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- // Copyright 2017, OpenCensus 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 tag
-
- import (
- "context"
-
- "go.opencensus.io/exemplar"
- )
-
- // FromContext returns the tag map stored in the context.
- func FromContext(ctx context.Context) *Map {
- // The returned tag map shouldn't be mutated.
- ts := ctx.Value(mapCtxKey)
- if ts == nil {
- return nil
- }
- return ts.(*Map)
- }
-
- // NewContext creates a new context with the given tag map.
- // To propagate a tag map to downstream methods and downstream RPCs, add a tag map
- // to the current context. NewContext will return a copy of the current context,
- // and put the tag map into the returned one.
- // If there is already a tag map in the current context, it will be replaced with m.
- func NewContext(ctx context.Context, m *Map) context.Context {
- return context.WithValue(ctx, mapCtxKey, m)
- }
-
- type ctxKey struct{}
-
- var mapCtxKey = ctxKey{}
-
- func init() {
- exemplar.RegisterAttachmentExtractor(extractTagsAttachments)
- }
-
- func extractTagsAttachments(ctx context.Context, a exemplar.Attachments) exemplar.Attachments {
- m := FromContext(ctx)
- if m == nil {
- return a
- }
- if len(m.m) == 0 {
- return a
- }
- if a == nil {
- a = make(map[string]string)
- }
-
- for k, v := range m.m {
- a[exemplar.KeyPrefixTag+k.Name()] = v
- }
- return a
- }
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