refactor(core): Encode string as empty (instead of NULL) when the dat…

…a-pointer is > NULL

Before we required the data pointer to be exactly the UA_EMPTY_ARRAY_SENTINEL.
But there can be situations where the data pointers goes to "" (empty
string with the \0 ending). Then the string should be empty -- and not
null (length -1).

src/ua_types_encoding_binary.c

@@ -436,7 +436,7 @@ Array_encodeBinary(const void *src, size_t length, const UA_DataType *type, Ctx
         return UA_STATUSCODE_BADINTERNALERROR;
     if(length > 0)
         signed_length = (i32)length;
-    else if(src == UA_EMPTY_ARRAY_SENTINEL)
+    else if(src >= UA_EMPTY_ARRAY_SENTINEL) /* src != NULL */
         signed_length = 0;
 
     /* Encode the array length */

tests/check_types_builtin.c

@@ -946,6 +946,53 @@ START_TEST(UA_String_encodeShallWorkOnExample) {
 }
 END_TEST
 
+START_TEST(UA_String_encodeShallWorkOnEmpty) {
+    // given
+    UA_String src = UA_STRING_NULL;
+    UA_Byte data[] = { 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55,
+                       0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55,
+                       0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55 };
+    UA_ByteString dst = { 24, data };
+    UA_Byte *pos = dst.data;
+    const UA_Byte *end = &dst.data[dst.length];
+
+    // when
+    UA_StatusCode retval = UA_String_encodeBinary(&src, &pos, end);
+
+    // then
+    ck_assert_int_eq(retval, UA_STATUSCODE_GOOD);
+    ck_assert_int_eq(data[0], 0xFF);
+
+    ///////
+
+    // given
+    src = UA_STRING("");
+    pos = dst.data;
+    end = &dst.data[dst.length];
+
+    // when
+    retval = UA_String_encodeBinary(&src, &pos, end);
+
+    // then
+    ck_assert_int_eq(retval, UA_STATUSCODE_GOOD);
+    ck_assert_int_eq(data[0], 0x00);
+
+    ///////
+
+    // given
+    src.data = (UA_Byte*)"";
+    pos = dst.data;
+    end = &dst.data[dst.length];
+
+    // when
+    retval = UA_String_encodeBinary(&src, &pos, end);
+
+    // then
+    ck_assert_int_eq(retval, UA_STATUSCODE_GOOD);
+    ck_assert_int_eq(data[0], 0x00);
+}
+END_TEST
+
 START_TEST(UA_ExpandedNodeId_encodeShallWorkOnExample) {
     // given
     UA_ExpandedNodeId src = UA_EXPANDEDNODEID_NUMERIC(0, 15);
@@ -1757,6 +1804,7 @@ static Suite *testSuite_builtin(void) {
     tcase_add_test(tc_encode, UA_Float_encodeShallWorkOnExample);
     tcase_add_test(tc_encode, UA_Double_encodeShallWorkOnExample);
     tcase_add_test(tc_encode, UA_String_encodeShallWorkOnExample);
+    tcase_add_test(tc_encode, UA_String_encodeShallWorkOnEmpty);
     tcase_add_test(tc_encode, UA_ExpandedNodeId_encodeShallWorkOnExample);
     tcase_add_test(tc_encode, UA_DataValue_encodeShallWorkOnExampleWithoutVariant);
     tcase_add_test(tc_encode, UA_DataValue_encodeShallWorkOnExampleWithVariant);