redis client protocol 解析

在官网http://redis.io/topics/protocol有对redis通信协议有做说明。
基于下面的一些原因，我想解析redis client protocol：

1、足够了解通信协议，有助于做出更好的系统设计。

2、学习RESP的设计思想，不仅能扩展我的思维，也许将来能应用于我的代码中。

3、因为有些人想将redis client直接并入自己已有的系统中；包括我在内。这个将在我下一篇文章再做说明。

下面我翻译一下http://redis.io/topics/protocol一些我认为重要的内容：

Redis clients communicate with the Redis server using a protocol called RESP (REdis Serialization Protocol). While the protocol was designed specifically for Redis, it can be used for other client-server software projects.

RESP is a compromise between the following things:

• Simple to implement.
• Fast to parse.
• Human readable.

RESP can serialize different data types like integers, strings, arrays. There is also a specific type for errors. Requests are sent from the client to the Redis server as arrays of strings representing the arguments of the command to execute. Redis replies with a command-specific data type.

RESP is binary-safe and does not require processing of bulk data transferred from one process to another, because it uses prefixed-length to transfer bulk data.

Note: the protocol outlined here is only used for client-server communication. Redis Cluster uses a different binary protocol in order to exchange messages between nodes.

译：

redis客户端和redis服务端用一种名叫RESP(REdis Serialization Protocol)的协议通信。虽然这种协议专门为redis设计，但是它能被用于其它基于C/S模型的软件项目中。

RESP是基于下面一些事实的一种折衷方案：

• 易于实现
• 快速解释
• 人类可读

RESP is actually a serialization protocol that supports the following data types: Simple Strings, Errors, Integers, Bulk Strings and Arrays.

The way RESP is used in Redis as a request-response protocol is the following:

• Clients send commands to a Redis server as a RESP Array of Bulk Strings.
• The server replies with one of the RESP types according to the command implementation.

In RESP, the type of some data depends on the first byte:

• For Simple Strings the first byte of the reply is "+"
• For Errors the first byte of the reply is "-"
• For Integers the first byte of the reply is ":"
• For Bulk Strings the first byte of the reply is "$"
• For Arrays the first byte of the reply is "*"

Additionally RESP is able to represent a Null value using a special variation of Bulk Strings or Array as specified later.

In RESP different parts of the protocol are always terminated with "\r\n" (CRLF).

译：

RESP实际上是一种支持下面数据类型的序列化协议：短字符串，错误，整数，长字符串和数组。

RESP作为一种请求-回应协议，在Redis中的使用方法如下：

• 客户端发送一种犹如RESP中长字符串数组的命令到Redis服务端。
• Redis服务端根据命令实现回复其中一种RESP类型。

在RESP中，一种数据类型基于第一个字节：

• 对于短字符串，回复的第一个字节是"+"
• 对于错误，回复的第一个字节是"-"
• 对于整数，回复的第一个字节是":"
• 对于长字符串，回复的第一个字节是"$"
• 对于数组，回复的第一个字节是"*"

前面说到的协议，我有强调了是client，就是说server回复client请求时用到的协议；client请求server时，只需要在命令后面加上"\r\n"。

下面是5种类型的返回实例：

假设在redis server中存在以下键值对：
name1	cat
age1	10

短字符串
"set name2 fish\r\n"
"+OK\r\n"

错误
"seet name3 dog"
"-ERR unknown command 'seet'\r\n"

整数
"incr age1"
":11"

长字符串
①
"get name1\r\n"
"$3\r\ncat\r\n"
②
"get name3\r\n"
"$-1\r\n"

数组
①
"mget name1 age1\r\n"
"*2\r\n$3\r\ncat\r\n$2\r\n11\r\n"
②
"mget name2 age2\r\n"
"*2\r\n$4\r\nfish\r\n$-1\r\n"
③
其它情况会返回"*-1\r\n"和"*0\r\n",具体参考redis官方文档;

原文：http://blog.csdn.net/yitouhan/article/details/46612925