// parameters.
func ResolveUnixAddr(network, address string) (*UnixAddr, error) {
	switch network {
	case "unix", "unixgram", "unixpacket":
		return &UnixAddr{Name: address, Net: network}, nil
	default:
		return nil, UnknownNetworkError(network)
	}
}

// UnixConn is an implementation of the [Conn] interface for connections
// to Unix domain sockets.
type UnixConn struct {
	conn
}

// SyscallConn returns a raw network connection.

	if err != nil {
		return 0, err
	}
	if len(lines) == 0 {
		return 0, UnknownNetworkError(name)
	}
	f := getFields(lines[0])
	if len(f) < 2 {
		return 0, UnknownNetworkError(name)
	}
	s := f[1]
	if n, _, ok := dtoi(s[bytealg.IndexByteString(s, '=')+1:]); ok {
		return n, nil
	}
	return 0, UnknownNetworkError(name)
}

func ResolveUDPAddr(network, address string) (*UDPAddr, error) {
	switch network {
	case "udp", "udp4", "udp6":
	case "": // a hint wildcard for Go 1.0 undocumented behavior
		network = "udp"
	default:
		return nil, UnknownNetworkError(network)
	}
	addrs, err := DefaultResolver.internetAddrList(context.Background(), network, address)
	if err != nil {
		return nil, err
	}
	return addrs.forResolve(network, address).(*UDPAddr), nil
}

func ResolveTCPAddr(network, address string) (*TCPAddr, error) {
	switch network {
	case "tcp", "tcp4", "tcp6":
	case "": // a hint wildcard for Go 1.0 undocumented behavior
		network = "tcp"
	default:
		return nil, UnknownNetworkError(network)
	}
	addrs, err := DefaultResolver.internetAddrList(context.Background(), network, address)
	if err != nil {
		return nil, err
	}
	return addrs.forResolve(network, address).(*TCPAddr), nil
}

		}
	case "udp6":
		fd := ln.(*UDPConn).fd
		if fd.family != syscall.AF_INET6 {
			return fmt.Errorf("%v got %v; want %v", fd.laddr, fd.family, syscall.AF_INET6)
		}
	default:
		return UnknownNetworkError(network)
	}
	return nil
}

func checkSecondListener(network, address string, err error) error {
	switch network {
	case "tcp", "tcp4", "tcp6":
		if err == nil {

func (e *AddrError) Timeout() bool   { return false }
func (e *AddrError) Temporary() bool { return false }

type UnknownNetworkError string

func (e UnknownNetworkError) Error() string   { return "unknown network " + string(e) }
func (e UnknownNetworkError) Timeout() bool   { return false }
func (e UnknownNetworkError) Temporary() bool { return false }

type InvalidAddrError string

		switch network {
		case "tcp", "tcp4", "tcp6":
		case "udp", "udp4", "udp6":
		case "ip", "ip4", "ip6":
			if needsProto {
				return "", 0, UnknownNetworkError(network)
			}
		case "unix", "unixgram", "unixpacket":
		default:
			return "", 0, UnknownNetworkError(network)
		}
		return network, 0, nil
	}
	afnet = network[:i]
	switch afnet {
	case "ip", "ip4", "ip6":
		protostr := network[i+1:]

second:
	if isPlatformError(nestedErr) {
		return nil
	}
	switch err := nestedErr.(type) {
	case *AddrError, *timeoutError, *DNSError, InvalidAddrError, *ParseError, *poll.DeadlineExceededError, UnknownNetworkError:
		return nil
	case interface{ isAddrinfoErrno() }:
		return nil
	case *os.SyscallError:
		nestedErr = err.Err
		goto third
	case *fs.PathError: // for Plan 9
		nestedErr = err.Err
		goto third

	}
}

// The various errors should implement the Error interface.
func TestErrors(t *testing.T) {
	var (
		_ Error = &OpError{}
		_ Error = &ParseError{}
		_ Error = &AddrError{}
		_ Error = UnknownNetworkError("")
		_ Error = InvalidAddrError("")
		_ Error = &timeoutError{}
		_ Error = &DNSConfigError{}
		_ Error = &DNSError{}
	)

	// ErrClosed was introduced as type error, so we can't check

	{"", "[::1]:0", &UDPAddr{IP: ParseIP("::1"), Port: 0}, nil},         // Go 1.0 behavior

	{"udp", ":12345", &UDPAddr{Port: 12345}, nil},

	{"http", "127.0.0.1:0", nil, UnknownNetworkError("http")},

	{"udp", "127.0.0.1:domain", &UDPAddr{IP: ParseIP("127.0.0.1"), Port: 53}, nil},
	{"udp", "[::ffff:127.0.0.1]:domain", &UDPAddr{IP: ParseIP("::ffff:127.0.0.1"), Port: 53}, nil},