4 files changed, 55 insertions, 13 deletions
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 62f7c880e..ca15c0691 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -568,23 +568,19 @@ func (n *nic) primaryAddresses() []tcpip.ProtocolAddress {
 	return addrs
 }
 
-// primaryAddress returns the primary address associated with this NIC.
-//
-// primaryAddress will return the first non-deprecated address if such an
-// address exists. If no non-deprecated address exists, the first deprecated
-// address will be returned.
-func (n *nic) primaryAddress(proto tcpip.NetworkProtocolNumber) tcpip.AddressWithPrefix {
+// PrimaryAddress implements NetworkInterface.
+func (n *nic) PrimaryAddress(proto tcpip.NetworkProtocolNumber) (tcpip.AddressWithPrefix, tcpip.Error) {
 	ep, ok := n.networkEndpoints[proto]
 	if !ok {
-		return tcpip.AddressWithPrefix{}
+		return tcpip.AddressWithPrefix{}, &tcpip.ErrUnknownProtocol{}
 	}
 
 	addressableEndpoint, ok := ep.(AddressableEndpoint)
 	if !ok {
-		return tcpip.AddressWithPrefix{}
+		return tcpip.AddressWithPrefix{}, &tcpip.ErrNotSupported{}
 	}
 
-	return addressableEndpoint.MainAddress()
+	return addressableEndpoint.MainAddress(), nil
 }
 
 // removeAddress removes an address from n.
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index 85f0f471a..ff3a385e1 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -525,6 +525,14 @@ type NetworkInterface interface {
 	// assigned to it.
 	Spoofing() bool
 
+	// PrimaryAddress returns the primary address associated with the interface.
+	//
+	// PrimaryAddress will return the first non-deprecated address if such an
+	// address exists. If no non-deprecated addresses exist, the first deprecated
+	// address will be returned. If no deprecated addresses exist, the zero value
+	// will be returned.
+	PrimaryAddress(tcpip.NetworkProtocolNumber) (tcpip.AddressWithPrefix, tcpip.Error)
+
 	// CheckLocalAddress returns true if the address exists on the interface.
 	CheckLocalAddress(tcpip.NetworkProtocolNumber, tcpip.Address) bool
 
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 53370c354..1fffe9274 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1224,7 +1224,8 @@ func (s *Stack) GetMainNICAddress(id tcpip.NICID, protocol tcpip.NetworkProtocol
 		return tcpip.AddressWithPrefix{}, false
 	}
 
-	return nic.primaryAddress(protocol), true
+	addr, err := nic.PrimaryAddress(protocol)
+	return addr, err == nil
 }
 
 func (s *Stack) getAddressEP(nic *nic, localAddr, remoteAddr tcpip.Address, netProto tcpip.NetworkProtocolNumber) AssignableAddressEndpoint {
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index 880219007..0d95bc7d6 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -1926,6 +1926,39 @@ func TestGetMainNICAddressAddPrimaryNonPrimary(t *testing.T) {
 	}
 }
 
+func TestGetMainNICAddressErrors(t *testing.T) {
+	const nicID = 1
+
+	s := stack.New(stack.Options{
+		NetworkProtocols: []stack.NetworkProtocolFactory{ipv4.NewProtocol, arp.NewProtocol},
+	})
+	if err := s.CreateNIC(nicID, loopback.New()); err != nil {
+		t.Fatalf("CreateNIC(%d, _): %s", nicID, err)
+	}
+
+	// Sanity check with a successful call.
+	if addr, ok := s.GetMainNICAddress(nicID, ipv4.ProtocolNumber); !ok {
+		t.Errorf("got s.GetMainNICAddress(%d, %d) = (%s, false), want = (_, true)", nicID, ipv4.ProtocolNumber, addr)
+	} else if want := (tcpip.AddressWithPrefix{}); addr != want {
+		t.Errorf("got s.GetMainNICAddress(%d, %d) = (%s, _), want = (%s, _)", nicID, ipv4.ProtocolNumber, addr, want)
+	}
+
+	const unknownNICID = nicID + 1
+	if addr, ok := s.GetMainNICAddress(unknownNICID, ipv4.ProtocolNumber); ok {
+		t.Errorf("got s.GetMainNICAddress(%d, %d) = (%s, true), want = (_, false)", unknownNICID, ipv4.ProtocolNumber, addr)
+	}
+
+	// ARP is not an addressable network endpoint.
+	if addr, ok := s.GetMainNICAddress(nicID, arp.ProtocolNumber); ok {
+		t.Errorf("got s.GetMainNICAddress(%d, %d) = (%s, true), want = (_, false)", nicID, arp.ProtocolNumber, addr)
+	}
+
+	const unknownProtocolNumber = 1234
+	if addr, ok := s.GetMainNICAddress(nicID, unknownProtocolNumber); ok {
+		t.Errorf("got s.GetMainNICAddress(%d, %d) = (%s, true), want = (_, false)", nicID, unknownProtocolNumber, addr)
+	}
+}
+
 func TestGetMainNICAddressAddRemove(t *testing.T) {
 	s := stack.New(stack.Options{
 		NetworkProtocols: []stack.NetworkProtocolFactory{fakeNetFactory},
@@ -2507,11 +2540,15 @@ func TestNICAutoGenLinkLocalAddr(t *testing.T) {
 				}
 			}
 
-			// Check that we get no address after removal.
-			if err := checkGetMainNICAddress(s, 1, fakeNetNumber, tcpip.AddressWithPrefix{}); err != nil {
+			if err := checkGetMainNICAddress(s, nicID, header.IPv6ProtocolNumber, expectedMainAddr); err != nil {
 				t.Fatal(err)
 			}
-			if err := checkGetMainNICAddress(s, 1, header.IPv6ProtocolNumber, expectedMainAddr); err != nil {
+
+			// Disabling the NIC should remove the auto-generated address.
+			if err := s.DisableNIC(nicID); err != nil {
+				t.Fatalf("s.DisableNIC(%d): %s", nicID, err)
+			}
+			if err := checkGetMainNICAddress(s, nicID, header.IPv6ProtocolNumber, tcpip.AddressWithPrefix{}); err != nil {
 				t.Fatal(err)
 			}
 		})