Add 'so_linger' configuration parameter by juanjole · Pull Request #2547 · eclipse-zenoh/zenoh

juanjole · 2026-04-06T11:45:03Z

Description

Adding the 'so_linger' parameter to set the SO_LINGER of the TCP sockets using config files or locator expressions.

What does this PR do?

Making configurable the SO_LINGER parameter for TCP connections, the default value is None.

Why is this change needed?

The current version sets statically the SO_LINGER to 10 seconds.

Related Issues

Motivated by my concern in this Discord thread and related to #2350 issue.

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Labels: enhancement

✨ Enhancement Requirements

Since this PR enhances existing functionality:

Enhancement scope documented - Clear description of what is being improved
Minimum necessary code - Implementation is as simple as possible, doesn't overcomplicate the system
Backwards compatible - Existing code/APIs still work unchanged
No new APIs added - Only improving existing functionality
Tests updated - Existing tests pass, new test cases added if needed
Performance improvement measured - If applicable, before/after metrics provided
Documentation updated - Existing docs updated to reflect improvements
User impact documented - How users benefit from this enhancement

Remember: Enhancements should not introduce new APIs or breaking changes.

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… config file

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Pull request overview

Adds a configurable so_linger TCP socket option (via config files and locator parameters) and removes the previously hardcoded linger timeout behavior from the TCP/TLS link implementations.

Changes:

Introduces so_linger as a new TCP socket option (TCP_SO_LINGER) and wires it through config inspection + locator parameter parsing.
Extends TcpSocketConfig to carry/apply an optional linger timeout.
Removes the prior hardcoded *_LINGER_TIMEOUT = 10 constants and the per-link set_linger calls in TCP/TLS unicast setup.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
io/zenoh-links/zenoh-link-tls/src/utils.rs	Adds `so_linger` propagation into TLS locator parameters and parses it into `TcpSocketConfig`.
io/zenoh-links/zenoh-link-tls/src/unicast.rs	Removes the hardcoded TLS linger `set_linger` call.
io/zenoh-links/zenoh-link-tls/src/lib.rs	Removes the `TLS_LINGER_TIMEOUT` configurable constant.
io/zenoh-links/zenoh-link-tcp/src/utils.rs	Adds `so_linger` propagation into TCP locator parameters and parses it into `TcpLinkConfig`/`TcpSocketConfig`.
io/zenoh-links/zenoh-link-tcp/src/unicast.rs	Removes the hardcoded TCP linger `set_linger` call.
io/zenoh-links/zenoh-link-tcp/src/lib.rs	Removes the `TCP_LINGER_TIMEOUT` configurable constant.
io/zenoh-links/zenoh-link-quic/src/lib.rs	Removes unused QUIC linger timeout constant (legacy).
io/zenoh-links/zenoh-link-quic_datagram/src/lib.rs	Removes unused QUIC datagram linger timeout constant (legacy).
io/zenoh-link-commons/src/tcp.rs	Extends `TcpSocketConfig` to include/apply optional linger timeout (currently via deprecated Tokio API).
io/zenoh-link-commons/src/lib.rs	Adds `TCP_SO_LINGER` constant and documentation for the option.
DEFAULT_CONFIG.json5	Documents the new `so_linger` option in the default config template.
commons/zenoh-config/src/lib.rs	Adds `so_linger: Option<u32>` to validated transport link config structs.

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Copilot · 2026-04-06T11:49:04Z

+            #[allow(deprecated)]
+            socket.set_linger(Some(std::time::Duration::from_secs(timeout as u64)))?;


TcpSocket::set_linger is deprecated in Tokio (hence the #[allow(deprecated)]). Since this option is now configurable, it would be better to avoid the deprecated API by setting SO_LINGER via socket2::SockRef (the repo already uses socket2 elsewhere) or by removing linger support entirely per #2350. This avoids relying on an API that may be removed and keeps CI/lints clean without suppressions.

Suggested change

#[allow(deprecated)]

socket.set_linger(Some(std::time::Duration::from_secs(timeout as u64)))?;

socket2::SockRef::from(&socket)

.set_linger(Some(std::time::Duration::from_secs(timeout as u64)))?;

Copilot · 2026-04-06T11:49:05Z

+// The LINGER option causes the shutdown() call to block until (1) all application data is delivered
+// to the remote end or (2) a timeout expires. The timeout is expressed in seconds.


The comment describing SO_LINGER says it causes the shutdown() call to block. SO_LINGER affects the behavior of close()/dropping the socket (and whether it blocks / sends RST), not shutdown() itself. Please adjust this documentation to avoid misleading users about what this option does.

Suggested change

// The LINGER option causes the shutdown() call to block until (1) all application data is delivered

// to the remote end or (2) a timeout expires. The timeout is expressed in seconds.

// The LINGER option affects the behavior of close()/dropping the socket: it may cause the close

// operation to block until (1) pending application data is delivered to the remote end or

// (2) a timeout expires. The timeout is expressed in seconds.

Copilot · 2026-04-06T11:49:05Z

                    pub so_sndbuf: Option<u32>,
                    /// Configure TCP read buffer size
                    pub so_rcvbuf: Option<u32>,
+                    /// Configure TCP linger timeout


so_linger is documented here without specifying the unit, but the default config comment indicates seconds. Please clarify the unit in this doc comment (e.g., “seconds”) and, if possible, document any special semantics (e.g., 0 seconds causing an abortive close on many OSes).

Suggested change

/// Configure TCP linger timeout

/// Configure TCP linger timeout in seconds.

/// Setting this to `0` seconds typically requests an abortive close on many OSes.

Copilot · 2026-04-06T11:49:05Z

        /// Optional configuration for TCP system buffers sizes for TLS links
        ///
        /// Configure TCP read buffer size (bytes)
        // so_rcvbuf: 123456,
        /// Configure TCP write buffer size (bytes)
        // so_sndbuf: 123456,
+        /// Configure TCP linger timeout (seconds)
+        // so_linger: 10,


This section header says “Optional configuration for TCP system buffers sizes for TLS links”, but the newly added so_linger is not a buffer size. Consider updating the wording to something like “TCP socket options” to match the parameters listed below.

codecov · 2026-04-06T12:25:43Z

Codecov Report

❌ Patch coverage is 64.51613% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.66%. Comparing base (29b3e63) to head (bfe7360).
⚠️ Report is 64 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
io/zenoh-links/zenoh-link-tls/src/utils.rs	62.50%	6 Missing ⚠️
io/zenoh-links/zenoh-link-tcp/src/utils.rs	60.00%	4 Missing ⚠️
io/zenoh-link-commons/src/tcp.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2547      +/-   ##
==========================================
+ Coverage   72.49%   74.66%   +2.17%     
==========================================
  Files         390      399       +9     
  Lines       63360    59109    -4251     
==========================================
- Hits        45931    44134    -1797     
+ Misses      17429    14975    -2454

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juanjole added 3 commits April 5, 2026 19:18

Add TCP linger timeout configuration through 'so_linger' parameter in…

7d4a3f2

… config file

Add so_linger parameter to DEFAULT_CONFIG.json5

8fe7786

Include comment about SO_LINGER

bfe7360

Copilot AI review requested due to automatic review settings April 6, 2026 11:45

Copilot started reviewing on behalf of juanjole April 6, 2026 11:45 View session

Copilot AI reviewed Apr 6, 2026

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diogomatsubara added the enhancement Existing things could work better label Apr 13, 2026

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Add 'so_linger' configuration parameter#2547

Add 'so_linger' configuration parameter#2547
juanjole wants to merge 3 commits into
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juanjole:1.8.0-so_linger_conf

juanjole commented Apr 6, 2026 •

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		#[allow(deprecated)]
		socket.set_linger(Some(std::time::Duration::from_secs(timeout as u64)))?;

		// The LINGER option causes the shutdown() call to block until (1) all application data is delivered
		// to the remote end or (2) a timeout expires. The timeout is expressed in seconds.

-// The LINGER option causes the shutdown() call to block until (1) all application data is delivered
-// to the remote end or (2) a timeout expires. The timeout is expressed in seconds.
+// The LINGER option affects the behavior of close()/dropping the socket: it may cause the close
+// operation to block until (1) pending application data is delivered to the remote end or
+// (2) a timeout expires. The timeout is expressed in seconds.

	/// Configure TCP linger timeout
	/// Configure TCP linger timeout in seconds.
	/// Setting this to `0` seconds typically requests an abortive close on many OSes.

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Description

What does this PR do?

Why is this change needed?

Related Issues

🏷️ Label-Based Checklist

✨ Enhancement Requirements

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juanjole commented Apr 6, 2026 •

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