How to validate an input before parsing?

[Outstep]

Hello,

I am working on an API type project which will receive JSON string requests. I need to validate that the input string is a good JSON string before parsing it.

I thought that I saw something in my nlohmann searching that suggests that something was going to be, or is now already, integrated into the library.

Could you please tell me where to get more information on this and possibly a simple example, as the "try-catch" method does not seem to work well for me.

Thanks :)

[nlohmann]

You can use the accept function - it takes the same parameters as parse, but only returns a boolean: true if the input is valid JSON or false otherwise. In case of an error, no exception will be thrown.

[Outstep]

Thanks, that works great for the case in which I am validating if I have good JSON.

Now I just ran into the problem in which I need to validate that I have a JSON field "action"

I tried to use:

 string action = body["action"];

if (action.empty()) {
     cout << "Action NULL" << endl;
} else {
     cout << "Action GOOD" << endl;
}

just as a test since if I send a json like: {"test":"test"} then I get.

terminate called after throwing an instance of 'nlohmann::detail::type_error'
  what():  [json.exception.type_error.302] type must be string, but is null

Basically, I want to now cover the case in which I have good JSON but not the correct fields

{"action" : "test" }

would be good.

How can I check for this?
Thanks again.

[nlohmann]

operator[] can only be used on objects (when used with a string key). If value body is not an object, you get the exception you described. Instead of empty(), you should use is_object() to make sure you can actually use operator[].

[nlohmann]

(If you want to check against null, use is_null() instead of empty().)

[Outstep]

Thanks for your help.

I was able to get things working with is_null() and find()
Cheers