Re: master is broken due to latest changes to pk-mi-json

[Mohammad-Reza Nabipoor]

On Fri, Nov 26, 2021 at 04:41:57PM +0100, Jose E. Marchesi wrote:
> 
> > On Fri, Nov 26, 2021 at 04:14:15PM +0100, Jose E. Marchesi wrote:
> >> 
> >> > Or even better approach:
> >> >   Convert JSON to string representation (using 
> >> > `json_object_to_json_string`)
> >> >   and `strcmp` the string representation of objects.
> >> >
> >> > I think due to the fact that we just use `json_object_equal` in 
> >> > testsuite,
> >> > it's totally fine to use this not-so-optimized approach.
> >> > WDYT?
> >> 
> >> This would be feasible, but may lead to spurious results depending on
> >> how the conversion routine is implemented: there may not be a 1-1
> >> relationship between the written representation and the JSON object.
> >> 
> >
> >
> > The whole purpose of a JSON library is to encode/decode to/from string
> > representation. If a library fails on this simple thing, we should not use
> > it at all.
> 
> I think that this:
> 
> <<<<<<<
> { 10, 20 }
> >>>>>>>
> 
> and this:
> 
> <<<<<<<
> { 10,
>   20,
> }
> >>>>>>>
> 
> Denote the same JSON object using different written representations.


Yes. You're right.


> 
> I don't think that json_object_to_json_string makes any promise in that
> the returned string is identical when the passed JSON objects are
> "equal".
> 


Excerpt from `json-c/json_object.h`:


```c
/**
 * A flag for the json_object_to_json_string_ext() and
 * json_object_to_file_ext() functions which causes the output to have
 * minimal whitespace inserted to make things slightly more readable.
 */
#define JSON_C_TO_STRING_SPACED (1 << 0)

// ...

/** Stringify object to json format.
 * Equivalent to json_object_to_json_string_ext(obj, JSON_C_TO_STRING_SPACED)
 * The pointer you get is an internal of your json object. You don't
 * have to free it, later use of json_object_put() should be sufficient.
 * If you can not ensure there's no concurrent access to *obj use
 * strdup().
 * @param obj the json_object instance
 * @returns a string in JSON format
 */
JSON_EXPORT const char *json_object_to_json_string(struct json_object *obj);
```

So, I think it will produce the same amount of whitespace in two consecutive
calls in a single executable :)


> By the way, what does that mean, for a JSON object to be "equal" to
> another?  Is that equality by structure?
> 


IMHO if it has the same structure and fields, we can define them as equal.
We're talking equality in a very specific context, string represention from
a function in a single library in a single executable.
Yes, I consider `{"a":1,"b":2}` equal to `{"b":2,"a":1}` despite the fact that
they're not using the same string representation.
But here, we're talking about output of `json_object_to_json_string`.


```
static int
pk_json_object_equal_p (struct json_object *j1, struct json_object *j2)
{
  return STREQ (json_object_to_json_string (j1),
                json_object_to_json_string (j2));
}
```

> IMO this is way too complicated for little benefit.
> 
> I would still just skip() the tests that rely on comparing JSON objects
> if the json library doesn't provide a way to compare JSON objects.
> 


OK. You're the boss :)