| // 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)) |
| } |