Add a type to represent the NDP Router Advertisement message.

This change is in preparation for NDP Router Discovery where the stack will need
to handle NDP Router Advertisments.

Tests: Test that given an NDP Router Advertisement buffer (body of an ICMPv6
packet, correct values are returned by the field getters).
PiperOrigin-RevId: 276146817

pkg/tcpip/header/BUILD

@@ -19,6 +19,7 @@ go_library(
         "ndp_neighbor_advert.go",
         "ndp_neighbor_solicit.go",
         "ndp_options.go",
+        "ndp_router_advert.go",
         "tcp.go",
         "udp.go",
     ],

pkg/tcpip/header/ndp_neighbor_advert.go

@@ -18,6 +18,8 @@ import "gvisor.dev/gvisor/pkg/tcpip"
 
 // NDPNeighborAdvert is an NDP Neighbor Advertisement message. It will
 // only contain the body of an ICMPv6 packet.
+//
+// See RFC 4861 section 4.4 for more details.
 type NDPNeighborAdvert []byte
 
 const (

pkg/tcpip/header/ndp_neighbor_solicit.go

@@ -18,6 +18,8 @@ import "gvisor.dev/gvisor/pkg/tcpip"
 
 // NDPNeighborSolicit is an NDP Neighbor Solicitation message. It will only
 // contain the body of an ICMPv6 packet.
+//
+// See RFC 4861 section 4.3 for more details.
 type NDPNeighborSolicit []byte
 
 const (

pkg/tcpip/header/ndp_router_advert.go

@@ -0,0 +1,112 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package header
+
+import (
+	"encoding/binary"
+	"time"
+)
+
+// NDPRouterAdvert is an NDP Router Advertisement message. It will only contain
+// the body of an ICMPv6 packet.
+//
+// See RFC 4861 section 4.2 for more details.
+type NDPRouterAdvert []byte
+
+const (
+	// NDPRAMinimumSize is the minimum size of a valid NDP Router
+	// Advertisement message (body of an ICMPv6 packet).
+	NDPRAMinimumSize = 12
+
+	// ndpRACurrHopLimitOffset is the byte of the Curr Hop Limit field
+	// within an NDPRouterAdvert.
+	ndpRACurrHopLimitOffset = 0
+
+	// ndpRAFlagsOffset is the byte with the NDP RA bit-fields/flags
+	// within an NDPRouterAdvert.
+	ndpRAFlagsOffset = 1
+
+	// ndpRAManagedAddrConfFlagMask is the mask of the Managed Address
+	// Configuration flag within the bit-field/flags byte of an
+	// NDPRouterAdvert.
+	ndpRAManagedAddrConfFlagMask = (1 << 7)
+
+	// ndpRAOtherConfFlagMask is the mask of the Other Configuration flag
+	// within the bit-field/flags byte of an NDPRouterAdvert.
+	ndpRAOtherConfFlagMask = (1 << 6)
+
+	// ndpRARouterLifetimeOffset is the start of the 2-byte Router Lifetime
+	// field within an NDPRouterAdvert.
+	ndpRARouterLifetimeOffset = 2
+
+	// ndpRAReachableTimeOffset is the start of the 4-byte Reachable Time
+	// field within an NDPRouterAdvert.
+	ndpRAReachableTimeOffset = 4
+
+	// ndpRARetransTimerOffset is the start of the 4-byte Retrans Timer
+	// field within an NDPRouterAdvert.
+	ndpRARetransTimerOffset = 8
+
+	// ndpRAOptionsOffset is the start of the NDP options in an
+	// NDPRouterAdvert.
+	ndpRAOptionsOffset = 12
+)
+
+// CurrHopLimit returns the value of the Curr Hop Limit field.
+func (b NDPRouterAdvert) CurrHopLimit() uint8 {
+	return b[ndpRACurrHopLimitOffset]
+}
+
+// ManagedAddrConfFlag returns the value of the Managed Address Configuration
+// flag.
+func (b NDPRouterAdvert) ManagedAddrConfFlag() bool {
+	return b[ndpRAFlagsOffset]&ndpRAManagedAddrConfFlagMask != 0
+}
+
+// OtherConfFlag returns the value of the Other Configuration flag.
+func (b NDPRouterAdvert) OtherConfFlag() bool {
+	return b[ndpRAFlagsOffset]&ndpRAOtherConfFlagMask != 0
+}
+
+// RouterLifetime returns the lifetime associated with the default router. A
+// value of 0 means the source of the Router Advertisement is not a default
+// router and SHOULD NOT appear on the default router list. Note, a value of 0
+// only means that the router should not be used as a default router, it does
+// not apply to other information contained in the Router Advertisement.
+func (b NDPRouterAdvert) RouterLifetime() time.Duration {
+	// The field is the time in seconds, as per RFC 4861 section 4.2.
+	return time.Second * time.Duration(binary.BigEndian.Uint16(b[ndpRARouterLifetimeOffset:]))
+}
+
+// ReachableTime returns the time that a node assumes a neighbor is reachable
+// after having received a reachability confirmation. A value of 0 means
+// that it is unspecified by the source of the Router Advertisement message.
+func (b NDPRouterAdvert) ReachableTime() time.Duration {
+	// The field is the time in milliseconds, as per RFC 4861 section 4.2.
+	return time.Millisecond * time.Duration(binary.BigEndian.Uint32(b[ndpRAReachableTimeOffset:]))
+}
+
+// RetransTimer returns the time between retransmitted Neighbor Solicitation
+// messages. A value of 0 means that it is unspecified by the source of the
+// Router Advertisement message.
+func (b NDPRouterAdvert) RetransTimer() time.Duration {
+	// The field is the time in milliseconds, as per RFC 4861 section 4.2.
+	return time.Millisecond * time.Duration(binary.BigEndian.Uint32(b[ndpRARetransTimerOffset:]))
+}
+
+// Options returns an NDPOptions of the the options body.
+func (b NDPRouterAdvert) Options() NDPOptions {
+	return NDPOptions(b[ndpRAOptionsOffset:])
+}

pkg/tcpip/header/ndp_test.go

@@ -17,6 +17,7 @@ package header
 import (
 	"bytes"
 	"testing"
+	"time"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
 )
@@ -117,6 +118,40 @@ func TestNDPNeighborAdvert(t *testing.T) {
 	}
 }
 
+func TestNDPRouterAdvert(t *testing.T) {
+	b := []byte{
+		64, 128, 1, 2,
+		3, 4, 5, 6,
+		7, 8, 9, 10,
+	}
+
+	ra := NDPRouterAdvert(b)
+
+	if got := ra.CurrHopLimit(); got != 64 {
+		t.Fatalf("got ra.CurrHopLimit = %d, want = 64", got)
+	}
+
+	if got := ra.ManagedAddrConfFlag(); !got {
+		t.Fatalf("got ManagedAddrConfFlag = false, want = true")
+	}
+
+	if got := ra.OtherConfFlag(); got {
+		t.Fatalf("got OtherConfFlag = true, want = false")
+	}
+
+	if got, want := ra.RouterLifetime(), time.Second*258; got != want {
+		t.Fatalf("got ra.RouterLifetime = %d, want = %d", got, want)
+	}
+
+	if got, want := ra.ReachableTime(), time.Millisecond*50595078; got != want {
+		t.Fatalf("got ra.ReachableTime = %d, want = %d", got, want)
+	}
+
+	if got, want := ra.RetransTimer(), time.Millisecond*117967114; got != want {
+		t.Fatalf("got ra.RetransTimer = %d, want = %d", got, want)
+	}
+}
+
 // TestNDPTargetLinkLayerAddressOptionSerialize tests serializing a
 // NDPTargetLinkLayerAddressOption.
 func TestNDPTargetLinkLayerAddressOptionSerialize(t *testing.T) {