Get execution ID for Google Cloud Functions triggered from PubSub event

Issue

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?

Solution

EDIT: This appears to no longer be accurate. See the other answer from ProGirlXOXO.

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
}

Answered By – Lauren

Answer Checked By – Marilyn (GoLangFix Volunteer)