blob: bc6493d98be99c8e945db0d54eaa754896542b27 [file] [log] [blame]
// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package export
import (
// Labels builds an exporter that manipulates the context using the event.
// If the event is type IsLabel or IsStartSpan then it returns a context updated
// with label values from the event.
// For all other event types the event labels will be updated with values from the
// context if they are missing.
func Labels(output event.Exporter) event.Exporter {
return func(ctx context.Context, ev core.Event, lm label.Map) context.Context {
stored, _ := ctx.Value(labelContextKey).(label.Map)
if event.IsLabel(ev) || event.IsStart(ev) {
// update the label map stored in the context
fromEvent := label.Map(ev)
if stored == nil {
stored = fromEvent
} else {
stored = label.MergeMaps(fromEvent, stored)
ctx = context.WithValue(ctx, labelContextKey, stored)
// add the stored label context to the label map
lm = label.MergeMaps(lm, stored)
return output(ctx, ev, lm)