nltest: properly wrap syscall errors as netlink does

nltest/errors_others.go

@@ -0,0 +1,7 @@
+//+build plan9 windows
+
+package nltest
+
+func isSyscallError(_ error) bool {
+	return false
+}

nltest/errors_unix.go

@@ -0,0 +1,10 @@
+//+build !plan9,!windows
+
+package nltest
+
+import "golang.org/x/sys/unix"
+
+func isSyscallError(err error) bool {
+	_, ok := err.(unix.Errno)
+	return ok
+}

nltest/nltest.go

@@ -4,6 +4,7 @@ package nltest
 import (
 	"fmt"
 	"io"
+	"os"
 
 	"github.com/mdlayher/netlink"
 	"github.com/mdlayher/netlink/nlenc"
@@ -166,10 +167,16 @@ func (c *socket) Receive() ([]netlink.Message, error) {
 		case io.EOF:
 			// EOF, simulate no replies in multi-part message.
 			return nil, nil
-		default:
-			// Some error occurred and should be passed to the caller.
-			return nil, c.err
 		}
+
+		// If the error is a system call error, wrap it in os.NewSyscallError
+		// to simulate what the Linux netlink.Conn does.
+		if isSyscallError(c.err) {
+			return nil, os.NewSyscallError("recvmsg", c.err)
+		}
+
+		// Some generic error occurred and should be passed to the caller.
+		return nil, c.err
 	}
 
 	// Detect multi-part messages.

nltest/nltest_linux_test.go

@@ -1,6 +1,7 @@
 package nltest_test
 
 import (
+	"os"
 	"testing"
 
 	"github.com/mdlayher/netlink"
@@ -17,3 +18,17 @@ func TestLinuxDialError(t *testing.T) {
 		t.Fatalf("expected error is not exist, but got: %v", err)
 	}
 }
+
+func TestLinuxSyscallError(t *testing.T) {
+	c := nltest.Dial(func(req []netlink.Message) ([]netlink.Message, error) {
+		return nil, unix.ENOENT
+	})
+
+	_, err := c.Execute(netlink.Message{})
+	if !netlink.IsNotExist(err) {
+		t.Fatalf("expected error is not exist, but got: %v", err)
+	}
+
+	// Expect raw system call errors to be wrapped.
+	_ = err.(*netlink.OpError).Err.(*os.SyscallError)
+}