获取从PubSub事件触发的Google Cloud Functions的执行ID

Question

For Google Cloud Functions triggered from HTTP, it is possible to retrieve the execution id by inspecting the headers of the HTTP request ("Function-Execution-Id") :

package p

import (
    "fmt"
    "net/http"
)

func F(w http.ResponseWriter, r *http.Request) {
    executionID := r.Header.Get("Function-Execution-Id")
    fmt.Println(executionID)
}

However, for GCF triggered by PubSub events, I can't find how to retrieve this execution ID :

package p

import (
    "context"
)

type PubSubMessage struct {
    Data []byte `json:"data"`
}

func F(ctx context.Context, m PubSubMessage) error {
    executionID := "" // ???
    fmt.Println(executionID)
    return nil
}

I have looked into the PubSubMessage (https://cloud.google.com/pubsub/docs/reference/rest/v1/PubsubMessage), but it only contains data + an empty attributes map.

I have also checked if execution ID is in the metadata handled by the context. However, from my tests, and the docs (https://godoc.org/cloud.google.com/go/functions/metadata#FromContext), only EventID, Timestamp, EventType and Resource are present.

How can I retrieve the execution id of a GCF function triggered by a PubSub event?

Answer 1

A Pub/Sub-triggered event does not have an execution ID; instead it has an EventID contained in the context metadata, which is a unique ID for the event.

You can access the EventID as follows:

import (
    "context"
    "log"
    "cloud.google.com/go/functions/metadata"
)

func F(ctx context.Context, m PubSubMessage) error {
    ctxMetadata, err := metadata.FromContext(ctx)
    if err != nil {
        log.Fatal(err);
    }
    log.Println("EventID: " + ctxMetadata.EventID)
    return nil
}