Test that we have PAWS mechanism

If there is a Timestamps option in the arriving segment and SEG.TSval
< TS.Recent and if TS.Recent is valid, then treat the arriving segment
as not acceptable: Send an acknowledgement in reply as specified in
RFC-793 page 69 and drop the segment.

https://tools.ietf.org/html/rfc1323#page-19

PiperOrigin-RevId: 312590678

1 files changed, 17 insertions, 12 deletions

diff --git a/pkg/tcpip/header/tcp.go b/pkg/tcpip/header/tcp.go
index 29454c4b9..4c6f808e5 100644
--- a/pkg/tcpip/header/tcp.go
+++ b/pkg/tcpip/header/tcp.go
@@ -66,6 +66,14 @@ const (
 	TCPOptionSACK          = 5
 )
 
+// Option Lengths.
+const (
+	TCPOptionMSSLength           = 4
+	TCPOptionTSLength            = 10
+	TCPOptionWSLength            = 3
+	TCPOptionSackPermittedLength = 2
+)
+
 // TCPFields contains the fields of a TCP packet. It is used to describe the
 // fields of a packet that needs to be encoded.
 type TCPFields struct {
@@ -494,14 +502,11 @@ func ParseTCPOptions(b []byte) TCPOptions {
 // returns without encoding anything. It returns the number of bytes written to
 // the provided buffer.
 func EncodeMSSOption(mss uint32, b []byte) int {
-	// mssOptionSize is the number of bytes in a valid MSS option.
-	const mssOptionSize = 4
-
-	if len(b) < mssOptionSize {
+	if len(b) < TCPOptionMSSLength {
 		return 0
 	}
-	b[0], b[1], b[2], b[3] = TCPOptionMSS, mssOptionSize, byte(mss>>8), byte(mss)
-	return mssOptionSize
+	b[0], b[1], b[2], b[3] = TCPOptionMSS, TCPOptionMSSLength, byte(mss>>8), byte(mss)
+	return TCPOptionMSSLength
 }
 
 // EncodeWSOption encodes the WS TCP option with the WS value in the
@@ -509,10 +514,10 @@ func EncodeMSSOption(mss uint32, b []byte) int {
 // returns without encoding anything. It returns the number of bytes written to
 // the provided buffer.
 func EncodeWSOption(ws int, b []byte) int {
-	if len(b) < 3 {
+	if len(b) < TCPOptionWSLength {
 		return 0
 	}
-	b[0], b[1], b[2] = TCPOptionWS, 3, uint8(ws)
+	b[0], b[1], b[2] = TCPOptionWS, TCPOptionWSLength, uint8(ws)
 	return int(b[1])
 }
 
@@ -521,10 +526,10 @@ func EncodeWSOption(ws int, b []byte) int {
 // just returns without encoding anything. It returns the number of bytes
 // written to the provided buffer.
 func EncodeTSOption(tsVal, tsEcr uint32, b []byte) int {
-	if len(b) < 10 {
+	if len(b) < TCPOptionTSLength {
 		return 0
 	}
-	b[0], b[1] = TCPOptionTS, 10
+	b[0], b[1] = TCPOptionTS, TCPOptionTSLength
 	binary.BigEndian.PutUint32(b[2:], tsVal)
 	binary.BigEndian.PutUint32(b[6:], tsEcr)
 	return int(b[1])
@@ -535,11 +540,11 @@ func EncodeTSOption(tsVal, tsEcr uint32, b []byte) int {
 // encoding anything. It returns the number of bytes written to the provided
 // buffer.
 func EncodeSACKPermittedOption(b []byte) int {
-	if len(b) < 2 {
+	if len(b) < TCPOptionSackPermittedLength {
 		return 0
 	}
 
-	b[0], b[1] = TCPOptionSACKPermitted, 2
+	b[0], b[1] = TCPOptionSACKPermitted, TCPOptionSackPermittedLength
 	return int(b[1])
 }