add NewAdvertiseFromSolicit (#50)

add NewAdvertiseFromSolicit

2 files changed, 50 insertions, 0 deletions

diff --git a/dhcpv6/dhcpv6_test.go b/dhcpv6/dhcpv6_test.go
index 17a8896..2e79f1f 100644
--- a/dhcpv6/dhcpv6_test.go
+++ b/dhcpv6/dhcpv6_test.go
@@ -82,5 +82,23 @@ func TestFromAndToBytes(t *testing.T) {
 	require.Equal(t, expected, toBytes)
 }
 
+func withServerID(d DHCPv6) DHCPv6 {
+	sid := OptServerId{}
+	d.AddOption(&sid)
+	return d
+}
+
+func TestNewAdvertiseFromSolicit(t *testing.T) {
+	s := DHCPv6Message{}
+	s.SetMessage(SOLICIT)
+	s.SetTransactionID(0xabcdef)
+	cid := OptClientId{}
+	s.AddOption(&cid)
+
+	a, err := NewAdvertiseFromSolicit(&s, withServerID)
+	require.NoError(t, err)
+	require.Equal(t, a.(*DHCPv6Message).TransactionID(), s.TransactionID())
+}
+
 // TODO test NewSolicit
 //      test String and Summary
diff --git a/dhcpv6/dhcpv6message.go b/dhcpv6/dhcpv6message.go
index 0cf2360..60b7af5 100644
--- a/dhcpv6/dhcpv6message.go
+++ b/dhcpv6/dhcpv6message.go
@@ -3,6 +3,7 @@ package dhcpv6
 import (
 	"crypto/rand"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"log"
 	"net"
@@ -106,6 +107,37 @@ func NewSolicitForInterface(ifname string, modifiers ...Modifier) (DHCPv6, error
 	return d, nil
 }
 
+// NewAdvertiseFromSolicit creates a new ADVERTISE packet based on an SOLICIT packet.
+func NewAdvertiseFromSolicit(solicit DHCPv6, modifiers ...Modifier) (DHCPv6, error) {
+	if solicit == nil {
+		return nil, errors.New("SOLICIT cannot be nil")
+	}
+	if solicit.Type() != SOLICIT {
+		return nil, errors.New("The passed SOLICIT must have SOLICIT type set")
+	}
+	sol, ok := solicit.(*DHCPv6Message)
+	if !ok {
+		return nil, errors.New("The passed SOLICIT must be of DHCPv6Message type")
+	}
+	// build ADVERTISE from SOLICIT
+	adv := DHCPv6Message{}
+	adv.SetMessage(ADVERTISE)
+	adv.SetTransactionID(sol.TransactionID())
+	// add Client ID
+	cid := sol.GetOneOption(OPTION_CLIENTID)
+	if cid == nil {
+		return nil, errors.New("Client ID cannot be nil in SOLICIT when building ADVERTISE")
+	}
+	adv.AddOption(cid)
+
+	// apply modifiers
+	d := DHCPv6(&adv)
+	for _, mod := range modifiers {
+		d = mod(d)
+	}
+	return d, nil
+}
+
 // NewRequestFromAdvertise creates a new REQUEST packet based on an ADVERTISE
 // packet options.
 func NewRequestFromAdvertise(advertise DHCPv6, modifiers ...Modifier) (DHCPv6, error) {