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 .

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 Libraries to send and receive Pub/Sub messages in an App Engine app.

Prerequisites

Follow the instructions to build an app for your selected runtime to set up your environment and project, and to understand how App Engine apps are structured.
Write down and save your project ID, because you will need it to run the sample application described in this document.
Create a service account and service account key to use with your application.
Enable the Google Cloud Pub/Sub API.

Roles required to enable APIs

To enable APIs, you need the Service Usage Admin IAM role ( roles/serviceusage.serviceUsageAdmin ), which contains the serviceusage.services.enable permission. Learn how to grant roles .

Enable the API

Cloning the sample app

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

Go

  git 
  
 clone 
  
 https 
 : 
 //github.com/GoogleCloudPlatform/golang-samples.git 
 cd 
  
 golang 
 - 
 samples 
 / 
 appengine 
 / 
 go11x 
 / 
 pubsub 
 / 
 authenicated_push

Java

No example available for this runtime.

Note that Java demo apps are available in the flexible environment .

Node.js

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

PHP

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

Python

  git 
 clone 
 https 
 : 
 // 
 github 
 . 
 com 
 / 
 GoogleCloudPlatform 
 / 
 python 
 - 
 docs 
 - 
 samples 
 cd 
 python 
 - 
 docs 
 - 
 samples 
 / 
 appengine 
 / 
 standard_python3 
 / 
 pubsub

Ruby

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

Create a topic and subscription

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

Go

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

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

To use Pub/Sub with authentication, create another subscription:

 # Configure the push subscription 
gcloud  
pubsub  
subscriptions  
create  
 YOUR_SUBSCRIPTION_NAME 
  
 \ 
  
--topic = 
 YOUR_TOPIC_NAME 
  
 \ 
  
--push-auth-service-account = 
 YOUR-SERVICE-ACCOUNT-EMAIL 
 \ 
  
--push-auth-token-audience = 
 OPTIONAL_AUDIENCE_OVERRIDE 
 \ 
  
--push-endpoint = 
https:// YOUR_PROJECT_ID 
. REGION_ID 
.r.appspot.com/push-handlers/receive_messages?token = 
 YOUR_TOKEN 
  
 \ 
  
--ack-deadline = 
 10 
 # Your service agent 
 # `service-{PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com` needs to have the 
 # `iam.serviceAccountTokenCreator` role. 
 PUBSUB_SERVICE_ACCOUNT 
 = 
 "service- 
 ${ 
 PROJECT_NUMBER 
 } 
 @gcp-sa-pubsub.iam.gserviceaccount.com" 
gcloud  
projects  
add-iam-policy-binding  
 ${ 
 PROJECT_ID 
 } 
  
 \ 
  
--member = 
 "serviceAccount: 
 ${ 
 PUBSUB_SERVICE_ACCOUNT 
 } 
 " 
 \ 
  
--role = 
 'roles/iam.serviceAccountTokenCreator'

Replace YOUR-SERVICE-ACCOUNT-EMAIL with your service account email.

Java

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

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

To use Pub/Sub with authentication, create another subscription:

 # Configure the push subscription 
gcloud  
pubsub  
subscriptions  
create  
 YOUR_SUBSCRIPTION_NAME 
  
 \ 
  
--topic = 
 YOUR_TOPIC_NAME 
  
 \ 
  
--push-auth-service-account = 
 YOUR-SERVICE-ACCOUNT-EMAIL 
 \ 
  
--push-auth-token-audience = 
 OPTIONAL_AUDIENCE_OVERRIDE 
 \ 
  
--push-endpoint = 
https:// YOUR_PROJECT_ID 
. REGION_ID 
.r.appspot.com/push-handlers/receive_messages?token = 
 YOUR_TOKEN 
  
 \ 
  
--ack-deadline = 
 10 
 # Your service agent 
 # `service-{PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com` needs to have the 
 # `iam.serviceAccountTokenCreator` role. 
 PUBSUB_SERVICE_ACCOUNT 
 = 
 "service- 
 ${ 
 PROJECT_NUMBER 
 } 
 @gcp-sa-pubsub.iam.gserviceaccount.com" 
gcloud  
projects  
add-iam-policy-binding  
 ${ 
 PROJECT_ID 
 } 
  
 \ 
  
--member = 
 "serviceAccount: 
 ${ 
 PUBSUB_SERVICE_ACCOUNT 
 } 
 " 
 \ 
  
--role = 
 'roles/iam.serviceAccountTokenCreator'

Replace YOUR-SERVICE-ACCOUNT-EMAIL with your service account email.

Node.js

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

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

To use Pub/Sub with authentication, create another subscription:

 # Configure the push subscription 
gcloud  
pubsub  
subscriptions  
create  
 YOUR_SUBSCRIPTION_NAME 
  
 \ 
  
--topic = 
 YOUR_TOPIC_NAME 
  
 \ 
  
--push-auth-service-account = 
 YOUR-SERVICE-ACCOUNT-EMAIL 
 \ 
  
--push-auth-token-audience = 
 OPTIONAL_AUDIENCE_OVERRIDE 
 \ 
  
--push-endpoint = 
https:// YOUR_PROJECT_ID 
. REGION_ID 
.r.appspot.com/push-handlers/receive_messages?token = 
 YOUR_TOKEN 
  
 \ 
  
--ack-deadline = 
 10 
 # Your service agent 
 # `service-{PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com` needs to have the 
 # `iam.serviceAccountTokenCreator` role. 
 PUBSUB_SERVICE_ACCOUNT 
 = 
 "service- 
 ${ 
 PROJECT_NUMBER 
 } 
 @gcp-sa-pubsub.iam.gserviceaccount.com" 
gcloud  
projects  
add-iam-policy-binding  
 ${ 
 PROJECT_ID 
 } 
  
 \ 
  
--member = 
 "serviceAccount: 
 ${ 
 PUBSUB_SERVICE_ACCOUNT 
 } 
 " 
 \ 
  
--role = 
 'roles/iam.serviceAccountTokenCreator'

Replace YOUR-SERVICE-ACCOUNT-EMAIL with your service account email.

PHP

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

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

To use Pub/Sub with authentication, create another subscription:

 # Configure the push subscription 
gcloud  
pubsub  
subscriptions  
create  
 YOUR_SUBSCRIPTION_NAME 
  
 \ 
  
--topic = 
 YOUR_TOPIC_NAME 
  
 \ 
  
--push-auth-service-account = 
 YOUR-SERVICE-ACCOUNT-EMAIL 
 \ 
  
--push-auth-token-audience = 
 OPTIONAL_AUDIENCE_OVERRIDE 
 \ 
  
--push-endpoint = 
https:// YOUR_PROJECT_ID 
. REGION_ID 
.r.appspot.com/push-handlers/receive_messages?token = 
 YOUR_TOKEN 
  
 \ 
  
--ack-deadline = 
 10 
 # Your service agent 
 # `service-{PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com` needs to have the 
 # `iam.serviceAccountTokenCreator` role. 
 PUBSUB_SERVICE_ACCOUNT 
 = 
 "service- 
 ${ 
 PROJECT_NUMBER 
 } 
 @gcp-sa-pubsub.iam.gserviceaccount.com" 
gcloud  
projects  
add-iam-policy-binding  
 ${ 
 PROJECT_ID 
 } 
  
 \ 
  
--member = 
 "serviceAccount: 
 ${ 
 PUBSUB_SERVICE_ACCOUNT 
 } 
 " 
 \ 
  
--role = 
 'roles/iam.serviceAccountTokenCreator'

Replace YOUR-SERVICE-ACCOUNT-EMAIL with your service account email.

Python

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

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

To use Pub/Sub with authentication, create another subscription:

 # Configure the push subscription 
gcloud  
pubsub  
subscriptions  
create  
 YOUR_SUBSCRIPTION_NAME 
  
 \ 
  
--topic = 
 YOUR_TOPIC_NAME 
  
 \ 
  
--push-auth-service-account = 
 YOUR-SERVICE-ACCOUNT-EMAIL 
 \ 
  
--push-auth-token-audience = 
 OPTIONAL_AUDIENCE_OVERRIDE 
 \ 
  
--push-endpoint = 
https:// YOUR_PROJECT_ID 
. REGION_ID 
.r.appspot.com/push-handlers/receive_messages?token = 
 YOUR_TOKEN 
  
 \ 
  
--ack-deadline = 
 10 
 # Your service agent 
 # `service-{PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com` needs to have the 
 # `iam.serviceAccountTokenCreator` role. 
 PUBSUB_SERVICE_ACCOUNT 
 = 
 "service- 
 ${ 
 PROJECT_NUMBER 
 } 
 @gcp-sa-pubsub.iam.gserviceaccount.com" 
gcloud  
projects  
add-iam-policy-binding  
 ${ 
 PROJECT_ID 
 } 
  
 \ 
  
--member = 
 "serviceAccount: 
 ${ 
 PUBSUB_SERVICE_ACCOUNT 
 } 
 " 
 \ 
  
--role = 
 'roles/iam.serviceAccountTokenCreator'

Replace YOUR-SERVICE-ACCOUNT-EMAIL with your service account email.

Ruby

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

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

To use Pub/Sub with authentication, create another subscription:

 # Configure the push subscription 
gcloud  
pubsub  
subscriptions  
create  
 YOUR_SUBSCRIPTION_NAME 
  
 \ 
  
--topic = 
 YOUR_TOPIC_NAME 
  
 \ 
  
--push-auth-service-account = 
 YOUR-SERVICE-ACCOUNT-EMAIL 
 \ 
  
--push-auth-token-audience = 
 OPTIONAL_AUDIENCE_OVERRIDE 
 \ 
  
--push-endpoint = 
https:// YOUR_PROJECT_ID 
. REGION_ID 
.r.appspot.com/push-handlers/receive_messages?token = 
 YOUR_TOKEN 
  
 \ 
  
--ack-deadline = 
 10 
 # Your service agent 
 # `service-{PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com` needs to have the 
 # `iam.serviceAccountTokenCreator` role. 
 PUBSUB_SERVICE_ACCOUNT 
 = 
 "service- 
 ${ 
 PROJECT_NUMBER 
 } 
 @gcp-sa-pubsub.iam.gserviceaccount.com" 
gcloud  
projects  
add-iam-policy-binding  
 ${ 
 PROJECT_ID 
 } 
  
 \ 
  
--member = 
 "serviceAccount: 
 ${ 
 PUBSUB_SERVICE_ACCOUNT 
 } 
 " 
 \ 
  
--role = 
 'roles/iam.serviceAccountTokenCreator'

Replace YOUR-SERVICE-ACCOUNT-EMAIL with your service account email.

Setting environment variables

Go

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

  # Copyright 2020 Google LLC 
 # 
 # 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 
 # 
 #     https://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. 
 runtime 
 : 
  
 go122 
 env_variables 
 : 
  
 # This token is used to verify that requests originate from your 
  
 # application. It can be any sufficiently random string. 
  
 PUBSUB_VERIFICATION_TOKEN 
 : 
  
 check123

Java

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

  env_variables 
 : 
  
 PUBSUB_TOPIC 
 : 
  
< your 
 - 
 topic 
 - 
 name 
>  
 PUBSUB_VERIFICATION_TOKEN 
 : 
  
< your 
 - 
 verification 
 - 
 token 
>

Node.js

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

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

PHP

Edit your index.php file to set the environment variables for your topic and subscription:

  $container->set('topic', 'php-example-topic'); 
 $container->set('subscription', 'php-example-subscription');

Python

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

  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 
 : 
  
 '<YOUR_VERIFICATION_TOKEN>'

Ruby

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

  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 Pub/Sub Client Library .

Go

The sample app uses the environment variables you set in the app.yaml file ( PUBSUB_TOPIC and PUBSUB_VERIFICATION_TOKEN ) for configuration.

The messages received by this instance are stored in a slice:

  messages 
  
 [] 
 string

The receiveMessagesHandler function receives pushed messages , verifies the token, and adds the message to the messages slice:

  // receiveMessagesHandler validates authentication token and caches the Pub/Sub 
 // message received. 
 func 
  
 ( 
 a 
  
 * 
 app 
 ) 
  
 receiveMessagesHandler 
 ( 
 w 
  
 http 
 . 
 ResponseWriter 
 , 
  
 r 
  
 * 
 http 
 . 
 Request 
 ) 
  
 { 
  
 if 
  
 r 
 . 
 Method 
  
 != 
  
 "POST" 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 http 
 . 
 StatusText 
 ( 
 http 
 . 
 StatusMethodNotAllowed 
 ), 
  
 http 
 . 
 StatusMethodNotAllowed 
 ) 
  
 return 
  
 } 
  
 // Verify that the request originates from the application. 
  
 // a.pubsubVerificationToken = os.Getenv("PUBSUB_VERIFICATION_TOKEN") 
  
 if 
  
 token 
 , 
  
 ok 
  
 := 
  
 r 
 . 
 URL 
 . 
 Query 
 ()[ 
 "token" 
 ]; 
  
 ! 
 ok 
  
 || 
  
 len 
 ( 
 token 
 ) 
  
 != 
  
 1 
  
 || 
  
 token 
 [ 
 0 
 ] 
  
 != 
  
 a 
 . 
 pubsubVerificationToken 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 "Bad token" 
 , 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 // Get the Cloud Pub/Sub-generated JWT in the "Authorization" header. 
  
 authHeader 
  
 := 
  
 r 
 . 
 Header 
 . 
 Get 
 ( 
 "Authorization" 
 ) 
  
 if 
  
 authHeader 
  
 == 
  
 "" 
  
 || 
  
 len 
 ( 
 strings 
 . 
 Split 
 ( 
 authHeader 
 , 
  
 " " 
 )) 
  
 != 
  
 2 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 "Missing Authorization header" 
 , 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 token 
  
 := 
  
 strings 
 . 
 Split 
 ( 
 authHeader 
 , 
  
 " " 
 )[ 
 1 
 ] 
  
 // Verify and decode the JWT. 
  
 // If you don't need to control the HTTP client used you can use the 
  
 // convenience method idtoken.Validate instead of creating a Validator. 
  
 v 
 , 
  
 err 
  
 := 
  
 idtoken 
 . 
 NewValidator 
 ( 
 r 
 . 
 Context 
 (), 
  
 option 
 . 
 WithHTTPClient 
 ( 
 a 
 . 
 defaultHTTPClient 
 )) 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 "Unable to create Validator" 
 , 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 // Please change http://example.com to match with the value you are 
  
 // providing while creating the subscription. 
  
 payload 
 , 
  
 err 
  
 := 
  
 v 
 . 
 Validate 
 ( 
 r 
 . 
 Context 
 (), 
  
 token 
 , 
  
 "http://example.com" 
 ) 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 fmt 
 . 
 Sprintf 
 ( 
 "Invalid Token: %v" 
 , 
  
 err 
 ), 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 if 
  
 payload 
 . 
 Issuer 
  
 != 
  
 "accounts.google.com" 
 && 
 payload 
 . 
 Issuer 
  
 != 
  
 "https://accounts.google.com" 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 "Wrong Issuer" 
 , 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 // IMPORTANT: you should validate claim details not covered by signature 
  
 // and audience verification above, including: 
  
 //   - Ensure that `payload.Claims["email"]` is equal to the expected service 
  
 //     account set up in the push subscription settings. 
  
 //   - Ensure that `payload.Claims["email_verified"]` is set to true. 
  
 if 
  
 payload 
 . 
 Claims 
 [ 
 "email" 
 ] 
  
 != 
  
 "test-service-account-email@example.com" 
  
 || 
  
 payload 
 . 
 Claims 
 [ 
 "email_verified" 
 ] 
  
 != 
  
 true 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 "Unexpected email identity" 
 , 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 var 
  
 pr 
  
 pushRequest 
  
 if 
  
 err 
  
 := 
  
 json 
 . 
 NewDecoder 
 ( 
 r 
 . 
 Body 
 ). 
 Decode 
 ( 
& pr 
 ); 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 http 
 . 
 Error 
 ( 
 w 
 , 
  
 fmt 
 . 
 Sprintf 
 ( 
 "Could not decode body: %v" 
 , 
  
 err 
 ), 
  
 http 
 . 
 StatusBadRequest 
 ) 
  
 return 
  
 } 
  
 a 
 . 
 messagesMu 
 . 
 Lock 
 () 
  
 defer 
  
 a 
 . 
 messagesMu 
 . 
 Unlock 
 () 
  
 // Limit to ten. 
  
 a 
 . 
 messages 
  
 = 
  
 append 
 ( 
 a 
 . 
 messages 
 , 
  
 pr 
 . 
 Message 
 . 
 Data 
 ) 
  
 if 
  
 len 
 ( 
 a 
 . 
 messages 
 ) 
 > 
 maxMessages 
  
 { 
  
 a 
 . 
 messages 
  
 = 
  
 a 
 . 
 messages 
 [ 
 len 
 ( 
 a 
 . 
 messages 
 ) 
 - 
 maxMessages 
 :] 
  
 } 
  
 fmt 
 . 
 Fprint 
 ( 
 w 
 , 
  
 "OK" 
 ) 
 }

Java

No example available for this runtime.

Note that a Java demo app is available in the flexible environment .

Node.js

The sample app uses the values you set in your app.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:

  // The following environment variables are set by the `app.yaml` file when 
 // running on App Engine, but will need to be manually set when running locally. 
 var 
  
 PUBSUB_VERIFICATION_TOKEN 
  
 = 
  
 process 
 . 
 env 
 . 
 PUBSUB_VERIFICATION_TOKEN 
 ; 
 var 
  
 pubsub 
  
 = 
  
 gcloud 
 . 
 pubsub 
 ({ 
  
 projectId 
 : 
  
 process 
 . 
 env 
 . 
 GOOGLE_CLOUD_PROJECT 
 }); 
 var 
  
 topic 
  
 = 
  
 pubsub 
 . 
 topic 
 ( 
 process 
 . 
 env 
 . 
 PUBSUB_TOPIC 
 );

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

  // List of all messages received by this instance 
 var 
  
 messages 
  
 = 
  
 [];

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

  app 
 . 
 post 
 ( 
 '/pubsub/push' 
 , 
  
 jsonBodyParser 
 , 
  
 ( 
 req 
 , 
  
 res 
 ) 
  
 = 
>  
 { 
  
 if 
  
 ( 
 req 
 . 
 query 
 . 
 token 
  
 !== 
  
 PUBSUB_VERIFICATION_TOKEN 
 ) 
  
 { 
  
 res 
 . 
 status 
 ( 
 400 
 ). 
 send 
 (); 
  
 return 
 ; 
  
 } 
  
 // The message is a unicode string encoded in base64. 
  
 const 
  
 message 
  
 = 
  
 Buffer 
 . 
 from 
 ( 
 req 
 . 
 body 
 . 
 message 
 . 
 data 
 , 
  
 'base64' 
 ). 
 toString 
 ( 
  
 'utf-8' 
  
 ); 
  
 messages 
 . 
 push 
 ( 
 message 
 ); 
  
 res 
 . 
 status 
 ( 
 200 
 ). 
 send 
 (); 
 });

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

  app 
 . 
 get 
 ( 
 '/' 
 , 
  
 ( 
 req 
 , 
  
 res 
 ) 
  
 = 
>  
 { 
  
 res 
 . 
 render 
 ( 
 'index' 
 , 
  
 { 
 messages 
 , 
  
 tokens 
 , 
  
 claims 
 }); 
 }); 
 app 
 . 
 post 
 ( 
 '/' 
 , 
  
 formBodyParser 
 , 
  
 async 
  
 ( 
 req 
 , 
  
 res 
 , 
  
 next 
 ) 
  
 = 
>  
 { 
  
 if 
  
 ( 
 ! 
 req 
 . 
 body 
 . 
 payload 
 ) 
  
 { 
  
 res 
 . 
 status 
 ( 
 400 
 ). 
 send 
 ( 
 'Missing payload' 
 ); 
  
 return 
 ; 
  
 } 
  
 const 
  
 data 
  
 = 
  
 Buffer 
 . 
 from 
 ( 
 req 
 . 
 body 
 . 
 payload 
 ); 
  
 try 
  
 { 
  
 const 
  
 messageId 
  
 = 
  
 await 
  
 topic 
 . 
 publishMessage 
 ({ 
 data 
 }); 
  
 res 
 . 
 status 
 ( 
 200 
 ). 
 send 
 ( 
 `Message 
 ${ 
 messageId 
 } 
 sent.` 
 ); 
  
 } 
  
 catch 
  
 ( 
 error 
 ) 
  
 { 
  
 next 
 ( 
 error 
 ); 
  
 } 
 });

PHP

The sample app uses the values you set in the app.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:

  runtime 
 : 
  
 php81 
 handlers 
 : 
 - 
  
 url 
 : 
  
 /pubsub\.js 
  
 static_files 
 : 
  
 pubsub.js 
  
 upload 
 : 
  
 pubsub\.js

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

  $messages = [];

The pull method retrieves messages from the topic you created and adds them to the messages list:

  // get PULL pubsub messages 
 $pubsub = new PubSubClient([ 
 'projectId' => $projectId, 
 ]); 
 $subscription = $pubsub->subscription($subscriptionName); 
 $pullMessages = []; 
 foreach ($subscription->pull(['returnImmediately' => true]) as $pullMessage) { 
 $pullMessages[] = $pullMessage; 
 $messages[] = $pullMessage->data(); 
 } 
 // acknowledge PULL messages 
 if ($pullMessages) { 
 $subscription->acknowledgeBatch($pullMessages); 
 }

The publish method publishes new messages to the topic:

  if ($message = (string) $request->getBody()) { 
 // Publish the pubsub message to the topic 
 $pubsub = new PubSubClient([ 
 'projectId' => $projectId, 
 ]); 
 $topic = $pubsub->topic($topicName); 
 $topic->publish(['data' => $message]); 
 return $response->withStatus(204); 
 }

Python

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

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

  MESSAGES 
 = 
 []

The receive_messages_handler() method receives pushed messages and adds them to the MESSAGES global list:

  @app 
 . 
 route 
 ( 
 "/pubsub/push" 
 , 
 methods 
 = 
 [ 
 "POST" 
 ]) 
 def 
  
 receive_pubsub_messages_handler 
 (): 
 # Verify that the request originates from the application. 
 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

The index() method interacts with the App Engine web app to publish new messages and display received messages:

  @app 
 . 
 route 
 ( 
 "/" 
 , 
 methods 
 = 
 [ 
 "GET" 
 , 
 "POST" 
 ]) 
 def 
  
 index 
 (): 
 if 
 request 
 . 
 method 
 == 
 "GET" 
 : 
 return 
 render_template 
 ( 
 "index.html" 
 , 
 messages 
 = 
 MESSAGES 
 , 
 tokens 
 = 
 TOKENS 
 , 
 claims 
 = 
 CLAIMS 
 ) 
 data 
 = 
 request 
 . 
 form 
 . 
 get 
 ( 
 "payload" 
 , 
 "Example payload" 
 ) 
 . 
 encode 
 ( 
 "utf-8" 
 ) 
 # Consider initializing the publisher client outside this function 
 # for better latency performance. 
 publisher 
 = 
 pubsub_v1 
 . 
 PublisherClient 
 () 
 topic_path 
 = 
 publisher 
 . 
 topic_path 
 ( 
 app 
 . 
 config 
 [ 
 "GOOGLE_CLOUD_PROJECT" 
 ], 
 app 
 . 
 config 
 [ 
 "PUBSUB_TOPIC" 
 ] 
 ) 
 future 
 = 
 publisher 
 . 
 publish 
 ( 
 topic_path 
 , 
 data 
 ) 
 future 
 . 
 result 
 () 
 return 
 "OK" 
 , 
 200

Ruby

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:

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

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

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

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

  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:

  get 
  
 "/" 
  
 do 
  
 @claims 
  
 = 
  
 claims 
  
 @messages 
  
 = 
  
 messages 
  
 slim 
  
 :index 
 end 
 post 
  
 "/publish" 
  
 do 
  
 publisher 
 . 
 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.

Go

Set environment variables before starting your application:

  export 
  
 GOOGLE_CLOUD_PROJECT 
 =[ 
 your 
 - 
 project 
 - 
 id 
 ] 
 export 
  
 PUBSUB_VERIFICATION_TOKEN 
 =[ 
 your 
 - 
 token 
 ] 
 export 
  
 PUBSUB_TOPIC 
 =[ 
 your 
 - 
 topic 
 ] 
 go 
  
 run 
  
 pubsub 
 . 
 go

Java

Set environment variables before starting your application:

  export 
  
 PUBSUB_VERIFICATION_TOKEN 
 =[ 
 your 
 - 
 verification 
 - 
 token 
 ] 
 export 
  
 PUBSUB_TOPIC 
 =[ 
 your 
 - 
 topic 
 ]

To run your application locally, use the development tools that you usually use.

Node.js

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 
 ] 
 npm 
  
 install 
 npm 
  
 start

PHP

Install dependencies using Composer:

  composer 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] 
 php -S localhost:8080

Python

Install dependencies, preferably in a virtual environment.

Mac OS / Linux

Create an isolated Python environment :

 python3  
-m  
venv  
env 
  source 
  
env/bin/activate

If you're not in the directory that contains the sample code, navigate to the directory that contains the hello_world sample code. Then install dependencies:
```
  cd 
  
 YOUR_SAMPLE_CODE_DIR 
 
 pip  
install  
-r  
requirements.txt 
```

Windows

Use PowerShell to run your Python packages.

Locate your installation of PowerShell .
Right-click on the shortcut to PowerShell and start it as an administrator.

Create an isolated Python environment .

 python  
-m  
venv  
env 
 . \e 
nv \S 
cripts \a 
ctivate

Navigate to your project directory and install dependencies. If you're not in the directory that contains the sample code, navigate to the directory that contains the hello_world sample code. Then, install dependencies:
```
  cd 
  
 YOUR_SAMPLE_CODE_DIR 
 
 pip  
install  
-r  
requirements.txt 
```

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 
 ] 
 python 
  
 main 
 . 
 py

Ruby

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 .

Go

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

  curl 
  
 - 
 H 
  
 "Content-Type: application/json" 
  
 - 
 i 
  
 -- 
 data 
  
 @ 
 sample_message 
 . 
 json 
  
 "localhost:8080/push-handlers/receive_messages?token=[your-token]"

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

Response:

  HTTP 
 / 
 1.1 
  
 200 
  
 OK 
 Date 
 : 
  
 Tue 
 , 
  
 13 
  
 Nov 
  
 2018 
  
 16 
 : 
 04 
 : 
 18 
  
 GMT 
 Content 
 - 
 Length 
 : 
  
 0

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

Java

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

  curl 
  
 - 
 H 
  
 "Content-Type: application/json" 
  
 - 
 i 
  
 -- 
 data 
  
 @sample_message.json 
  
 "localhost:8080/push-handlers/receive_messages?token=[your-token]"

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

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

Node.js

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

  curl 
  
 - 
 H 
  
 "Content-Type: application/json" 
  
 - 
 i 
  
 -- 
 data 
  
 @ 
 sample_message 
 . 
 json 
  
 "localhost:8080/push-handlers/receive_messages?token=[your-token]"

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

Response:

  HTTP 
 / 
 1.1 
  
 200 
  
 OK 
 Connection 
 : 
  
 keep 
 - 
 alive 
 Date 
 : 
  
 Mon 
 , 
  
 31 
  
 Aug 
  
 2015 
  
 22 
 : 
 19 
 : 
 50 
  
 GMT 
 Transfer 
 - 
 Encoding 
 : 
  
 chunked 
 X 
 - 
 Powered 
 - 
 By 
 : 
  
 Express

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

PHP

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

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

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

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

Python

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

  curl 
 - 
 H 
 "Content-Type: application/json" 
 - 
 i 
 -- 
 data 
 @sample_message 
 . 
 json 
 "localhost:8080/pubsub/push?token=[your-token]"

  http 
 POST 
 ":8080/pubsub/push?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.

Ruby

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

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

  http 
  
 POST 
  
 ":4567/push-handlers/receive_messages?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 using the gcloud command-line tool:

Go

Run the following command from the directory where your app.yaml file is located:

  gcloud 
  
 app 
  
 deploy

Java

Run the gcloud command from the directory where your app.yaml file is located:

  gcloud 
  
 app 
  
 deploy

To deploy your app using Maven, run the following:

mvn package appengine:deploy -Dapp.deploy.projectId= PROJECT_ID

Replace PROJECT_ID with the ID of your Google Cloud project. If your pom.xml file already specifies your project ID , you don't need to include the -Dapp.deploy.projectId property in the command you run.

Node.js

Run the following command from the directory where your app.yaml file is located:

  gcloud 
  
 app 
  
 deploy

PHP

Run the following command from the directory where your app.yaml file is located:

  gcloud app deploy

Python

Run the following command from the directory where your app.yaml file is located:

  gcloud 
 app 
 deploy

Ruby

Run the following command from the directory where your app.yaml file 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.