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package server6
import (
"errors"
"fmt"
"net"
"os"
"github.com/insomniacslk/dhcp/interfaces"
"golang.org/x/sys/unix"
)
// NewIPv6UDPConn returns a UDPv6-only connection bound to both the interface and port
// given based on a IPv6 DGRAM socket.
// As a bonus, you can actually listen on a multicast address instead of being punted to the wildcard
//
// The interface must already be configured.
func NewIPv6UDPConn(iface string, addr *net.UDPAddr) (net.PacketConn, error) {
fd, err := unix.Socket(unix.AF_INET6, unix.SOCK_DGRAM, unix.IPPROTO_UDP)
if err != nil {
return nil, fmt.Errorf("cannot get a UDP socket: %v", err)
}
f := os.NewFile(uintptr(fd), "")
// net.FilePacketConn dups the FD, so we have to close this in any case.
defer f.Close()
// Allow broadcasting.
if err := unix.SetsockoptInt(fd, unix.IPPROTO_IPV6, unix.IPV6_V6ONLY, 1); err != nil {
if errno, ok := err.(unix.Errno); !ok {
return nil, fmt.Errorf("unexpected socket error: %v", err)
} else if errno != unix.ENOPROTOOPT { // Unsupported on some OSes (but in that case v6only is default), so we ignore ENOPROTOOPT
return nil, fmt.Errorf("cannot bind socket v6only %v", err)
}
}
// Allow reusing the addr to aid debugging.
if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEADDR, 1); err != nil {
return nil, fmt.Errorf("cannot set reuseaddr on socket: %v", err)
}
if len(iface) != 0 {
// Bind directly to the interface.
if err := interfaces.BindToInterface(fd, iface); err != nil {
if errno, ok := err.(unix.Errno); ok && errno == unix.EACCES {
// Return a more helpful error message in this (fairly common) case
return nil, errors.New("Cannot bind to interface without CAP_NET_RAW or root permissions. " +
"Restart with elevated privilege, or run without specifying an interface to bind to all available interfaces.")
}
return nil, fmt.Errorf("cannot bind to interface %s: %v", iface, err)
}
}
if addr == nil {
return nil, errors.New("An address to listen on needs to be specified")
}
// Bind to the port.
saddr := unix.SockaddrInet6{Port: addr.Port}
copy(saddr.Addr[:], addr.IP)
if err := unix.Bind(fd, &saddr); err != nil {
return nil, fmt.Errorf("cannot bind to address %v: %v", addr, err)
}
return net.FilePacketConn(f)
}
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