最简单的回声服务器：

package mainimport (        "io"        "net"        "log")func main() {        listener, err := net.Listen("tcp", ":8040")        if err != nil {                log.Fatal(err)        }           for {                conn, err := listener.Accept()                if err != nil {                        log.Print(err) // e.g., connection aborted                        continue                }                   go handleConn(conn) //新建goroutines处理连接        }   }func handleConn(c net.Conn) {    io.Copy(c, c) // NOTE: ignoring errors    c.Close()}

原理：

1.io.Copy()方法

func Copy(dst Writer, src Reader) (written int64, err error)

2.net.Conn类型

type Conn interface {

Read(b []byte) (n int, err error)

Write(b []byte) (n int, err error)

...

}

一个类型如果拥有一个接口需要的所有方法，那么这个类型就实现了这个接口

3.io.Writer

type Writer interface {

Write(p []byte) (n int, err error)

}

4.io.Reader

type Reader interface {

Read(p []byte) (n int, err error)

}

升级版，每条连接一个goroutine,每个goroutine中分出多个输出goroutine

package mainimport (        "bufio"        "fmt"        "log"        "net"        "strings"        "time")func main() {        listener, err := net.Listen("tcp", ":8040")        if err != nil {                log.Fatal(err)        }           for {                conn, err := listener.Accept()                if err != nil {                        log.Print(err) // e.g., connection aborted                        continue                }                   go handleConn(conn) //新建goroutines处理连接        }   }func handleConn(c net.Conn) {        input := bufio.NewScanner(c)        for input.Scan() {                go echo(c, input.Text(), 1*time.Second)        }           // NOTE: ignoring potential errors from input.Err()        c.Close()}func echo(c net.Conn, shout string, delay time.Duration) {        fmt.Fprintln(c, "\t", strings.ToUpper(shout))        time.Sleep(delay)        fmt.Fprintln(c, "\t", shout)        time.Sleep(delay)        fmt.Fprintln(c, "\t", strings.ToLower(shout))}

　　

1.fmt.Fprintln()

func Fprintln(w io.Writer, a ...interface{}) (n int, err error)

2.bufio.NewScanner()

func NewScanner(r io.Reader) *Scanner

func (s *Scanner) Scan() bool

func (s *Scanner) Text() string

也用到了大量的7.3节 实现接口的条件