[FEATURE] remove ujson dependency (it is dead)

FastAPI is using ujson which has not been actively developed for about 3 years by now. Here is a relevant issue. It’s starting to be problematic to actually compile ujson on newer platforms.

Possible alternative maybe orjson.

[dmontagu]

I would be in favor of recommending orjson instead of ujson.

I recall the creator of orjson reaching about this many months ago and there was some confusion due to slow responses, and also some issues on the pydantic side, but I think many/most of the barriers to usage have since been removed. If orjson seems to be taking over as the go-to high-performance json library, I think it would make sense to use that for development and recommend it.

To the extent that there is any difference in json encoding/decoding between json and orjson (or ujson and orjson), it would probably be best to document it.

I’d be willing to review a PR making this change (including updates to the docs). (I’d leave the ultimate decision about merging to @tiangolo though.)

[ahtik]

@ahmadazizi, orjson wheels are now available also for Windows Python 3.9.