Implement support for SACK based recovery(RFC 6675).

PiperOrigin-RevId: 246536003
Change-Id: I118b745f45040be9c70cb6a1028acdb06c78d8c9

1 files changed, 28 insertions, 4 deletions

diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index fa721a7f8..e08eb6533 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -355,13 +355,27 @@ func (c *Context) SendPacket(payload []byte, h *Headers) {
 
 // SendAck sends an ACK packet.
 func (c *Context) SendAck(seq seqnum.Value, bytesReceived int) {
+	c.SendAckWithSACK(seq, bytesReceived, nil)
+}
+
+// SendAckWithSACK sends an ACK packet which includes the sackBlocks specified.
+func (c *Context) SendAckWithSACK(seq seqnum.Value, bytesReceived int, sackBlocks []header.SACKBlock) {
+	options := make([]byte, 40)
+	offset := 0
+	if len(sackBlocks) > 0 {
+		offset += header.EncodeNOP(options[offset:])
+		offset += header.EncodeNOP(options[offset:])
+		offset += header.EncodeSACKBlocks(sackBlocks, options[offset:])
+	}
+
 	c.SendPacket(nil, &Headers{
 		SrcPort: TestPort,
 		DstPort: c.Port,
 		Flags:   header.TCPFlagAck,
-		SeqNum:  seqnum.Value(testInitialSequenceNumber).Add(1),
+		SeqNum:  seq,
 		AckNum:  c.IRS.Add(1 + seqnum.Size(bytesReceived)),
 		RcvWnd:  30000,
+		TCPOpts: options[:offset],
 	})
 }
 
@@ -369,9 +383,17 @@ func (c *Context) SendAck(seq seqnum.Value, bytesReceived int) {
 // verifies that the packet packet payload of packet matches the slice
 // of data indicated by offset & size.
 func (c *Context) ReceiveAndCheckPacket(data []byte, offset, size int) {
+	c.ReceiveAndCheckPacketWithOptions(data, offset, size, 0)
+}
+
+// ReceiveAndCheckPacketWithOptions reads a packet from the link layer endpoint
+// and verifies that the packet packet payload of packet matches the slice of
+// data indicated by offset & size and skips optlen bytes in addition to the IP
+// TCP headers when comparing the data.
+func (c *Context) ReceiveAndCheckPacketWithOptions(data []byte, offset, size, optlen int) {
 	b := c.GetPacket()
 	checker.IPv4(c.t, b,
-		checker.PayloadLen(size+header.TCPMinimumSize),
+		checker.PayloadLen(size+header.TCPMinimumSize+optlen),
 		checker.TCP(
 			checker.DstPort(TestPort),
 			checker.SeqNum(uint32(c.IRS.Add(seqnum.Size(1+offset)))),
@@ -381,7 +403,7 @@ func (c *Context) ReceiveAndCheckPacket(data []byte, offset, size int) {
 	)
 
 	pdata := data[offset:][:size]
-	if p := b[header.IPv4MinimumSize+header.TCPMinimumSize:]; bytes.Compare(pdata, p) != 0 {
+	if p := b[header.IPv4MinimumSize+header.TCPMinimumSize+optlen:]; bytes.Compare(pdata, p) != 0 {
 		c.t.Fatalf("Data is different: expected %v, got %v", pdata, p)
 	}
 }
@@ -683,12 +705,14 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 	b := c.GetPacket()
 	// Validate that the syn has the timestamp option and a valid
 	// TS value.
+	mss := uint16(c.linkEP.MTU() - header.IPv4MinimumSize - header.TCPMinimumSize)
+
 	checker.IPv4(c.t, b,
 		checker.TCP(
 			checker.DstPort(TestPort),
 			checker.TCPFlags(header.TCPFlagSyn),
 			checker.TCPSynOptions(header.TCPSynOptions{
-				MSS:           uint16(c.linkEP.MTU() - header.IPv4MinimumSize - header.TCPMinimumSize),
+				MSS:           mss,
 				TS:            true,
 				WS:            defaultWindowScale,
 				SACKPermitted: c.SACKEnabled(),