Test locally with the Pub/Sub emulator

You can test functions locally before you deploy them, by using Functions Framework in conjunction with the Pub/Sub emulator. The examples on this page use Cloud Functions (2nd gen).

Use Functions Framework with Pub/Sub emulator

You can trigger a function locally using a push message from the Pub/Sub emulator.

Test this feature as described here. Note that it requires you to use three separate terminal instances:

1. Make sure you have the pack tool and Docker installed.

2. In the first terminal, start the Pub/Sub emulator on port 8043 in a local project:

   gcloud beta emulators pubsub start \
       --project=abc \
       --host-port='localhost:8043'
   

3. In the second terminal, create a Pub/Sub topic and subscription:

   curl -s -X PUT 'http://localhost:8043/v1/projects/abc/topics/mytopic'
   

   Use http://localhost:8080 as the push subscription's endpoint.

   curl -s -X PUT 'http://localhost:8043/v1/projects/abc/subscriptions/mysub' \
       -H 'Content-Type: application/json' \
       --data '{"topic":"projects/abc/topics/mytopic","pushConfig":{"pushEndpoint":"http://localhost:8080/projects/abc/topics/mytopic"}}'
   

4. In the third terminal, clone the sample repository to your local machine:

   Node.js

   git clone https://github.com/GoogleCloudPlatform/nodejs-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Python

   git clone https://github.com/GoogleCloudPlatform/python-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Go

   git clone https://github.com/GoogleCloudPlatform/golang-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Change to the directory that contains the Cloud Functions sample code:

   Node.js

   cd nodejs-docs-samples/functions/v2/helloPubSub/

   Python

   cd python-docs-samples/functions/v2/pubsub/

   Go

   cd golang-samples/functions/functionsv2/hellopubsub/

   Take a look at the sample code:

   Node.js

   const functions = require('@google-cloud/functions-framework');
   
   // Register a CloudEvent callback with the Functions Framework that will
   // be executed when the Pub/Sub trigger topic receives a message.
   functions.cloudEvent('helloPubSub', cloudEvent => {
     // The Pub/Sub message is passed as the CloudEvent's data payload.
     const base64name = cloudEvent.data.message.data;
   
     const name = base64name
       ? Buffer.from(base64name, 'base64').toString()
       : 'World';
   
     console.log(`Hello, ${name}!`);
   });

   Python

   import base64
   
   from cloudevents.http import CloudEvent
   import functions_framework
   
   
   # Triggered from a message on a Cloud Pub/Sub topic.
   @functions_framework.cloud_event
   def subscribe(cloud_event: CloudEvent) -> None:
       # Print out the data from Pub/Sub, to prove that it worked
       print(
           "Hello, " + base64.b64decode(cloud_event.data["message"]["data"]).decode() + "!"
       )
   
   

   Go

   
   // Package helloworld provides a set of Cloud Functions samples.
   package helloworld
   
   import (
   	"context"
   	"fmt"
   	"log"
   
   	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
   	"github.com/cloudevents/sdk-go/v2/event"
   )
   
   func init() {
   	functions.CloudEvent("HelloPubSub", helloPubSub)
   }
   
   // MessagePublishedData contains the full Pub/Sub message
   // See the documentation for more details:
   // https://cloud.google.com/eventarc/docs/cloudevents#pubsub
   type MessagePublishedData struct {
   	Message PubSubMessage
   }
   
   // PubSubMessage is the payload of a Pub/Sub event.
   // See the documentation for more details:
   // https://cloud.google.com/pubsub/docs/reference/rest/v1/PubsubMessage
   type PubSubMessage struct {
   	Data []byte `json:"data"`
   }
   
   // helloPubSub consumes a CloudEvent message and extracts the Pub/Sub message.
   func helloPubSub(ctx context.Context, e event.Event) error {
   	var msg MessagePublishedData
   	if err := e.DataAs(&msg); err != nil {
   		return fmt.Errorf("event.DataAs: %w", err)
   	}
   
   	name := string(msg.Message.Data) // Automatically decoded from base64.
   	if name == "" {
   		name = "World"
   	}
   	log.Printf("Hello, %s!", name)
   	return nil
   }
   

   Create the buildpack (this may take a few minutes):

   Node.js

   pack build \
     --builder gcr.io/buildpacks/builder:v1 \
     --env GOOGLE_FUNCTION_SIGNATURE_TYPE=event \
     --env GOOGLE_FUNCTION_TARGET=helloPubSub \
     my-function
   

   Python

   pack build \
     --builder gcr.io/buildpacks/builder:v1 \
     --env GOOGLE_FUNCTION_SIGNATURE_TYPE=event \
     --env GOOGLE_FUNCTION_TARGET=subscribe \
     my-function
   

   Go

   pack build \
     --builder gcr.io/buildpacks/builder:v1 \
     --env GOOGLE_FUNCTION_SIGNATURE_TYPE=event \
     --env GOOGLE_FUNCTION_TARGET=HelloPubSub \
     my-function
   

   Start the Pub/Sub function on port 8080. This is where the emulator will send push messages:

   docker run --rm -p 8080:8080 my-function
   

5. In the second terminal, invoke the function by publishing a message. The message data needs to be encoded in base64. This example uses the base64 encoded string {"foo":"bar"}.

   curl -s -X POST 'http://localhost:8043/v1/projects/abc/topics/mytopic:publish' \
       -H 'Content-Type: application/json' \
       --data '{"messages":[{"data":"eyJmb28iOiJiYXIifQ=="}]}'
   

   You should see the function output in the third terminal.

   Press Ctrl+C to abort.