Writing and Responding to Pub/Sub Messages

Region ID

The REGION_ID is an abbreviated code that Google assigns based on the region you select when you create your app. The code does not correspond to a country or province, even though some region IDs may appear similar to commonly used country and province codes. For apps created after February 2020, REGION_ID.r is included in App Engine URLs. For existing apps created before this date, the region ID is optional in the URL.

Learn more about region IDs.

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Pub/Sub provides reliable, many-to-many, asynchronous messaging between applications. Publisher applications can send messages to a topic, and other applications can subscribe to that topic to receive the messages.

This document describes how to use the Cloud Client Library to send and receive Pub/Sub messages in a Ruby app.

Prerequisites

• Follow the instructions in "Hello, World!" for Ruby on App Engine to set up your environment and project, and to understand how App Engine Ruby apps are structured.
• Write down and save your project ID, because you will need it to run the sample application described in this document.

  Cloning the sample app

  Copy the sample apps to your local machine, and navigate to the pubsub directory:

  git clone https://github.com/GoogleCloudPlatform/ruby-docs-samples
  cd ruby-docs-samples/appengine/pubsub
  

  Creating a topic and subscription

  Create a topic and subscription, which includes specifying the endpoint to which the Pub/Sub server should send requests:

  gcloud pubsub topics create YOUR_TOPIC_NAME
  gcloud pubsub subscriptions create YOUR_SUBSCRIPTION_NAME \
      --topic YOUR_TOPIC_NAME \
      --push-endpoint \
      https://YOUR_PROJECT_ID.REGION_ID.r.appspot.com/pubsub/push?token=YOUR_TOKEN \
      --ack-deadline 10
  

  Replace YOUR_TOKEN with a secret random token. The push endpoint uses this to verify requests.

  Setting environment variables

  Edit the app.standard.yaml file to set the environment variables for your project ID, topic, and verification token:

  appengine/pubsub/app.standard.yaml

  View on GitHub

  env_variables:
      PUBSUB_TOPIC: gaeflex_net_pubsub_auth_push_1
      # This token is used to verify that requests originate from your
      # application. It can be any sufficiently random string.
      PUBSUB_VERIFICATION_TOKEN: abc123

  Code review

  The sample app uses the Cloud Client Library.

  The sample app uses the values you set in the app.standard.yaml file to configure environment variables. The push request handler uses these values to confirm that the request came from Pub/Sub and originated from a trusted source:

  appengine/pubsub/app.rb

  View on GitHub

  topic = pubsub.topic ENV["PUBSUB_TOPIC"]
  PUBSUB_VERIFICATION_TOKEN = ENV["PUBSUB_VERIFICATION_TOKEN"]

  The sample app maintains a global list to store messages received by this instance:

  appengine/pubsub/app.rb

  View on GitHub

  # List of all messages received by this instance
  messages = []

  This method receives pushed messages and adds them to the messages global list:

  Note: This tutorial is using an instance level global variable, messages, to store messages received from Pub/Sub. In production, that should be converted to an external storage solution, such as Firestore.
  appengine/pubsub/app.rb

  View on GitHub

  post "/pubsub/push" do
    halt 400 if params[:token] != PUBSUB_VERIFICATION_TOKEN
  
    message = JSON.parse request.body.read
    payload = Base64.decode64 message["message"]["data"]
  
    messages.push payload
  end

  This method interacts with the App Engine web app to publish new messages and display received messages:

  appengine/pubsub/app.rb

  View on GitHub

  get "/" do
    @claims = claims
    @messages = messages
  
    slim :index
  end
  
  post "/publish" do
    topic.publish params[:payload]
  
    redirect "/", 303
  end

  Running the sample locally

  When running locally, you can use the Google Cloud CLI to provide authentication to use Google Cloud APIs. Assuming you set up your environment as described in Prerequisites, you have already run the gcloud init command, which provides this authentication.

  Install dependencies:

  bundle install
  

  Then set environment variables before starting your application:

  export GOOGLE_CLOUD_PROJECT=[your-project-id]
  export PUBSUB_VERIFICATION_TOKEN=[your-verification-token]
  export PUBSUB_TOPIC=[your-topic]
  bundle exec ruby app.rb -p 8080
  

  Simulating push notifications

  The application can send messages locally, but it is not able to receive push messages locally. You can, however, simulate a push message by making an HTTP request to the local push notification endpoint. The sample includes the file sample_message.json.

  You can use curl or a httpie client to send an HTTP POST request:

  curl -i --data @sample_message.json "localhost:4567/pubsub/push?token=[your-token]"
  

  Or

  http POST ":4567/pubsub/push?token=[your-token]" < sample_message.json
  

  Response:

  HTTP/1.1 200 OK
  Content-Type: text/html;charset=utf-8
  Content-Length: 13
  X-Xss-Protection: 1; mode=block
  X-Content-Type-Options: nosniff
  X-Frame-Options: SAMEORIGIN
  Server: WEBrick/1.3.1 (Ruby/2.3.0/2015-12-25)
  Date: Wed, 20 Apr 2016 20:56:23 GMT
  Connection: Keep-Alive
  
  Hello, World!
  

  After the request completes, you can refresh localhost:8080 and see the message in the list of received messages.

  Running on App Engine

  To deploy the demo app to App Engine by using the gcloud command-line tool, you run the following command from the directory where your app.standard.yaml is located:

  gcloud app deploy app.standard.yaml
  

  You can now access the application at https://PROJECT_ID.REGION_ID.r.appspot.com. You can use the form to submit messages, but there's no guarantee of which instance of your application will receive the notification. You can send multiple messages and refresh the page to see the received message.