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larry-safranlarry-safran
authoredAug 8, 2024··
Dualstack example (#11451)
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v1.72.0v1.67.1
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‎examples/example-dualstack/README.md

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# gRPC Dualstack Example
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The dualstack example uses a custom name resolver that provides both IPv4 and IPv6 localhost
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endpoints for each of 3 server instances. The client will first use the default name resolver and
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load balancers which will only connect tot he first server. It will then use the
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custom name resolver with round robin to connect to each of the servers in turn. The 3 instances
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of the server will bind respectively to: both IPv4 and IPv6, IPv4 only, and IPv6 only.
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The example requires grpc-java to already be built. You are strongly encouraged
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to check out a git release tag, since there will already be a build of grpc
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available. Otherwise, you must follow [COMPILING](../../COMPILING.md).
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### Build the example
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To build the dualstack example server and client. From the
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`grpc-java/examples/example-dualstack` directory run:
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```bash
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$ ../gradlew installDist
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```
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This creates the scripts
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`build/install/example-dualstack/bin/dual-stack-server`
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and `build/install/example-dualstack/bin/dual-stack-client`.
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To run the dualstack example, run the server with:
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```bash
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$ ./build/install/example-dualstack/bin/dual-stack-server
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```
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And in a different terminal window run the client.
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```bash
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$ ./build/install/example-dualstack/bin/dual-stack-client
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```
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### Maven
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If you prefer to use Maven:
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Run in the example-debug directory:
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```bash
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$ mvn verify
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$ # Run the server in one terminal
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$ mvn exec:java -Dexec.mainClass=io.grpc.examples.dualstack.DualStackServer
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```
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```bash
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$ # In another terminal run the client
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$ mvn exec:java -Dexec.mainClass=io.grpc.examples.dualstack.DualStackClient
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```
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‎examples/example-dualstack/build.gradle

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plugins {
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id 'application' // Provide convenience executables for trying out the examples.
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id 'java'
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id "com.google.protobuf" version "0.9.4"
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// Generate IntelliJ IDEA's .idea & .iml project files
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id 'idea'
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}
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repositories {
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maven { // The google mirror is less flaky than mavenCentral()
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url "https://maven-central.storage-download.googleapis.com/maven2/" }
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mavenCentral()
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mavenLocal()
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}
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java {
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sourceCompatibility = JavaVersion.VERSION_1_8
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targetCompatibility = JavaVersion.VERSION_1_8
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}
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// IMPORTANT: You probably want the non-SNAPSHOT version of gRPC. Make sure you
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// are looking at a tagged version of the example and not "master"!
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// Feel free to delete the comment at the next line. It is just for safely
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// updating the version in our release process.
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def grpcVersion = '1.67.0-SNAPSHOT' // CURRENT_GRPC_VERSION
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def protobufVersion = '3.25.3'
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dependencies {
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implementation "io.grpc:grpc-protobuf:${grpcVersion}"
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implementation "io.grpc:grpc-netty:${grpcVersion}"
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implementation "io.grpc:grpc-stub:${grpcVersion}"
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implementation "io.grpc:grpc-services:${grpcVersion}"
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compileOnly "org.apache.tomcat:annotations-api:6.0.53"
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}
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protobuf {
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protoc {
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artifact = "com.google.protobuf:protoc:${protobufVersion}"
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}
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plugins {
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grpc {
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artifact = "io.grpc:protoc-gen-grpc-java:${grpcVersion}"
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}
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}
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generateProtoTasks {
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all()*.plugins {
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grpc {}
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}
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}
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}
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startScripts.enabled = false
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task DualStackClient(type: CreateStartScripts) {
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mainClass = 'io.grpc.examples.dualstack.DualStackClient'
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applicationName = 'dual-stack-client'
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outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
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classpath = startScripts.classpath
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}
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task DualStackServer(type: CreateStartScripts) {
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mainClass = 'io.grpc.examples.dualstack.DualStackServer'
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applicationName = 'dual-stack-server'
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outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
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classpath = startScripts.classpath
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}
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application {
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applicationDistribution.into('bin') {
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from(DualStackClient)
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from(DualStackServer)
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filePermissions {
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unix(0755)
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}
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}
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}

‎examples/example-dualstack/pom.xml

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>io.grpc</groupId>
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<artifactId>example-dualstack</artifactId>
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<packaging>jar</packaging>
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<!-- Feel free to delete the comment at the end of these lines. It is just
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for safely updating the version in our release process. -->
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<version>1.67.0-SNAPSHOT</version><!-- CURRENT_GRPC_VERSION -->
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<name>example-dualstack</name>
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<url>https://github.com/grpc/grpc-java</url>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<grpc.version>1.67.0-SNAPSHOT</grpc.version><!-- CURRENT_GRPC_VERSION -->
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<protoc.version>3.25.3</protoc.version>
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<!-- required for jdk9 -->
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<maven.compiler.source>1.8</maven.compiler.source>
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<maven.compiler.target>1.8</maven.compiler.target>
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</properties>
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<dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-bom</artifactId>
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<version>${grpc.version}</version>
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<type>pom</type>
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<scope>import</scope>
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</dependency>
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</dependencies>
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</dependencyManagement>
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<dependencies>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-services</artifactId>
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-protobuf</artifactId>
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-stub</artifactId>
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-netty</artifactId>
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</dependency>
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<dependency>
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<groupId>org.apache.tomcat</groupId>
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<artifactId>annotations-api</artifactId>
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<version>6.0.53</version>
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<scope>provided</scope> <!-- not needed at runtime -->
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-netty-shaded</artifactId>
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<scope>runtime</scope>
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</dependency>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.13.2</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>io.grpc</groupId>
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<artifactId>grpc-testing</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<extensions>
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<extension>
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<groupId>kr.motd.maven</groupId>
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<artifactId>os-maven-plugin</artifactId>
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<version>1.7.1</version>
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</extension>
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</extensions>
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<plugins>
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<plugin>
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<groupId>org.xolstice.maven.plugins</groupId>
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<artifactId>protobuf-maven-plugin</artifactId>
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<version>0.6.1</version>
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<configuration>
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<protocArtifact>com.google.protobuf:protoc:${protoc.version}:exe:${os.detected.classifier}</protocArtifact>
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<pluginId>grpc-java</pluginId>
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<pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc.version}:exe:${os.detected.classifier}</pluginArtifact>
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</configuration>
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<executions>
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<execution>
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<goals>
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<goal>compile</goal>
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<goal>compile-custom</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-enforcer-plugin</artifactId>
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<version>1.4.1</version>
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<executions>
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<execution>
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<id>enforce</id>
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<goals>
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<goal>enforce</goal>
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</goals>
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<configuration>
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<rules>
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<requireUpperBoundDeps/>
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</rules>
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</configuration>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

‎examples/example-dualstack/settings.gradle

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pluginManagement {
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repositories {
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maven { // The google mirror is less flaky than mavenCentral()
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url "https://maven-central.storage-download.googleapis.com/maven2/"
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}
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gradlePluginPortal()
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}
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}
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rootProject.name = 'example-dualstack'

‎examples/example-dualstack/src/main/java/io/grpc/examples/dualstack/DualStackClient.java

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/*
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* Copyright 2024 The gRPC Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc.examples.dualstack;
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import io.grpc.Channel;
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import io.grpc.ManagedChannel;
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import io.grpc.ManagedChannelBuilder;
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import io.grpc.NameResolverRegistry;
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import io.grpc.StatusRuntimeException;
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import io.grpc.examples.helloworld.GreeterGrpc;
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import io.grpc.examples.helloworld.HelloReply;
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import io.grpc.examples.helloworld.HelloRequest;
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import java.util.concurrent.TimeUnit;
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import java.util.logging.Level;
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import java.util.logging.Logger;
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/**
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* A client that requests greetings from the {@link DualStackServer}.
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* First it sends 5 requests using the default nameresolver and load balancer.
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* Then it sends 10 requests using the example nameresolver and round robin load balancer. These
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* requests are evenly distributed among the 3 servers rather than favoring the server listening
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* on both addresses because the ExampleDualStackNameResolver groups the 3 servers as 3 endpoints
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* each with 2 addresses.
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*/
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public class DualStackClient {
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public static final String channelTarget = "example:///lb.example.grpc.io";
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private static final Logger logger = Logger.getLogger(DualStackClient.class.getName());
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private final GreeterGrpc.GreeterBlockingStub blockingStub;
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public DualStackClient(Channel channel) {
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blockingStub = GreeterGrpc.newBlockingStub(channel);
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}
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public static void main(String[] args) throws Exception {
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NameResolverRegistry.getDefaultRegistry()
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.register(new ExampleDualStackNameResolverProvider());
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logger.info("\n **** Use default DNS resolver ****");
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ManagedChannel channel = ManagedChannelBuilder.forTarget("localhost:50051")
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.usePlaintext()
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.build();
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try {
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DualStackClient client = new DualStackClient(channel);
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for (int i = 0; i < 5; i++) {
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client.greet("request:" + i);
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}
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} finally {
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channel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
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}
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logger.info("\n **** Change to use example name resolver ****");
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/*
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Dial to "example:///resolver.example.grpc.io", use {@link ExampleNameResolver} to create connection
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"resolver.example.grpc.io" is converted to {@link java.net.URI.path}
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*/
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channel = ManagedChannelBuilder.forTarget(channelTarget)
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.defaultLoadBalancingPolicy("round_robin")
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.usePlaintext()
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.build();
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try {
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DualStackClient client = new DualStackClient(channel);
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for (int i = 0; i < 10; i++) {
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client.greet("request:" + i);
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}
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} finally {
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channel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
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}
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}
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public void greet(String name) {
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HelloRequest request = HelloRequest.newBuilder().setName(name).build();
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HelloReply response;
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try {
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response = blockingStub.sayHello(request);
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} catch (StatusRuntimeException e) {
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logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());
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return;
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}
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logger.info("Greeting: " + response.getMessage());
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}
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}

‎examples/example-dualstack/src/main/java/io/grpc/examples/dualstack/DualStackServer.java

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/*
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* Copyright 2024 The gRPC Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc.examples.dualstack;
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import io.grpc.Server;
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import io.grpc.ServerBuilder;
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import io.grpc.examples.helloworld.GreeterGrpc;
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import io.grpc.examples.helloworld.HelloReply;
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import io.grpc.examples.helloworld.HelloRequest;
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import io.grpc.netty.NettyServerBuilder;
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import io.grpc.stub.StreamObserver;
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import java.io.IOException;
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import java.net.InetSocketAddress;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.concurrent.TimeUnit;
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import java.util.logging.Logger;
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/**
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* Starts 3 different greeter services each on its own port, but all for localhost.
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* The first service listens on both IPv4 and IPv6,
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* the second on just IPv4, and the third on just IPv6.
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*/
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public class DualStackServer {
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private static final Logger logger = Logger.getLogger(DualStackServer.class.getName());
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private List<Server> servers;
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public static void main(String[] args) throws IOException, InterruptedException {
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final DualStackServer server = new DualStackServer();
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server.start();
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server.blockUntilShutdown();
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}
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private void start() throws IOException {
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InetSocketAddress inetSocketAddress;
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servers = new ArrayList<>();
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int[] serverPorts = ExampleDualStackNameResolver.SERVER_PORTS;
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for (int i = 0; i < serverPorts.length; i++ ) {
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String addressType;
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int port = serverPorts[i];
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ServerBuilder<?> serverBuilder;
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switch (i) {
58+
case 0:
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serverBuilder = ServerBuilder.forPort(port); // bind to both IPv4 and IPv6
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addressType = "both IPv4 and IPv6";
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break;
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case 1:
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// bind to IPv4 only
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inetSocketAddress = new InetSocketAddress("127.0.0.1", port);
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serverBuilder = NettyServerBuilder.forAddress(inetSocketAddress);
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addressType = "IPv4 only";
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break;
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case 2:
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// bind to IPv6 only
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inetSocketAddress = new InetSocketAddress("::1", port);
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serverBuilder = NettyServerBuilder.forAddress(inetSocketAddress);
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addressType = "IPv6 only";
73+
break;
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default:
75+
throw new IllegalStateException("Unexpected value: " + i);
76+
}
77+
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servers.add(serverBuilder
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.addService(new GreeterImpl(port, addressType))
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.build()
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.start());
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logger.info("Server started, listening on " + port);
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}
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Runtime.getRuntime().addShutdownHook(new Thread(() -> {
85+
System.err.println("*** shutting down gRPC server since JVM is shutting down");
86+
try {
87+
DualStackServer.this.stop();
88+
} catch (InterruptedException e) {
89+
e.printStackTrace(System.err);
90+
}
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System.err.println("*** server shut down");
92+
}));
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}
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private void stop() throws InterruptedException {
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for (Server server : servers) {
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server.shutdown().awaitTermination(30, TimeUnit.SECONDS);
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}
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}
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private void blockUntilShutdown() throws InterruptedException {
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for (Server server : servers) {
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server.awaitTermination();
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}
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}
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static class GreeterImpl extends GreeterGrpc.GreeterImplBase {
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int port;
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String addressType;
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public GreeterImpl(int port, String addressType) {
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this.port = port;
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this.addressType = addressType;
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}
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@Override
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public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
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String msg = String.format("Hello %s from server<%d> type: %s",
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req.getName(), this.port, addressType);
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HelloReply reply = HelloReply.newBuilder().setMessage(msg).build();
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responseObserver.onNext(reply);
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responseObserver.onCompleted();
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}
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}
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}

‎examples/example-dualstack/src/main/java/io/grpc/examples/dualstack/ExampleDualStackNameResolver.java

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/*
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* Copyright 2024 The gRPC Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
11+
* distributed under the License is distributed on an "AS IS" BASIS,
12+
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13+
* See the License for the specific language governing permissions and
14+
* limitations under the License.
15+
*/
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package io.grpc.examples.dualstack;
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import com.google.common.collect.ImmutableMap;
20+
import io.grpc.EquivalentAddressGroup;
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import io.grpc.NameResolver;
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import io.grpc.Status;
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import java.net.InetSocketAddress;
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import java.net.SocketAddress;
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import java.net.URI;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
29+
import java.util.stream.Collectors;
30+
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/**
32+
* A fake name resolver that resolves to a hard-coded list of 3 endpoints (EquivalentAddressGropu)
33+
* each with 2 addresses (one IPv4 and one IPv6).
34+
*/
35+
public class ExampleDualStackNameResolver extends NameResolver {
36+
static public final int[] SERVER_PORTS = {50051, 50052, 50053};
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// This is a fake name resolver, so we just hard code the address here.
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private static final ImmutableMap<String, List<List<SocketAddress>>> addrStore =
40+
ImmutableMap.<String, List<List<SocketAddress>>>builder()
41+
.put("lb.example.grpc.io",
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Arrays.stream(SERVER_PORTS)
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.mapToObj(port -> getLocalAddrs(port))
44+
.collect(Collectors.toList())
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)
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.build();
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private Listener2 listener;
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private final URI uri;
51+
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public ExampleDualStackNameResolver(URI targetUri) {
53+
this.uri = targetUri;
54+
}
55+
56+
private static List<SocketAddress> getLocalAddrs(int port) {
57+
return Arrays.asList(
58+
new InetSocketAddress("127.0.0.1", port),
59+
new InetSocketAddress("::1", port));
60+
}
61+
62+
@Override
63+
public String getServiceAuthority() {
64+
return uri.getPath().substring(1);
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}
66+
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@Override
68+
public void shutdown() {
69+
}
70+
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@Override
72+
public void start(Listener2 listener) {
73+
this.listener = listener;
74+
this.resolve();
75+
}
76+
77+
@Override
78+
public void refresh() {
79+
this.resolve();
80+
}
81+
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private void resolve() {
83+
List<List<SocketAddress>> addresses = addrStore.get(uri.getPath().substring(1));
84+
try {
85+
List<EquivalentAddressGroup> eagList = new ArrayList<>();
86+
for (List<SocketAddress> endpoint : addresses) {
87+
// every server is an EquivalentAddressGroup, so they can be accessed randomly
88+
eagList.add(new EquivalentAddressGroup(endpoint));
89+
}
90+
91+
this.listener.onResult(ResolutionResult.newBuilder().setAddresses(eagList).build());
92+
} catch (Exception e){
93+
// when error occurs, notify listener
94+
this.listener.onError(Status.UNAVAILABLE.withDescription("Unable to resolve host ").withCause(e));
95+
}
96+
}
97+
98+
}

‎examples/example-dualstack/src/main/java/io/grpc/examples/dualstack/ExampleDualStackNameResolverProvider.java

+47
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,47 @@
1+
/*
2+
* Copyright 2024 The gRPC Authors
3+
*
4+
* Licensed under the Apache License, Version 2.0 (the "License");
5+
* you may not use this file except in compliance with the License.
6+
* You may obtain a copy of the License at
7+
*
8+
* http://www.apache.org/licenses/LICENSE-2.0
9+
*
10+
* Unless required by applicable law or agreed to in writing, software
11+
* distributed under the License is distributed on an "AS IS" BASIS,
12+
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13+
* See the License for the specific language governing permissions and
14+
* limitations under the License.
15+
*/
16+
17+
package io.grpc.examples.dualstack;
18+
19+
import io.grpc.NameResolver;
20+
import io.grpc.NameResolverProvider;
21+
22+
import java.net.URI;
23+
24+
public class ExampleDualStackNameResolverProvider extends NameResolverProvider {
25+
public static final String exampleScheme = "example";
26+
27+
@Override
28+
public NameResolver newNameResolver(URI targetUri, NameResolver.Args args) {
29+
return new ExampleDualStackNameResolver(targetUri);
30+
}
31+
32+
@Override
33+
protected boolean isAvailable() {
34+
return true;
35+
}
36+
37+
@Override
38+
protected int priority() {
39+
return 5;
40+
}
41+
42+
@Override
43+
// gRPC choose the first NameResolverProvider that supports the target URI scheme.
44+
public String getDefaultScheme() {
45+
return exampleScheme;
46+
}
47+
}

‎examples/example-dualstack/src/main/proto/helloworld/helloworld.proto

+37
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,37 @@
1+
// Copyright 2015 The gRPC Authors
2+
//
3+
// Licensed under the Apache License, Version 2.0 (the "License");
4+
// you may not use this file except in compliance with the License.
5+
// You may obtain a copy of the License at
6+
//
7+
// http://www.apache.org/licenses/LICENSE-2.0
8+
//
9+
// Unless required by applicable law or agreed to in writing, software
10+
// distributed under the License is distributed on an "AS IS" BASIS,
11+
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12+
// See the License for the specific language governing permissions and
13+
// limitations under the License.
14+
syntax = "proto3";
15+
16+
option java_multiple_files = true;
17+
option java_package = "io.grpc.examples.helloworld";
18+
option java_outer_classname = "HelloWorldProto";
19+
option objc_class_prefix = "HLW";
20+
21+
package helloworld;
22+
23+
// The greeting service definition.
24+
service Greeter {
25+
// Sends a greeting
26+
rpc SayHello (HelloRequest) returns (HelloReply) {}
27+
}
28+
29+
// The request message containing the user's name.
30+
message HelloRequest {
31+
string name = 1;
32+
}
33+
34+
// The response message containing the greetings
35+
message HelloReply {
36+
string message = 1;
37+
}

‎examples/src/main/java/io/grpc/examples/loadbalance/ExampleNameResolver.java

+6-7
Original file line numberDiff line numberDiff line change
@@ -28,12 +28,12 @@
2828
import java.util.List;
2929
import java.util.Map;
3030
import java.util.stream.Collectors;
31-
import java.util.stream.Stream;
3231

3332
import static io.grpc.examples.loadbalance.LoadBalanceClient.exampleServiceName;
3433

3534
public class ExampleNameResolver extends NameResolver {
3635

36+
static private final int[] SERVER_PORTS = {50051, 50052, 50053};
3737
private Listener2 listener;
3838

3939
private final URI uri;
@@ -44,12 +44,11 @@ public ExampleNameResolver(URI targetUri) {
4444
this.uri = targetUri;
4545
// This is a fake name resolver, so we just hard code the address here.
4646
addrStore = ImmutableMap.<String,List<InetSocketAddress>>builder()
47-
.put(exampleServiceName,
48-
Stream.iterate(LoadBalanceServer.startPort,p->p+1)
49-
.limit(LoadBalanceServer.serverCount)
50-
.map(port->new InetSocketAddress("localhost",port))
51-
.collect(Collectors.toList())
52-
)
47+
.put(exampleServiceName,
48+
Arrays.stream(SERVER_PORTS)
49+
.mapToObj(port->new InetSocketAddress("localhost",port))
50+
.collect(Collectors.toList())
51+
)
5352
.build();
5453
}
5554

‎examples/src/main/java/io/grpc/examples/loadbalance/LoadBalanceServer.java

+15-17
Original file line numberDiff line numberDiff line change
@@ -24,23 +24,24 @@
2424
import io.grpc.stub.StreamObserver;
2525

2626
import java.io.IOException;
27+
import java.util.ArrayList;
28+
import java.util.List;
2729
import java.util.concurrent.TimeUnit;
2830
import java.util.logging.Logger;
2931

3032
public class LoadBalanceServer {
3133
private static final Logger logger = Logger.getLogger(LoadBalanceServer.class.getName());
32-
static public final int serverCount = 3;
33-
static public final int startPort = 50051;
34-
private Server[] servers;
34+
static final int[] SERVER_PORTS = {50051, 50052, 50053};
35+
private List<Server> servers;
3536

3637
private void start() throws IOException {
37-
servers = new Server[serverCount];
38-
for (int i = 0; i < serverCount; i++) {
39-
int port = startPort + i;
40-
servers[i] = ServerBuilder.forPort(port)
38+
servers = new ArrayList<>();
39+
for (int port : SERVER_PORTS) {
40+
servers.add(
41+
ServerBuilder.forPort(port)
4142
.addService(new GreeterImpl(port))
4243
.build()
43-
.start();
44+
.start());
4445
logger.info("Server started, listening on " + port);
4546
}
4647
Runtime.getRuntime().addShutdownHook(new Thread(() -> {
@@ -55,18 +56,14 @@ private void start() throws IOException {
5556
}
5657

5758
private void stop() throws InterruptedException {
58-
for (int i = 0; i < serverCount; i++) {
59-
if (servers[i] != null) {
60-
servers[i].shutdown().awaitTermination(30, TimeUnit.SECONDS);
61-
}
59+
for (Server server : servers) {
60+
server.shutdown().awaitTermination(30, TimeUnit.SECONDS);
6261
}
6362
}
6463

6564
private void blockUntilShutdown() throws InterruptedException {
66-
for (int i = 0; i < serverCount; i++) {
67-
if (servers[i] != null) {
68-
servers[i].awaitTermination();
69-
}
65+
for (Server server : servers) {
66+
server.awaitTermination();
7067
}
7168
}
7269

@@ -86,7 +83,8 @@ public GreeterImpl(int port) {
8683

8784
@Override
8885
public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
89-
HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName() + " from server<" + this.port + ">").build();
86+
HelloReply reply = HelloReply.newBuilder()
87+
.setMessage("Hello " + req.getName() + " from server<" + this.port + ">").build();
9088
responseObserver.onNext(reply);
9189
responseObserver.onCompleted();
9290
}

‎examples/src/main/java/io/grpc/examples/nameresolve/NameResolveClient.java

+5-7
Original file line numberDiff line numberDiff line change
@@ -26,8 +26,7 @@
2626
import java.util.logging.Logger;
2727

2828
public class NameResolveClient {
29-
public static final String exampleScheme = "example";
30-
public static final String exampleServiceName = "lb.example.grpc.io";
29+
public static final String channelTarget = "example:///lb.example.grpc.io";
3130
private static final Logger logger = Logger.getLogger(NameResolveClient.class.getName());
3231
private final GreeterGrpc.GreeterBlockingStub blockingStub;
3332

@@ -56,11 +55,10 @@ public static void main(String[] args) throws Exception {
5655
Dial to "example:///resolver.example.grpc.io", use {@link ExampleNameResolver} to create connection
5756
"resolver.example.grpc.io" is converted to {@link java.net.URI.path}
5857
*/
59-
channel = ManagedChannelBuilder.forTarget(
60-
String.format("%s:///%s", exampleScheme, exampleServiceName))
61-
.defaultLoadBalancingPolicy("round_robin")
62-
.usePlaintext()
63-
.build();
58+
channel = ManagedChannelBuilder.forTarget(channelTarget)
59+
.defaultLoadBalancingPolicy("round_robin")
60+
.usePlaintext()
61+
.build();
6462
try {
6563
NameResolveClient client = new NameResolveClient(channel);
6664
for (int i = 0; i < 5; i++) {

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