Grpc-java: google/protobuf/empty.proto: File not found

[JBayangosB]

Hi,

I'm trying to use grpc-java in an Android app to hit an API that makes uses of protobufs. It seems when using java-lite and then adding this line to a .proto file import google/protobuf/empty.proto, I'm receiving this error:

ERROR: Cause: protoc: stdout: . stderr: google/protobuf/empty.proto: File not found.
helloworld.proto: Import "google/protobuf/empty.proto" was not found or had errors.

Full .proto file:

// Copyright 2015, gRPC Authors
// All rights reserved.
//
// 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
// 
//     http://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.
syntax = "proto3";

option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";
option objc_class_prefix = "HLW";

import "google/protobuf/empty.proto";

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;
}

App level build.gradle

apply plugin: 'com.android.application'
apply plugin: 'com.google.protobuf'

android {
    compileSdkVersion 29

    defaultConfig {
        applicationId "io.grpc.android.helloworldexample"
        minSdkVersion 26
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    lintOptions {
        disable 'InvalidPackage', 'HardcodedText'
        textReport true
        textOutput "stdout"
    }
}

protobuf {
    protoc {
        artifact = 'com.google.protobuf:protoc:3.7.1'
    }
    plugins {
        javalite {
            artifact = "com.google.protobuf:protoc-gen-javalite:3.0.0"
        }
        grpc {
            artifact = 'io.grpc:protoc-gen-grpc-java:1.25.0' // CURRENT_GRPC_VERSION
        }
    }
    generateProtoTasks {
        all().each { task ->
            task.plugins {
                javalite {}
                grpc {
                    // Options added to --grpc_out
                    option 'lite'
                }
            }
        }
    }
}

dependencies {
    implementation 'androidx.appcompat:appcompat:1.0.0'

    // You need to build grpc-java to obtain these libraries below.
    implementation 'io.grpc:grpc-okhttp:1.25.0' // CURRENT_GRPC_VERSION
    implementation 'io.grpc:grpc-protobuf-lite:1.25.0' // CURRENT_GRPC_VERSION
    implementation 'io.grpc:grpc-stub:1.25.0' // CURRENT_GRPC_VERSION
    implementation 'javax.annotation:javax.annotation-api:1.2'
}

Project level build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.2'
        classpath "com.google.protobuf:protobuf-gradle-plugin:0.8.8"

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
        mavenLocal()
    }
}

Any help would be greatly appreciated!

[creamsoup]

~there was a similar question in stackoverflow answered by grpc java maintainer.
basically empty.proto is not provided and you may need to copy the definition.~

hmm actually the previous answer doesn't seem correct. the empty.proto should be included as it included as resources in the protobuf library. possibly bug from the protobuf-gradle-plugin. i'll take a look into it

[creamsoup]

the empty.proto definition(proto file) is not in the com:google.protobuf:protobuf-lite. you need to add empty.proto definition, in app/build.gradle

protobuf 'com.google.protobuf:protobuf-java:3.10.0'

btw, protobuf team fixed this issue in new protobuf-javalite artifact which will be part of grpc 1.26.0. so, in newer version of grpc (will be release in couple weeks), this problem will be gone.

[JBayangosB]

the empty.proto definition(proto file) is not in the com:google.protobuf:protobuf-lite. you need to add empty.proto definition, in app/build.gradle

protobuf 'com.google.protobuf:protobuf-java:3.10.0'

btw, protobuf team fixed this issue in new protobuf-javalite artifact which will be part of grpc 1.26.0. so, in newer version of grpc (will be release in couple weeks), this problem will be gone.

Thanks for the help! I look forward to this update 🙂