Pass RouteInfo to the route resolve callback

The route resolution callback will be called with a
stack.ResolvedFieldsResult which will hold the route info so callers
can avoid attempting resolution again to check if a previous resolution
attempt succeeded or not.

Test: integration_test.TestRouteResolvedFields
PiperOrigin-RevId: 353319019

3 files changed, 170 insertions, 11 deletions

diff --git a/pkg/tcpip/stack/pending_packets.go b/pkg/tcpip/stack/pending_packets.go
index 22dfc7960..c4769b17e 100644
--- a/pkg/tcpip/stack/pending_packets.go
+++ b/pkg/tcpip/stack/pending_packets.go
@@ -145,7 +145,7 @@ func (f *packetsPendingLinkResolution) enqueue(r *Route, gso *GSO, proto tcpip.N
 	//
 	// To make sure B does not interleave with A and C, we make sure A and C are
 	// done while holding the lock.
-	routeInfo, ch, err := r.ResolvedFields(nil)
+	routeInfo, ch, err := r.resolvedFields(nil)
 	switch err {
 	case nil:
 		// The route resolved immediately, so we don't need to wait for link
diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index 4523e4746..d9a8554e2 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -315,23 +315,42 @@ func (r *Route) ResolveWith(addr tcpip.LinkAddress) {
 	r.mu.remoteLinkAddress = addr
 }
 
-// ResolvedFields is like Fields but also attempts to resolve the remote link
-// address if it is not yet known.
+// ResolvedFieldsResult is the result of a route resolution attempt.
+type ResolvedFieldsResult struct {
+	RouteInfo RouteInfo
+	Success   bool
+}
+
+// ResolvedFields attempts to resolve the remote link address if it is not
+// known.
 //
-// If address resolution is required, returns tcpip.ErrWouldBlock and a
-// notification channel for the caller to block on. The channel will be readable
-// once address resolution is complete (successful or not). If a callback is
-// provided, it will be called when address resolution is complete, regardless
-// of success or failure before the notification channel is readable.
+// If a callback is provided, it will be called before ResolvedFields returns
+// when address resolution is not required. If address resolution is required,
+// the callback will be called once address resolution is complete, regardless
+// of success or failure.
 //
 // Note, the route will not cache the remote link address when address
 // resolution completes.
-func (r *Route) ResolvedFields(afterResolve func()) (RouteInfo, <-chan struct{}, *tcpip.Error) {
+func (r *Route) ResolvedFields(afterResolve func(ResolvedFieldsResult)) *tcpip.Error {
+	_, _, err := r.resolvedFields(afterResolve)
+	return err
+}
+
+// resolvedFields is like ResolvedFields but also returns a notification channel
+// when address resolution is required. This channel will become readable once
+// address resolution is complete.
+//
+// The route's fields will also be returned, regardless of whether address
+// resolution is required or not.
+func (r *Route) resolvedFields(afterResolve func(ResolvedFieldsResult)) (RouteInfo, <-chan struct{}, *tcpip.Error) {
 	r.mu.RLock()
 	fields := r.fieldsLocked()
 	resolutionRequired := r.isResolutionRequiredRLocked()
 	r.mu.RUnlock()
 	if !resolutionRequired {
+		if afterResolve != nil {
+			afterResolve(ResolvedFieldsResult{RouteInfo: fields, Success: true})
+		}
 		return fields, nil, nil
 	}
 
@@ -347,9 +366,14 @@ func (r *Route) ResolvedFields(afterResolve func()) (RouteInfo, <-chan struct{},
 		linkAddressResolutionRequestLocalAddr = r.LocalAddress
 	}
 
-	linkAddr, ch, err := r.outgoingNIC.getNeighborLinkAddress(nextAddr, linkAddressResolutionRequestLocalAddr, r.linkRes, func(LinkResolutionResult) {
+	afterResolveFields := fields
+	linkAddr, ch, err := r.outgoingNIC.getNeighborLinkAddress(nextAddr, linkAddressResolutionRequestLocalAddr, r.linkRes, func(r LinkResolutionResult) {
 		if afterResolve != nil {
-			afterResolve()
+			if r.Success {
+				afterResolveFields.RemoteLinkAddress = r.LinkAddress
+			}
+
+			afterResolve(ResolvedFieldsResult{RouteInfo: afterResolveFields, Success: r.Success})
 		}
 	})
 	if err == nil {
diff --git a/pkg/tcpip/tests/integration/link_resolution_test.go b/pkg/tcpip/tests/integration/link_resolution_test.go
index d0d0e4ef2..f85164c5b 100644
--- a/pkg/tcpip/tests/integration/link_resolution_test.go
+++ b/pkg/tcpip/tests/integration/link_resolution_test.go
@@ -471,6 +471,141 @@ func TestGetLinkAddress(t *testing.T) {
 	}
 }
 
+func TestRouteResolvedFields(t *testing.T) {
+	const (
+		host1NICID = 1
+		host2NICID = 4
+	)
+
+	tests := []struct {
+		name                  string
+		netProto              tcpip.NetworkProtocolNumber
+		localAddr             tcpip.Address
+		remoteAddr            tcpip.Address
+		immediatelyResolvable bool
+		expectedSuccess       bool
+		expectedLinkAddr      tcpip.LinkAddress
+	}{
+		{
+			name:                  "IPv4 immediately resolvable",
+			netProto:              ipv4.ProtocolNumber,
+			localAddr:             ipv4Addr1.AddressWithPrefix.Address,
+			remoteAddr:            header.IPv4AllSystems,
+			immediatelyResolvable: true,
+			expectedSuccess:       true,
+			expectedLinkAddr:      header.EthernetAddressFromMulticastIPv4Address(header.IPv4AllSystems),
+		},
+		{
+			name:                  "IPv6 immediately resolvable",
+			netProto:              ipv6.ProtocolNumber,
+			localAddr:             ipv6Addr1.AddressWithPrefix.Address,
+			remoteAddr:            header.IPv6AllNodesMulticastAddress,
+			immediatelyResolvable: true,
+			expectedSuccess:       true,
+			expectedLinkAddr:      header.EthernetAddressFromMulticastIPv6Address(header.IPv6AllNodesMulticastAddress),
+		},
+		{
+			name:                  "IPv4 resolvable",
+			netProto:              ipv4.ProtocolNumber,
+			localAddr:             ipv4Addr1.AddressWithPrefix.Address,
+			remoteAddr:            ipv4Addr2.AddressWithPrefix.Address,
+			immediatelyResolvable: false,
+			expectedSuccess:       true,
+			expectedLinkAddr:      linkAddr2,
+		},
+		{
+			name:                  "IPv6 resolvable",
+			netProto:              ipv6.ProtocolNumber,
+			localAddr:             ipv6Addr1.AddressWithPrefix.Address,
+			remoteAddr:            ipv6Addr2.AddressWithPrefix.Address,
+			immediatelyResolvable: false,
+			expectedSuccess:       true,
+			expectedLinkAddr:      linkAddr2,
+		},
+		{
+			name:                  "IPv4 not resolvable",
+			netProto:              ipv4.ProtocolNumber,
+			localAddr:             ipv4Addr1.AddressWithPrefix.Address,
+			remoteAddr:            ipv4Addr3.AddressWithPrefix.Address,
+			immediatelyResolvable: false,
+			expectedSuccess:       false,
+		},
+		{
+			name:                  "IPv6 not resolvable",
+			netProto:              ipv6.ProtocolNumber,
+			localAddr:             ipv6Addr1.AddressWithPrefix.Address,
+			remoteAddr:            ipv6Addr3.AddressWithPrefix.Address,
+			immediatelyResolvable: false,
+			expectedSuccess:       false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			for _, useNeighborCache := range []bool{true, false} {
+				t.Run(fmt.Sprintf("UseNeighborCache=%t", useNeighborCache), func(t *testing.T) {
+					stackOpts := stack.Options{
+						NetworkProtocols: []stack.NetworkProtocolFactory{arp.NewProtocol, ipv4.NewProtocol, ipv6.NewProtocol},
+						UseNeighborCache: useNeighborCache,
+					}
+
+					host1Stack, _ := setupStack(t, stackOpts, host1NICID, host2NICID)
+					r, err := host1Stack.FindRoute(host1NICID, "", test.remoteAddr, test.netProto, false /* multicastLoop */)
+					if err != nil {
+						t.Fatalf("host1Stack.FindRoute(%d, '', %s, %d, false): %s", host1NICID, test.remoteAddr, test.netProto, err)
+					}
+					defer r.Release()
+
+					var wantRouteInfo stack.RouteInfo
+					wantRouteInfo.LocalLinkAddress = linkAddr1
+					wantRouteInfo.LocalAddress = test.localAddr
+					wantRouteInfo.RemoteAddress = test.remoteAddr
+					wantRouteInfo.NetProto = test.netProto
+					wantRouteInfo.Loop = stack.PacketOut
+					wantRouteInfo.RemoteLinkAddress = test.expectedLinkAddr
+
+					ch := make(chan stack.ResolvedFieldsResult, 1)
+
+					if !test.immediatelyResolvable {
+						wantUnresolvedRouteInfo := wantRouteInfo
+						wantUnresolvedRouteInfo.RemoteLinkAddress = ""
+
+						if err := r.ResolvedFields(func(r stack.ResolvedFieldsResult) {
+							ch <- r
+						}); err != tcpip.ErrWouldBlock {
+							t.Errorf("got r.ResolvedFields(_) = %s, want = %s", err, tcpip.ErrWouldBlock)
+						}
+						if diff := cmp.Diff(stack.ResolvedFieldsResult{RouteInfo: wantRouteInfo, Success: test.expectedSuccess}, <-ch, cmp.AllowUnexported(stack.RouteInfo{})); diff != "" {
+							t.Errorf("route resolve result mismatch (-want +got):\n%s", diff)
+						}
+
+						if !test.expectedSuccess {
+							return
+						}
+
+						// At this point the neighbor table should be populated so the route
+						// should be immediately resolvable.
+					}
+
+					if err := r.ResolvedFields(func(r stack.ResolvedFieldsResult) {
+						ch <- r
+					}); err != nil {
+						t.Errorf("r.ResolvedFields(_): %s", err)
+					}
+					select {
+					case routeResolveRes := <-ch:
+						if diff := cmp.Diff(stack.ResolvedFieldsResult{RouteInfo: wantRouteInfo, Success: true}, routeResolveRes, cmp.AllowUnexported(stack.RouteInfo{})); diff != "" {
+							t.Errorf("route resolve result from resolved route mismatch (-want +got):\n%s", diff)
+						}
+					default:
+						t.Fatal("expected route to be immediately resolvable")
+					}
+				})
+			}
+		})
+	}
+}
+
 func TestWritePacketsLinkResolution(t *testing.T) {
 	const (
 		host1NICID = 1