JSON Pointer resolve failure resulting in incorrect exception code

[cmannett85]

int main()
{
    auto model = R"({
        "a": {
            "b": 42
        }
    })"_json;

    try {
        model.at("/a/c"_json_pointer);
    } catch (json::exception& e) {
        std::cout << "ID: " << e.id << std::endl;
    }

    return EXIT_SUCCESS;
}

Prints:

ID: 403

According to the json::out_of_range and json::at(const json_pointer&) docs, a JSON pointer that cannot be resolved should return a 404, but it actually returns a 403.

[nlohmann]

Thanks for the info! I'll check.

[nlohmann]

Fixed. See http://nlohmann.github.io/json/classnlohmann_1_1basic__json_a8ab61397c10f18b305520da7073b2b45.html#a8ab61397c10f18b305520da7073b2b45

[nlohmann]

@cmannett85 Can you please have a look whether the updated documentation better describes the behavior of the function?

[cmannett85]

@nlohmann, can you explain the difference between a 403 and 404 error? In the example code:

    // out_of_range.403
    try
    {
        // try to use a JSON pointer to an nonexistent object key
        json::const_reference ref = j.at("/foo"_json_pointer);
    }
    catch (json::out_of_range& e)
    {
        std::cout << e.what() << '\n';
    }

    // out_of_range.404
    try
    {
        // try to use a JSON pointer that cannot be resolved
        json::reference ref = j.at("/number/foo"_json_pointer);
    }
    catch (json::out_of_range& e)
    {
        std::cout << e.what() << '\n';
    }

In the latter example foo is a non-existent object key in number, so why does not it not also throw a 403?

[nlohmann]

Take

{"one": 1, "two": 2, "list": [1,2,3]}

as example.

• JSON Pointer /bar yields 403, because / is an object, but key bar was not found.
• JSON Pointer /list/foo yields 404, because /list is an array, and foo makes no sense here.

[cmannett85]

Ah, so a 403 is always thrown when a missing object member is requested, whilst a 404 is thrown when the JSON pointer is invalid (as opposed to 'malformed')? If so, why does the last example in your link throw a 404 instead of a 403 (as number is an object)?

[nlohmann]

In the example, / is an object, /number is the number 1, so /number/foo fails, because a number is not an object, so there cannot be a key foo.

[cmannett85]

I finally understand! Your documentation update addresses the issue, so I'll close this issue.

[nlohmann]

:)