Improve type safety for transport protocol options

The existing implementation for TransportProtocol.{Set}Option take
arguments of an empty interface type which all types (implicitly)
implement; any type may be passed to the functions.

This change introduces marker interfaces for transport protocol options
that may be set or queried which transport protocol option types
implement to ensure that invalid types are caught at compile time.
Different interfaces are used to allow the compiler to enforce read-only
or set-only socket options.

RELNOTES: n/a
PiperOrigin-RevId: 330559811

1 files changed, 16 insertions, 43 deletions

diff --git a/pkg/tcpip/stack/transport_test.go b/pkg/tcpip/stack/transport_test.go
index 9292bfccb..ef3457e32 100644
--- a/pkg/tcpip/stack/transport_test.go
+++ b/pkg/tcpip/stack/transport_test.go
@@ -291,22 +291,20 @@ func (*fakeTransportProtocol) HandleUnknownDestinationPacket(*stack.Route, stack
 	return true
 }
 
-func (f *fakeTransportProtocol) SetOption(option interface{}) *tcpip.Error {
+func (f *fakeTransportProtocol) SetOption(option tcpip.SettableTransportProtocolOption) *tcpip.Error {
 	switch v := option.(type) {
-	case fakeTransportGoodOption:
-		f.opts.good = bool(v)
+	case *tcpip.TCPModerateReceiveBufferOption:
+		f.opts.good = bool(*v)
 		return nil
-	case fakeTransportInvalidValueOption:
-		return tcpip.ErrInvalidOptionValue
 	default:
 		return tcpip.ErrUnknownProtocolOption
 	}
 }
 
-func (f *fakeTransportProtocol) Option(option interface{}) *tcpip.Error {
+func (f *fakeTransportProtocol) Option(option tcpip.GettableTransportProtocolOption) *tcpip.Error {
 	switch v := option.(type) {
-	case *fakeTransportGoodOption:
-		*v = fakeTransportGoodOption(f.opts.good)
+	case *tcpip.TCPModerateReceiveBufferOption:
+		*v = tcpip.TCPModerateReceiveBufferOption(f.opts.good)
 		return nil
 	default:
 		return tcpip.ErrUnknownProtocolOption
@@ -533,41 +531,16 @@ func TestTransportOptions(t *testing.T) {
 		TransportProtocols: []stack.TransportProtocol{fakeTransFactory()},
 	})
 
-	// Try an unsupported transport protocol.
-	if err := s.SetTransportProtocolOption(tcpip.TransportProtocolNumber(99999), fakeTransportGoodOption(false)); err != tcpip.ErrUnknownProtocol {
-		t.Fatalf("SetTransportProtocolOption(fakeTrans2, blah, false) = %v, want = tcpip.ErrUnknownProtocol", err)
-	}
-
-	testCases := []struct {
-		option   interface{}
-		wantErr  *tcpip.Error
-		verifier func(t *testing.T, p stack.TransportProtocol)
-	}{
-		{fakeTransportGoodOption(true), nil, func(t *testing.T, p stack.TransportProtocol) {
-			t.Helper()
-			fakeTrans := p.(*fakeTransportProtocol)
-			if fakeTrans.opts.good != true {
-				t.Fatalf("fakeTrans.opts.good = false, want = true")
-			}
-			var v fakeTransportGoodOption
-			if err := s.TransportProtocolOption(fakeTransNumber, &v); err != nil {
-				t.Fatalf("s.TransportProtocolOption(fakeTransNumber, &v) = %v, want = nil, where v is option %T", v, err)
-			}
-			if v != true {
-				t.Fatalf("s.TransportProtocolOption(fakeTransNumber, &v) returned v = %v, want = true", v)
-			}
-
-		}},
-		{fakeTransportBadOption(true), tcpip.ErrUnknownProtocolOption, nil},
-		{fakeTransportInvalidValueOption(1), tcpip.ErrInvalidOptionValue, nil},
-	}
-	for _, tc := range testCases {
-		if got := s.SetTransportProtocolOption(fakeTransNumber, tc.option); got != tc.wantErr {
-			t.Errorf("s.SetTransportProtocolOption(fakeTrans, %v) = %v, want = %v", tc.option, got, tc.wantErr)
-		}
-		if tc.verifier != nil {
-			tc.verifier(t, s.TransportProtocolInstance(fakeTransNumber))
-		}
+	v := tcpip.TCPModerateReceiveBufferOption(true)
+	if err := s.SetTransportProtocolOption(fakeTransNumber, &v); err != nil {
+		t.Errorf("s.SetTransportProtocolOption(fakeTrans, &%T(%t)): %s", v, v, err)
+	}
+	v = false
+	if err := s.TransportProtocolOption(fakeTransNumber, &v); err != nil {
+		t.Fatalf("s.TransportProtocolOption(fakeTransNumber, &%T): %s", v, err)
+	}
+	if !v {
+		t.Fatalf("got tcpip.TCPModerateReceiveBufferOption = false, want = true")
 	}
 }