grpc-java/README.md

gRPC-Java - An RPC library and framework
========================================

gRPC-Java works with JDK 6. gRPC-Java clients are supported on Android API
levels 14 and up (Ice Cream Sandwich and later). Deploying gRPC servers on an
Android device is not supported.

TLS usage typically requires using Java 8, or Play Services Dynamic Security
Provider on Android. Please see the [Security Readme](SECURITY.md).

<table>
  <tr>
    <td><b>Homepage:</b></td>
    <td><a href="https://grpc.io/">grpc.io</a></td>
  </tr>
  <tr>
    <td><b>Mailing List:</b></td>
    <td><a href="https://groups.google.com/forum/#!forum/grpc-io">grpc-io@googlegroups.com</a></td>
  </tr>
</table>

[![Join the chat at https://gitter.im/grpc/grpc](https://badges.gitter.im/grpc/grpc.svg)](https://gitter.im/grpc/grpc?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
[![Build Status](https://travis-ci.org/grpc/grpc-java.svg?branch=master)](https://travis-ci.org/grpc/grpc-java)
[![Coverage Status](https://coveralls.io/repos/grpc/grpc-java/badge.svg?branch=master&service=github)](https://coveralls.io/github/grpc/grpc-java?branch=master)

Download
--------

Download [the JARs][]. Or for Maven with non-Android, add to your `pom.xml`:
```xml
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-netty</artifactId>
  <version>1.14.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.14.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.14.0</version>
</dependency>
```

Or for Gradle with non-Android, add to your dependencies:
```gradle
compile 'io.grpc:grpc-netty:1.14.0'
compile 'io.grpc:grpc-protobuf:1.14.0'
compile 'io.grpc:grpc-stub:1.14.0'
```

For Android client, use `grpc-okhttp` instead of `grpc-netty` and
`grpc-protobuf-lite` or `grpc-protobuf-nano` instead of `grpc-protobuf`:
```gradle
compile 'io.grpc:grpc-okhttp:1.14.0'
compile 'io.grpc:grpc-protobuf-lite:1.14.0'
compile 'io.grpc:grpc-stub:1.14.0'
```

[the JARs]:
http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22io.grpc%22%20AND%20v%3A%221.14.0%22

Development snapshots are available in [Sonatypes's snapshot
repository](https://oss.sonatype.org/content/repositories/snapshots/).

For protobuf-based codegen, you can put your proto files in the `src/main/proto`
and `src/test/proto` directories along with an appropriate plugin.

For protobuf-based codegen integrated with the Maven build system, you can use
[protobuf-maven-plugin][] (Eclipse and NetBeans users should also look at
`os-maven-plugin`'s
[IDE documentation](https://github.com/trustin/os-maven-plugin#issues-with-eclipse-m2e-or-other-ides)):
```xml
<build>
  <extensions>
    <extension>
      <groupId>kr.motd.maven</groupId>
      <artifactId>os-maven-plugin</artifactId>
      <version>1.5.0.Final</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>org.xolstice.maven.plugins</groupId>
      <artifactId>protobuf-maven-plugin</artifactId>
      <version>0.5.1</version>
      <configuration>
        <protocArtifact>com.google.protobuf:protoc:3.5.1-1:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.14.0:exe:${os.detected.classifier}</pluginArtifact>
      </configuration>
      <executions>
        <execution>
          <goals>
            <goal>compile</goal>
            <goal>compile-custom</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>
```

[protobuf-maven-plugin]: https://www.xolstice.org/protobuf-maven-plugin/

For protobuf-based codegen integrated with the Gradle build system, you can use
[protobuf-gradle-plugin][]:
```gradle
apply plugin: 'java'
apply plugin: 'com.google.protobuf'

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    // ASSUMES GRADLE 2.12 OR HIGHER. Use plugin version 0.7.5 with earlier
    // gradle versions
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.3'
  }
}

protobuf {
  protoc {
    artifact = "com.google.protobuf:protoc:3.5.1-1"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:1.14.0'
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {}
    }
  }
}
```

[protobuf-gradle-plugin]: https://github.com/google/protobuf-gradle-plugin

How to Build
------------

If you are making changes to gRPC-Java, see the [compiling
instructions](COMPILING.md).

Navigating Around the Source
----------------------------

Here's a quick readers' guide to the code to help folks get started. At a high
level there are three distinct layers to the library: __Stub__, __Channel__ &
__Transport__.

### Stub

The Stub layer is what is exposed to most developers and provides type-safe
bindings to whatever datamodel/IDL/interface you are adapting. gRPC comes with
a [plugin](https://github.com/google/grpc-java/blob/master/compiler) to the
protocol-buffers compiler that generates Stub interfaces out of `.proto` files,
but bindings to other datamodel/IDL should be trivial to add and are welcome.

#### Key Interfaces

[Stream Observer](https://github.com/google/grpc-java/blob/master/stub/src/main/java/io/grpc/stub/StreamObserver.java)

### Channel

The Channel layer is an abstraction over Transport handling that is suitable for
interception/decoration and exposes more behavior to the application than the
Stub layer. It is intended to be easy for application frameworks to use this
layer to address cross-cutting concerns such as logging, monitoring, auth etc.
Flow-control is also exposed at this layer to allow more sophisticated
applications to interact with it directly.

#### Common

* [Metadata - headers & trailers](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/Metadata.java)
* [Status - error code namespace & handling](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/Status.java)

#### Client
* [Channel - client side binding](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/Channel.java)
* [Client Call](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/ClientCall.java)
* [Client Interceptor](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/ClientInterceptor.java)

#### Server
* [Server call handler - analog to Channel on server](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/ServerCallHandler.java)
* [Server Call](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/ServerCall.java)


### Transport

The Transport layer does the heavy lifting of putting and taking bytes off the
wire. The interfaces to it are abstract just enough to allow plugging in of
different implementations. Transports are modeled as `Stream` factories. The
variation in interface between a server Stream and a client Stream exists to
codify their differing semantics for cancellation and error reporting.

Note the transport layer API is considered internal to gRPC and has weaker API
guarantees than the core API under package `io.grpc`.

gRPC comes with three Transport implementations:

1. The [Netty-based](https://github.com/google/grpc-java/blob/master/netty)
   transport is the main transport implementation based on
   [Netty](http://netty.io). It is for both the client and the server.
2. The [OkHttp-based](https://github.com/google/grpc-java/blob/master/okhttp)
   transport is a lightweight transport based on
   [OkHttp](http://square.github.io/okhttp/). It is mainly for use on Android
   and is for client only.
3. The
   [inProcess](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/inprocess)
   transport is for when a server is in the same process as the client. It is
   useful for testing.

#### Common

* [Stream](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/internal/Stream.java)
* [Stream Listener](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/internal/StreamListener.java)

#### Client

* [Client Stream](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/internal/ClientStream.java)
* [Client Stream Listener](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/internal/ClientStreamListener.java)

#### Server

* [Server Stream](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/internal/ServerStream.java)
* [Server Stream Listener](https://github.com/google/grpc-java/blob/master/core/src/main/java/io/grpc/internal/ServerStreamListener.java)


Examples
--------

The [examples](https://github.com/grpc/grpc-java/tree/master/examples)
and the
[Android example](https://github.com/grpc/grpc-java/tree/master/examples/android) are standalone projects that
showcase the usage of gRPC.

Tools
-----

APIs annotated with `@Internal` are for internal use by the gRPC library and
should not be used by gRPC users. APIs annotated with `@ExperimentalApi` are
subject to change in future releases, and library code that other projects
may depend on should not use these APIs. We recommend using the
[grpc-java-api-checker](https://github.com/grpc/grpc-java-api-checker)
(an [Error Prone](https://github.com/google/error-prone) plugin)
to check for usages of `@ExperimentalApi` and `@Internal` in any library code
that depends on gRPC. It may also be used to check for `@Internal` usage or 
unintended `@ExperimentalApi` consumption in non-library code.