golang-samber-slog

Use slogmulti.Router() with predicates like slogmulti.LevelIs(slog.LevelError) to send errors to Sentry while other levels go to Loki or stdout. Add a catch-all handler with no predicate, since records matching no predicate are silently dropped.

Use slogsampling options such as ThresholdSamplingOption or UniformSamplingOption as a Pipe middleware, placed as the outermost stage before formatting and routing. Matchers like MatchByLevelAndMessage() group records so each unique message gets its own counter.

Fanout broadcasts every record to all handlers sequentially with latency equal to their sum. Router sends records to handlers whose predicates match, and Pool load-balances each record to one handler, giving latency of a single handler.

Yes, sloggin.NewWithConfig accepts a Config struct with DefaultLevel, ClientErrorLevel, and ServerErrorLevel fields. Set ClientErrorLevel to Warn and ServerErrorLevel to Error so 4xx and 5xx responses log at distinct levels without custom middleware.

Batch handlers like slog-datadog, slog-loki, slog-kafka, and slog-parquet buffer records internally and must be flushed on shutdown. Call handler.Stop(ctx) for Datadog, lokiClient.Stop() for Loki, writer.Close() for Kafka, or buffer.Flush(true) for Parquet.

AttrFromContext only works when an HTTP middleware such as slog-gin, slog-echo, slog-fiber, or slog-chi has populated the context with request attributes first. Without that middleware, the extraction functions silently return nil.