/usr/share/go-1.6/src/net/udpsock.go is in golang-1.6-src 1.6.1-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 | // Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package net
// UDPAddr represents the address of a UDP end point.
type UDPAddr struct {
	IP   IP
	Port int
	Zone string // IPv6 scoped addressing zone
}
// Network returns the address's network name, "udp".
func (a *UDPAddr) Network() string { return "udp" }
func (a *UDPAddr) String() string {
	if a == nil {
		return "<nil>"
	}
	ip := ipEmptyString(a.IP)
	if a.Zone != "" {
		return JoinHostPort(ip+"%"+a.Zone, itoa(a.Port))
	}
	return JoinHostPort(ip, itoa(a.Port))
}
func (a *UDPAddr) isWildcard() bool {
	if a == nil || a.IP == nil {
		return true
	}
	return a.IP.IsUnspecified()
}
func (a *UDPAddr) opAddr() Addr {
	if a == nil {
		return nil
	}
	return a
}
// ResolveUDPAddr parses addr as a UDP address of the form "host:port"
// or "[ipv6-host%zone]:port" and resolves a pair of domain name and
// port name on the network net, which must be "udp", "udp4" or
// "udp6".  A literal address or host name for IPv6 must be enclosed
// in square brackets, as in "[::1]:80", "[ipv6-host]:http" or
// "[ipv6-host%zone]:80".
func ResolveUDPAddr(net, addr string) (*UDPAddr, error) {
	switch net {
	case "udp", "udp4", "udp6":
	case "": // a hint wildcard for Go 1.0 undocumented behavior
		net = "udp"
	default:
		return nil, UnknownNetworkError(net)
	}
	addrs, err := internetAddrList(net, addr, noDeadline)
	if err != nil {
		return nil, err
	}
	return addrs.first(isIPv4).(*UDPAddr), nil
}
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