a:addr: implemented with ALTERNATE-SERVER

addr.go

@@ -0,0 +1,105 @@
+package stun
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+)
+
+// MappedAddress represents MAPPED-ADDRESS attribute.
+//
+// This attribute is used only by servers for achieving backwards
+// compatibility with RFC 3489 clients.
+// https://tools.ietf.org/html/rfc5389#section-15.4
+type MappedAddress struct {
+	IP   net.IP
+	Port int
+}
+
+// AlternateServer represents ALTERNATE-SERVER attribute.
+//
+// https://tools.ietf.org/html/rfc5389#section-15.4
+type AlternateServer struct {
+	IP   net.IP
+	Port int
+}
+
+// AddTo adds ALTERNATE-SERVER attribute to message.
+func (s *AlternateServer) AddTo(m *Message) error {
+	a := (*MappedAddress)(s)
+	return a.addAs(m, AttrAlternateServer)
+}
+
+// GetFrom decodes ALTERNATE-SERVER from message.
+func (s *AlternateServer) GetFrom(m *Message) error {
+	a := (*MappedAddress)(s)
+	return a.getAs(m, AttrAlternateServer)
+}
+
+func (a MappedAddress) String() string {
+	return net.JoinHostPort(a.IP.String(), strconv.Itoa(a.Port))
+}
+
+func (a *MappedAddress) getAs(m *Message, t AttrType) error {
+	v, err := m.Get(t)
+	if err != nil {
+		return err
+	}
+	family := bin.Uint16(v[0:2])
+	if family != familyIPv6 && family != familyIPv4 {
+		return newDecodeErr("xor-mapped address", "family",
+			fmt.Sprintf("bad value %d", family),
+		)
+	}
+	ipLen := net.IPv4len
+	if family == familyIPv6 {
+		ipLen = net.IPv6len
+	}
+	// Ensuring len(a.IP) == ipLen and reusing a.IP.
+	if len(a.IP) < ipLen {
+		a.IP = a.IP[:cap(a.IP)]
+		for len(a.IP) < ipLen {
+			a.IP = append(a.IP, 0)
+		}
+	}
+	a.IP = a.IP[:ipLen]
+	for i := range a.IP {
+		a.IP[i] = 0
+	}
+	a.Port = int(bin.Uint16(v[2:4]))
+	copy(a.IP, v[4:])
+	return nil
+}
+
+func (a *MappedAddress) addAs(m *Message, t AttrType) error {
+	var (
+		family = familyIPv4
+		ip     = a.IP
+	)
+	if len(a.IP) == net.IPv6len {
+		if isIPv4(ip) {
+			ip = ip[12:16] // like in ip.To4()
+		} else {
+			family = familyIPv6
+		}
+	} else if len(ip) != net.IPv4len {
+		return ErrBadIPLength
+	}
+	value := make([]byte, 128)
+	value[0] = 0 // first 8 bits are zeroes
+	bin.PutUint16(value[0:2], family)
+	bin.PutUint16(value[2:4], uint16(a.Port))
+	copy(value[4:], ip)
+	m.Add(t, value[:4+len(ip)])
+	return nil
+}
+
+// AddTo adds MAPPED-ADDRESS to message.
+func (a *MappedAddress) AddTo(m *Message) error {
+	return a.addAs(m, AttrMappedAddress)
+}
+
+// GetFrom decodes MAPPED-ADDRESS from message.
+func (a *MappedAddress) GetFrom(m *Message) error {
+	return a.getAs(m, AttrMappedAddress)
+}