Structured logging extensions for Golang using samber/slog-* — multi-handler pipelines, sampling, attribute formatting, HTTP middleware (gin, echo, fiber, chi), backend routing (datadog, sentry, loki, syslog). Apply when using slog or on github.com/samber/slog-* imports.
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name
golang-samber-slog
description
Structured logging extensions for Golang using samber/slog-* — multi-handler pipelines, sampling, attribute formatting, HTTP middleware (gin, echo, fiber, chi), backend routing (datadog, sentry, loki, syslog). Apply when using slog or on github.com/samber/slog-* imports.
user-invocable
true
license
MIT
compatibility
Designed for Claude Code, Codex or similar harness, and for projects using Golang.
Persona: You are a Go logging architect. You design log pipelines where every record flows through the right handlers — sampling drops noise early, formatters strip PII before records leave the process, and routers send errors to Sentry while info goes to Loki.
samber/slog-**** — Structured Logging Pipeline for Go
20+ composable slog.Handler packages for Go 1.21+. Three core pipeline libraries plus HTTP middlewares and backend sinks that all implement the standard slog.Handler interface.
This skill is not exhaustive. Please refer to library documentation and code examples for more information. For Go package docs, symbols, versions, importers, and known vulnerabilities, → See samber/cc-skills-golang@golang-pkg-go-dev skill (godig) — prefer it over Context7 for Go package facts. To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See samber/cc-skills-golang@golang-gopls skill (gopls). Context7 remains a fallback for docs not indexed on pkg.go.dev.
The Pipeline Model
Every samber/slog pipeline follows a canonical ordering. Records flow left to right — place sampling first to drop early and avoid wasting CPU on records that never reach a sink.
record → [Sampling] → [Pipe: trace/PII] → [Router] → [Sinks]
Order matters: sampling before formatting saves CPU. Formatting before routing ensures all sinks receive clean attributes. Reversing this wastes work on records that get dropped.
Sampling MUST be the outermost handler in the pipeline — placing it after formatting wastes CPU on records that get dropped.
// Threshold: log first 10 per 5s, then 10% — errors always pass through via Router
logger := slog.New(
slogmulti.
Pipe(slogsampling.ThresholdSamplingOption{
Tick: 5 * time.Second, Threshold: 10, Rate: 0.1,
}.NewMiddleware()).
Handler(innerHandler),
)
Matchers group similar records for deduplication: MatchByLevel(), MatchByMessage(), MatchByLevelAndMessage() (default), MatchBySource(), MatchByAttribute(groups, key).
Batch handlers require graceful shutdown — slog-datadog, slog-loki, slog-kafka, and slog-parquet buffer records internally. Flush on shutdown (e.g., handler.Stop(ctx) for Datadog, lokiClient.Stop() for Loki, writer.Close() for Kafka) or buffered logs are lost.
For configuration examples and shutdown patterns, see Backend Handlers.
Fanout latency = sum of all handler latencies (sequential). With 5 handlers at 10ms each, every log call costs 50ms. Use Pool() to reduce to max(latencies)
Pipe middleware adds per-record function call overhead — keep chains short (2-4 middlewares)
slog-formatter processes attributes sequentially — many formatters compound. For hot-path attribute formatting, prefer implementing slog.LogValuer on your types instead
Benchmark your pipeline with go test -bench before production deployment
Diagnose: measure per-record allocation and latency of your pipeline and identify which handler in the chain allocates most.
Best Practices
Sample first, format second, route last — this canonical ordering minimizes wasted work and ensures all sinks see clean data
Use Pipe for cross-cutting concerns — trace ID injection and PII scrubbing belong in middleware, not per-handler logic
Test pipelines with slogmulti.NewHandleInlineHandler — assert on records reaching each stage without real sinks
Use AttrFromContext to propagate request-scoped attributes from HTTP middleware to all handlers
Prefer Router over Fanout when handlers need different record subsets — Router evaluates predicates and skips non-matching handlers
Cross-References
→ See samber/cc-skills-golang@golang-observability skill for slog fundamentals (levels, context, handler setup, migration)
→ See samber/cc-skills-golang@golang-error-handling skill for the log-or-return rule
→ See samber/cc-skills-golang@golang-security skill for PII handling in logs
→ See samber/cc-skills-golang@golang-samber-oops skill for structured error context with samber/oops
If you encounter a bug or unexpected behavior in any samber/slog-* package, open an issue at the relevant repository (e.g., slog-multi/issues, slog-sampling/issues).
