Vert.x gRPC Protoc Plugin
The easiest way to start using vertx-grpc is to utilize its built-in code generator plugin. To do so, one must define
the protocol in the protobuffer format as required by gRPC.
syntax = "proto3";
option java_multiple_files = true;
option java_package = "examples";
option java_outer_classname = "HelloWorldProto";
package helloworld;
// The greeting service definition.
service Greeter {
// Sends a greeting
rpc SayHello (HelloRequest) returns (HelloReply) {}
}
// The request message containing the user's name.
message HelloRequest {
string name = 1;
}
// The response message containing the greetings
message HelloReply {
string message = 1;
}
This is a very simple example showing the single request, single response mode.
Compile the RPC definition
Using the definition above we need to compile it.
You can compile the proto file using the protoc compiler if you like
or you can integrate it in your build.
If you’re using Apache Maven you need to add the plugin:
<plugin>
<groupId>org.xolstice.maven.plugins</groupId>
<artifactId>protobuf-maven-plugin</artifactId>
<version>0.6.1</version>
<configuration>
<protocArtifact>com.google.protobuf:protoc:${protoc.version}:exe:${os.detected.classifier}</protocArtifact>
<pluginId>grpc-java</pluginId>
<pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc.version}:exe:${os.detected.classifier}</pluginArtifact>
<protocPlugins>
<protocPlugin>
<id>vertx-grpc-protoc-plugin2</id>
<groupId>io.vertx</groupId>
<artifactId>vertx-grpc-protoc-plugin2</artifactId>
<version>${stack.version}</version>
<mainClass>io.vertx.grpc.plugin.VertxGrpcGenerator</mainClass>
</protocPlugin>
</protocPlugins>
</configuration>
<executions>
<execution>
<id>compile</id>
<configuration>
<outputDirectory>${project.basedir}/src/main/java</outputDirectory>
<clearOutputDirectory>false</clearOutputDirectory>
</configuration>
<goals>
<goal>compile</goal>
<goal>compile-custom</goal>
</goals>
</execution>
</executions>
</plugin>
The ${os.detected.classifier} property is used to make the build OS independant, on OSX it is replaced
by osx-x86_64 and so on. To use it you need to add the os-maven-plugin[https://github.com/trustin/os-maven-plugin]
in the build section of your pom.xml:
<build>
...
<extensions>
<extension>
<groupId>kr.motd.maven</groupId>
<artifactId>os-maven-plugin</artifactId>
<version>1.4.1.Final</version>
</extension>
</extensions>
...
</build>
This plugin will compile your proto files under src/main/proto and make them available to your project.
If you’re using Gradle you need to add the plugin:
...
apply plugin: 'com.google.protobuf'
...
buildscript {
...
dependencies {
// ASSUMES GRADLE 2.12 OR HIGHER. Use plugin version 0.7.5 with earlier gradle versions
classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.0'
}
}
...
protobuf {
protoc {
artifact = 'com.google.protobuf:protoc:3.2.0'
}
plugins {
grpc {
artifact = "io.grpc:protoc-gen-grpc-java:1.25.0"
}
vertx {
artifact = "io.vertx:vertx-grpc-protoc-plugin2:${vertx.grpc.version}"
}
}
generateProtoTasks {
all()*.plugins {
grpc
vertx
}
}
}
This plugin will compile your proto files under build/generated/source/proto/main and make them available to your project.
Writing a service
The plugin generates vertx idiomatic Vert.x service stubs.
Each service comes in two flavors, you can override the method you like depending on the style.
Unary services can return a Vert.x Future:
VertxGreeterGrpcServer.GreeterApi stub = new VertxGreeterGrpcServer.GreeterApi() {
@Override
public Future<HelloReply> sayHello(HelloRequest request) {
return Future.succeededFuture(HelloReply.newBuilder().setMessage("Hello " + request.getName()).build());
}
};
or process a Vert.x Promise
VertxGreeterGrpcServer.GreeterApi stub = new VertxGreeterGrpcServer.GreeterApi() {
@Override
public void sayHello(HelloRequest request, Promise<HelloReply> response) {
response.complete(HelloReply.newBuilder().setMessage("Hello " + request.getName()).build());
}
};
In both case you need to bind the stub to an existing GrpcServer:
server.bindAll(stub);
Streaming requests
Streaming requests are implemented with Vert.x ReadStream:
VertxStreamingGrpcServer.StreamingApi stub = new VertxStreamingGrpcServer.StreamingApi() {
@Override
public void sink(ReadStream<Item> stream, Promise<Empty> response) {
stream.handler(item -> {
System.out.println("Process item " + item.getValue());
});
// Send response
stream.endHandler(v -> response.complete(Empty.getDefaultInstance()));
}
};
Streaming responses
Streaming responses are implemented with Vert.x streams and comes in two flavors.
You can return a Vert.x ReadStream and let the service send it for you:
VertxStreamingGrpcServer.StreamingApi stub = new VertxStreamingGrpcServer.StreamingApi() {
@Override
public ReadStream<Item> source(Empty request) {
return streamOfItem();
}
};
or you can process a WriteStream:
VertxStreamingGrpcServer.StreamingApi stub = new VertxStreamingGrpcServer.StreamingApi() {
@Override
public void source(Empty request, WriteStream<Item> response) {
response.write(Item.newBuilder().setValue("value-1").build());
response.end(Item.newBuilder().setValue("value-2").build());
}
};
Writing a client
The plugin generates Vert.x service clients.
A client wraps a GrpcClient and provides Vert.x idiomatic API to interact with the service:
VertxGreeterGrpcClient client = new VertxGreeterGrpcClient(grpcClient, server);
Unary services returns a Vert.x Future
Future<HelloReply> response = client.sayHello(HelloRequest.newBuilder().setName("John").build());
response.onSuccess(result -> System.out.println("Service responded: " + ar.result().getMessage()));
response.onFailure(err -> System.out.println("Service failure: " + ar.cause().getMessage()));
Streaming requests
Streaming requests use a lambda passed a Vert.x WriteStream of messages sent to the service
Future<Empty> response = client.sink(stream -> {
stream.write(Item.newBuilder().setValue("Value 1").build());
stream.write(Item.newBuilder().setValue("Value 2").build());
stream.end(Item.newBuilder().setValue("Value 3").build());
});
Streaming responses
Streaming responses get a Vert.x ReadStream of messages sent by the service
Future<ReadStream<Item>> response = client.source(Empty.getDefaultInstance());
response.onSuccess(stream -> stream
.handler(item -> System.out.println("Item " + item.getValue()))
.exceptionHandler(err -> System.out.println("Stream failed " + err.getMessage()));
.endHandler(v -> System.out.println("Stream ended")));
response.onFailure(err -> System.out.println("Service failure: " + ar.cause().getMessage()));