github.com/v2fly/tools@v0.100.0/internal/event/export/tag.go (about)

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package export
     6  
     7  import (
     8  	"context"
     9  
    10  	"github.com/v2fly/tools/internal/event"
    11  	"github.com/v2fly/tools/internal/event/core"
    12  	"github.com/v2fly/tools/internal/event/label"
    13  )
    14  
    15  // Labels builds an exporter that manipulates the context using the event.
    16  // If the event is type IsLabel or IsStartSpan then it returns a context updated
    17  // with label values from the event.
    18  // For all other event types the event labels will be updated with values from the
    19  // context if they are missing.
    20  func Labels(output event.Exporter) event.Exporter {
    21  	return func(ctx context.Context, ev core.Event, lm label.Map) context.Context {
    22  		stored, _ := ctx.Value(labelContextKey).(label.Map)
    23  		if event.IsLabel(ev) || event.IsStart(ev) {
    24  			// update the label map stored in the context
    25  			fromEvent := label.Map(ev)
    26  			if stored == nil {
    27  				stored = fromEvent
    28  			} else {
    29  				stored = label.MergeMaps(fromEvent, stored)
    30  			}
    31  			ctx = context.WithValue(ctx, labelContextKey, stored)
    32  		}
    33  		// add the stored label context to the label map
    34  		lm = label.MergeMaps(lm, stored)
    35  		return output(ctx, ev, lm)
    36  	}
    37  }