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, 10 insertions, 7 deletions

diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 8bb5e5f6d..baf7df197 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -146,19 +146,22 @@ func New(t *testing.T, mtu uint32) *Context {
 	const sendBufferSize = 1 << 20 // 1 MiB
 	const recvBufferSize = 1 << 20 // 1 MiB
 	// Allow minimum send/receive buffer sizes to be 1 during tests.
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.SendBufferSizeOption{Min: 1, Default: sendBufferSize, Max: 10 * sendBufferSize}); err != nil {
-		t.Fatalf("SetTransportProtocolOption failed: %s", err)
+	sendBufOpt := tcpip.TCPSendBufferSizeRangeOption{Min: 1, Default: sendBufferSize, Max: 10 * sendBufferSize}
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, &sendBufOpt); err != nil {
+		t.Fatalf("SetTransportProtocolOption(%d, &%#v) failed: %s", tcp.ProtocolNumber, sendBufOpt, err)
 	}
 
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.ReceiveBufferSizeOption{Min: 1, Default: recvBufferSize, Max: 10 * recvBufferSize}); err != nil {
-		t.Fatalf("SetTransportProtocolOption failed: %s", err)
+	rcvBufOpt := tcpip.TCPReceiveBufferSizeRangeOption{Min: 1, Default: recvBufferSize, Max: 10 * recvBufferSize}
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, &rcvBufOpt); err != nil {
+		t.Fatalf("SetTransportProtocolOption(%d, &%#v) failed: %s", tcp.ProtocolNumber, rcvBufOpt, err)
 	}
 
 	// Increase minimum RTO in tests to avoid test flakes due to early
 	// retransmit in case the test executors are overloaded and cause timers
 	// to fire earlier than expected.
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcpip.TCPMinRTOOption(3*time.Second)); err != nil {
-		t.Fatalf("failed to set stack-wide minRTO: %s", err)
+	minRTOOpt := tcpip.TCPMinRTOOption(3 * time.Second)
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, &minRTOOpt); err != nil {
+		t.Fatalf("s.SetTransportProtocolOption(%d, &%T(%d)): %s", tcp.ProtocolNumber, minRTOOpt, minRTOOpt, err)
 	}
 
 	// Some of the congestion control tests send up to 640 packets, we so
@@ -1096,7 +1099,7 @@ func (c *Context) PassiveConnectWithOptions(maxPayload, wndScale int, synOptions
 // SACKEnabled returns true if the TCP Protocol option SACKEnabled is set to true
 // for the Stack in the context.
 func (c *Context) SACKEnabled() bool {
-	var v tcp.SACKEnabled
+	var v tcpip.TCPSACKEnabled
 	if err := c.Stack().TransportProtocolOption(tcp.ProtocolNumber, &v); err != nil {
 		// Stack doesn't support SACK. So just return.
 		return false