Segmentation fault in destructor in case of large inputs

[nlohmann]

• What is the issue you have?

Project bad_json_parsers tested how JSON parser libraries react on deeply nested inputs. It turns out that this library segfaults at a certain nesting depth. I analyzed the result, and it turned out that the segmentation fault does not occur in the parser/construction part, but rather during destruction. But avoiding destruction (i.e., by adjusting the program as follows:

#include <iostream>
#include <cstdlib>
#include "json.hpp"

// for convenience
using json = nlohmann::json;

int main(void) {
	auto j = json::parse(std::cin);
	std::cout << j.type_name() << std::endl;
	_Exit(0);
}

the library can process much longer inputs (46875000 and greater).

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?

Either use bad_json_parsers, or generate a deeply nested file (like input.json.zip), parse it, and let the destructor be called.

• What is the expected behavior?

No segmentation fault, but rather an out-of-memory error during parsing of large inputs.

• And what is the actual behavior instead?

On my machine, I get

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x7ffeef3ffff8)
  * frame #0: 0x0000000100016528 JSON Debug`nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::adl_serializer>::assert_invariant(this=<unavailable>) const at json.hpp:15588

and a stack trace of 94000 frames.

• Which compiler and operating system are you using? Is it a supported compiler?

MacOS Version 10.14.6 (18G1007), Xcode Version 11.0 (11A420a). It is a supported compiler.

• Did you use a released version of the library or the version from the develop branch?

Both develop and version 3.7.1.

• If you experience a compilation error: can you compile and run the unit tests?

Yes, everything compiles and runs fine.

[nlohmann]

There was a proposal to fix this: #1436. Also related: #832, #1419.

[nlohmann]

Fixed by merging #1436.