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labels.go
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labels.go
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// Copyright 2024 The original author or authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package gslog
import (
"context"
)
// LabelPair represents a key-value string pair.
type LabelPair struct {
valid bool
key string
val string
}
// Label returns a new LabelPair from a key and a value.
func Label(key, value string) LabelPair {
return LabelPair{valid: true, key: key, val: value}
}
type labelsKey struct{}
type labeler func(ctx context.Context, lbls map[string]string)
func doNothing(context.Context, map[string]string) {}
// WithLabels returns a new Context with labels to be used in the GCP log
// entries produced using that context.
func WithLabels(ctx context.Context, labels ...LabelPair) context.Context {
parent := labelsFrom(ctx)
return context.WithValue(ctx, labelsKey{},
labeler(func(ctx context.Context, lbls map[string]string) {
parent(ctx, lbls)
for _, l := range labels {
if !l.valid {
panic("invalid label passed to WithLabels()")
}
lbls[l.key] = l.val
}
}),
)
}
// ExtractLabels extracts labels from the ctx. These labels were associated
// with the context using WithLabels.
func ExtractLabels(ctx context.Context) map[string]string {
labels := make(map[string]string)
lblr := labelsFrom(ctx)
lblr(ctx, labels)
return labels
}
func labelsFrom(ctx context.Context) labeler {
v, ok := ctx.Value(labelsKey{}).(labeler)
if !ok {
return doNothing
}
return v
}