Listener with SO_REUSEPORT for linux

listen.go

// +build !linux

package socket

import "net"

func Listen(network, address string) (net.Listener, error) { return net.Listen(network, address) }

listen_linux.go

package socket

import (
	"errors"
	"net"
	"os"
	"syscall"
	"time"

	"golang.org/x/sys/unix"
)

func Listen(network, address string) (net.Listener, error) {
	if network != "tcp" {
		return nil, errors.New("only tcp network is supported")
	}
	addr, err := net.ResolveTCPAddr(network, address)
	if err != nil {
		return nil, err
	}
	sockaddr, err := tcpAddrToSockaddr(addr)
	if err != nil {
		return nil, err
	}
	syscall.ForkLock.Lock()
	defer syscall.ForkLock.Unlock()
	s, err := unix.Socket(unix.AF_INET, unix.SOCK_STREAM|unix.SOCK_CLOEXEC|unix.SOCK_NONBLOCK, 0)
	if err != nil {
		return nil, err
	}
	if err := unix.SetsockoptInt(s, unix.SOL_SOCKET, unix.SO_REUSEADDR, 0); err != nil {
		unix.Close(s)
		return nil, err
	}
	if err := unix.SetsockoptInt(s, unix.SOL_SOCKET, unix.SO_REUSEPORT, 1); err != nil {
		unix.Close(s)
		return nil, err
	}
	if err := unix.Bind(s, sockaddr); err != nil {
		unix.Close(s)
		return nil, err
	}
	if err := unix.Listen(s, unix.SOMAXCONN); err != nil {
		unix.Close(s)
		return nil, err
	}
	f := os.NewFile(uintptr(s), address)
	defer f.Close()
	ln, err := net.FileListener(f)
	if err != nil {
		return nil, err
	}
	if tln, ok := ln.(*net.TCPListener); ok {
		return tcpKeepAliveListener{tln}, nil
	}
	return ln, nil
}

func tcpAddrToSockaddr(a *net.TCPAddr) (unix.Sockaddr, error) {
	if a == nil {
		return nil, errors.New("nil *net.TCPAddr")
	}
	if ip := a.IP.To4(); ip != nil {
		b := [net.IPv4len]byte{}
		copy(b[:], a.IP.To4())
		return &unix.SockaddrInet4{Addr: b, Port: a.Port}, nil
	}
	return nil, errors.New("ipv6 listener not implemented yet")
}

type tcpKeepAliveListener struct {
	*net.TCPListener
}

func (ln tcpKeepAliveListener) Accept() (c net.Conn, err error) {
	tc, err := ln.AcceptTCP()
	if err != nil {
		return
	}
	tc.SetKeepAlive(true)
	tc.SetKeepAlivePeriod(3 * time.Minute)
	return tc, nil
}