2 files changed, 85 insertions, 0 deletions

diff --git a/dhcpv6/dhcpv6relay.go b/dhcpv6/dhcpv6relay.go
index 68f3cf0..fb2a0c1 100644
--- a/dhcpv6/dhcpv6relay.go
+++ b/dhcpv6/dhcpv6relay.go
@@ -1,6 +1,7 @@
 package dhcpv6
 
 import (
+	"errors"
 	"fmt"
 	"net"
 )
@@ -180,3 +181,53 @@ func (r *DHCPv6Relay) GetInnerPeerAddr() (net.IP, error) {
 	}
 	return addr, nil
 }
+
+// NewRelayReplFromRelayForw creates a RELAY_REPL packet based on a RELAY_FORW
+// packet and replaces the inner message with the passed DHCPv6 message.
+func NewRelayReplFromRelayForw(relayForw, msg DHCPv6) (DHCPv6, error) {
+	var (
+		err                error
+		linkAddr, peerAddr []net.IP
+		optiids            []Option
+	)
+	if relayForw == nil {
+		return nil, errors.New("RELAY_FORW cannot be nil")
+	}
+	relay, ok := relayForw.(*DHCPv6Relay)
+	if !ok {
+		return nil, errors.New("Not a DHCPv6Relay")
+	}
+	if relay.Type() != RELAY_FORW {
+		return nil, errors.New("The passed packet is not of type RELAY_FORW")
+	}	
+	if msg == nil {
+		return nil, errors.New("The passed message cannot be nil")
+	}
+	if msg.IsRelay() {
+		return nil, errors.New("The passed message cannot be a relay")
+	}
+	for {
+		linkAddr = append(linkAddr, relay.LinkAddr())
+		peerAddr = append(peerAddr, relay.PeerAddr())
+		optiids = append(optiids, relay.GetOneOption(OPTION_INTERFACE_ID))
+		decap, err := DecapsulateRelay(relay)
+		if err != nil {
+			return nil, err
+		}
+		if decap.IsRelay() {
+			relay = decap.(*DHCPv6Relay)
+		} else {
+			break
+		}
+	}
+	for i := len(linkAddr) - 1; i >= 0; i-- {
+		msg, err = EncapsulateRelay(msg, RELAY_REPL, linkAddr[i], peerAddr[i])
+		if opt := optiids[i]; opt != nil {
+			msg.AddOption(opt)
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+	return msg, nil
+}
diff --git a/dhcpv6/dhcpv6relay_test.go b/dhcpv6/dhcpv6relay_test.go
index c5989e5..e08e6a4 100644
--- a/dhcpv6/dhcpv6relay_test.go
+++ b/dhcpv6/dhcpv6relay_test.go
@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"net"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestDHCPv6Relay(t *testing.T) {
@@ -104,3 +106,35 @@ func TestDHCPv6RelayToBytes(t *testing.T) {
 		t.Fatalf("Invalid ToBytes result. Expected %v, got %v", expected, relayBytes)
 	}
 }
+
+func TestNewRelayRepFromRelayForw(t *testing.T) {
+	rf := DHCPv6Relay{}
+	rf.SetMessageType(RELAY_FORW)
+	rf.SetPeerAddr(net.IPv6linklocalallrouters)
+	rf.SetLinkAddr(net.IPv6interfacelocalallnodes)
+	oro := OptRelayMsg{}
+	s := DHCPv6Message{}
+	s.SetMessage(SOLICIT)
+	cid := OptClientId{}
+	s.AddOption(&cid)
+	oro.SetRelayMessage(&s)
+	rf.AddOption(&oro)
+
+	a, err := NewAdvertiseFromSolicit(&s)
+	require.NoError(t, err)
+	rr, err := NewRelayReplFromRelayForw(&rf, a)
+	require.NoError(t, err)
+	relay := rr.(*DHCPv6Relay)
+	require.Equal(t, rr.Type(), RELAY_REPL)
+	require.Equal(t, relay.HopCount(), rf.HopCount())
+	require.Equal(t, relay.PeerAddr(), rf.PeerAddr())
+	require.Equal(t, relay.LinkAddr(), rf.LinkAddr())
+	m, err := relay.GetInnerMessage()
+	require.NoError(t, err)
+	require.Equal(t, m, a)
+
+	rr, err = NewRelayReplFromRelayForw(nil, a)
+	require.Error(t, err)
+	rr, err = NewRelayReplFromRelayForw(&rf, nil)
+	require.Error(t, err)
+}