Add support for TCP receive buffer auto tuning.

The implementation is similar to linux where we track the number of bytes
consumed by the application to grow the receive buffer of a given TCP endpoint.

This ensures that the advertised window grows at a reasonable rate to accomodate
for the sender's rate and prevents large amounts of data being held in stack
buffers if the application is not actively reading or not reading fast enough.

The original paper that was used to implement the linux receive buffer auto-
tuning is available @ https://public.lanl.gov/radiant/pubs/drs/lacsi2001.pdf

NOTE: Linux does not implement DRS as defined in that paper, it's just a good
reference to understand the solution space.

Updates #230

PiperOrigin-RevId: 253168283

1 files changed, 29 insertions, 12 deletions

diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 2cfeed224..630dd7925 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -72,12 +72,6 @@ const (
 	testInitialSequenceNumber = 789
 )
 
-// defaultWindowScale value specified here depends on the tcp.DefaultBufferSize
-// constant defined in the tcp/endpoint.go because the tcp.DefaultBufferSize is
-// used in tcp.newHandshake to determine the window scale to use when sending a
-// SYN/SYN-ACK.
-var defaultWindowScale = tcp.FindWndScale(tcp.DefaultBufferSize)
-
 // Headers is used to represent the TCP header fields when building a
 // new packet.
 type Headers struct {
@@ -134,6 +128,10 @@ type Context struct {
 	// TimeStampEnabled is true if ep is connected with the timestamp option
 	// enabled.
 	TimeStampEnabled bool
+
+	// WindowScale is the expected window scale in SYN packets sent by
+	// the stack.
+	WindowScale uint8
 }
 
 // New allocates and initializes a test context containing a new
@@ -142,11 +140,11 @@ func New(t *testing.T, mtu uint32) *Context {
 	s := stack.New([]string{ipv4.ProtocolName, ipv6.ProtocolName}, []string{tcp.ProtocolName}, stack.Options{})
 
 	// Allow minimum send/receive buffer sizes to be 1 during tests.
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.SendBufferSizeOption{1, tcp.DefaultBufferSize, tcp.DefaultBufferSize * 10}); err != nil {
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.SendBufferSizeOption{1, tcp.DefaultSendBufferSize, 10 * tcp.DefaultSendBufferSize}); err != nil {
 		t.Fatalf("SetTransportProtocolOption failed: %v", err)
 	}
 
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.ReceiveBufferSizeOption{1, tcp.DefaultBufferSize, tcp.DefaultBufferSize * 10}); err != nil {
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.ReceiveBufferSizeOption{1, tcp.DefaultReceiveBufferSize, 10 * tcp.DefaultReceiveBufferSize}); err != nil {
 		t.Fatalf("SetTransportProtocolOption failed: %v", err)
 	}
 
@@ -184,9 +182,10 @@ func New(t *testing.T, mtu uint32) *Context {
 	})
 
 	return &Context{
-		t:      t,
-		s:      s,
-		linkEP: linkEP,
+		t:           t,
+		s:           s,
+		linkEP:      linkEP,
+		WindowScale: uint8(tcp.FindWndScale(tcp.DefaultReceiveBufferSize)),
 	}
 }
 
@@ -672,6 +671,21 @@ func (r *RawEndpoint) VerifyACKWithTS(tsVal uint32) {
 	r.RecentTS = opts.TSVal
 }
 
+// VerifyACKRcvWnd verifies that the window advertised by the incoming ACK
+// matches the provided rcvWnd.
+func (r *RawEndpoint) VerifyACKRcvWnd(rcvWnd uint16) {
+	ackPacket := r.C.GetPacket()
+	checker.IPv4(r.C.t, ackPacket,
+		checker.TCP(
+			checker.DstPort(r.SrcPort),
+			checker.TCPFlags(header.TCPFlagAck),
+			checker.SeqNum(uint32(r.AckNum)),
+			checker.AckNum(uint32(r.NextSeqNum)),
+			checker.Window(rcvWnd),
+		),
+	)
+}
+
 // VerifyACKNoSACK verifies that the ACK does not contain a SACK block.
 func (r *RawEndpoint) VerifyACKNoSACK() {
 	r.VerifyACKHasSACK(nil)
@@ -732,7 +746,7 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 			checker.TCPSynOptions(header.TCPSynOptions{
 				MSS:           mss,
 				TS:            true,
-				WS:            defaultWindowScale,
+				WS:            int(c.WindowScale),
 				SACKPermitted: c.SACKEnabled(),
 			}),
 		),
@@ -747,6 +761,9 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 	// Build options w/ tsVal to be sent in the SYN-ACK.
 	synAckOptions := make([]byte, header.TCPOptionsMaximumSize)
 	offset := 0
+	if wantOptions.WS != -1 {
+		offset += header.EncodeWSOption(wantOptions.WS, synAckOptions[offset:])
+	}
 	if wantOptions.TS {
 		offset += header.EncodeTSOption(wantOptions.TSVal, synOptions.TSVal, synAckOptions[offset:])
 	}