chat.go/chatserver.go

package main

import (
  "flag"
  "fmt"
  "io"
  "net"
  "os"
  "strconv"
  "time"
)

type myMsg struct {
  sender net.Conn
  bytes []byte
  receivedAt time.Time
}

var myMsgs chan myMsg
var myConns map[net.Conn]bool

func usage() {
  fmt.Fprintf(os.Stderr, "\nusage: go run chatserver.go\n")
  flag.PrintDefaults();
  fmt.Println()

  os.Exit(1)
}

func handleConnection(conn net.Conn) {
  // Why don't these work?
  //buf := make([]byte, 0, 1024)
  //buf := []byte{}
  // But this does
  fmt.Fprintf(conn, "Welcome! This is an open relay chat server. There is no security yet.\n")
  buf := make([]byte, 1024)
  for {
    count, err := conn.Read(buf)
    if nil != err {
      if io.EOF != err {
        fmt.Fprintf(os.Stderr, "Non-EOF socket error: %s\n", err)
      }
      fmt.Fprintf(os.Stdout, "Ending socket\n")
      break
    }
    // not so sure about why this case exists
    // we'll just ignore it for now...
    if 0 == count {
      // fmt.Fprintf(os.Stdout, "Weird")
      continue
    }
    myMsgs <- myMsg{
      receivedAt: time.Now(),
      sender: conn,
      bytes: buf[0:count],
    }
  }
}

func main() {
  myMsgs = make(chan myMsg, 128)
  myConns = make(map[net.Conn]bool)
  flag.Usage = usage
  port:= flag.Uint("telnet-port", 4080, "tcp telnet chat port")
  flag.Parse()
  addr := ":" + strconv.Itoa(int(*port))


  // https://golang.org/pkg/net/#Conn
  sock, err := net.Listen("tcp", addr)
  if nil != err {
		fmt.Fprintf(os.Stderr, "Couldn't bind to TCP socket %q: %s\n", addr, err)
		os.Exit(2)
  }
  fmt.Println("Listening on", addr);

  go func() {
    for {
      fmt.Fprintf(os.Stdout, "Waiting for message...\n");
      msg := <- myMsgs
      ts, err := msg.receivedAt.MarshalJSON()
      if nil != err {
        fmt.Fprintf(os.Stderr, "[Error] %s\n", err)
      }
      fmt.Fprintf(os.Stdout, "[Timestamp] %s\n", ts)
      fmt.Fprintf(os.Stdout, "[Remote] %s\n", msg.sender.RemoteAddr().String())
      fmt.Fprintf(os.Stdout, "[Message] %s\n", msg.bytes);
      for conn, _ := range myConns {
        if msg.sender == conn {
          continue
        }
        // backlogged connections could prevent a next write,
        // so this should be refactored into a goroutine
        // And what to do about slow clients that get behind (or DoS)?
        // SetDeadTime and Disconnect them?
        conn.Write(msg.bytes)
      }
    }
  }()

  for {
    conn, err := sock.Accept()
    if err != nil {
      // Not sure what kind of error this could be or how it could happen.
      // Could a connection abort or end before it's handled?
      fmt.Fprintf(os.Stderr, "Error accepting connection:\n%s\n", err)
    }
    fmt.Fprintf(os.Stdout, "Accepting socket\n")
    myConns[conn] = true
    go handleConnection(conn)
  }
}