Better error for JSON Pointer "overshooting" the actual JSON structure.

[ateska]

Hello,

I post after a longer time 👋🏻 - but we still very intensively use SIMDJSON (thru cysimdjson).

Is your feature request related to a problem? Please describe.

{
	"document": {
		"key1": 1,
		"key2": "2",
		"key3": "3",
		"key4": 40,
		"key5": "50"
	}
}

The call .at_pointer("/document/key4/sub") fails (correctly) but the reported error is INVALID_JSON_POINTER (Invalid JSON pointer syntax).

The JSON Pointer syntax is correct (at least in my understanding) - in a different JSON document, the JSON pointer will be perfectly fine.
When this error is reported to users, it is misleading what to fix.

Describe the solution you'd like

Return different error code for this situation such as NO_SUCH_FIELD, so that the problem has a structure that can be used for a correct problem reporting to users.

Describe alternatives you've considered

We consider to build a validator of JSON Pointer that will be applied before the JSON pointer is applied to the JSON.
So that we can capture real syntax errors, report them to the user and this one will be reported as a "missing field/incorrect JSON structure" for a given JSON Pointer

Additional context

N/A

Are you willing to contribute code or documentation toward this new feature?

No, I don't write C++ well enough to contribute, sorry.

[lemire]

It is a reasonable issue. The reason why we get this error is that we arrive at a number, and we are asked, at the number to resolve 'sub'. This falls through and reports INVALID_JSON_POINTER. It would be easy to do better, although it is not entirely clear right now what we should do instead. We almost surely need a different error code. See the code (it is quite simple):

simdjson_inline simdjson_result<value> value::at_pointer(std::string_view json_pointer) noexcept {
  json_type t;
  SIMDJSON_TRY(type().get(t)); // <==== the type is number, so not array or object
  switch (t)
  {
    case json_type::array:
      return (*this).get_array().at_pointer(json_pointer);
    case json_type::object:
      return (*this).get_object().at_pointer(json_pointer);
    default:
      return INVALID_JSON_POINTER;// <===== We get here
  }
}

We could throw a different error just by changing one line.

[lemire]

This is actually not a difficult issue. I am inviting contributions.

[lemire]

Marking as a good first issue.

[yankov-pt]

Hi, would NO_SUCH_FIELD be the right error code for this?

[lemire]

@yankov-pt I suppose so, yes.