logger: allocation-free component level resolution, yaml.Marshaler on Config

[paulwe]

Two independent changes to logger.Config.

ResolveComponentLevel without allocations

It split the component on "." and rejoined the remaining parts on every lookup, so resolving rtc.room.track allocated a slice and a string per level. It now walks backwards from the end of the string, reslicing to the last "." after each miss, and the map lookups take those substrings directly.

Measured with testing.AllocsPerRun: the walk is 0 allocs. The one that remains is ParseZapLevel, whose []byte(level) conversion escapes because zapcore's UnmarshalText hands the bytes to fmt.Errorf. Killing that means duplicating zapcore's level table in a string switch — not done here.

Edge cases match the old behavior exactly: empty string, leading dot, and trailing dot all resolve as before.

yaml.Marshaler on Config

Marshaling read the fields alongside whatever Update was writing. MarshalYAML now snapshots under the same lock.

The snapshot needs a type without the mutex. The usual type config Config cast doesn't give one: returning (*config)(c) defers the field reads until after the lock is released, and dereferencing to snapshot trips copylocks. Encoding into a yaml.Node inside the lock looked like a way out, but yaml's encoder dereferences the pointer and calls in.Interface() on the struct (encode.go:117), which copies the locked mutex where neither vet nor -race can see it. So the yaml-visible fields are mirrored on configYAML, with TestConfigYAMLFields reflecting over both types to fail if a field or tag drifts.

ComponentLevels is cloned because the encoder walks the returned value after the lock drops.

Note that yaml.v3 does not take the address of struct fields, so a config holding logger.Config by value skips this method and falls back to field reflection — same output, no locked snapshot. Holding *logger.Config gets the lock.

Considered and rejected

Moving the fields into an embedded struct would define them once and collapse Update to a single assignment. Go 1.27 allows promoted fields in composite literals, so Config{Level: "info"} keeps compiling — but only for callers whose own module declares go 1.27; the library's directive doesn't matter. Callers on 1.26 would need to bump or rewrite the literal, and that's 93 sites across ~20 repos here, all still on 1.26. Worth revisiting once the fleet moves, at which point it costs consumers nothing.

Test plan

• go test -race ./logger/..., go vet ./logger/...
• Byte-exact marshal output, round-trip through Unmarshal, and a mutate-after-marshal check that the snapshot held
• Both commits verified green independently

[changeset-bot]

🦋 Changeset detected

Latest commit: d77b4a5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
github.com/livekit/protocol	Patch
@livekit/protocol	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR