Use available helpers to set fields

...and introduce a helper to set the Checksum.

PiperOrigin-RevId: 417437300

pkg/tcpip/header/checksum.go

@@ -24,6 +24,11 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 )
 
+// PutChecksum puts the checksum in the provided byte slice.
+func PutChecksum(b []byte, xsum uint16) {
+	binary.BigEndian.PutUint16(b, xsum)
+}
+
 func calculateChecksum(buf []byte, odd bool, initial uint32) (uint16, bool) {
 	v := initial
 

pkg/tcpip/header/icmpv4.go

@@ -139,7 +139,7 @@ func (b ICMPv4) Checksum() uint16 {
 
 // SetChecksum sets the ICMP checksum field.
 func (b ICMPv4) SetChecksum(checksum uint16) {
-	binary.BigEndian.PutUint16(b[icmpv4ChecksumOffset:], checksum)
+	PutChecksum(b[icmpv4ChecksumOffset:], checksum)
 }
 
 // SourcePort implements Transport.SourcePort.

pkg/tcpip/header/icmpv6.go

@@ -199,7 +199,7 @@ func (b ICMPv6) Checksum() uint16 {
 
 // SetChecksum sets the ICMP checksum field.
 func (b ICMPv6) SetChecksum(checksum uint16) {
-	binary.BigEndian.PutUint16(b[icmpv6ChecksumOffset:], checksum)
+	PutChecksum(b[icmpv6ChecksumOffset:], checksum)
 }
 
 // SourcePort implements Transport.SourcePort.

pkg/tcpip/header/ipv4.go

@@ -380,7 +380,7 @@ func (b IPv4) SetTotalLength(totalLength uint16) {
 
 // SetChecksum sets the checksum field of the IPv4 header.
 func (b IPv4) SetChecksum(v uint16) {
-	binary.BigEndian.PutUint16(b[checksum:], v)
+	PutChecksum(b[checksum:], v)
 }
 
 // SetFlagsFragmentOffset sets the "flags" and "fragment offset" fields of the

pkg/tcpip/header/tcp.go

@@ -289,7 +289,7 @@ func (b TCP) SetDestinationPort(port uint16) {
 
 // SetChecksum sets the checksum field of the TCP header.
 func (b TCP) SetChecksum(checksum uint16) {
-	binary.BigEndian.PutUint16(b[TCPChecksumOffset:], checksum)
+	PutChecksum(b[TCPChecksumOffset:], checksum)
 }
 
 // SetDataOffset sets the data offset field of the TCP header. headerLen should
@@ -318,8 +318,8 @@ func (b TCP) SetWindowSize(rcvwnd uint16) {
 	binary.BigEndian.PutUint16(b[TCPWinSizeOffset:], rcvwnd)
 }
 
-// SetUrgentPoiner sets the window size field of the TCP header.
-func (b TCP) SetUrgentPoiner(urgentPointer uint16) {
+// SetUrgentPointer sets the window size field of the TCP header.
+func (b TCP) SetUrgentPointer(urgentPointer uint16) {
 	binary.BigEndian.PutUint16(b[TCPUrgentPtrOffset:], urgentPointer)
 }
 
@@ -360,11 +360,11 @@ func (b TCP) encodeSubset(seq, ack uint32, flags TCPFlags, rcvwnd uint16) {
 // Encode encodes all the fields of the TCP header.
 func (b TCP) Encode(t *TCPFields) {
 	b.encodeSubset(t.SeqNum, t.AckNum, t.Flags, t.WindowSize)
-	binary.BigEndian.PutUint16(b[TCPSrcPortOffset:], t.SrcPort)
-	binary.BigEndian.PutUint16(b[TCPDstPortOffset:], t.DstPort)
-	b[TCPDataOffset] = (t.DataOffset / 4) << 4
-	binary.BigEndian.PutUint16(b[TCPChecksumOffset:], t.Checksum)
-	binary.BigEndian.PutUint16(b[TCPUrgentPtrOffset:], t.UrgentPointer)
+	b.SetSourcePort(t.SrcPort)
+	b.SetDestinationPort(t.DstPort)
+	b.SetDataOffset(t.DataOffset)
+	b.SetChecksum(t.Checksum)
+	b.SetUrgentPointer(t.UrgentPointer)
 }
 
 // EncodePartial updates a subset of the fields of the TCP header. It is useful

pkg/tcpip/header/udp.go

@@ -101,7 +101,7 @@ func (b UDP) SetDestinationPort(port uint16) {
 
 // SetChecksum sets the "checksum" field of the UDP header.
 func (b UDP) SetChecksum(checksum uint16) {
-	binary.BigEndian.PutUint16(b[udpChecksum:], checksum)
+	PutChecksum(b[udpChecksum:], checksum)
 }
 
 // SetLength sets the "length" field of the UDP header.
@@ -125,10 +125,10 @@ func (b UDP) IsChecksumValid(src, dst tcpip.Address, payloadChecksum uint16) boo
 
 // Encode encodes all the fields of the UDP header.
 func (b UDP) Encode(u *UDPFields) {
-	binary.BigEndian.PutUint16(b[udpSrcPort:], u.SrcPort)
-	binary.BigEndian.PutUint16(b[udpDstPort:], u.DstPort)
-	binary.BigEndian.PutUint16(b[udpLength:], u.Length)
-	binary.BigEndian.PutUint16(b[udpChecksum:], u.Checksum)
+	b.SetSourcePort(u.SrcPort)
+	b.SetDestinationPort(u.DstPort)
+	b.SetLength(u.Length)
+	b.SetChecksum(u.Checksum)
 }
 
 // SetSourcePortWithChecksumUpdate implements ChecksummableTransport.

test/packetimpact/testbench/layers.go

@@ -1089,7 +1089,7 @@ func (l *TCP) ToBytes() ([]byte, error) {
 		h.SetWindowSize(32768)
 	}
 	if l.UrgentPointer != nil {
-		h.SetUrgentPoiner(*l.UrgentPointer)
+		h.SetUrgentPointer(*l.UrgentPointer)
 	}
 	copy(b[header.TCPMinimumSize:], l.Options)
 	header.AddTCPOptionPadding(b[header.TCPMinimumSize:], len(l.Options))