Go Context

LogLayer can attach a context.Context to log entries. Transports and plugins that opt in can extract anything the context carries: trace IDs, span context, deadlines, request-scoped values.

WithContext works two ways depending on the receiver, mirroring the WithGroup pattern:

• (*LogLayer).WithContext(ctx) returns a derived logger with the context bound to every subsequent emission. This is the recommended pattern for per-request handlers.
• (*LogBuilder).WithContext(ctx) attaches the context to a single emission only. Useful as an override on a logger that already has a different context bound.

Binding to a logger (recommended)

import "context"

func handle(ctx context.Context, base *loglayer.LogLayer) {
    log := base.WithContext(ctx) // bind once
    log.Info("entry received")
    log.WithMetadata(loglayer.Metadata{"step": 1}).Info("step done")
    log.Error("something failed")
    // every emission carries ctx
}

Assign the result

(*LogLayer).WithContext returns a new logger; without assignment nothing is bound and transports/plugins see no context.

log.WithContext(r.Context())          // ❌ no assignment, ctx not bound
log = log.WithContext(r.Context())    // ✅ persistent on logger

The builder-level (*LogBuilder).WithContext(ctx).Info(...) form doesn't have this trap because the builder is single-use, but it only attaches for one emission.

Inside an HTTP handler, the loghttp middleware does this automatically: the per-request logger from loghttp.FromRequest(r) already has r.Context() bound, so handlers just write loghttp.FromRequest(r).Info(...) and any plugin reading params.Ctx gets the request context.

func handler(w http.ResponseWriter, r *http.Request) {
    log := loghttp.FromRequest(r)
    log.Info("processing")        // already bound to r.Context()
    log.Info("calling downstream") // same
}

The pattern works for any code path with a context:

• gRPC interceptors: bind stream.Context() (or unary's first arg) to the per-RPC logger.
• Background workers: bind the worker's cancellation context so log-trace correlation reflects the actual unit of work.
• Database / cache calls: extract the parent span from the call's context if your plugin reads it.

Per-call override

The builder still has WithContext for the rare cases where you want to override the bound context for a single emission:

log := base.WithContext(rootCtx)        // bound

log.Info("uses rootCtx")
log.WithContext(otherCtx).Info("uses otherCtx, just this call")
log.Info("back to rootCtx")

Useful when you create a child span mid-handler and want the next log to reference it:

childCtx, span := tracer.StartSpanFromContext(rootCtx, "subop")
log.WithContext(childCtx).Info("doing subop") // child span's IDs land in this entry
span.Finish()
log.Info("back to root span")

Use the Raw entry for context

If you're constructing entries via Raw, set Ctx on the RawLogEntry. It overrides the logger's bound context for that entry:

log.Raw(loglayer.RawLogEntry{
    LogLevel: loglayer.LogLevelInfo,
    Messages: []any{"replayed"},
    Ctx:      ctx,
})

Lifetime concerns

Binding a context to a long-lived logger can outlive the context's intended scope. Two things to be aware of:

• Cancelled contexts. If you bind a request context and the request finishes (deadline, cancellation), plugins reading ctx.Err() will see context.Canceled. Most plugins should be fine with this; some (e.g. plugins that gate dispatch on ctx.Err() == nil) explicitly use it as a signal.
• Garbage retention. A bound context might transitively reference request-scoped data. Don't bind a request context to a long-lived (e.g. package-global) logger or you'll keep that data alive. The loghttp middleware sidesteps this by scoping the bound logger to the request.

For background workers: bind the worker's own cancellation context, not the parent's.

Embedding the logger in a context

LogLayer also supports the inverse pattern: store the logger inside a context.Context so downstream code can extract it. This is useful for HTTP/gRPC middleware (the loghttp middleware does this for you).

ctx = loglayer.NewContext(ctx, reqLog) // middleware

log := loglayer.FromContext(ctx)        // handler: returns nil if absent
log := loglayer.MustFromContext(ctx)    // panics if absent

These two APIs use "context" for different things:

• WithContext(ctx) binds a context.Context to a logger so transports/plugins read its values (trace IDs, deadlines).
• NewContext(ctx, log) / FromContext(ctx) stores the logger inside a context.Context for downstream retrieval.

The loghttp middleware does both: it derives a per-request logger, binds r.Context() to it, and also stores the logger in r.Context() for handlers to retrieve.