Declare Plugin and Repository

pluginManagement {
    plugins {
        id("org.jetbrains.kotlin.jvm") version "2.0.0" apply false
        id("com.google.protobuf") version "0.9.2" apply false
    }
}

dependencyResolutionManagement {
    repositoriesMode = RepositoriesMode.PREFER_SETTINGS
    repositories {
        mavenLocal()
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}

Apply Plugin and Dependency

plugins {
    id("org.jetbrains.kotlin.jvm")
    id("com.google.protobuf")
}


java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(8)
    }
}

dependencies {
    api("io.github.hellogoogle2000:kotlin-commons:+")
    api("com.google.protobuf:protobuf-kotlin:3.22.2")
    api("io.grpc:grpc-protobuf:1.54.0")
    api("io.grpc:grpc-netty-shaded:1.54.0")
    api("io.grpc:grpc-kotlin-stub:1.3.0")
    api("org.apache.tomcat:annotations-api:6.0.53")
}

Configure Code Generation Dir and Tools

protobuf {
    protoc {
        artifact = "com.google.protobuf:protoc:3.22.2"
    }
    plugins {
        create("rpc-java") {
            artifact = "io.grpc:protoc-gen-grpc-java:1.54.0"
        }
        create("rpc-kotlin") {
            artifact = "io.grpc:protoc-gen-grpc-kotlin:1.3.0:jdk8@jar"
        }
    }
    generateProtoTasks {
        all().forEach {
            it.plugins {
                create("rpc-java")
            }
            it.plugins {
                create("rpc-kotlin")
            }
            it.builtins {
                create("kotlin")
            }
        }
    }
}

Compile Proto File

syntax = "proto3";

package com.kotlin.sample;

option java_multiple_files = true;
option java_package = "com.kotlin.sample.proto";
option java_outer_classname = "UserProto";

message UserListWrapper {
  repeated User list = 1;
}

message User {
  int32 id = 1;
  string name = 2;
  repeated Course courses = 3;
}

message Course {
  int32 id = 1;
  string name = 2;
}

message GetUserRequest {
  int32 pageSize = 1;
  int32 pageIndex = 2;
}

message GetUserResponse {
  repeated User users = 1;
}

service UserService {
  rpc GetUserList (GetUserRequest) returns (GetUserResponse) {}
}

Auto Generate Class Files

rebuild project, plugin will auto-generate all required files

Write and Read Data Directly Through PB File

import com.kotlin.sample.proto.User
import com.kotlin.sample.proto.UserListWrapper
import com.kotlin.sample.proto.user
import com.kotlin.sample.proto.userListWrapper
import x.kotlin.commons.string.UUID
import kotlin.io.path.Path
import kotlin.io.path.inputStream
import kotlin.io.path.outputStream

fun main() {
    // create user objects
    val users = mutableListOf<User>()
    repeat(2) {
        val user = user {
            id = UUID.hashCode()
            name = UUID.short()
        }
        users.add(user)
    }
    // create pb file
    val path = Path("/home/easing/temp/users.pb")
    // write to pb file
    val userListWrapper1 = userListWrapper { list.addAll(users) }
    path.outputStream().use { userListWrapper1.writeTo(it) }
    // read from pb file
    val userListWrapper2 = path.inputStream().use { UserListWrapper.parser().parseFrom(it) }
    println(userListWrapper1 == userListWrapper2)
}

Create a Google RPC Server Transmitting with ProtoBuffer

import com.kotlin.sample.proto.*
import io.grpc.ServerBuilder
import x.kotlin.commons.string.UUID

private class UserService : UserServiceGrpcKt.UserServiceCoroutineImplBase() {
    override suspend fun getUserList(request: GetUserRequest): GetUserResponse {
        val users = mutableListOf<User>()
        repeat(2) {
            val user = user {
                id = UUID.hashCode()
                name = UUID.short()
            }
            users.add(user)
        }
        return getUserResponse { this.users.addAll(users) }
    }
}

fun main() {
    val server = ServerBuilder
        .forPort(10001)
        .addService(UserService())
        .build()
    server.start()
    server.awaitTermination()
}

Create a Google RPC Client

import com.kotlin.sample.proto.UserServiceGrpcKt
import com.kotlin.sample.proto.getUserRequest
import io.grpc.ManagedChannelBuilder

suspend fun main() {
    val channel = ManagedChannelBuilder
        .forTarget("localhost:10001")
        .usePlaintext()
        .build()
    val service = UserServiceGrpcKt.UserServiceCoroutineStub(channel)
    val request = getUserRequest {
        pageSize = 10
        pageIndex = 0
    }
    val getUserResponse = service.getUserList(request)
    println(getUserResponse.usersList)
}