1、前言

其实我前面一篇笔记的例子就是socket的一个例子，但是由于大部分的笔记说明都是在整理基础的东西，所以socket的笔记单独列在这里。

server.go

package socket

import (
    "fmt"
    "net"
)

func  StartServer() {
    service := ":3338"
    tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
    checkError(err)
    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)
    for {
        conn, err := listener.Accept()
        if err != nil {
            continue
        }
        fmt.Println("新连接：", conn.RemoteAddr().String())
        go handleConn(conn)
    }
}

func handleConn(conn net.Conn) {
    defer conn.Close()

    for {
        buffer := make([]byte, 1024)

        length, _:= conn.Read(buffer)

        if length > 12 {
            data := buffer[:length]

            switch data[11] & 0xff {
            case 0x80:
                //桌子
                fmt.Println("桌子")
            case 0x90:
                //椅子


            case 0xA0:
                //台灯

            default:
                //其它

            }

            //写数据

            //      conn.Write(data)
        }
    }

}

func isProtocol(data []byte) bool {
    if (data[0]&0xff) == 0xC0 && (data[len(data)-1]&0xff) == 0xC1 {
        return true
    }
    return false
}

func checkError(err error) {
    if err != nil {
        fmt.Println(err.Error())
    }
}

2、TCP Socket Server

2.1 导包

和java一样，golang提供了比较强大的网络编程的基础库net。

当然我们想使用golang的网络相关的库，先导入net包。而fmt包，则是为了测试一些结果，作为终端输出的工具包。

import (
    "fmt"
    "net"
)

2.2 声明地址

通过net包的ResolveTCPAddr函数声明一个TCPAddr。

// TCPAddr represents the address of a TCP end point.
type TCPAddr struct {
    IP   IP
    Port int
    Zone string // IPv6 scoped addressing zone
}

func ResolveTCPAddr(net, addr string) (*TCPAddr, error)

• net参数是”tcp4”、”tcp6”、”tcp”中的任意一个，分别表示TCPv4、TCPv6或者任意。查看ResolveTCPAddr的源码后，net参数甚至可以是一个空字符串，估计是为了兼容之前的Go版本的原因。

    switch net {
    case "tcp", "tcp4", "tcp6":
    case "": // a hint wildcard for Go 1.0 undocumented behavior
        net = "tcp"
    default:
        return nil, UnknownNetworkError(net)
    }

• addr表示域名或者IP地址，例如”www.baidu.com:80” 或者”127.0.0.1:22”。

从源码上看，ip是可以缺省的，但端口不能缺省。ip缺省的话，默认使用的是本地地址。ip和端口使用英文的冒号（:）分开，net包是通过冒号分隔字符串的方式来处理ResolveTCPAddr的net参数的。

ResolveTCPAddr可供服务器及客户端共用的，不像java那样区分Socket和ServerSocket。所以缺省ip的逻辑很好理解。

我们这里写的是服务器端的逻辑，只输入端口号。

// SplitHostPort splits a network address of the form "host:port",
// "[host]:port" or "[ipv6-host%zone]:port" into host or
// ipv6-host%zone and port.  A literal address or host name for IPv6
// must be enclosed in square brackets, as in "[::1]:80",
// "[ipv6-host]:http" or "[ipv6-host%zone]:80".
func SplitHostPort(hostport string) (host, port string, err error) {
    j, k := 0, 0

    // The port starts after the last colon.
    i := last(hostport, ':')
    if i < 0 {
        goto missingPort
    }

    if hostport[0] == '[' {
        // Expect the first ']' just before the last ':'.
        end := byteIndex(hostport, ']')
        if end < 0 {
            err = &AddrError{Err: "missing ']' in address", Addr: hostport}
            return
        }
        switch end + 1 {
        case len(hostport):
            // There can't be a ':' behind the ']' now.
            goto missingPort
        case i:
            // The expected result.
        default:
            // Either ']' isn't followed by a colon, or it is
            // followed by a colon that is not the last one.
            if hostport[end+1] == ':' {
                goto tooManyColons
            }
            goto missingPort
        }
        host = hostport[1:end]
        j, k = 1, end+1 // there can't be a '[' resp. ']' before these positions
    } else {
        host = hostport[:i]
        if byteIndex(host, ':') >= 0 {
            goto tooManyColons
        }
        if byteIndex(host, '%') >= 0 {
            goto missingBrackets
        }
    }
    if byteIndex(hostport[j:], '[') >= 0 {
        err = &AddrError{Err: "unexpected '[' in address", Addr: hostport}
        return
    }
    if byteIndex(hostport[k:], ']') >= 0 {
        err = &AddrError{Err: "unexpected ']' in address", Addr: hostport}
        return
    }

    port = hostport[i+1:]
    return

missingPort:
    err = &AddrError{Err: "missing port in address", Addr: hostport}
    return

tooManyColons:
    err = &AddrError{Err: "too many colons in address", Addr: hostport}
    return

missingBrackets:
    err = &AddrError{Err: "missing brackets in address", Addr: hostport}
    return
}

2.3 启动监听器

• 通过net包的ListenTCP之前的TCPAddr启动一个监听器。

func ListenTCP(net string, laddr *TCPAddr) (*TCPListener, error) 

这里的net参数也是支付”tcp”, “tcp4”, “tcp6”。但不支持空字符串。

• 通过TCPListener的Accept方法阻塞式接收客户端的连接

func (l *TCPListener) Accept() (Conn, error) 

整个过程和java socket server的思想基本是一至的。

2.4 Conn

type Conn interface {
    // Read reads data from the connection.
    // Read can be made to time out and return a Error with Timeout() == true
    // after a fixed time limit; see SetDeadline and SetReadDeadline.
    Read(b []byte) (n int, err error)

    // Write writes data to the connection.
    // Write can be made to time out and return a Error with Timeout() == true
    // after a fixed time limit; see SetDeadline and SetWriteDeadline.
    Write(b []byte) (n int, err error)

    // Close closes the connection.
    // Any blocked Read or Write operations will be unblocked and return errors.
    Close() error

    // LocalAddr returns the local network address.
    LocalAddr() Addr

    // RemoteAddr returns the remote network address.
    RemoteAddr() Addr

    // SetDeadline sets the read and write deadlines associated
    // with the connection. It is equivalent to calling both
    // SetReadDeadline and SetWriteDeadline.
    //
    // A deadline is an absolute time after which I/O operations
    // fail with a timeout (see type Error) instead of
    // blocking. The deadline applies to all future I/O, not just
    // the immediately following call to Read or Write.
    //
    // An idle timeout can be implemented by repeatedly extending
    // the deadline after successful Read or Write calls.
    //
    // A zero value for t means I/O operations will not time out.
    SetDeadline(t time.Time) error

    // SetReadDeadline sets the deadline for future Read calls.
    // A zero value for t means Read will not time out.
    SetReadDeadline(t time.Time) error

    // SetWriteDeadline sets the deadline for future Write calls.
    // Even if write times out, it may return n > 0, indicating that
    // some of the data was successfully written.
    // A zero value for t means Write will not time out.
    SetWriteDeadline(t time.Time) error
}

• Conn接口的Read和Write方法进行IO操作。
• 通过SetDeadline、SetReadDeadline、SetWriteDeadline方法设置IO超时时间
• RemoteAddr方法可以获取到客户端的ip及端口信息。

fmt.Println("新连接：", conn.RemoteAddr().String())

注意：Conn接口的Read也是阻塞的。

2.5 defer

func handleConn(conn net.Conn) {
    defer conn.Close()

    for {
        ...
    }

}

关键字 defer 的用法类似于面向对象编程语言 Java 和 C# 的 finally 语句块，它一般用于释放某些已分配的资源，比如常见的关闭文件、释放缓存。

这里是操作完写操作后，就把conn连接关掉。

3、Goroutine

在Go中，每个并发处理的部分被称作 goroutines（协程），它可以进行更有效的并发运算。在协程和操作系统线程之间并无一对一的关系：协程是根据一个或多个线程的可用性，映射（多路复用，执行于）在他们之上的；协程调度器在 Go 运行时很好的完成了这个工作。

golang想使用协程的方式很简单，只要在需要使用协程的方法调用的前面加上go关键字就可以了。
如：

go handleConn(conn)

这种方式相比java的线程，太优雅了。