From 735b3a96b7e61be03de3b6495ea5a274998fc7cd Mon Sep 17 00:00:00 2001
From: Sean Purser-Haskell <sean.purserhaskell@gmail.com>
Date: Mon, 9 May 2016 16:17:22 +0800
Subject: [PATCH 1/2] add port accessors and modifiers for TCP/UDP

---
 waterutil/tun_ipv4.go | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/waterutil/tun_ipv4.go b/waterutil/tun_ipv4.go
index 6878174..6a6bd36 100644
--- a/waterutil/tun_ipv4.go
+++ b/waterutil/tun_ipv4.go
@@ -28,11 +28,42 @@ func IPv4Source(packet []byte) net.IP {
 	return net.IPv4(packet[12], packet[13], packet[14], packet[15])
 }
 
+func SetIPv4Source(packet []byte, source net.IP) {
+	copy(packet[12:16], source)
+}
+
 func IPv4Destination(packet []byte) net.IP {
 	return net.IPv4(packet[16], packet[17], packet[18], packet[19])
 }
 
+func SetIPv4Destination(packet []byte, dest net.IP) {
+	copy(packet[16:20], dest)
+}
+
 func IPv4Payload(packet []byte) []byte {
 	ihl := packet[0] & 0x0F
 	return packet[ihl*4:]
 }
+
+// For TCP/UDP
+func IPv4SourcePort(packet []byte) uint16 {
+	payload := IPv4Payload(packet)
+	return (uint16(payload[0]) << 8) | uint16(payload[1])
+}
+
+func IPv4DestinationPort(packet []byte) uint16 {
+	payload := IPv4Payload(packet)
+	return (uint16(payload[2]) << 8) | uint16(payload[3])
+}
+
+func SetIPv4SourcePort(packet []byte, port uint16) {
+	payload := IPv4Payload(packet)
+	payload[0] = byte(port >> 8)
+	payload[1] = byte(port & 0xFF)
+}
+
+func SetIPv4DestinationPort(packet []byte, port uint16) {
+	payload := IPv4Payload(packet)
+	payload[2] = byte(port >> 8)
+	payload[3] = byte(port & 0xFF)
+}

From 93f6384fddf18bf1bc66e718d9e0edf6058fc12b Mon Sep 17 00:00:00 2001
From: Sean Purser-Haskell <sean.purserhaskell@gmail.com>
Date: Tue, 10 May 2016 11:30:32 +0800
Subject: [PATCH 2/2] Fix to use To4()

This will also produce a runtime error if non-IPv4 addresses are passed
in.
---
 waterutil/tun_ipv4.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/waterutil/tun_ipv4.go b/waterutil/tun_ipv4.go
index 6a6bd36..6e249e5 100644
--- a/waterutil/tun_ipv4.go
+++ b/waterutil/tun_ipv4.go
@@ -29,7 +29,7 @@ func IPv4Source(packet []byte) net.IP {
 }
 
 func SetIPv4Source(packet []byte, source net.IP) {
-	copy(packet[12:16], source)
+	copy(packet[12:16], source.To4())
 }
 
 func IPv4Destination(packet []byte) net.IP {
@@ -37,7 +37,7 @@ func IPv4Destination(packet []byte) net.IP {
 }
 
 func SetIPv4Destination(packet []byte, dest net.IP) {
-	copy(packet[16:20], dest)
+	copy(packet[16:20], dest.To4())
 }
 
 func IPv4Payload(packet []byte) []byte {