Do not resolve remote link address at transport layer

Link address resolution is performed at the link layer (if required) so
we can defer it from the transport layer. When link resolution is
required, packets will be queued and sent once link resolution
completes. If link resolution fails, the transport layer will receive a
control message indicating that the stack failed to route the packet.

tcpip.Endpoint.Write no longer returns a channel now that writes do not
wait for link resolution at the transport layer.

tcpip.ErrNoLinkAddress is no longer used so it is removed.

Removed calls to stack.Route.ResolveWith from the transport layer so
that link resolution is performed when a route is created in response
to an incoming packet (e.g. to complete TCP handshakes or send a RST).

Tests:
- integration_test.TestForwarding
- integration_test.TestTCPLinkResolutionFailure

Fixes #4458

RELNOTES: n/a
PiperOrigin-RevId: 351684158

1 files changed, 6 insertions, 8 deletions

diff --git a/pkg/tcpip/stack/transport_test.go b/pkg/tcpip/stack/transport_test.go
index 0ff32c6ea..a2ab7537c 100644
--- a/pkg/tcpip/stack/transport_test.go
+++ b/pkg/tcpip/stack/transport_test.go
@@ -90,14 +90,14 @@ func (*fakeTransportEndpoint) Read(io.Writer, int, tcpip.ReadOptions) (tcpip.Rea
 	return tcpip.ReadResult{}, nil
 }
 
-func (f *fakeTransportEndpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
+func (f *fakeTransportEndpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, *tcpip.Error) {
 	if len(f.route.RemoteAddress) == 0 {
-		return 0, nil, tcpip.ErrNoRoute
+		return 0, tcpip.ErrNoRoute
 	}
 
 	v, err := p.FullPayload()
 	if err != nil {
-		return 0, nil, err
+		return 0, err
 	}
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 		ReserveHeaderBytes: int(f.route.MaxHeaderLength()) + fakeTransHeaderLen,
@@ -105,10 +105,10 @@ func (f *fakeTransportEndpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions
 	})
 	_ = pkt.TransportHeader().Push(fakeTransHeaderLen)
 	if err := f.route.WritePacket(nil /* gso */, stack.NetworkHeaderParams{Protocol: fakeTransNumber, TTL: 123, TOS: stack.DefaultTOS}, pkt); err != nil {
-		return 0, nil, err
+		return 0, err
 	}
 
-	return int64(len(v)), nil, nil
+	return int64(len(v)), nil
 }
 
 // SetSockOpt sets a socket option. Currently not supported.
@@ -222,7 +222,6 @@ func (f *fakeTransportEndpoint) HandlePacket(id stack.TransportEndpointID, pkt *
 	if err != nil {
 		return
 	}
-	route.ResolveWith(pkt.SourceLinkAddress())
 
 	ep := &fakeTransportEndpoint{
 		TransportEndpointInfo: stack.TransportEndpointInfo{
@@ -522,8 +521,7 @@ func TestTransportSend(t *testing.T) {
 
 	// Create buffer that will hold the payload.
 	view := buffer.NewView(30)
-	_, _, err = ep.Write(tcpip.SlicePayload(view), tcpip.WriteOptions{})
-	if err != nil {
+	if _, err := ep.Write(tcpip.SlicePayload(view), tcpip.WriteOptions{}); err != nil {
 		t.Fatalf("write failed: %v", err)
 	}