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
5.7 KiB
109 lines
5.7 KiB
[](https://grpc-testing.appspot.com/job/gRPC_master) |
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[gRPC - An RPC library and framework](http://github.com/grpc/grpc) |
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[](https://gitter.im/grpc/grpc?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) |
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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 [doc](doc) and [examples](examples) directories respectively. |
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# Installation & Testing |
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See [INSTALL](INSTALL.md) for installation instructions for various platforms. |
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See [tools/run_tests](tools/run_tests) for more guidance on how to run various test suites (e.g. unit tests, interop tests, benchmarks) |
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See [Performance dashboard](http://performance-dot-grpc-testing.appspot.com/explore?dashboard=5636470266134528) for the performance numbers for the latest released version. |
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# Repository Structure & Status |
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This repository contains source code for gRPC libraries for multiple languages written on top of shared C core library [src/core](src/core). |
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Libraries in different languages may be in different states of development. We are seeking contributions for all of these libraries. |
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| Language | Source | Status | |
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| Shared C [core library] | [src/core](src/core) | 1.8 | |
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| C++ | [src/cpp](src/cpp) | 1.8 | |
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| Ruby | [src/ruby](src/ruby) | 1.8 | |
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| Python | [src/python](src/python) | 1.8 | |
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| PHP | [src/php](src/php) | 1.8 | |
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| C# | [src/csharp](src/csharp) | 1.8 | |
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| Objective-C | [src/objective-c](src/objective-c) | 1.8 | |
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Java source code is in the [grpc-java](http://github.com/grpc/grpc-java) |
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repository. Go source code is in the |
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[grpc-go](http://github.com/grpc/grpc-go) repository. NodeJS source code is in the |
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[grpc-node](https://github.com/grpc/grpc-node) repository. |
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See [MANIFEST.md](MANIFEST.md) for a listing of top-level items in the |
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repository. |
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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](doc/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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