fix(cgo): support byte slices in Call argument conversion

Co-Authored-By: Virgil <virgil@lethean.io>

call_test.go

@@ -186,6 +186,15 @@ func TestCallSupportsByteSliceArgument(t *testing.T) {
 	}
 }
 
+func TestCallSupportsEmptyByteSliceArgument(t *testing.T) {
+	t.Parallel()
+
+	payload := []byte{}
+	if err := Call(callZeroByteSliceArgumentFunction(), payload); err != nil {
+		t.Fatalf("expected success for empty byte slice, got %v", err)
+	}
+}
+
 func TestErrnoMapping(t *testing.T) {
 	t.Parallel()
 

call_test_support.go

@@ -75,6 +75,10 @@ int call_buffer_argument(uintptr_t value) {
     return value == 0 ? 13 : 0;
 }
 
+int call_zero_byte_slice_argument(uintptr_t value) {
+    return value == 0 ? 0 : 13;
+}
+
 int call_c_types_arguments(long a0, unsigned long a1, long long a2, unsigned long long a3) {
     if (a0 == 10 && a1 == 11 && a2 == 12 && a3 == 13) {
         return 0;
@@ -130,6 +134,10 @@ uintptr_t call_buffer_argument_ptr(void) {
     return (uintptr_t)&call_buffer_argument;
 }
 
+uintptr_t call_zero_byte_slice_argument_ptr(void) {
+    return (uintptr_t)&call_zero_byte_slice_argument;
+}
+
 uintptr_t call_c_types_arguments_ptr(void) {
     return (uintptr_t)&call_c_types_arguments;
 }
@@ -198,6 +206,11 @@ func callBufferArgumentFunction() unsafe.Pointer {
 	return *(*unsafe.Pointer)(unsafe.Pointer(&function))
 }
 
+func callZeroByteSliceArgumentFunction() unsafe.Pointer {
+	function := C.call_zero_byte_slice_argument_ptr()
+	return *(*unsafe.Pointer)(unsafe.Pointer(&function))
+}
+
 func callCTypeArgumentFunction() unsafe.Pointer {
 	function := C.call_c_types_arguments_ptr()
 	return *(*unsafe.Pointer)(unsafe.Pointer(&function))

string_conversion.go

@@ -805,6 +805,11 @@ func toSyscallArg(value interface{}) (uintptr, bool) {
 		return uintptr(typed), true
 	case uint64:
 		return uintptr(typed), true
+	case []byte:
+		if len(typed) == 0 {
+			return 0, true
+		}
+		return uintptr(unsafe.Pointer(&typed[0])), true
 	default:
 		reflected := reflect.ValueOf(value)
 		switch reflected.Kind() {
@@ -819,11 +824,6 @@ func toSyscallArg(value interface{}) (uintptr, bool) {
 			return 0, true
 		}
 		return 0, false
-	case []byte:
-		if len(typed) == 0 {
-			return 0, true
-		}
-		return uintptr(unsafe.Pointer(&typed[0])), true
 	}
 }