Redis introduction complete tutorial: client communication protocol

Almost all mainstream programming languages have Redis The client of （http://redis.io/clients）,
Don't consider Redis The reason why it is very popular , From the perspective of technology, there are two reasons ： The first
One , The communication protocol between client and server is TCP Built on top of the agreement . second ,
Redis Formulated the RESP（REdis Serialization Protocol,Redis Serialization protocol ） Realize customer
The normal interaction between the client and the server , This protocol is simple and efficient , It can be parsed by the machine , It's easy
Recognized by humans . For example, the client sends a message set hello world Give the command to the server , according to RESP
Standards for , The client needs to encapsulate it in the following format （ For each line \r\n Separate ）：
*3
$3
SET
$5
hello
$5
world
such Redis The server can follow RESP It is interpreted as set hello world command , After execution
The format of the reply is as follows ：
+OK
You can see that in addition to the command （set hello world） And return results （OK） It also contains
Some special characters and numbers , These formats will be described below .
1. Send command format
RESP The format of a command is as follows ,CRLF representative "\r\n".
*< The number of arguments > CRLF
$< Parameters 1 Number of bytes > CRLF
< Parameters 1> CRLF
...
$< Parameters N Number of bytes > CRLF
< Parameters N> CRLF
Still in set hell world This command describes .
The number of parameters is 3 individual , So the first act ：
*3
The number of parameter bytes is 355, So the following behaviors ：
$3
SET
$5
hello
$5
world
One thing to note is that , The above is just the result of formatting the display , The actual transmission format is as follows
Code , The whole process is as shown in the figure 4-1 Shown ：
*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n$5\r\nworld\r\n
2. Return the result format
Redis There are five types of returned results , Pictured 4-2 Shown ：
· State the reply ： stay RESP The first byte in the is "+".
· Error response ： stay RESP The first byte in the is "-".
· Integer reply ： stay RESP The first byte in the is "：".
· String reply ： stay RESP The first byte in the is "$".
· Multiple string replies ： stay RESP The first byte in the is "*".

 

We know redis-cli Only the final execution result can be seen , That's because redis-cli Itself is
according to RESP For result analysis , So there is no intermediate result ,redis-cli.c The source code ends with the command
The analytic structure of the fruit is as follows ：
static sds cliFormatReplyTTY(redisReply *r, char *prefix) {
sds out = sdsempty();
switch (r->type) {
case REDIS_REPLY_ERROR:
//   Handle error replies
case REDIS_REPLY_STATUS:
//   Process status reply
case REDIS_REPLY_INTEGER:
//   Handle integer replies
case REDIS_REPLY_STRING:
//   Handle string replies
case REDIS_REPLY_NIL:
//   Processing empty
case REDIS_REPLY_ARRAY:
//   Handle multiple string replies
return out;
}
For example, to perform set hello world, The return is OK, You can't see the plus sign ：
127.0.0.1:6379> set hello world
OK
In order to see Redis Returned by the server “ real ” result , have access to nc command 、telnet life
Make 、 Even write a socket Program simulation . Let's say nc Command to demonstrate , use first
nc127.0.0.16379 Connect to Redis：
nc 127.0.0.1 6379
State the reply ：set hello world The return result of is +OK：
set hello world
+OK
Error response ： because sethx This command does not exist , So the return result is "-" Number plus error
Error message ： 

sethx
-ERR unknown command 'sethx'
Integer reply ： When the execution result of the command is an integer , The result is an integer reply , for example
incr、exists、del、dbsize The returned results are all integers , For example, to perform incr counter Return results
Namely “：” Add an integer ：
incr counter
:1
String reply ： When the execution result of the command is a string , The return result is string return
complex . for example get、hget The returned results are all strings , for example get hello Result
by “$5\r\nworld\r\n”：
get hello
$5
world
Multiple string replies ： When the execution result of the command is multiple strings , The return result is more
String reply . for example mget、hgetall、lrange The command will return multiple results , For example, the following
operation ：
use first mset Set multiple key value pairs ：
mset java jedis python redis-py
+OK
And then execute mget The command returns multiple results , first *2 Represents the number of returned results , Back
The format of is consistent with the string reply ：
mget java python
*2
$5
jedis
$8
redis-py
There is one caveat , Whether it's a string reply or multiple string replies , If there is nil
value , So it will return $-1.
for example , Execute on a nonexistent key get operation , The return result is ：
get not_exist_key
$-1
If a batch operation contains one item, it is nil The result of the value , So the return result is as follows ：
mget hello not_exist_key java
*3
$5
world
$-1
$5
jedis
With RESP The protocol format of sending command and returning result provided , Various programming languages can
To use it to achieve the corresponding Redis client , The following two sections will introduce Java and Python Two programming
Linguistic Redis client .