Improve type safety for network protocol options

The existing implementation for NetworkProtocol.{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 network protocol options
that may be set or queried which network 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.

PiperOrigin-RevId: 328980359

1 files changed, 16 insertions, 0 deletions

diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index cd72d4f02..47a8d7c86 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -841,10 +841,26 @@ const (
 	PMTUDiscoveryProbe
 )
 
+// GettableNetworkProtocolOption is a marker interface for network protocol
+// options that may be queried.
+type GettableNetworkProtocolOption interface {
+	isGettableNetworkProtocolOption()
+}
+
+// SettableNetworkProtocolOption is a marker interface for network protocol
+// options that may be set.
+type SettableNetworkProtocolOption interface {
+	isSettableNetworkProtocolOption()
+}
+
 // DefaultTTLOption is used by stack.(*Stack).NetworkProtocolOption to specify
 // a default TTL.
 type DefaultTTLOption uint8
 
+func (*DefaultTTLOption) isGettableNetworkProtocolOption() {}
+
+func (*DefaultTTLOption) isSettableNetworkProtocolOption() {}
+
 // AvailableCongestionControlOption is used to query the supported congestion
 // control algorithms.
 type AvailableCongestionControlOption string