mirror of https://github.com/grpc/grpc.git
The C based gRPC (C++, Python, Ruby, Objective-C, PHP, C#)
https://grpc.io/
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109 lines
5.4 KiB
109 lines
5.4 KiB
[](https://travis-ci.org/grpc/grpc) |
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[](https://coveralls.io/r/grpc/grpc?branch=master) |
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[gRPC - An RPC library and framework](http://github.com/grpc/grpc) |
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Copyright 2015 Google Inc. |
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#Documentation |
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You can find more detailed documentation and examples in the [grpc-common repository](http://github.com/grpc/grpc-common). |
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#Installation |
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See grpc/INSTALL for installation instructions for various platforms. |
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#Repository Structure |
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This repository contains source code for gRPC libraries for multiple languages written on top |
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of shared C core library [src/core] (src/core). |
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* C++ source code: [src/cpp] (src/cpp) |
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* Ruby source code: [src/ruby] (src/ruby) |
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* NodeJS source code: [src/node] (src/node) |
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* Python source code: [src/python] (src/python) |
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* PHP source code: [src/php] (src/php) |
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* C# source code: [src/csharp] (src/csharp) |
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* Objective-C source code: [src/objective-c] (src/objective-c) |
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Java source code is in [grpc-java] (http://github.com/grpc/grpc-java) repository. |
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Go source code is in [grpc-go] (http://github.com/grpc/grpc-go) repository. |
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#Current Status of libraries |
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Libraries in different languages are in different state of development. We are seeking contributions for all of these libraries. |
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* shared C core library [src/core] (src/core) : Early adopter ready - Alpha. |
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* C++ Library: [src/cpp] (src/cpp) : Early adopter ready - Alpha. |
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* Ruby Library: [src/ruby] (src/ruby) : Early adopter ready - Alpha. |
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* NodeJS Library: [src/node] (src/node) : Early adopter ready - Alpha. |
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* Python Library: [src/python] (src/python) : Early adopter ready - Alpha. |
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* PHP Library: [src/php] (src/php) : Pre-Alpha. |
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* C# Library: [src/csharp] (src/csharp) : Pre-Alpha. |
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* Objective-C Library: [src/objective-c] (src/objective-c): Pre-Alpha. |
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#Overview |
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Remote Procedure Calls (RPCs) provide a useful abstraction for building |
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distributed applications and services. The libraries in this repository |
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provide a concrete implementation of the gRPC protocol, layered over HTTP/2. |
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These libraries enable communication between clients and servers using any |
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combination of the supported languages. |
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##Interface |
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Developers using gRPC typically start with the description of an RPC service |
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(a collection of methods), and generate client and server side interfaces |
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which they use on the client-side and implement on the server side. |
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By default, gRPC uses [Protocol Buffers](https://github.com/google/protobuf) as the |
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Interface Definition Language (IDL) for describing both the service interface |
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and the structure of the payload messages. It is possible to use other |
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alternatives if desired. |
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###Surface API |
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Starting from an interface definition in a .proto file, gRPC provides |
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Protocol Compiler plugins that generate Client- and Server-side APIs. |
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gRPC users typically call into these APIs on the Client side and implement |
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the corresponding API on the server side. |
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#### Synchronous vs. asynchronous |
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Synchronous RPC calls, that block until a response arrives from the server, are |
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the closest approximation to the abstraction of a procedure call that RPC |
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aspires to. |
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On the other hand, networks are inherently asynchronous and in many scenarios, |
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it is desirable to have the ability to start RPCs without blocking the current |
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thread. |
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The gRPC programming surface in most languages comes in both synchronous and |
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asynchronous flavors. |
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## Streaming |
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gRPC supports streaming semantics, where either the client or the server (or both) |
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send a stream of messages on a single RPC call. The most general case is |
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Bidirectional Streaming where a single gRPC call establishes a stream where both |
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the client and the server can send a stream of messages to each other. The streamed |
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messages are delivered in the order they were sent. |
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#Protocol |
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The [gRPC protocol](https://github.com/grpc/grpc-common/blob/master/PROTOCOL-HTTP2.md) specifies the abstract requirements for communication between |
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clients and servers. A concrete embedding over HTTP/2 completes the picture by |
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fleshing out the details of each of the required operations. |
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## Abstract gRPC protocol |
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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`). |
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## Implementation over HTTP/2 |
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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). |
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## Flow Control |
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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.
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