Add function to get error from a tcpip.Endpoint

In an upcoming CL, socket option types are made to implement a marker
interface with pointer receivers. Since this results in calling methods
of an interface with a pointer, we incur an allocation when attempting
to get an Endpoint's last error with the current implementation.

When calling the method of an interface, the compiler is unable to
determine what the interface implementation does with the pointer
(since calling a method on an interface uses virtual dispatch at runtime
so the compiler does not know what the interface method will do) so it
allocates on the heap to be safe incase an implementation continues to
hold the pointer after the functioon returns (the reference escapes the
scope of the object).

In the example below, the compiler does not know what b.foo does with
the reference to a it allocates a on the heap as the reference to a may
escape the scope of a.
```
var a int
var b someInterface
b.foo(&a)
```

This change removes the opportunity for that allocation.

RELNOTES: n/a
PiperOrigin-RevId: 328796559

14 files changed, 47 insertions, 67 deletions

diff --git a/pkg/tcpip/adapters/gonet/gonet.go b/pkg/tcpip/adapters/gonet/gonet.go
index d82ed5205..68a954a10 100644
--- a/pkg/tcpip/adapters/gonet/gonet.go
+++ b/pkg/tcpip/adapters/gonet/gonet.go
@@ -541,7 +541,7 @@ func DialContextTCP(ctx context.Context, s *stack.Stack, addr tcpip.FullAddress,
 		case <-notifyCh:
 		}
 
-		err = ep.GetSockOpt(tcpip.ErrorOption{})
+		err = ep.LastError()
 	}
 	if err != nil {
 		ep.Close()
diff --git a/pkg/tcpip/adapters/gonet/gonet_test.go b/pkg/tcpip/adapters/gonet/gonet_test.go
index 3c552988a..c975ad9cf 100644
--- a/pkg/tcpip/adapters/gonet/gonet_test.go
+++ b/pkg/tcpip/adapters/gonet/gonet_test.go
@@ -104,7 +104,7 @@ func connect(s *stack.Stack, addr tcpip.FullAddress) (*testConnection, *tcpip.Er
 	err = ep.Connect(addr)
 	if err == tcpip.ErrConnectStarted {
 		<-ch
-		err = ep.GetSockOpt(tcpip.ErrorOption{})
+		err = ep.LastError()
 	}
 	if err != nil {
 		return nil, err
diff --git a/pkg/tcpip/sample/tun_tcp_connect/main.go b/pkg/tcpip/sample/tun_tcp_connect/main.go
index 0ab089208..91fc26722 100644
--- a/pkg/tcpip/sample/tun_tcp_connect/main.go
+++ b/pkg/tcpip/sample/tun_tcp_connect/main.go
@@ -182,7 +182,7 @@ func main() {
 	if terr == tcpip.ErrConnectStarted {
 		fmt.Println("Connect is pending...")
 		<-notifyCh
-		terr = ep.GetSockOpt(tcpip.ErrorOption{})
+		terr = ep.LastError()
 	}
 	wq.EventUnregister(&waitEntry)
 
diff --git a/pkg/tcpip/stack/transport_test.go b/pkg/tcpip/stack/transport_test.go
index 6c6e44468..7869bb98b 100644
--- a/pkg/tcpip/stack/transport_test.go
+++ b/pkg/tcpip/stack/transport_test.go
@@ -53,11 +53,11 @@ func (f *fakeTransportEndpoint) Info() tcpip.EndpointInfo {
 	return &f.TransportEndpointInfo
 }
 
-func (f *fakeTransportEndpoint) Stats() tcpip.EndpointStats {
+func (*fakeTransportEndpoint) Stats() tcpip.EndpointStats {
 	return nil
 }
 
-func (f *fakeTransportEndpoint) SetOwner(owner tcpip.PacketOwner) {}
+func (*fakeTransportEndpoint) SetOwner(owner tcpip.PacketOwner) {}
 
 func newFakeTransportEndpoint(s *stack.Stack, proto *fakeTransportProtocol, netProto tcpip.NetworkProtocolNumber, uniqueID uint64) tcpip.Endpoint {
 	return &fakeTransportEndpoint{stack: s, TransportEndpointInfo: stack.TransportEndpointInfo{NetProto: netProto}, proto: proto, uniqueID: uniqueID}
@@ -100,7 +100,7 @@ func (f *fakeTransportEndpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions
 	return int64(len(v)), nil, nil
 }
 
-func (f *fakeTransportEndpoint) Peek([][]byte) (int64, tcpip.ControlMessages, *tcpip.Error) {
+func (*fakeTransportEndpoint) Peek([][]byte) (int64, tcpip.ControlMessages, *tcpip.Error) {
 	return 0, tcpip.ControlMessages{}, nil
 }
 
@@ -131,10 +131,6 @@ func (*fakeTransportEndpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.E
 
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
 func (*fakeTransportEndpoint) GetSockOpt(opt interface{}) *tcpip.Error {
-	switch opt.(type) {
-	case tcpip.ErrorOption:
-		return nil
-	}
 	return tcpip.ErrInvalidEndpointState
 }
 
@@ -169,7 +165,7 @@ func (f *fakeTransportEndpoint) UniqueID() uint64 {
 	return f.uniqueID
 }
 
-func (f *fakeTransportEndpoint) ConnectEndpoint(e tcpip.Endpoint) *tcpip.Error {
+func (*fakeTransportEndpoint) ConnectEndpoint(e tcpip.Endpoint) *tcpip.Error {
 	return nil
 }
 
@@ -239,19 +235,19 @@ func (f *fakeTransportEndpoint) HandleControlPacket(stack.TransportEndpointID, s
 	f.proto.controlCount++
 }
 
-func (f *fakeTransportEndpoint) State() uint32 {
+func (*fakeTransportEndpoint) State() uint32 {
 	return 0
 }
 
-func (f *fakeTransportEndpoint) ModerateRecvBuf(copied int) {}
+func (*fakeTransportEndpoint) ModerateRecvBuf(copied int) {}
 
-func (f *fakeTransportEndpoint) IPTables() (stack.IPTables, error) {
-	return stack.IPTables{}, nil
-}
+func (*fakeTransportEndpoint) Resume(*stack.Stack) {}
 
-func (f *fakeTransportEndpoint) Resume(*stack.Stack) {}
+func (*fakeTransportEndpoint) Wait() {}
 
-func (f *fakeTransportEndpoint) Wait() {}
+func (*fakeTransportEndpoint) LastError() *tcpip.Error {
+	return nil
+}
 
 type fakeTransportGoodOption bool
 
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index 609b8af33..cae943608 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -620,6 +620,9 @@ type Endpoint interface {
 
 	// SetOwner sets the task owner to the endpoint owner.
 	SetOwner(owner PacketOwner)
+
+	// LastError clears and returns the last error reported by the endpoint.
+	LastError() *Error
 }
 
 // LinkPacketInfo holds Link layer information for a received packet.
@@ -839,10 +842,6 @@ const (
 	PMTUDiscoveryProbe
 )
 
-// ErrorOption is used in GetSockOpt to specify that the last error reported by
-// the endpoint should be cleared and returned.
-type ErrorOption struct{}
-
 // BindToDeviceOption is used by SetSockOpt/GetSockOpt to specify that sockets
 // should bind only on a specific NIC.
 type BindToDeviceOption NICID
diff --git a/pkg/tcpip/transport/icmp/endpoint.go b/pkg/tcpip/transport/icmp/endpoint.go
index bd6f49eb8..c545c8367 100644
--- a/pkg/tcpip/transport/icmp/endpoint.go
+++ b/pkg/tcpip/transport/icmp/endpoint.go
@@ -415,14 +415,8 @@ func (e *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
 }
 
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
-func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
-	switch opt.(type) {
-	case tcpip.ErrorOption:
-		return nil
-
-	default:
-		return tcpip.ErrUnknownProtocolOption
-	}
+func (*endpoint) GetSockOpt(interface{}) *tcpip.Error {
+	return tcpip.ErrUnknownProtocolOption
 }
 
 func send4(r *stack.Route, ident uint16, data buffer.View, ttl uint8, owner tcpip.PacketOwner) *tcpip.Error {
@@ -836,3 +830,8 @@ func (e *endpoint) Stats() tcpip.EndpointStats {
 
 // Wait implements stack.TransportEndpoint.Wait.
 func (*endpoint) Wait() {}
+
+// LastError implements tcpip.Endpoint.LastError.
+func (*endpoint) LastError() *tcpip.Error {
+	return nil
+}
diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index 1b03ad6bb..95dc8ed57 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -356,7 +356,7 @@ func (ep *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 	}
 }
 
-func (ep *endpoint) takeLastError() *tcpip.Error {
+func (ep *endpoint) LastError() *tcpip.Error {
 	ep.lastErrorMu.Lock()
 	defer ep.lastErrorMu.Unlock()
 
@@ -366,11 +366,7 @@ func (ep *endpoint) takeLastError() *tcpip.Error {
 }
 
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
-func (ep *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
-	switch opt.(type) {
-	case tcpip.ErrorOption:
-		return ep.takeLastError()
-	}
+func (*endpoint) GetSockOpt(interface{}) *tcpip.Error {
 	return tcpip.ErrNotSupported
 }
 
diff --git a/pkg/tcpip/transport/raw/endpoint.go b/pkg/tcpip/transport/raw/endpoint.go
index edc2b5b61..2087bcfa8 100644
--- a/pkg/tcpip/transport/raw/endpoint.go
+++ b/pkg/tcpip/transport/raw/endpoint.go
@@ -577,14 +577,8 @@ func (e *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 }
 
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
-func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
-	switch opt.(type) {
-	case tcpip.ErrorOption:
-		return nil
-
-	default:
-		return tcpip.ErrUnknownProtocolOption
-	}
+func (*endpoint) GetSockOpt(interface{}) *tcpip.Error {
+	return tcpip.ErrUnknownProtocolOption
 }
 
 // GetSockOptBool implements tcpip.Endpoint.GetSockOptBool.
@@ -739,3 +733,7 @@ func (e *endpoint) Stats() tcpip.EndpointStats {
 
 // Wait implements stack.TransportEndpoint.Wait.
 func (*endpoint) Wait() {}
+
+func (*endpoint) LastError() *tcpip.Error {
+	return nil
+}
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 290172ac9..72df5c2a1 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -491,7 +491,7 @@ func (h *handshake) resolveRoute() *tcpip.Error {
 				h.ep.mu.Lock()
 			}
 			if n&notifyError != 0 {
-				return h.ep.takeLastError()
+				return h.ep.LastError()
 			}
 		}
 
@@ -620,7 +620,7 @@ func (h *handshake) execute() *tcpip.Error {
 				h.ep.mu.Lock()
 			}
 			if n&notifyError != 0 {
-				return h.ep.takeLastError()
+				return h.ep.LastError()
 			}
 
 		case wakerForNewSegment:
diff --git a/pkg/tcpip/transport/tcp/dual_stack_test.go b/pkg/tcpip/transport/tcp/dual_stack_test.go
index 804e95aea..6074cc24e 100644
--- a/pkg/tcpip/transport/tcp/dual_stack_test.go
+++ b/pkg/tcpip/transport/tcp/dual_stack_test.go
@@ -86,8 +86,7 @@ func testV4Connect(t *testing.T, c *context.Context, checkers ...checker.Network
 	// Wait for connection to be established.
 	select {
 	case <-ch:
-		err = c.EP.GetSockOpt(tcpip.ErrorOption{})
-		if err != nil {
+		if err := c.EP.LastError(); err != nil {
 			t.Fatalf("Unexpected error when connecting: %v", err)
 		}
 	case <-time.After(1 * time.Second):
@@ -194,8 +193,7 @@ func testV6Connect(t *testing.T, c *context.Context, checkers ...checker.Network
 	// Wait for connection to be established.
 	select {
 	case <-ch:
-		err = c.EP.GetSockOpt(tcpip.ErrorOption{})
-		if err != nil {
+		if err := c.EP.LastError(); err != nil {
 			t.Fatalf("Unexpected error when connecting: %v", err)
 		}
 	case <-time.After(1 * time.Second):
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index ff9b8804d..8a5e993b5 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1234,7 +1234,7 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 	e.owner = owner
 }
 
-func (e *endpoint) takeLastError() *tcpip.Error {
+func (e *endpoint) LastError() *tcpip.Error {
 	e.lastErrorMu.Lock()
 	defer e.lastErrorMu.Unlock()
 	err := e.lastError
@@ -1995,9 +1995,6 @@ func (e *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
 func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 	switch o := opt.(type) {
-	case tcpip.ErrorOption:
-		return e.takeLastError()
-
 	case *tcpip.BindToDeviceOption:
 		e.LockUser()
 		*o = tcpip.BindToDeviceOption(e.bindToDevice)
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 9650bb06c..3d3034d50 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -74,8 +74,8 @@ func TestGiveUpConnect(t *testing.T) {
 
 	// Wait for ep to become writable.
 	<-notifyCh
-	if err := ep.GetSockOpt(tcpip.ErrorOption{}); err != tcpip.ErrAborted {
-		t.Fatalf("got ep.GetSockOpt(tcpip.ErrorOption{}) = %s, want = %s", err, tcpip.ErrAborted)
+	if err := ep.LastError(); err != tcpip.ErrAborted {
+		t.Fatalf("got ep.LastError() = %s, want = %s", err, tcpip.ErrAborted)
 	}
 
 	// Call Connect again to retreive the handshake failure status
@@ -3023,8 +3023,8 @@ func TestSynOptionsOnActiveConnect(t *testing.T) {
 	// Wait for connection to be established.
 	select {
 	case <-ch:
-		if err := c.EP.GetSockOpt(tcpip.ErrorOption{}); err != nil {
-			t.Fatalf("GetSockOpt failed: %s", err)
+		if err := c.EP.LastError(); err != nil {
+			t.Fatalf("Connect failed: %s", err)
 		}
 	case <-time.After(1 * time.Second):
 		t.Fatalf("Timed out waiting for connection")
@@ -4411,7 +4411,7 @@ func TestSelfConnect(t *testing.T) {
 	}
 
 	<-notifyCh
-	if err := ep.GetSockOpt(tcpip.ErrorOption{}); err != nil {
+	if err := ep.LastError(); err != nil {
 		t.Fatalf("Connect failed: %s", err)
 	}
 
diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index b6031354e..1f5340cd0 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -638,7 +638,7 @@ func (c *Context) Connect(iss seqnum.Value, rcvWnd seqnum.Size, options []byte)
 	// Wait for connection to be established.
 	select {
 	case <-notifyCh:
-		if err := c.EP.GetSockOpt(tcpip.ErrorOption{}); err != nil {
+		if err := c.EP.LastError(); err != nil {
 			c.t.Fatalf("Unexpected error when connecting: %v", err)
 		}
 	case <-time.After(1 * time.Second):
@@ -882,8 +882,7 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 	// Wait for connection to be established.
 	select {
 	case <-notifyCh:
-		err = c.EP.GetSockOpt(tcpip.ErrorOption{})
-		if err != nil {
+		if err := c.EP.LastError(); err != nil {
 			c.t.Fatalf("Unexpected error when connecting: %v", err)
 		}
 	case <-time.After(1 * time.Second):
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 0a9d3c6cf..1d5ebe3f2 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -209,7 +209,7 @@ func (e *endpoint) UniqueID() uint64 {
 	return e.uniqueID
 }
 
-func (e *endpoint) takeLastError() *tcpip.Error {
+func (e *endpoint) LastError() *tcpip.Error {
 	e.lastErrorMu.Lock()
 	defer e.lastErrorMu.Unlock()
 
@@ -268,7 +268,7 @@ func (e *endpoint) ModerateRecvBuf(copied int) {}
 // Read reads data from the endpoint. This method does not block if
 // there is no data pending.
 func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
-	if err := e.takeLastError(); err != nil {
+	if err := e.LastError(); err != nil {
 		return buffer.View{}, tcpip.ControlMessages{}, err
 	}
 
@@ -411,7 +411,7 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 }
 
 func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
-	if err := e.takeLastError(); err != nil {
+	if err := e.LastError(); err != nil {
 		return 0, nil, err
 	}
 
@@ -962,8 +962,6 @@ func (e *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
 func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 	switch o := opt.(type) {
-	case tcpip.ErrorOption:
-		return e.takeLastError()
 	case *tcpip.MulticastInterfaceOption:
 		e.mu.Lock()
 		*o = tcpip.MulticastInterfaceOption{