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Go实现Redis协议解析器

Redis网络协议详解

在解决完通信后，下一步就是搞清楚 Redis 的协议-RESP协议，其实就是一套类似JSON、Protocol Buffers的序列化协议，也就是我们的客户端和服务端通信的协议

RESP定义了5种格式

• 简单字符串(Simple String) : 服务器用来返回简单的结果，以"+"开头，"\r\n"结尾的字符串形式，比如 "+OK\r\n" 
• 错误信息(Error) : 服务器用来返回简单的错误信息，以"-"开头，"\r\n"结尾的字符串形式，比如 "-ERR message\r\n" 
• 整数(Integer) : 服务器端和客户端用来互相通信的格式，以":"开头，"\r\n"结尾的字符串形式，比如":123456\r\n"
• 字符串(Bulk String) : 以"$"开头，后跟实际发送字节数，以"\r\n"结尾，比如"$3\r\nSET\r\n",空字符串"$0\r\n\r\n"，"$9\r\nLBJ\r\nAD"
• 数组(Array) : 以*开头,后跟成员个数，比如"*3\r\n$3\r\nSET\r\n$3\r\nkey\r\n$5\r\nvalue\r\n"

实现RESP协议

创建两个resp协议接口，首先是conn.go，这个接口是在Redis协议层代表客户端的连接，里面定义3个方法，分别是：Write()用来给客户端回复消息；GetDBIndex()用来查询客户端用的哪个DB；SelectDB()用来切换Redis间的库

type Connection interface {Write([]byte) errorGetDBIndex() intSelectDB(int)
}

然后是reply.go，这个接口是代表各种客户端对服务端数据的回复，他是用来把回复的内容转成字节，因为TCP协议来回写就是写字节

type Reply interface {ToBytes() []byte
}

接下来就是RESP协议的实现，在resp文件夹里实现各种服务端对客户端的回复

consts.go 固定正常回复

type PongReply struct{}
var pongBytes = []byte("+PONG\r\n")
func (r *PongReply) ToBytes() []byte {return pongBytes
}
func MakePangReply() *PongReply {return &PongReply{}
}type OkReply struct{}
var okBytes = []byte("+OK\r\n")
func (r *OkReply) ToBytes() []byte {return okBytes
}
//回复常量，节约内存
var theOkReply = new(OkReply)
func MakeOkReply() *OkReply {return theOkReply
}//空字符串 null
var nullBulkBytes = []byte("$-1\r\n")
type NullBulkReply struct{}
func (r *NullBulkReply) ToBytes() []byte {return nullBulkBytes
}
func MakeNullBulkReply() *NullBulkReply {return &NullBulkReply{}
}//空数组
var emptyMultiBulkBytes = []byte("*0\r\n")
type EmptyMultiBulkReply struct{}
func (r *EmptyMultiBulkReply) ToBytes() []byte {return emptyMultiBulkBytes
}
func MakeEmptyMultiBulkReply() *EmptyMultiBulkReply {return &EmptyMultiBulkReply{}
}type NoReply struct{}
var noBytes = []byte("")
func (r *NoReply) ToBytes() []byte {return noBytes
}

然后是创建一个reply.go接口承载错误回复，其中Error()是系统的错误方法

type ErrorReply interface {Error() stringToBytes() []byte
}

error.go 固定异常回复

type UnknownErrReply struct{}
var unknownErrBytes = []byte("-Err unknown\r\n")
func (r *UnknownErrReply) ToBytes() []byte {return unknownErrBytes
}
func (r *UnknownErrReply) Error() string {return "Err unknown"
}// ArgNumErrReply represents wrong number of arguments for command
type ArgNumErrReply struct {Cmd string
}
func (r *ArgNumErrReply) ToBytes() []byte {return []byte("-ERR wrong number of arguments for '" + r.Cmd + "' command\r\n")
}
func (r *ArgNumErrReply) Error() string {return "ERR wrong number of arguments for '" + r.Cmd + "' command"
}
func MakeArgNumErrReply(cmd string) *ArgNumErrReply {return &ArgNumErrReply{Cmd: cmd,}
}// SyntaxErrReply represents meeting unexpected arguments
type SyntaxErrReply struct{}
var syntaxErrBytes = []byte("-Err syntax error\r\n")
var theSyntaxErrReply = &SyntaxErrReply{}
func MakeSyntaxErrReply() *SyntaxErrReply {return theSyntaxErrReply
}
func (r *SyntaxErrReply) ToBytes() []byte {return syntaxErrBytes
}
func (r *SyntaxErrReply) Error() string {return "Err syntax error"
}// WrongTypeErrReply represents operation against a key holding the wrong kind of value
type WrongTypeErrReply struct{}
var wrongTypeErrBytes = []byte("-WRONGTYPE Operation against a key holding the wrong kind of value\r\n")
func (r *WrongTypeErrReply) ToBytes() []byte {return wrongTypeErrBytes
}
func (r *WrongTypeErrReply) Error() string {return "WRONGTYPE Operation against a key holding the wrong kind of value"
}// ProtocolErrReply represents meeting unexpected byte during parse requests
type ProtocolErrReply struct {Msg string
}
func (r *ProtocolErrReply) ToBytes() []byte {