fix: eliminate port TOCTOU race and framed test compile failure breaking CI (#767)

[strawgate]

Summary

Fixes two test failures on macOS/Linux CI introduced by the nextest switch in #761:

1. diagnostics.rs — Address already in use on macOS

free_port() + TEST_LOCK assumed shared process state, but nextest runs each test as its own process. The static AtomicU16 resets to 19100 per process, so concurrent test processes pick the same starting port.

Fix: DiagnosticsServer::start() now returns (JoinHandle<()>, SocketAddr) so the actual OS-assigned port is available without a separate probe step. Tests use "127.0.0.1:0" and extract the port from the returned SocketAddr. Removes free_port(), TEST_LOCK, and all per-test port management — no more TOCTOU window.

2. framed.rs — test compile failure

FormatProcessor::Passthrough became a struct variant in #755 but 3 EOF-flush tests were not updated. Tests now use FormatProcessor::passthrough(stats.clone()).

Test plan

• cargo test -p logfwd-io passes locally (previously failed to compile)
• CI green on both macOS and Linux
• No change to production behavior — DiagnosticsServer API is internal to the binary

🤖 Generated with Claude Code

[coderabbitai]

Caution

Review failed

The pull request is closed.

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📥 Commits

Reviewing files that changed from the base of the PR and between 9f43073 and 7e2af91.

📒 Files selected for processing (3)

• crates/logfwd-io/src/diagnostics.rs
• crates/logfwd-io/src/framed.rs
• crates/logfwd/src/main.rs

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Walkthrough

The pull request updates DiagnosticsServer::start to return a tuple containing both the JoinHandle and the actual bound SocketAddr instead of only the handle. This enables callers to retrieve the server's bound address after startup. The diagnostics test infrastructure was refactored to use ephemeral port binding (port 0) rather than manually selecting and locking TCP ports via a free_port() function. Additionally, FramedInput unit tests were updated to use the new FormatProcessor::passthrough() API, and the call site in main.rs was adjusted to destructure the new return value.

Possibly related PRs

• feat: 1 MiB log buffer, always-on capture, clean startup output #680: Modifies DiagnosticsServer::start to return a tuple with JoinHandle and SocketAddr, along with corresponding call site updates in main.rs.
• feat: logfwd-core is now #![no_std] + #![forbid(unsafe_code)] #375: Introduces DiagnosticsServer to the logfwd-io crate, establishing the foundational implementation modified by this PR.
• refactor: move format handling and framing out of pipeline into input layer #581: Updates the FormatProcessor::passthrough() API that is adopted in the FramedInput tests within this PR.

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