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- // Copyright 2018 Google LLC
- //
- // 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 metadata
-
- import (
- "context"
- "encoding/json"
- "errors"
- "fmt"
- "time"
- )
-
- // Metadata holds Google Cloud Functions metadata.
- type Metadata struct {
- // EventID is a unique ID for the event. For example: "70172329041928".
- EventID string `json:"eventId"`
- // Timestamp is the date/time this event was created.
- Timestamp time.Time `json:"timestamp"`
- // EventType is the type of the event. For example: "google.pubsub.topic.publish".
- EventType string `json:"eventType"`
- // Resource is the resource that triggered the event.
- Resource *Resource `json:"resource"`
- }
-
- // Resource holds Google Cloud Functions resource metadata.
- // Resource values are dependent on the event type they're from.
- type Resource struct {
- // Service is the service that triggered the event.
- Service string `json:"service"`
- // Name is the name associated with the event.
- Name string `json:"name"`
- // Type is the type of event.
- Type string `json:"type"`
- }
-
- type contextKey string
-
- // GCFContextKey satisfies an interface to be able to use contextKey to read
- // metadata from a Cloud Functions context.Context.
- //
- // Be careful making changes to this function. See FromContext.
- func (k contextKey) GCFContextKey() string {
- return string(k)
- }
-
- const metadataContextKey = contextKey("metadata")
-
- // FromContext extracts the Metadata from the Context, if present.
- func FromContext(ctx context.Context) (*Metadata, error) {
- if ctx == nil {
- return nil, errors.New("nil ctx")
- }
- // The original JSON is inserted by the Cloud Functions worker. So, the
- // format must not change, or the message may fail to unmarshal. We use
- // JSON as a common format between the worker and this package to ensure
- // this package can be updated independently from the worker. The contextKey
- // type and the metadataContextKey value use an interface to avoid using
- // a built-in type as a context key (which is easy to have collisions with).
- // If we need another value to be stored in the context, we can use a new
- // key or interface and avoid needing to change this one. Similarly, if we
- // need to change the format of the message, we should add an additional key
- // to keep backward compatibility.
- b, ok := ctx.Value(metadataContextKey).(json.RawMessage)
- if !ok {
- return nil, errors.New("unable to find metadata")
- }
- meta := &Metadata{}
- if err := json.Unmarshal(b, meta); err != nil {
- return nil, fmt.Errorf("json.Unmarshal: %v", err)
- }
- return meta, nil
- }
-
- // NewContext returns a new Context carrying m. If m is nil, NewContext returns
- // ctx. NewContext is only used for writing tests which rely on Metadata.
- func NewContext(ctx context.Context, m *Metadata) context.Context {
- if m == nil {
- return ctx
- }
- b, err := json.Marshal(m)
- if err != nil {
- return ctx
- }
- return context.WithValue(ctx, metadataContextKey, json.RawMessage(b))
- }
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