基於Golang實現Redis協定解析器

2023-03-25 06:01:55

本文實現Redis的協定層，協定層負責解析指令，然後將指令交給核心database執行

echo database用來測試協定層的程式碼

https://github.com/csgopher/go-redis

RESP協定

RESP是使用者端與伺服器端通訊的協定，格式有五種：

正常回復：以“+”開頭，以“rn”結尾的字串形式

錯誤回覆：以“-”開頭，以“rn”結尾的字串形式

整數：以“:”開頭，以“rn”結尾的字串形式

多行字串：以“$”開頭，後跟實際傳送位元組數，再以“rn”開頭和結尾

$3rnabcrn

陣列：以“*”開頭，後跟成員個數

SET key value
*3rn$3rnSETrn$3rnkeyrn$5rnvaluern

使用者端和伺服器傳送的命令或資料一律以 rn （CRLF）作為換行符。

當我們輸入*3rn$3rnSETrn$3rnkeyrn$5rnvaluern這樣一串命令，伺服器端接收到的是如下的命令：
*3rn
$3rn
SETrn
$3rn
keyrn
$5rn
valuern

interface/resp/conn.go

type Connection interface {
   Write([]byte) error
   GetDBIndex() int
   SelectDB(int)
}

interface/resp/reply.go
type Reply interface {
	ToBytes() []byte
}

Connection介面：Redis使用者端的一個連線
Write：給使用者端回覆訊息
GetDBIndex：Redis有16個DB
Reply介面：響應介面

resp/reply/consts.go

type PongReply struct{}

var pongBytes = []byte("+PONGrn")

func (r *PongReply) ToBytes() []byte {
    return pongBytes
}

var thePongReply = new(PongReply)

func MakePongReply() *PongReply {
    return thePongReply
}

type OkReply struct{}

var okBytes = []byte("+OKrn")

func (r *OkReply) ToBytes() []byte {
    return okBytes
}

var theOkReply = new(OkReply)

func MakeOkReply() *OkReply {
    return theOkReply
}

var nullBulkBytes = []byte("$-1rn")

type NullBulkReply struct{}

func (r *NullBulkReply) ToBytes() []byte {
    return nullBulkBytes
}

func MakeNullBulkReply() *NullBulkReply {
    return &NullBulkReply{}
}

var emptyMultiBulkBytes = []byte("*0rn")

type EmptyMultiBulkReply struct{}

func (r *EmptyMultiBulkReply) ToBytes() []byte {
    return emptyMultiBulkBytes
}

type NoReply struct{}

var noBytes = []byte("")

func (r *NoReply) ToBytes() []byte {
    return noBytes
}

定義五種回覆：回覆pong，ok，null，空陣列，空

resp/reply/reply.go

type ErrorReply interface {
   Error() string
   ToBytes() []byte
}

ErrorReply：定義錯誤介面

resp/reply/errors.go

type UnknownErrReply struct{}

var unknownErrBytes = []byte("-Err unknownrn")

func (r *UnknownErrReply) ToBytes() []byte {
   return unknownErrBytes
}

func (r *UnknownErrReply) Error() string {
   return "Err unknown"
}

type ArgNumErrReply struct {
   Cmd string
}

func (r *ArgNumErrReply) ToBytes() []byte {
   return []byte("-ERR wrong number of arguments for '" + r.Cmd + "' commandrn")
}

func (r *ArgNumErrReply) Error() string {
   return "ERR wrong number of arguments for '" + r.Cmd + "' command"
}

func MakeArgNumErrReply(cmd string) *ArgNumErrReply {
   return &ArgNumErrReply{
      Cmd: cmd,
   }
}

type SyntaxErrReply struct{}

var syntaxErrBytes = []byte("-Err syntax errorrn")
var theSyntaxErrReply = &SyntaxErrReply{}

func MakeSyntaxErrReply() *SyntaxErrReply {
   return theSyntaxErrReply
}

func (r *SyntaxErrReply) ToBytes() []byte {
   return syntaxErrBytes
}

func (r *SyntaxErrReply) Error() string {
   return "Err syntax error"
}

type WrongTypeErrReply struct{}

var wrongTypeErrBytes = []byte("-WRONGTYPE Operation against a key holding the wrong kind of valuern")

func (r *WrongTypeErrReply) ToBytes() []byte {
   return wrongTypeErrBytes
}

func (r *WrongTypeErrReply) Error() string {
   return "WRONGTYPE Operation against a key holding the wrong kind of value"
}

type ProtocolErrReply struct {
   Msg string
}

func (r *ProtocolErrReply) ToBytes() []byte {
   return []byte("-ERR Protocol error: '" + r.Msg + "'rn")
}

func (r *ProtocolErrReply) Error() string {
   return "ERR Protocol error: '" + r.Msg
}

errors定義5種錯誤：UnknownErrReply 未知錯誤，ArgNumErrReply 引數個數錯誤，SyntaxErrReply 語法錯誤，WrongTypeErrReply 資料型別錯誤，ProtocolErrReply 協定錯誤

resp/reply/reply.go

var (
   nullBulkReplyBytes = []byte("$-1")
   // 協定的結尾
   CRLF = "rn"
)

type BulkReply struct {
   Arg []byte
}

func MakeBulkReply(arg []byte) *BulkReply {
   return &BulkReply{
      Arg: arg,
   }
}

func (r *BulkReply) ToBytes() []byte {
   if len(r.Arg) == 0 {
      return nullBulkReplyBytes
   }
   return []byte("$" + strconv.Itoa(len(r.Arg)) + CRLF + string(r.Arg) + CRLF)
}

type MultiBulkReply struct {
   Args [][]byte
}

func (r *MultiBulkReply) ToBytes() []byte {
   argLen := len(r.Args)
   var buf bytes.Buffer
   buf.WriteString("*" + strconv.Itoa(argLen) + CRLF)
   for _, arg := range r.Args {
      if arg == nil {
         buf.WriteString("$-1" + CRLF)
      } else {
         buf.WriteString("$" + strconv.Itoa(len(arg)) + CRLF + string(arg) + CRLF)
      }
   }
   return buf.Bytes()
}

func MakeMultiBulkReply(args [][]byte) *MultiBulkReply {
   return &MultiBulkReply{
      Args: args,
   }
}

type StatusReply struct {
   Status string
}

func MakeStatusReply(status string) *StatusReply {
   return &StatusReply{
      Status: status,
   }
}

func (r *StatusReply) ToBytes() []byte {
   return []byte("+" + r.Status + CRLF)
}

type IntReply struct {
   Code int64
}

func MakeIntReply(code int64) *IntReply {
   return &IntReply{
      Code: code,
   }
}

func (r *IntReply) ToBytes() []byte {
   return []byte(":" + strconv.FormatInt(r.Code, 10) + CRLF)
}

type StandardErrReply struct {
   Status string
}

func (r *StandardErrReply) ToBytes() []byte {
   return []byte("-" + r.Status + CRLF)
}

func (r *StandardErrReply) Error() string {
   return r.Status
}

func MakeErrReply(status string) *StandardErrReply {
   return &StandardErrReply{
      Status: status,
   }
}

func IsErrorReply(reply resp.Reply) bool {
   return reply.ToBytes()[0] == '-'
}

BulkReply：回覆一個字串
MultiBulkReply：回覆字串陣列
StatusReply：狀態回覆
IntReply：數位回覆
StandardErrReply：標準錯誤回覆
IsErrorReply：判斷是否為錯誤回覆
ToBytes：將字串轉成RESP協定規定的格式

resp/parser/parser.go

type Payload struct {
   Data resp.Reply
   Err  error
}

type readState struct {
   readingMultiLine  bool     
   expectedArgsCount int     
   msgType           byte    
   args              [][]byte 
   bulkLen           int64    
}

func (s *readState) finished() bool {
   return s.expectedArgsCount > 0 && len(s.args) == s.expectedArgsCount
}

func ParseStream(reader io.Reader) <-chan *Payload {
   ch := make(chan *Payload)
   go parse0(reader, ch)
   return ch
}

func parse0(reader io.Reader, ch chan<- *Payload) {
	 ......
}

Payload結構體：客服端給我們發的資料

Reply：使用者端與伺服器端互相發的資料都稱為Reply

readState結構體：

readingMultiLine：解析單行還是多行資料
expectedArgsCount：應該讀取的引數個數
msgType：訊息型別
args：訊息內容
bulkLen：資料長度

finished方法：判斷解析是否完成

ParseStream方法：非同步解析資料後放入管道，返回管道資料

func readLine(bufReader *bufio.Reader, state *readState) ([]byte, bool, error) {
   var msg []byte
   var err error
   if state.bulkLen == 0 {
      msg, err = bufReader.ReadBytes('n')
      if err != nil {
         return nil, true, err
      }
      if len(msg) == 0 || msg[len(msg)-2] != 'r' {
         return nil, false, errors.New("protocol error: " + string(msg))
      }
   } else {
      msg = make([]byte, state.bulkLen+2)
      _, err = io.ReadFull(bufReader, msg)
      if err != nil {
         return nil, true, err
      }
      if len(msg) == 0 || msg[len(msg)-2] != 'r' || msg[len(msg)-1] != 'n' {
         return nil, false, errors.New("protocol error: " + string(msg))
      }
      state.bulkLen = 0
   }
   return msg, false, nil
}

readLine：一行一行的讀取。讀正常的行，以n分隔。讀正文中包含rn字元的行時，state.bulkLen加上換行符rn（state.bulkLen+2）

func parseMultiBulkHeader(msg []byte, state *readState) error {
   var err error
   var expectedLine uint64
   expectedLine, err = strconv.ParseUint(string(msg[1:len(msg)-2]), 10, 32)
   if err != nil {
      return errors.New("protocol error: " + string(msg))
   }
   if expectedLine == 0 {
      state.expectedArgsCount = 0
      return nil
   } else if expectedLine > 0 {
      state.msgType = msg[0]
      state.readingMultiLine = true
      state.expectedArgsCount = int(expectedLine)
      state.args = make([][]byte, 0, expectedLine)
      return nil
   } else {
      return errors.New("protocol error: " + string(msg))
   }
}

func parseBulkHeader(msg []byte, state *readState) error {
   var err error
   state.bulkLen, err = strconv.ParseInt(string(msg[1:len(msg)-2]), 10, 64)
   if err != nil {
      return errors.New("protocol error: " + string(msg))
   }
   if state.bulkLen == -1 { // null bulk
      return nil
   } else if state.bulkLen > 0 {
      state.msgType = msg[0]
      state.readingMultiLine = true
      state.expectedArgsCount = 1
      state.args = make([][]byte, 0, 1)
      return nil
   } else {
      return errors.New("protocol error: " + string(msg))
   }
}

parseMultiBulkHeader：解析陣列的頭部，設定期望的行數和相關引數。

parseBulkHeader：解析多行字串的頭部。

func parseSingleLineReply(msg []byte) (resp.Reply, error) {
   str := strings.TrimSuffix(string(msg), "rn")
   var result resp.Reply
   switch msg[0] {
   case '+': // status reply
      result = reply.MakeStatusReply(str[1:])
   case '-': // err reply
      result = reply.MakeErrReply(str[1:])
   case ':': // int reply
      val, err := strconv.ParseInt(str[1:], 10, 64)
      if err != nil {
         return nil, errors.New("protocol error: " + string(msg))
      }
      result = reply.MakeIntReply(val)
   }
   return result, nil
}

func readBody(msg []byte, state *readState) error {
   line := msg[0 : len(msg)-2]
   var err error
   if line[0] == '$' {
      // bulk reply
      state.bulkLen, err = strconv.ParseInt(string(line[1:]), 10, 64)
      if err != nil {
         return errors.New("protocol error: " + string(msg))
      }
      if state.bulkLen <= 0 { // null bulk in multi bulks
         state.args = append(state.args, []byte{})
         state.bulkLen = 0
      }
   } else {
      state.args = append(state.args, line)
   }
   return nil
}

parseSingleLineReply：解析單行命令

readBody：讀取多行的命令，如果是$開頭，設定bulkLen，讀取下一行時根據這個+2，不是$開頭則直接新增到args

func parse0(reader io.Reader, ch chan<- *Payload) {
    defer func() {
       if err := recover(); err != nil {
          logger.Error(string(debug.Stack()))
      }
   }()
    bufReader := bufio.NewReader(reader)
    var state readState
    var err error
    var msg []byte
    for {
       var ioErr bool
       msg, ioErr, err = readLine(bufReader, &state)
       if err != nil {
          if ioErr {
             ch <- &Payload{
                Err: err,
            }
             close(ch)
             return
         }
          ch <- &Payload{
             Err: err,
         }
          state = readState{}
          continue
      }

       if !state.readingMultiLine {
          if msg[0] == '*' {
             // multi bulk reply
             err = parseMultiBulkHeader(msg, &state)
             if err != nil {
                ch <- &Payload{
                   Err: errors.New("protocol error: " + string(msg)),
               }
                state = readState{}
                continue
            }
             if state.expectedArgsCount == 0 {
                ch <- &Payload{
                   Data: &reply.EmptyMultiBulkReply{},
               }
                state = readState{}
                continue
            }
         } else if msg[0] == '$' { // bulk reply
             err = parseBulkHeader(msg, &state)
             if err != nil {
                ch <- &Payload{
                   Err: errors.New("protocol error: " + string(msg)),
               }
                state = readState{} // reset state
                continue
            }
             if state.bulkLen == -1 { // null bulk reply
                ch <- &Payload{
                   Data: &reply.NullBulkReply{},
               }
                state = readState{} // reset state
                continue
            }
         } else {
             // single line reply
             result, err := parseSingleLineReply(msg)
             ch <- &Payload{
                Data: result,
                Err:  err,
            }
             state = readState{} // reset state
             continue
         }
      } else {
          // read bulk reply
          err = readBody(msg, &state)
          if err != nil {
             ch <- &Payload{
                Err: errors.New("protocol error: " + string(msg)),
            }
             state = readState{} // reset state
             continue
         }
          // if sending finished
          if state.finished() {
             var result resp.Reply
             if state.msgType == '*' {
                result = reply.MakeMultiBulkReply(state.args)
            } else if state.msgType == '$' {
                result = reply.MakeBulkReply(state.args[0])
            }
             ch <- &Payload{
                Data: result,
                Err:  err,
            }
             state = readState{}
         }
      }
   }
}

parse0：解析指令，解析完成後通過channel發出去

resp/connection/conn.go

type Connection struct {
    conn net.Conn
    waitingReply wait.Wait
    mu sync.Mutex // 避免多個協程往使用者端中寫
    selectedDB int
}

func NewConn(conn net.Conn) *Connection {
    return &Connection{
        conn: conn,
    }
}

func (c *Connection) RemoteAddr() net.Addr {
    return c.conn.RemoteAddr()
}

func (c *Connection) Close() error {
    c.waitingReply.WaitWithTimeout(10 * time.Second)
    _ = c.conn.Close()
    return nil
}

func (c *Connection) Write(b []byte) error {
    if len(b) == 0 {
        return nil
    }
    c.mu.Lock()
    c.waitingReply.Add(1)
    defer func() {
        c.waitingReply.Done()
        c.mu.Unlock()
    }()

    _, err := c.conn.Write(b)
    return err
}

func (c *Connection) GetDBIndex() int {
    return c.selectedDB
}

func (c *Connection) SelectDB(dbNum int) {
    c.selectedDB = dbNum
}

之前寫的EchoHandler是使用者傳過來什麼，我們傳回去什麼。現在要寫一個RespHandler來代替EchoHandler，讓解析器來解析。RespHandler中要有一個管理使用者端連線的結構體Connection。

Connection：使用者端連線，在協定層的handler中會用到

resp/handler/handler.go

var (
   unknownErrReplyBytes = []byte("-ERR unknownrn")
)

type RespHandler struct {
   activeConn sync.Map
   db         databaseface.Database
   closing    atomic.Boolean
}

func MakeHandler() *RespHandler {
   var db databaseface.Database
   db = database.NewEchoDatabase()
   return &RespHandler{
      db: db,
   }
}

func (h *RespHandler) closeClient(client *connection.Connection) {
   _ = client.Close()
   h.db.AfterClientClose(client)
   h.activeConn.Delete(client)
}

func (h *RespHandler) Handle(ctx context.Context, conn net.Conn) {
   if h.closing.Get() {
      // closing handler refuse new connection
      _ = conn.Close()
   }

   client := connection.NewConn(conn)
   h.activeConn.Store(client, 1)

   ch := parser.ParseStream(conn)
   for payload := range ch {
      if payload.Err != nil {
         if payload.Err == io.EOF ||
            payload.Err == io.ErrUnexpectedEOF ||
            strings.Contains(payload.Err.Error(), "use of closed network connection") {
            // connection closed
            h.closeClient(client)
            logger.Info("connection closed: " + client.RemoteAddr().String())
            return
         }
         // protocol err
         errReply := reply.MakeErrReply(payload.Err.Error())
         err := client.Write(errReply.ToBytes())
         if err != nil {
            h.closeClient(client)
            logger.Info("connection closed: " + client.RemoteAddr().String())
            return
         }
         continue
      }
      if payload.Data == nil {
         logger.Error("empty payload")
         continue
      }
      r, ok := payload.Data.(*reply.MultiBulkReply)
      if !ok {
         logger.Error("require multi bulk reply")
         continue
      }
      result := h.db.Exec(client, r.Args)
      if result != nil {
         _ = client.Write(result.ToBytes())
      } else {
         _ = client.Write(unknownErrReplyBytes)
      }
   }
}

func (h *RespHandler) Close() error {
   logger.Info("handler shutting down...")
   h.closing.Set(true)
   // TODO: concurrent wait
   h.activeConn.Range(func(key interface{}, val interface{}) bool {
      client := key.(*connection.Connection)
      _ = client.Close()
      return true
   })
   h.db.Close()
   return nil
}

RespHandler：和之前的echo類似，加了核心層的db.exec執行解析的指令

interface/database/database.go

type CmdLine = [][]byte

type Database interface {
	Exec(client resp.Connection, args [][]byte) resp.Reply
	AfterClientClose(c resp.Connection)
	Close()
}

type DataEntity struct {
	Data interface{}
}

Exec：核心層的執行

AfterClientClose：關閉之後的善後方法

CmdLine：二維位元組陣列的指令別名

DataEntity：表示Redis的資料，包括string, list, set等等

database/echo_database.go

type EchoDatabase struct {
}

func NewEchoDatabase() *EchoDatabase {
   return &EchoDatabase{}
}

func (e EchoDatabase) Exec(client resp.Connection, args [][]byte) resp.Reply {
   return reply.MakeMultiBulkReply(args)
}

func (e EchoDatabase) AfterClientClose(c resp.Connection) {
   logger.Info("EchoDatabase AfterClientClose")
}

func (e EchoDatabase) Close() {
   logger.Info("EchoDatabase Close")
}

echo_database：測試協定層

Exec：指令解析後，再使用MakeMultiBulkReply包裝一下返回去

main.go

err := tcp.ListenAndServeWithSignal(
   &tcp.Config{
      Address: fmt.Sprintf("%s:%d",
         config.Properties.Bind,
         config.Properties.Port),
   },
   handler.MakeHandler())
if err != nil {
   logger.Error(err)
}

main改成剛才寫的：handler.MakeHandler()

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