectionAborted`]). Such an error does not indicate a
+    /// problem with the listener itself, which remains usable. Code serving a
+    /// long-lived listener will usually want to log the error and continue
+    /// accepting connections rather than treat it as fatal. Which errors can
+    /// occur this way is platform-specific.
+    ///
+    /// On Unix, [`Interrupted`] errors are retried internally rather than being
+    /// returned.


If we're going to start documenting the set of errors, then we should probably also mention that it can fail with an error if the FD limit has been reached, in which case the call can be retried once other fds have been closed (often done via a timeout).

Darksonn · 2026-06-18T10:40:06Z

@rustbot author

rustbot · 2026-06-18T10:40:11Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

Darksonn · 2026-06-18T12:30:34Z

May also be worth mentioning ENOMEM if an allocation failed while trying to accept it.

Darksonn

Overall LGTM, just one more thing we could add.

View changes since this review

Darksonn · 2026-06-18T13:12:25Z

+    /// - An error from reaching the per-process or system-wide open file
+    ///   descriptor limit. The call can be retried once other file descriptors
+    ///   have been closed, typically after a short delay.


Which error kind is used for this?

It's Uncategorized. EMFILE/ENFILE aren't mapped in decode_error_kind, so they're only distinguishable via raw_os_error(), which is what std itself does:

rust/library/std/src/sys/process/unix/unix.rs

Lines 513 to 517 in 693b3e4

Err(e) if e.raw_os_error() == Some(libc::EMFILE) => {

// We're temporarily(?) out of file descriptors. In this case pidfd_spawnp would also fail

// Don't update the support flag so we can probe again later.

return Err(e)

}

With no matchable kind, I went with prose here.

Ok, that makes sense, thanks.

valentynkit · 2026-06-18T13:13:55Z

Added the OutOfMemory case too, thanks!

On scope: I kept this as a non-exhaustive list ("include, but are not limited
to") covering the main retryable cases rather than enumerating everything. Is
that the level you'd prefer, or should I expand it?

Darksonn · 2026-06-18T13:15:37Z

Keeping it non-exhasutive is good.

Darksonn · 2026-06-18T13:35:22Z

Looks good, thanks.

@bors r+ rollup

rust-bors · 2026-06-18T13:35:26Z

📌 Commit 1447519 has been approved by Darksonn

It is now in the queue for this repository.

…rrors, r=Darksonn Document transient connection errors from TcpListener::accept `TcpListener::accept` can return an error that belongs to a single incoming connection, not to the listener, for example a connection aborted by the peer before it could be accepted (`ConnectionAborted`). The listener stays usable, so a server looping over connections usually wants to log the error and keep accepting rather than treat it as fatal. This was not documented, and the `incoming` example treated every error as a failed connection. This implements the libs-team decision in rust-lang#142557: document these transient errors instead of changing `accept` to retry them, since retrying would hide errors that some callers want to observe. Changes: - Add an `# Errors` section to `accept` describing this behavior, without listing specific error codes since some may be more permanent than others. - Note that `Interrupted` errors are retried internally on Unix. - Add the same pointer to `incoming` and `into_incoming`, which are `accept` in a loop. Addresses rust-lang#142557. r? rust-lang/libs

…uwer Rollup of 6 pull requests Successful merges: - #158026 (`RegionValues`: disable unnecessary range check) - #156795 (Handle generic reborrow in expression-use adjustment walking) - #157694 (Enhance documentation on wake call memory ordering) - #158034 (Fix reborrow source expression visits) - #158074 (Document transient connection errors from TcpListener::accept) - #158086 (renovate: Loosen dashboard approval and adopt recommended config)

…rrors, r=Darksonn Document transient connection errors from TcpListener::accept `TcpListener::accept` can return an error that belongs to a single incoming connection, not to the listener, for example a connection aborted by the peer before it could be accepted (`ConnectionAborted`). The listener stays usable, so a server looping over connections usually wants to log the error and keep accepting rather than treat it as fatal. This was not documented, and the `incoming` example treated every error as a failed connection. This implements the libs-team decision in rust-lang#142557: document these transient errors instead of changing `accept` to retry them, since retrying would hide errors that some callers want to observe. Changes: - Add an `# Errors` section to `accept` describing this behavior, without listing specific error codes since some may be more permanent than others. - Note that `Interrupted` errors are retried internally on Unix. - Add the same pointer to `incoming` and `into_incoming`, which are `accept` in a loop. Addresses rust-lang#142557. r? rust-lang/libs

…uwer Rollup of 10 pull requests Successful merges: - #158026 (`RegionValues`: disable unnecessary range check) - #156795 (Handle generic reborrow in expression-use adjustment walking) - #157694 (Enhance documentation on wake call memory ordering) - #157935 (Make `proc_macro::ConversionErrorKind` non exhaustive) - #158002 (Replace `unwrap` with `expect` in `get_module_children`) - #158034 (Fix reborrow source expression visits) - #158072 (Bump thin-vec to 0.2.18 to address RUSTSEC-2026-0103) - #158074 (Document transient connection errors from TcpListener::accept) - #158077 (rustdoc-json-types: Replace bincode dev-dependency with postcard) - #158086 (renovate: Loosen dashboard approval and adopt recommended config)

Rollup of 12 pull requests Successful merges: - #156795 (Handle generic reborrow in expression-use adjustment walking) - #157694 (Enhance documentation on wake call memory ordering) - #157935 (Make `proc_macro::ConversionErrorKind` non exhaustive) - #158002 (Replace `unwrap` with `expect` in `get_module_children`) - #158009 (Reject `impl const Trait` since the right syntax is `const impl Trait` now) - #158034 (Fix reborrow source expression visits) - #158072 (Bump thin-vec to 0.2.18 to address RUSTSEC-2026-0103) - #158074 (Document transient connection errors from TcpListener::accept) - #158077 (rustdoc-json-types: Replace bincode dev-dependency with postcard) - #158086 (renovate: Loosen dashboard approval and adopt recommended config) - #158088 (codegen_ssa: no dbginfo for scalable vec local w/ `-O0`) - #158089 (Fix invalid "jump-to-def" doc link generation when an item has a `derive` proc-macro)

Rollup merge of #158074 - valentynkt:docs/accept-transient-errors, r=Darksonn Document transient connection errors from TcpListener::accept `TcpListener::accept` can return an error that belongs to a single incoming connection, not to the listener, for example a connection aborted by the peer before it could be accepted (`ConnectionAborted`). The listener stays usable, so a server looping over connections usually wants to log the error and keep accepting rather than treat it as fatal. This was not documented, and the `incoming` example treated every error as a failed connection. This implements the libs-team decision in #142557: document these transient errors instead of changing `accept` to retry them, since retrying would hide errors that some callers want to observe. Changes: - Add an `# Errors` section to `accept` describing this behavior, without listing specific error codes since some may be more permanent than others. - Note that `Interrupted` errors are retried internally on Unix. - Add the same pointer to `incoming` and `into_incoming`, which are `accept` in a loop. Addresses #142557. r? rust-lang/libs

Rollup of 12 pull requests Successful merges: - rust-lang/rust#156795 (Handle generic reborrow in expression-use adjustment walking) - rust-lang/rust#157694 (Enhance documentation on wake call memory ordering) - rust-lang/rust#157935 (Make `proc_macro::ConversionErrorKind` non exhaustive) - rust-lang/rust#158002 (Replace `unwrap` with `expect` in `get_module_children`) - rust-lang/rust#158009 (Reject `impl const Trait` since the right syntax is `const impl Trait` now) - rust-lang/rust#158034 (Fix reborrow source expression visits) - rust-lang/rust#158072 (Bump thin-vec to 0.2.18 to address RUSTSEC-2026-0103) - rust-lang/rust#158074 (Document transient connection errors from TcpListener::accept) - rust-lang/rust#158077 (rustdoc-json-types: Replace bincode dev-dependency with postcard) - rust-lang/rust#158086 (renovate: Loosen dashboard approval and adopt recommended config) - rust-lang/rust#158088 (codegen_ssa: no dbginfo for scalable vec local w/ `-O0`) - rust-lang/rust#158089 (Fix invalid "jump-to-def" doc link generation when an item has a `derive` proc-macro)

rustbot assigned Darksonn Jun 18, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jun 18, 2026

Darksonn reviewed Jun 18, 2026

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Darksonn added A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools A-io Area: `std::io`, `std::fs`, `std::net` and `std::path` labels Jun 18, 2026

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 18, 2026

Document the file-descriptor-limit error from TcpListener::accept

34d3eed

Document the out-of-memory error from TcpListener::accept

1447519

Darksonn approved these changes Jun 18, 2026

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 18, 2026

jhpratt mentioned this pull request Jun 18, 2026

Rollup of 3 pull requests #158087

Closed

JonathanBrouwer mentioned this pull request Jun 18, 2026

Rollup of 6 pull requests #158094

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JonathanBrouwer mentioned this pull request Jun 18, 2026

Rollup of 10 pull requests #158095

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GuillaumeGomez mentioned this pull request Jun 18, 2026

Rollup of 12 pull requests #158098

Merged

rust-bors Bot merged commit 6433d9b into rust-lang:main Jun 18, 2026
13 checks passed

rustbot added this to the 1.98.0 milestone Jun 18, 2026

	Err(e) if e.raw_os_error() == Some(libc::EMFILE) => {
	// We're temporarily(?) out of file descriptors. In this case pidfd_spawnp would also fail
	// Don't update the support flag so we can probe again later.
	return Err(e)
	}

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