Adds support to dump out cubic internal state.

PiperOrigin-RevId: 207754087
Change-Id: I83abce64348ea93f8692da81a881b364dae2158b

pkg/tcpip/stack/stack.go

@@ -56,6 +56,20 @@ type transportProtocolState struct {
 // passed to stack.AddTCPProbe.
 type TCPProbeFunc func(s TCPEndpointState)
 
+// TCPCubicState is used to hold a copy of the internal cubic state when the
+// TCPProbeFunc is invoked.
+type TCPCubicState struct {
+	WLastMax                float64
+	WMax                    float64
+	T                       time.Time
+	TimeSinceLastCongestion time.Duration
+	C                       float64
+	K                       float64
+	Beta                    float64
+	WC                      float64
+	WEst                    float64
+}
+
 // TCPEndpointID is the unique 4 tuple that identifies a given endpoint.
 type TCPEndpointID struct {
 	// LocalPort is the local port associated with the endpoint.
@@ -180,6 +194,9 @@ type TCPSenderState struct {
 
 	// FastRecovery holds the fast recovery state for the endpoint.
 	FastRecovery TCPFastRecoveryState
+
+	// Cubic holds the state related to CUBIC congestion control.
+	Cubic TCPCubicState
 }
 
 // TCPSACKInfo holds TCP SACK related information for a given TCP endpoint.

pkg/tcpip/transport/tcp/endpoint.go

@@ -1452,5 +1452,19 @@ func (e *endpoint) completeState() stack.TCPEndpointState {
 		SndWndScale:      e.snd.sndWndScale,
 		MaxSentAck:       e.snd.maxSentAck,
 	}
+
+	if cubic, ok := e.snd.cc.(*cubicState); ok {
+		s.Sender.Cubic = stack.TCPCubicState{
+			WMax:                    cubic.wMax,
+			WLastMax:                cubic.wLastMax,
+			T:                       cubic.t,
+			TimeSinceLastCongestion: time.Since(cubic.t),
+			C:                       cubic.c,
+			K:                       cubic.k,
+			Beta:                    cubic.beta,
+			WC:                      cubic.wC,
+			WEst:                    cubic.wEst,
+		}
+	}
 	return s
 }