golang源码分析:redcon基于redis协议的框架

https://github.com/tidwall/redcon 是一个 Go实现 的 Redis 兼容服务器框架。它实现了redis协议，封装了网络连接，我们可以基于这个库快速实现一个基于redis协议的服务器。简单的redis服务器https://github.com/redis-go/redis 就是基于这个包实现的。

package main


import (
  "log"
  "strings"
  "sync"


  "github.com/tidwall/redcon"
)


var addr = ":6380"


func main() {
  var mu sync.RWMutex
  var items = make(map[string][]byte)
  var ps redcon.PubSub
  go log.Printf("started server at %s", addr)
  err := redcon.ListenAndServe(addr,
    func(conn redcon.Conn, cmd redcon.Command) {
      switch strings.ToLower(string(cmd.Args[0])) {
      default:
        conn.WriteError("ERR unknown command '" + string(cmd.Args[0]) + "'")
      case "ping":
        conn.WriteString("PONG")
      case "quit":
        conn.WriteString("OK")
        conn.Close()
      case "set":
        if len(cmd.Args) != 3 {
          conn.WriteError("ERR wrong number of arguments for '" + string(cmd.Args[0]) + "' command")
          return
        }
        mu.Lock()
        items[string(cmd.Args[1])] = cmd.Args[2]
        mu.Unlock()
        conn.WriteString("OK")
      case "get":
        if len(cmd.Args) != 2 {
          conn.WriteError("ERR wrong number of arguments for '" + string(cmd.Args[0]) + "' command")
          return
        }
        mu.RLock()
        val, ok := items[string(cmd.Args[1])]
        mu.RUnlock()
        if !ok {
          conn.WriteNull()
        } else {
          conn.WriteBulk(val)
        }
      case "del":
        if len(cmd.Args) != 2 {
          conn.WriteError("ERR wrong number of arguments for '" + string(cmd.Args[0]) + "' command")
          return
        }
        mu.Lock()
        _, ok := items[string(cmd.Args[1])]
        delete(items, string(cmd.Args[1]))
        mu.Unlock()
        if !ok {
          conn.WriteInt(0)
        } else {
          conn.WriteInt(1)
        }
      case "publish":
        if len(cmd.Args) != 3 {
          conn.WriteError("ERR wrong number of arguments for '" + string(cmd.Args[0]) + "' command")
          return
        }
        conn.WriteInt(ps.Publish(string(cmd.Args[1]), string(cmd.Args[2])))
      case "subscribe", "psubscribe":
        if len(cmd.Args) < 2 {
          conn.WriteError("ERR wrong number of arguments for '" + string(cmd.Args[0]) + "' command")
          return
        }
        command := strings.ToLower(string(cmd.Args[0]))
        for i := 1; i < len(cmd.Args); i++ {
          if command == "psubscribe" {
            ps.Psubscribe(conn, string(cmd.Args[i]))
          } else {
            ps.Subscribe(conn, string(cmd.Args[i]))
          }
        }
      }
    },
    func(conn redcon.Conn) bool {
      // Use this function to accept or deny the connection.
      // log.Printf("accept: %s", conn.RemoteAddr())
      return true
    },
    func(conn redcon.Conn, err error) {
      // This is called when the connection has been closed
      // log.Printf("closed: %s, err: %v", conn.RemoteAddr(), err)
    },
  )
  if err != nil {
    log.Fatal(err)
  }
}

下面看下源码实现，源码很简单，主要是两个文件：redcon/redcon.go，redcon/resp.go前者实现了网络连接的包装，后者实现了redis协议。依赖了两个网络包https://github.com/tidwall/btree，https://github.com/tidwall/match

我们还是从例子的入口函数ListenAndServe开始学习

func ListenAndServe(addr string,
  handler func(conn Conn, cmd Command),
  accept func(conn Conn) bool,
  closed func(conn Conn, err error),
) error {
  return ListenAndServeNetwork("tcp", addr, handler, accept, closed)
}

传入了4个参数，地址、服务handler（服务核心逻辑实现的地方，处理请求并返回结果）、accept函数和close函数。核心逻辑只是对ListenAndServeNetwork的一个包装，确定了网络协议是tcp协议

func ListenAndServeNetwork(
  net, laddr string,
  handler func(conn Conn, cmd Command),
  accept func(conn Conn) bool,
  closed func(conn Conn, err error),
) error {
  return NewServerNetwork(net, laddr, handler, accept, closed).ListenAndServe()
}

NewServerNetwort函数初始化了server，最终调用的是server的ListenAndServe()函数。

func NewServerNetwork(
  net, laddr string,
  handler func(conn Conn, cmd Command),
  accept func(conn Conn) bool,
  closed func(conn Conn, err error),
) *Server {
  if handler == nil {
    panic("handler is nil")
  }
  s := &Server{
    net:     net,
    laddr:   laddr,
    handler: handler,
    accept:  accept,
    closed:  closed,
    conns:   make(map[*conn]bool),
  }
  return s
}

func (s *Server) ListenAndServe() error {
  return s.ListenServeAndSignal(nil)
}

func (s *Server) ListenServeAndSignal(signal chan error) error {
  ln, err := net.Listen(s.net, s.laddr)
  if err != nil {
    if signal != nil {
      signal <- err
    }
    return err
  }
  s.ln = ln
  if signal != nil {
    signal <- nil
  }
  return serve(s)
}

在这里初始化了网络连接，侦听网络端口，最后调用serve服务

func serve(s *Server) error {
      for {
        lnconn, err := s.ln.Accept()
          if s.accept != nil && !s.accept(c) {
            go handle(s, c)
          }
        }
}

serve是整个服务的大循环，里面不断accept请求，对每个连接，启用一个协程去处理请求内容。

func handle(s *Server, c *conn) {
    for {
      cmds, err := c.rd.readCommands(nil)
      for len(c.cmds) > 0 {
        cmd := c.cmds[0]
        s.handler(c, cmd)
      }
}

在handle函数内部调用server的handler去处理服务端请求的内容。至此整个服务端的框架基本介绍完毕。里面还封装了一套TLS的server逻辑，内容基本相似。

func NewServerTLS(addr string,
  handler func(conn Conn, cmd Command),
  accept func(conn Conn) bool,
  closed func(conn Conn, err error),
  config *tls.Config,
) *TLSServer {
  return NewServerNetworkTLS("tcp", addr, handler, accept, closed, config)
}

下面重点介绍下handler函数，它是server结构体的一个属性

type Server struct {
  mu        sync.Mutex
  net       string
  laddr     string
  handler   func(conn Conn, cmd Command)
  accept    func(conn Conn) bool
  closed    func(conn Conn, err error)
  conns     map[*conn]bool
  ln        net.Listener
  done      bool
  idleClose time.Duration
  // AcceptError is an optional function used to handle Accept errors.
  AcceptError func(err error)
}

 有两个参数Conn 网络连接、Command请求参数

type Conn interface {}

type conn struct {
  conn      net.Conn
  wr        *Writer
  rd        *Reader
  addr      string
  ctx       interface{}
  detached  bool
  closed    bool
  cmds      []Command
  idleClose time.Duration
}

包裹了网络连接和reader、writer

redis协议resp的定义如下

type RESP struct {
  Type  Type
  Raw   []byte
  Data  []byte
  Count int
}

并且也实现了相关协议的解析函数

    func ReadNextRESP(b []byte) (n int, resp RESP) 
    func ReadNextCommand(packet []byte, argsbuf [][]byte) 
    func readTelnetCommand(packet []byte, argsbuf [][]byte)
    func AppendAny(b []byte, v interface{}) []byte 

redcon只是一个server框架，基于这个框架，我们可以向开发httpserver一样非常方便地开发出一个兼容redis协议的服务端。