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

9 files changed, 30 insertions, 45 deletions

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{