Go语言的IPv4/IPv6服务

IPv4 connections can be handled with the v6 API by using the v4-mapped-on-v6 address type;
thus a program needs to support only this API type to support both protocols.
This is handled transparently by the address handling functions in the C library.


IPv4 and IPv6 share the local port space.
When you get an IPv4 connection or packet to a IPv6 socket,
its source address will be mapped to v6 and it will be mapped to v6.


The address notation for IPv6 is a group of 8 4-digit hexadecimal numbers, separated with a ':'.
"::" stands for a string of 0 bits.
Special addresses are ::1 for loopback and ::FFFF:<IPv4 address> for IPv4-mapped-on-IPv6.

func favoriteAddrFamily(network string, laddr, raddr sockaddr, mode string) (family int, ipv6only bool) {
    switch network[len(network)-1] {
    case '4':
        return syscall.AF_INET, false
    case '6':
        return syscall.AF_INET6, true
    }


    if mode == "listen" && (laddr == nil || laddr.isWildcard()) {
        if supportsIPv4map() || !supportsIPv4() {
            return syscall.AF_INET6, false
        }
        if laddr == nil {
            return syscall.AF_INET, false
        }
        return laddr.family(), false
    }


    if (laddr == nil || laddr.family() == syscall.AF_INET) &&
        (raddr == nil || raddr.family() == syscall.AF_INET) {
        return syscall.AF_INET, false
    }
    return syscall.AF_INET6, false
}

package main


import (
  "fmt"
  "net"
  "net/http"
)


type helloHandler struct{}


func (h *helloHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  w.Write([]byte("Hello, world!"))
}


func main() {
  var err error
  http.Handle("/", &helloHandler{})
  //err = http.ListenAndServe(":8083", nil) // IPv4 或 IPv6
  //err = http.ListenAndServe("[2604:180:3:dd3::276e]:8083", nil) // 具体指定，仅 IPv6
  err = ListenAndServe(":8083", nil) // 重构 ListenAndServe 函数
  if err != nil {
    fmt.Println(err)
  }


}


type tcpKeepAliveListener struct {
  *net.TCPListener
}


func ListenAndServe(addr string, handler http.Handler) error {
  srv := &http.Server{Addr: addr, Handler: handler}
  addr = srv.Addr
  if addr == "" {
    addr = ":http"
  }
  ln, err := net.Listen("tcp6", addr) // 仅指定 IPv6
  if err != nil {
    return err
  }
  return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
}