Pub/Sub is a nice tool provided by GCP. It is really handy and can help you with the messaging challenges you application might face. Actually if you work with GCP it is the managed messaging solution that you can use.
As expected working with the actual Pub/Sub solution comes with some quota, so for
development it is essential to use something which is not going to cost you.
In these cases you can use the Pub/Sub emulator. To get started with the emulator you need to install it
1 | gcloud components install pubsub-emulator |
It is indeed convenient, however having a docker image since it is way more portable. Unfortunately there is no official image for that from google cloud however you can use one of the solutions available on Docker Hub.
Now let’s run it
1 | gcloud beta emulators pubsub start --project=test-project |
After that your application can connect to the pub/sub emulator. The default port is 8085
I will use a Java unit test as an example for this one.
001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 | package org.gkatzioura.pubsub;import java.io.IOException;import java.nio.charset.Charset;import org.junit.After;import org.junit.Assert;import org.junit.Before;import org.junit.Test;import com.google.api.gax.core.CredentialsProvider;import com.google.api.gax.core.NoCredentialsProvider;import com.google.api.gax.grpc.GrpcTransportChannel;import com.google.api.gax.rpc.FixedTransportChannelProvider;import com.google.api.gax.rpc.TransportChannelProvider;import com.google.cloud.pubsub.v1.Publisher;import com.google.cloud.pubsub.v1.SubscriptionAdminClient;import com.google.cloud.pubsub.v1.SubscriptionAdminSettings;import com.google.cloud.pubsub.v1.TopicAdminClient;import com.google.cloud.pubsub.v1.TopicAdminSettings;import com.google.cloud.pubsub.v1.stub.GrpcSubscriberStub;import com.google.cloud.pubsub.v1.stub.SubscriberStub;import com.google.cloud.pubsub.v1.stub.SubscriberStubSettings;import com.google.protobuf.ByteString;import com.google.pubsub.v1.ProjectSubscriptionName;import com.google.pubsub.v1.ProjectTopicName;import com.google.pubsub.v1.PubsubMessage;import com.google.pubsub.v1.PullRequest;import com.google.pubsub.v1.PullResponse;import com.google.pubsub.v1.PushConfig;import com.google.pubsub.v1.Subscription;import io.grpc.ManagedChannel;import io.grpc.ManagedChannelBuilder;public class LocalPubSubTest { private static final String PROJECT = "test-project"; private static final String SUBSCRIPTION_NAME = "SUBSCRIBER"; private static final String TOPIC_NAME = "test-topic-id"; private static final String hostPort = "127.0.0.1:8085"; private ManagedChannel channel; private TransportChannelProvider channelProvider; private TopicAdminClient topicAdmin; private Publisher publisher; private SubscriberStub subscriberStub; private SubscriptionAdminClient subscriptionAdminClient; private ProjectTopicName topicName = ProjectTopicName.of(PROJECT, TOPIC_NAME); private ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(PROJECT, SUBSCRIPTION_NAME); private Subscription subscription; @Before public void setUp() throws Exception { channel = ManagedChannelBuilder.forTarget(hostPort).usePlaintext().build(); channelProvider = FixedTransportChannelProvider.create(GrpcTransportChannel.create(channel)); CredentialsProvider credentialsProvider = NoCredentialsProvider.create(); topicAdmin = createTopicAdmin(credentialsProvider); topicAdmin.createTopic(topicName); publisher = createPublisher(credentialsProvider); subscriberStub = createSubscriberStub(credentialsProvider); subscriptionAdminClient = createSubscriptionAdmin(credentialsProvider); subscription = subscriptionAdminClient.createSubscription(subscriptionName, topicName, PushConfig.getDefaultInstance(), 0); } @After public void tearDown() throws Exception { topicAdmin.deleteTopic(topicName); subscriptionAdminClient.deleteSubscription(subscription.getName()); channel.shutdownNow(); } @Test public void testLocalPubSub() throws Exception { final String messageText = "text"; PubsubMessage pubsubMessage = PubsubMessage.newBuilder() .setData(ByteString.copyFrom(messageText, Charset.defaultCharset())) .build(); publisher.publish(pubsubMessage).get(); PullRequest pullRequest = PullRequest.newBuilder() .setMaxMessages(1) .setReturnImmediately(true) // return immediately if messages are not available .setSubscription(subscription.getName()) .build(); PullResponse pullResponse = subscriberStub.pullCallable().call(pullRequest); String receiveMessageText = pullResponse.getReceivedMessages(0).getMessage().getData().toStringUtf8(); Assert.assertEquals(messageText, receiveMessageText); } private TopicAdminClient createTopicAdmin(CredentialsProvider credentialsProvider) throws IOException { return TopicAdminClient.create( TopicAdminSettings.newBuilder() .setTransportChannelProvider(channelProvider) .setCredentialsProvider(credentialsProvider) .build() ); } private SubscriptionAdminClient createSubscriptionAdmin(CredentialsProvider credentialsProvider) throws IOException { SubscriptionAdminSettings subscriptionAdminSettings = SubscriptionAdminSettings.newBuilder() .setCredentialsProvider(credentialsProvider) .setTransportChannelProvider(channelProvider) .build(); return SubscriptionAdminClient.create(subscriptionAdminSettings); } private Publisher createPublisher(CredentialsProvider credentialsProvider) throws IOException { return Publisher.newBuilder(topicName) .setChannelProvider(channelProvider) .setCredentialsProvider(credentialsProvider) .build(); } private SubscriberStub createSubscriberStub(CredentialsProvider credentialsProvider) throws IOException { SubscriberStubSettings subscriberStubSettings = SubscriberStubSettings.newBuilder() .setTransportChannelProvider(channelProvider) .setCredentialsProvider(credentialsProvider) .build(); return GrpcSubscriberStub.create(subscriberStubSettings); }} |
That’s it. Now you can have some cost efficient unit tests!
Published on Java Code Geeks with permission by Emmanouil Gkatziouras, partner at our JCG program. See the original article here: Pub/Sub local emulator Opinions expressed by Java Code Geeks contributors are their own. |
