Redis Communication Protocol Specification

Redis Communication Protocol Specification

Redis is a key-value-based memory-based database. Program Then we know that we can use redis-CLI to connect to redis-server for communication and perform various operations. So how do we use advanced languages such as C, Java, Python, and C # To send a request to operate data and get the relevant data from the database (replies? If you have these questions Article Suitable for you to continue to see PS: the official website has recommended a variety of language client implementation program http://redis.io/clients interested can be analyzed Source code
How to send commands? Socket! Through the socket in the form of TCP protocol, we can connect to the redis-server, and then send some Specific format Command and related data. All commands end with \ r \ n (cr lf)
Special Command? The special format mentioned above is the so-called redis communication protocol, which ensures the specification of the format of the sent command, data, and returned data. In this way, we can correctly send commands to the redis-server, and then parse the returned data (reply data) according to the protocol format to get the desired form.
Protocol specifications: Standard protocol: this protocol has been introduced in redis1.2, but it is only used as a standard way to communicate with redis-server in version 2.0. In this new protocol, all parameters sent to the redis-server are binary safe (to ensure binary security). The basic format is as follows: * <number of parameters> cr lf $ <number of 1 bytes> cr lf <parameter 1> Cr lf... $ <parameter n Bytes> cr lf <parameter n> CR LF
For example, the form corresponding to set mykey myvalue should be as follows, * 3 cr lf // three parameters $3 cr lf // The first parameter set has three bytes set cr lf // parameter content set $5 cr lf // The second parameter mykey has five bytes mykey cr lf // parameter 2 content mykey $7 cr lf // The third parameter has seven bytes myvalue cr lf // parameter 3 content myvalue

The result in string format is:"* 3 \ r \ N $3 \ r \ NSET \ r \ N $5 \ r \ nmykey \ r \ N $7 \ r \ nmyvalue \ r \ n"
 

In fact, the returned data also complies with the Protocol format. For example, $6 \ r \ nmydata \ r \ n is a data returned from redis-server, called block response data, usually a string (there are several other types, later ). In addition, redis can also return a data list, which can return multiple pieces of data (called multiple pieces of data ). The returned results always start with "* Number of parameters \ r \ n". The number of parameters indicates a total of several pieces of data (which can be understood as returning multiple strings)

Response type: Determining the type of a response is determined by the first byte of the returned data. There are several types: "+" Indicates a status information such as + OK "-" Indicates that an error has been sent (for example, the type of operation error) ":" Return an integer, for example, ": 11 \ r \ n. Some commands return integers without any meaning. For example, lastsave returns an integer of the timestamp, and incr returns a value after 1; some commands, such as exists, will return 0 or 1, indicating whether to be true or false; others, such as sadd, Srem returns 1 when the operation is actually executed; otherwise, return 0 "$" Returns a piece of data that is used to return a binary secure string, such as get mykey: "$6 \ r \ nsongzh \ r \ n "; if the requested value does not exist, $-1 is returned. When implementing the client program, you should actually prompt that the user value does not exist and return null "*" Returns multiple pieces of data (used to return multiple values ). , The first byte is always "*", followed by the number of corresponding values, such: C: lrange mylist 0 3 S: * 4 S: $3 S: foo S: $3 S: bar S: $5 $: World If the specified value does not exist, * 0 is returned.