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This demonstrates how to send and receive messages using [Google Cloud Pub/Sub](https://cloud.google.com/pubsub) on [Google App Engine Standard Environment](https://cloud.google.com/appengine/docs/standard/).

Before you can run or deploy the sample, you will need to do the following:

1. Enable the Cloud Pub/Sub API in the [Google Developers Console](https://console.developers.google.com/project/_/apiui/apiview/pubsub/overview).

2. Create a topic and subscription.

$ gcloud pubsub topics create [your-topic-name]

$ gcloud pubsub subscriptions create [your-subscription-name] \

--topic [your-topic-name] \

--push-endpoint \

https://[your-app-id].appspot.com/_ah/push-handlers/receive_messages/token=[your-token] \

--ack-deadline 30

3. Update the environment variables in ``app.yaml``.

Refer to the [top-level README](../README.md) for instructions on running and deploying.

When running locally, you can use the [Google Cloud SDK](https://cloud.google.com/sdk) to provide authentication to use Google Cloud APIs:

$ gcloud init

Install dependencies, preferably with a virtualenv:

$ virtualenv env

$ source env/bin/activate

$ pip install -r requirements.txt

Then set environment variables before starting your application:

$ export GOOGLE_CLOUD_PROJECT=[your-project-name]

$ export PUBSUB_VERIFICATION_TOKEN=[your-verification-token]

$ export PUBSUB_TOPIC=[your-topic]

$ python main.py

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. There is an included ``sample_message.json``. You can use

``curl`` or [httpie](https://github.com/jkbrzt/httpie) to POST this:

$ curl -i --data @sample_message.json ":8080/_ah/push-handlers/receive_messages?token=[your-token]"

Or

$ http POST ":8080/_ah/push-handlers/receive_messages?token=[your-token]" < sample_message.json

Response:

HTTP/1.0 200 OK

Content-Length: 2

Content-Type: text/html; charset=utf-8

Date: Mon, 10 Aug 2015 17:52:03 GMT

Server: Werkzeug/0.10.4 Python/2.7.10

OK

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

Deploy using `gcloud`:

gcloud app deploy app.yaml

You can now access the application at `https://your-app-id.appspot.com`. You can use the form to submit messages, but it's non-deterministic which instance of your application will receive the notification. You can send multiple messages and refresh the page to see the received message.

runtime: python27

api_version: 1

threadsafe: yes

handlers:

- url: /

script: main.app

- url: /_ah/push-handlers/.*

script: main.app

login: admin

env_variables:

PUBSUB_TOPIC: your-topic

# This token is used to verify that requests originate from your

# application. It can be any sufficiently random string.

PUBSUB_VERIFICATION_TOKEN: 1234abc

import base64

import json

import logging

import os

from flask import current_app, Flask, render_template, request

from googleapiclient.discovery import build

app = Flask(__name__)

app.config['PUBSUB_VERIFICATION_TOKEN'] = \

os.environ['PUBSUB_VERIFICATION_TOKEN']

app.config['PUBSUB_TOPIC'] = os.environ['PUBSUB_TOPIC']

app.config['GCLOUD_PROJECT'] = os.environ['GOOGLE_CLOUD_PROJECT']

MESSAGES = []

def index():

if request.method == 'GET':

return render_template('index.html', messages=MESSAGES)

data = request.form.get('payload', 'Example payload').encode('utf-8')

service = build('pubsub', 'v1')

topic_path = 'projects/{project_id}/topics/{topic}'.format(

project_id=app.config['GCLOUD_PROJECT'],

topic=app.config['PUBSUB_TOPIC']

)

service.projects().topics().publish(

topic=topic_path, body={

"messages": [{

"data": base64.b64encode(data)

}]

}).execute()

return 'OK', 200

def receive_messages_handler():

if (request.args.get('token', '') !=

current_app.config['PUBSUB_VERIFICATION_TOKEN']):

return 'Invalid request', 400

envelope = json.loads(request.data.decode('utf-8'))

payload = base64.b64decode(envelope['message']['data'])

MESSAGES.append(payload)

# Returning any 2xx status indicates successful receipt of the message.

return 'OK', 200

def server_error(e):

logging.exception('An error occurred during a request.')

return """

""".format(e), 500

if __name__ == '__main__':

# This is used when running locally. Gunicorn is used to run the

# application on Google App Engine. See entrypoint in app.yaml.

app.run(host='127.0.0.1', port=8080, debug=True)

import base64

import json

import os

import pytest

import main

def client():

main.app.testing = True

return main.app.test_client()

def test_index(client):

r = client.get('/')

assert r.status_code == 200

def test_post_index(client):

r = client.post('/', data={'payload': 'Test payload'})

assert r.status_code == 200

def test_push_endpoint(client):

url = '/_ah/push-handlers/receive_messages?token=' + \

os.environ['PUBSUB_VERIFICATION_TOKEN']

r = client.post(

url,

data=json.dumps({

"message": {

"data": base64.b64encode(

u'Test message'.encode('utf-8')

).decode('utf-8')

}

})

)

assert r.status_code == 200

# Make sure the message is visible on the home page.

r = client.get('/')

assert r.status_code == 200

assert 'Test message' in r.data.decode('utf-8')

def test_push_endpoint_errors(client):

# no token

r = client.post('/_ah/push-handlers/receive_messages')

assert r.status_code == 400

# invalid token

r = client.post('/_ah/push-handlers/receive_messages?token=bad')

assert r.status_code == 400

{

"message": {

"data": "SGVsbG8sIFdvcmxkIQ=="

}

}

{#

# Copyright 2015 Google Inc. All Rights Reserved.

#

# 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.

#}

<title>Pub/Sub Python on Google App Engine Flexible Environment</title>

<p>Messages received by this instance:</p>

<ul>

{% for message in messages: %}

<li>{{message}}</li>

{% endfor %}

</ul>

<p><small>Note: because your application is likely running multiple instances, each instance will have a different list of messages.</small></p>

<form method="post">

<textarea name="payload" placeholder="Enter message here"></textarea>

<input type="submit">