2. 函数使用
1）Go语言函数格式
func GetMsg(i int) (str string) {
fmt.Println(i)
str = "hello mimvp.com"
return str
}
解释说明：
func 说明这是个函数
GetMsg是函数名
(i int) 函数接收一个int参数，是传入参数
(str string) 函数返回一个string类型返回值，是返回参数
2）Go语言函数可返回多个值
函数返回多个值，跟Java、PHP、C等主流语言都不一样，但和Python、lua等脚本语言是一样的
<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))
}
编译执行：
$ go build mimvp_func.go
$ ./mimvp_func
100
hello mimvp.com no err
3）defer的使用
defer的意思是"在函数退出时调用"，特别用于对文件进行读写操作的时候，需要在open之后要调用close操作，将close操作使用defer
func ReadFile(filePath string)(){
file.Open(filePath)
defer file.Close()
if true {
file.Read()
} else {
return false
}
}
上述代码含义是在file.Open后不立即调用close，当return false的时候调用file.Close()，这样就有效避免了C语言中的内存泄露问题。
4）理解 panic，recover
上面讲述了很多变量和函数，还没介绍 throw - try - catch 的用法
Go语言里，Panic和Recover就是其他语言中的throw和catch
示例代码：
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)
}
运行结果：
$ ./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.
Panic抛出了信息，并且跳出函数。Recover接受到了信息，并且继续处理。
这个例子理解了基本就掌握了Recover和Panic
3. Socks5代理服务器
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 %sn", 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 %sn", 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("closen")
in.Close()
out.Close()
return
}
fmt.Printf("serv %dn", 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 errorn")
return
}
for {
conn, err := ln.Accept()
if err != nil {
fmt.Printf("accept errorn")
continue
}
go DefaultProxy.ProxyConn(conn)
//go handleConnection(conn)
}
}
