[![Build Status](https://grpc-testing.appspot.com/job/gRPC_master/badge/icon)](https://grpc-testing.appspot.com/job/gRPC_master) [gRPC - An RPC library and framework](http://github.com/grpc/grpc) =================================== [![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) Copyright 2015 Google Inc. #Documentation You can find more detailed documentation and examples in the [doc](doc) and [examples](examples) directories respectively. #Installation & Testing See [INSTALL](INSTALL.md) for installation instructions for various platforms. See [tools/run_tests](tools/run_tests) for more guidance on how to run various test suites (e.g. unit tests, interop tests, benchmarks) See [Performance dashboard](http://performance-dot-grpc-testing.appspot.com/explore?dashboard=5712453606309888) for the performance numbers for v1.0.x. #Repository Structure & Status This repository contains source code for gRPC libraries for multiple languages written on top of shared C core library [src/core] (src/core). Libraries in different languages may be in different states of development. We are seeking contributions for all of these libraries. | Language | Source | Status | |-------------------------|-------------------------------------|---------| | Shared C [core library] | [src/core] (src/core) | 1.0 | | C++ | [src/cpp] (src/cpp) | 1.0 | | Ruby | [src/ruby] (src/ruby) | 1.0 | | NodeJS | [src/node] (src/node) | 1.0 | | Python | [src/python] (src/python) | 1.0 | | PHP | [src/php] (src/php) | 1.0 | | C# | [src/csharp] (src/csharp) | 1.0 | | Objective-C | [src/objective-c] (src/objective-c) | 1.0 | <small> Java source code is in the [grpc-java] (http://github.com/grpc/grpc-java) repository. Go source code is in the [grpc-go] (http://github.com/grpc/grpc-go) repository. </small> See [MANIFEST.md](MANIFEST.md) for a listing of top-level items in the repository. #Overview Remote Procedure Calls (RPCs) provide a useful abstraction for building distributed applications and services. The libraries in this repository provide a concrete implementation of the gRPC protocol, layered over HTTP/2. These libraries enable communication between clients and servers using any combination of the supported languages. ##Interface Developers using gRPC typically start with the description of an RPC service (a collection of methods), and generate client and server side interfaces which they use on the client-side and implement on the server side. By default, gRPC uses [Protocol Buffers](https://github.com/google/protobuf) as the Interface Definition Language (IDL) for describing both the service interface and the structure of the payload messages. It is possible to use other alternatives if desired. ###Surface API Starting from an interface definition in a .proto file, gRPC provides Protocol Compiler plugins that generate Client- and Server-side APIs. gRPC users typically call into these APIs on the Client side and implement the corresponding API on the server side. #### Synchronous vs. asynchronous Synchronous RPC calls, that block until a response arrives from the server, are the closest approximation to the abstraction of a procedure call that RPC aspires to. On the other hand, networks are inherently asynchronous and in many scenarios, it is desirable to have the ability to start RPCs without blocking the current thread. The gRPC programming surface in most languages comes in both synchronous and asynchronous flavors. ## Streaming gRPC supports streaming semantics, where either the client or the server (or both) send a stream of messages on a single RPC call. The most general case is Bidirectional Streaming where a single gRPC call establishes a stream where both the client and the server can send a stream of messages to each other. The streamed messages are delivered in the order they were sent. #Protocol The [gRPC protocol](doc/PROTOCOL-HTTP2.md) specifies the abstract requirements for communication between clients and servers. A concrete embedding over HTTP/2 completes the picture by fleshing out the details of each of the required operations. ## Abstract gRPC protocol A gRPC RPC comprises of a bidirectional stream of messages, initiated by the client. In the client-to-server direction, this stream begins with a mandatory `Call Header`, followed by optional `Initial-Metadata`, followed by zero or more `Payload Messages`. The server-to-client direction contains an optional `Initial-Metadata`, followed by zero or more `Payload Messages` terminated with a mandatory `Status` and optional `Status-Metadata` (a.k.a.,`Trailing-Metadata`). ## Implementation over HTTP/2 The abstract protocol defined above is implemented over [HTTP/2](https://http2.github.io/). gRPC bidirectional streams are mapped to HTTP/2 streams. The contents of `Call Header` and `Initial Metadata` are sent as HTTP/2 headers and subject to HPACK compression. `Payload Messages` are serialized into a byte stream of length prefixed gRPC frames which are then fragmented into HTTP/2 frames at the sender and reassembled at the receiver. `Status` and `Trailing-Metadata` are sent as HTTP/2 trailing headers (a.k.a., trailers). ## Flow Control gRPC inherits the flow control mechanisms in HTTP/2 and uses them to enable fine-grained control of the amount of memory used for buffering in-flight messages.