Add method to forwarder to handle experiment option values.

PiperOrigin-RevId: 703625219

pkg/tcpip/stack/nic.go

@@ -1100,9 +1100,9 @@ func (n *nic) multicastForwarding(protocol tcpip.NetworkProtocolNumber) (bool, t
 	return ep.MulticastForwarding(), nil
 }
 
-// ExperimentIPOptionEnabled returns whether the NIC is responsible for
+// GetExperimentIPOptionEnabled returns whether the NIC is responsible for
 // passing the experiment IP option.
-func (n *nic) ExperimentIPOptionEnabled() bool {
+func (n *nic) GetExperimentIPOptionEnabled() bool {
 	return n.experimentIPOptionEnabled
 }
 

pkg/tcpip/transport/internal/network/endpoint.go

@@ -311,7 +311,7 @@ func (c *WriteContext) newPacketBufferLocked(reserveHdrBytes int, data buffer.Bu
 	// https://github.com/torvalds/linux/blob/38d741cb70b/include/net/sock.h#L2519
 	// https://github.com/torvalds/linux/blob/38d741cb70b/net/core/sock.c#L2588
 	var expOptVal uint16
-	if nic, err := c.e.stack.GetNICByID(c.route.OutgoingNIC()); err == nil && nic.ExperimentIPOptionEnabled() {
+	if nic, err := c.e.stack.GetNICByID(c.route.OutgoingNIC()); err == nil && nic.GetExperimentIPOptionEnabled() {
 		expOptVal = c.e.ops.GetExperimentOptionValue()
 	}
 	if c.route.NetProto() == header.IPv6ProtocolNumber && expOptVal != 0 {
@@ -352,7 +352,7 @@ func (c *WriteContext) WritePacket(pkt *stack.PacketBuffer, headerIncluded bool)
 	}
 
 	var expOptVal uint16
-	if nic, err := c.e.stack.GetNICByID(c.route.OutgoingNIC()); err == nil && nic.ExperimentIPOptionEnabled() {
+	if nic, err := c.e.stack.GetNICByID(c.route.OutgoingNIC()); err == nil && nic.GetExperimentIPOptionEnabled() {
 		expOptVal = c.e.ops.GetExperimentOptionValue()
 	}
 

pkg/tcpip/transport/tcp/endpoint.go

@@ -3319,7 +3319,7 @@ func (e *Endpoint) GetAcceptConn() bool {
 // getExperimentOptionValue returns the experiment option value set on the
 // endpoint if experiment IP options are enabled on outgoing NIC of the route.
 func (e *Endpoint) getExperimentOptionValue(route *stack.Route) uint16 {
-	if nic, err := e.stack.GetNICByID(route.OutgoingNIC()); err == nil && nic.ExperimentIPOptionEnabled() {
+	if nic, err := e.stack.GetNICByID(route.OutgoingNIC()); err == nil && nic.GetExperimentIPOptionEnabled() {
 		return e.ops.GetExperimentOptionValue()
 	}
 	return 0

pkg/tcpip/transport/tcp/forwarder.go

@@ -15,6 +15,9 @@
 package tcp
 
 import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/buffer"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -170,3 +173,56 @@ func (r *ForwarderRequest) CreateEndpoint(queue *waiter.Queue) (tcpip.Endpoint,
 
 	return ep, nil
 }
+
+// ForwardedPacketExperimentOption returns the experiment option value from the
+// forwarded packet and a bool indicating whether an experiment option value was
+// found.
+func (r *ForwarderRequest) ForwardedPacketExperimentOption() (uint16, bool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	switch r.segment.pkt.NetworkProtocolNumber {
+	case header.IPv4ProtocolNumber:
+		h := header.IPv4(r.segment.pkt.NetworkHeader().Slice())
+		opts := h.Options()
+		iter := opts.MakeIterator()
+		for {
+			opt, done, err := iter.Next()
+			if err != nil {
+				return 0, false
+			}
+			if done {
+				return 0, false
+			}
+			if opt.Type() == header.IPv4OptionExperimentType {
+				return opt.(*header.IPv4OptionExperiment).Value(), true
+			}
+		}
+	case header.IPv6ProtocolNumber:
+		h := header.IPv6(r.segment.pkt.NetworkHeader().Slice())
+		v := r.segment.pkt.NetworkHeader().View()
+		if v != nil {
+			v.TrimFront(header.IPv6MinimumSize)
+		}
+		buf := buffer.MakeWithView(v)
+		buf.Append(r.segment.pkt.TransportHeader().View())
+		dataBuf := r.segment.pkt.Data().ToBuffer()
+		buf.Merge(&dataBuf)
+		it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(h.NextHeader()), buf)
+
+		for {
+			hdr, done, err := it.Next()
+			if done || err != nil {
+				break
+			}
+			if h, ok := hdr.(header.IPv6ExperimentExtHdr); ok {
+				hdr.Release()
+				return h.Value, true
+			}
+			hdr.Release()
+		}
+	default:
+		panic(fmt.Sprintf("Unexpected network protocol number %d", r.segment.pkt.NetworkProtocolNumber))
+	}
+	return 0, false
+}