Incremental parsing does not work when `parse_some()` is called multiple times.

[ergonjona]

We use jsoncons to parse JSON in HTTP bodies and want to support streaming as much as possible.
In jsoncons version 0.178.0 using the old incremental parsing methods we were able to parse JSON like so:

void parse_stream(std::vector<std::string_view> chunks, bool final) {
  for ( auto chunk : chunks ) {
    parser.update(chunk);
    parser.parse_some(decoder);
  }
  if ( final ) {
    parser.finish_parse(); 
    parser.check_done();
  }
  ...
}

This function would be called multiple times with some chunks and final == false and finally with zero or more chunks and final == true.

Since jsoncons 1.0.0 this is no longer possible.
I changed our code to use the new incremental parsing methods and it does still not work.
As long as the whole JSON string can be parsed in one call of parser.parse_some() everything works.
When we try to call parser.parse_some() multiple times an exception is thrown (some kind of syntax error). If we are not allowed to call parser.parse_some() multiple times we need to buffer all chunks before parsing, which destroys the streaming capability of our code.

I wrote a test program that reproduces the bug: https://gist.github.com/ergonjona/514e3b2581d96a78b765d153b4c5e556

• Compiler: clang++ 18.1.8
• Architecture: x64
• Operating system: Arch Linux
• jsoncons version 1.0.0

[danielaparker]

parse_some can't be called multiple times in 1.0.0. It's called once, and all further input is received through the chunk reader callback. For your use case, you'd need to perform parsing on a worker thread, and wait in the chunk reader until another thread was ready to send a chunk of data.

To be honest, I hadn't fully thought about this use case, my primary use case is reading and parsing large files in chunks. But on reflection, I think it's worth preserving the 0.178.0 API. I would suggest staying with 0.178.0 for now, and we'll revert this change.

[danielaparker]

We've reverted the json_parser API back to the way it was in 0.178.0, currently on master, will be released as 1.1.0.

[ergonjona]

@danielaparker Thank you very much!
I really like jsoncons and appreciate your work!