From c41aa7926550e6138d4c8aef021ede01fc5e02d4 Mon Sep 17 00:00:00 2001
From: Matt Layher <mdlayher@gmail.com>
Date: Sat, 3 Feb 2018 08:42:56 -0500
Subject: [PATCH] dhcp4: parse transaction ID as a byte slice

---
 dhcp4/conn_test.go         | 2 +-
 dhcp4/packet.go            | 6 +++---
 dhcp4/testdata/dhcp.parsed | 8 ++++----
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/dhcp4/conn_test.go b/dhcp4/conn_test.go
index 2bce235..8070946 100644
--- a/dhcp4/conn_test.go
+++ b/dhcp4/conn_test.go
@@ -36,7 +36,7 @@ func testConn(t *testing.T, impl conn, addr string) {
 
 	p := &Packet{
 		Type:          MsgDiscover,
-		TransactionID: "1234",
+		TransactionID: []byte("1234"),
 		Broadcast:     true,
 		HardwareAddr:  mac,
 	}
diff --git a/dhcp4/packet.go b/dhcp4/packet.go
index bb0ccc6..114874b 100644
--- a/dhcp4/packet.go
+++ b/dhcp4/packet.go
@@ -67,7 +67,7 @@ func (mt MessageType) String() string {
 // Packet represents a DHCP packet.
 type Packet struct {
 	Type          MessageType
-	TransactionID string
+	TransactionID []byte // Always 4 bytes
 	Broadcast     bool
 	HardwareAddr  net.HardwareAddr // Only ethernet supported at the moment
 
@@ -175,7 +175,7 @@ func (p *Packet) Marshal() ([]byte, error) {
 	// Hops = 0
 	ret.WriteByte(0)
 	// Transaction ID
-	ret.WriteString(p.TransactionID)
+	ret.Write(p.TransactionID)
 	// Seconds elapsed
 	ret.Write([]byte{0, 0})
 	// Broadcast flag
@@ -267,7 +267,7 @@ func Unmarshal(bs []byte) (*Packet, error) {
 		return nil, fmt.Errorf("packet has unsupported hardware address type/length %d/%d", bs[1], bs[2])
 	}
 	ret.HardwareAddr = net.HardwareAddr(bs[28:34])
-	ret.TransactionID = string(bs[4:8])
+	ret.TransactionID = bs[4:8]
 	if binary.BigEndian.Uint16(bs[10:12])&0x8000 != 0 {
 		ret.Broadcast = true
 	}
diff --git a/dhcp4/testdata/dhcp.parsed b/dhcp4/testdata/dhcp.parsed
index e1f9bf7..d129287 100644
--- a/dhcp4/testdata/dhcp.parsed
+++ b/dhcp4/testdata/dhcp.parsed
@@ -1,5 +1,5 @@
 DHCPDISCOVER
-  "\x9bN\x05W"
+  []byte{0x9b, 0x4e, 0x5, 0x57}
   Broadcast
   MAC: d0:50:99:4e:05:57
   ClientIP: 0.0.0.0
@@ -19,7 +19,7 @@ DHCPDISCOVER
     97: []byte{0x0, 0x0, 0x2, 0x0, 0x3, 0x0, 0x4, 0x0, 0x5, 0x0, 0x6, 0x0, 0x7, 0x0, 0x8, 0x0, 0x9}
 ======
 DHCPOFFER
-  "\x9bN\x05W"
+  []byte{0x9b, 0x4e, 0x5, 0x57}
   Broadcast
   MAC: d0:50:99:4e:05:57
   ClientIP: 0.0.0.0
@@ -37,7 +37,7 @@ DHCPOFFER
     97: []byte{0x0, 0x0, 0x2, 0x0, 0x3, 0x0, 0x4, 0x0, 0x5, 0x0, 0x6, 0x0, 0x7, 0x0, 0x8, 0x0, 0x9}
 ======
 DHCPOFFER
-  "\x9bN\x05W"
+  []byte{0x9b, 0x4e, 0x5, 0x57}
   Broadcast
   MAC: d0:50:99:4e:05:57
   ClientIP: 0.0.0.0
@@ -61,7 +61,7 @@ DHCPOFFER
     59: []byte{0x0, 0x0, 0xc, 0x4e}
 ======
 DHCPREQUEST
-  "R\xcf\xf0\a"
+  []byte{0x52, 0xcf, 0xf0, 0x7}
   Unicast
   MAC: 00:24:d7:ba:0b:20
   ClientIP: 0.0.0.0