README.md

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

[![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)

gRPC-Java works with JDK 6. TLS usage typically requires using Java 8, or Play
Services Dynamic Security Provider on Android. Please see the [Security
Readme](SECURITY.md).

Download
--------

Download [the JAR][]. Or for Maven, add to your `pom.xml`:
```xml
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-all</artifactId>
  <version>0.7.1</version>
</dependency>
```

Or for Gradle, add to your dependencies:
```gradle
compile 'io.grpc:grpc-all:0.7.1'
```

[the JAR]: https://search.maven.org/remote_content?g=io.grpc&a=grpc-all&v=0.7.1

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

For protobuf-based codegen integrated with the Maven build system, you can use
[maven-protoc-plugin][]:
```xml
<pluginRepositories>
  <pluginRepository>
    <releases>
      <updatePolicy>never</updatePolicy>
    </releases>
    <snapshots>
      <enabled>false</enabled>
    </snapshots>
    <id>central</id>
    <name>Central Repository</name>
    <url>https://repo.maven.apache.org/maven2</url>
  </pluginRepository>
  <pluginRepository>
    <id>protoc-plugin</id>
    <url>https://dl.bintray.com/sergei-ivanov/maven/</url>
  </pluginRepository>
</pluginRepositories>
<build>
  <extensions>
    <extension>
      <groupId>kr.motd.maven</groupId>
      <artifactId>os-maven-plugin</artifactId>
      <version>1.2.3.Final</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>com.google.protobuf.tools</groupId>
      <artifactId>maven-protoc-plugin</artifactId>
      <version>0.4.2</version>
      <configuration>
        <!--
          The version of protoc must match protobuf-java. If you don't depend on
          protobuf-java directly, you will be transitively depending on the
          protobuf-java version that grpc depends on.
        -->
        <protocArtifact>com.google.protobuf:protoc:3.0.0-alpha-2:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:0.7.1:exe:${os.detected.classifier}</pluginArtifact>
      </configuration>
      <executions>
        <execution>
          <goals>
            <goal>compile</goal>
            <goal>compile-custom</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>
```

[maven-protoc-plugin]: http://sergei-ivanov.github.io/maven-protoc-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 {
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.6.1'
  }
}

protobuf {
  protoc {
    // The version of protoc must match protobuf-java. If you don't depend on
    // protobuf-java directly, you will be transitively depending on the
    // protobuf-java version that grpc depends on.
    artifact = "com.google.protobuf:protoc:3.0.0-alpha-2"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:0.7.1'
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {}
    }
  }
}
```

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

How to Build
------------
This section is only necessary if you are making changes to gRPC-Java.

Building requires JDK 8, as our tests use TLS.

grpc-java has a C++ code generation plugin for protoc. Since many Java
developers don't have C compilers installed and don't need to modify the
codegen, the build can skip it. To skip, create the file
`<project-root>/gradle.properties` and add `skipCodegen=true`.

Then, to build, run:
```
$ ./gradlew build
```

To install the artifacts to your Maven local repository for use in your own
project, run:
```
$ ./gradlew install
```

How to Build Code Generation Plugin
-----------------------------------
This section is only necessary if you are making changes to the code
generation. Most users only need to use `skipCodegen=true` as discussed above.

### Build Protobuf
The codegen plugin is C++ code and requires protobuf 3.0.0-alpha-3.1.

For Linux, Mac and MinGW:
```
$ git clone https://github.com/google/protobuf.git
$ cd protobuf
$ git checkout v3.0.0-alpha-3.1
$ ./autogen.sh
$ ./configure
$ make
$ make check
$ sudo make install
```

If you are comfortable with C++ compilation and autotools, you can specify a
``--prefix`` for Protobuf and use ``-I`` in ``CXXFLAGS``, ``-L`` in
``LDFLAGS``, ``LD_LIBRARY_PATH``, and ``PATH`` to reference it. The
environment variables will be used when building grpc-java.

Protobuf installs to ``/usr/local`` by default.

For Visual C++, please refer to the [Protobuf README](https://github.com/google/protobuf/blob/master/vsprojects/readme.txt)
for how to compile Protobuf.

#### Linux and MinGW
If ``/usr/local/lib`` is not in your library search path, you can add it by running:
```
$ sudo sh -c 'echo /usr/local/lib >> /etc/ld.so.conf'
$ sudo ldconfig
```

#### Mac
Some versions of Mac OS X (e.g., 10.10) doesn't have ``/usr/local`` in the
default search paths for header files and libraries. It will fail the build of
the codegen. To work around this, you will need to set environment variables:
```
$ export CXXFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib"
```

### Notes for Visual C++

When building on Windows and VC++, you need to specify project properties for
Gradle to find protobuf:
```
.\gradlew install ^
    -PvcProtobufInclude=C:\path\to\protobuf-3.0.0-alpha-3.1\src ^
    -PvcProtobufLibs=C:\path\to\protobuf-3.0.0-alpha-3.1\vsprojects\Release
```

Since specifying those properties every build is bothersome, you can instead
create ``<project-root>\gradle.properties`` with contents like:
```
vcProtobufInclude=C:\\path\\to\\protobuf-3.0.0-alpha-3.1\\src
vcProtobufLibs=C:\\path\\to\\protobuf-3.0.0-alpha-3.1\\vsprojects\\Release
```

The build script will build the codegen for the same architecture as the Java
runtime installed on your system. If you are using 64-bit JVM, the codegen will
be compiled for 64-bit, that means you must have compiled Protobuf in 64-bit.

### Notes for MinGW on Windows
If you have both MinGW and VC++ installed on Windows, VC++ will be used by
default. To override this default and use MinGW, add ``-PvcDisable=true``
to your Gradle command line or add ``vcDisable=true`` to your
``<project-root>\gradle.properties``.

### Notes for Unsupported Operating Systems
The build script pulls pre-compiled ``protoc`` from Maven Central by default.
We have built ``protoc`` binaries for popular systems, but they may not work
for your system. If ``protoc`` cannot be downloaded or would not run, you can
use the one that has been built by your own, by adding this property to
``<project-root>/gradle.properties``:
```
protoc=/path/to/protoc
```

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

#### Client

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

#### Server

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


### Examples

Tests showing how these layers are composed to execute calls using protobuf
messages can be found here
https://github.com/google/grpc-java/tree/master/interop-testing/src/main/java/io/grpc/testing/integration