Go语言的变量、函数、Socks5代理服务器示例详解

// 声明并初始化一个变量
var m int = 10
// 声明初始化多个变量
var i, j, k = 1, 2, 3
// 多个变量的声明(注意小括号的使用)
var(
 no int
 name string
)
// 声明时不指明类型，通过初始化值来推导
var b = true // bool型
// := 隐含声明变量并赋值
str := "mimvp.com"  // 等价于var str string = "mimvp.com"

// = 使用必须使用先var声明例如：
var a
a = 100
// 或
var b = 100
// 或
var c int = 100
// := 是声明并赋值，并且系统自动推断类型，不需要var关键字
d := 100
// Go中有一个特殊的变量下划线"_" 表示任何赋给它的值将被丢弃
_, Ret:= 2, 3  // 2赋值被丢弃

const ( 
 constName1 [type] = val1 
 constName2 [type] = val2 
) 

/**
* mimvp.com
* 2017.1.20
*/
// 声明当前文件所属的包名，main是一个可独立运行的包，编译后会生成可执行文件 
package main 
import "fmt" // 导入包 
var id = 123456 
/* 
id2 := 654321 
// 在函数外用 := ，编译时会出现错误，局部变量声明应在函数内部
// non-declaration statement outside function body 
*/ 
const PI = 3.14  // 常量声明
// 每个可独立运行的程序，都包含入口函数 main ，与其他语言相同，但无参数和返回值 
func main() { 
 var num int 
 num = 100 
 fmt.Println(num)  // 输出 100 
 var num1, num2 int 
 num1, num2 = 1, 2 
 fmt.Println(num1, num2) // 输出 1 2 
 var no1, no2 = 3, 4 
 fmt.Println(no1, no2)  // 输出 3 4 
 n1, n2 := 5, 6 
 fmt.Println(n1, n2)  // 输出 5 6 
 _, n := 7, 8 
 fmt.Println(n)    // 输出 8 
 var ( 
  key1 string 
  key2 string 
 ) 
 key1, key2 = "k1", "k2" 
 fmt.Println(key1, key2) // 输出 k1 k2 
 var ( 
  a = 9 
  b = 10 
 ) 
 fmt.Println(a, b)   // 输出 9 10 
 fmt.Println(id)   // 输出 123456 
 fmt.Println(PI)   // 输出 3.14 
 /* 
 PI = 3.1415 
 // 改变常量的值，编译会出现错误 
 // cannot assign to PI 
 // cannot use 3.1415 (type float64) as type ideal in assignment 
 */ 
}

func GetMsg(i int) (str string) {
 fmt.Println(i)
 str = "hello mimvp.com"
 return str
}

<span style="color:#0000FF;">vim mimvp_func.go</span>
func GetMsg(i int) (str string, err string) {
 fmt.Println(i)
 str = "hello mimvp.com"
 err = "no err"
 return str, err
}
func main() {
 fmt.Println(GetMsg(100))
}

$ go build mimvp_func.go 
$ ./mimvp_func   
100
hello mimvp.com no err

func ReadFile(filePath string)(){
 file.Open(filePath)
 defer file.Close()
  
 if true {
  file.Read()
 } else {
  return false
 }
}

package main
import "fmt"
func main() {
 f()
 fmt.Println("Returned normally from f.")
}
func f() {
 defer func() {
  if r := recover(); r != nil {
   fmt.Println("Recovered in f", r)
  }
 }()
 fmt.Println("Calling g.")
 g(0)
 fmt.Println("Returned normally from g.")
}
func g(i int) {
 if i > 3 {
  fmt.Println("Panicking!")
  panic(fmt.Sprintf("%v", i))
 }
 defer fmt.Println("Defer in g", i)
 fmt.Println("Printing in g", i)
 g(i + 1)
}

$ ./mimvp-try-catch   
Calling g.
Printing in g 0
Printing in g 1
Printing in g 2
Printing in g 3
Panicking!
Defer in g 3
Defer in g 2
Defer in g 1
Defer in g 0
Recovered in f 4
Returned normally from f.

package main
import (
 "net"
 "fmt"
 "io"
 "bytes"
 "encoding/binary"
)
type Methods struct{
 ver, nmethods uint8
 methods uint8
}
type sock5cmd struct{
 ver, cmd, rsv, atyp uint8
 dst [255]uint8
}
type proxyCoder struct {
 conn net.Conn
}
func (c *proxyCoder) readMethods() Methods {
 var m Methods
 b := make([]byte, 1024)
 n, err := c.conn.Read(b)
 if err != nil && err != io.EOF { panic(err) }
 buf := bytes.NewBuffer(b[0:n])
 err = binary.Read(buf, binary.LittleEndian, &m.ver)
 if err != nil {
  fmt.Println("binary.Read failed:", err)
 }
 err = binary.Read(buf, binary.LittleEndian, &m.nmethods)
 if err != nil {
  fmt.Println("binary.Read failed:", err)
 }
 err = binary.Read(buf, binary.BigEndian, &m.methods)
 if err != nil {
  fmt.Println("binary.Read failed:", err)
 }
 return m
}
func (c *proxyCoder) returnMethod() {
 buf := make([]byte, 2)
 buf[0] = 5
 buf[1] = 0
 c.conn.Write(buf)
 fmt.Println(buf)
}
func (c *proxyCoder) serve() {
 buf := make([]byte, 128)
 n, err := c.conn.Read(buf)
 if err != nil && err != io.EOF { panic(err) }
 fmt.Println(buf[:n])
 var s string
 var t string
 var i int
 if(buf[3] == 3){//domail
  for i = 4; i < n-2; i++ {
   s += fmt.Sprintf("%c", buf[i])
  }
 } else {//ip4 or ip6
  s += fmt.Sprintf("%d", buf[4])
  for i = 5; i < n-2; i++ {
   s += fmt.Sprintf(".%d", buf[i])
  }
 }
 p := make([]byte, 2)
 var port uint16
 p[1] = buf[n-1]
 p[0] = buf[n-2]
 b := bytes.NewBuffer(p)
 err = binary.Read(b, binary.BigEndian, &port)
 if err != nil {
  fmt.Println("binary.Read failed:", err)
 }
 s += fmt.Sprintf(":%d", port)
 switch buf[1] {
  case 1://TCP
   t = "tcp"
  case 2://BIND
  case 3://UDP
   t = "udp"
 }
 conn, err := net.Dial(t, s)
 if err != nil {
  fmt.Printf("%s connect error %s\n", t, s)
  buf[1] = 4
  c.conn.Write(buf[:n])
  c.conn.Close()
  return
 }
 buf[1] = 0
 c.conn.Write(buf[:n])
 fmt.Printf("%s connect success %s\n", t, s)
 go serv(conn, c.conn)
 go serv(c.conn, conn)
}
func serv(in net.Conn, out net.Conn){
 b := make([]byte, 10240)
 for ;;{
  n, err := in.Read(b)
  if( err != nil ){
   fmt.Printf("close\n")
   in.Close()
   out.Close()
   return
  }
  fmt.Printf("serv %d\n", n)
  out.Write(b[:n]);
 }
}
type Proxy struct {
}
func NewProxy() *Proxy {
 return &Proxy{}
}
var DefaultProxy = NewProxy()
func (p *Proxy) ProxyConn(conn net.Conn ){
 c := &proxyCoder{conn}
 m := c.readMethods()
 fmt.Println(m)
 c.returnMethod()
 c.serve()
}
func handleConnection(conn net.Conn){
 buf := make([]byte, 1024)
 n, err := conn.Read(buf)
 if err != nil && err != io.EOF { panic(err) }
 fmt.Println(buf[:n])
 //answer
 buf[0] = 5
 buf[1] = 0
 conn.Write(buf[:2])
 fmt.Println(buf[:2])
 //serve
 n, err = conn.Read(buf)
 if err != nil && err != io.EOF { panic(err) }
 fmt.Println(buf[:n])
 conn.Close()
}
func main() {
 ln, err := net.Listen("tcp", ":1080")
 if err != nil {
  fmt.Printf("bind error\n")
  return
 }
 for {
  conn, err := ln.Accept()
  if err != nil {
   fmt.Printf("accept error\n")
   continue
  }
  go DefaultProxy.ProxyConn(conn)
  //go handleConnection(conn)
 }
}