Anyio compatability

[dolamroth]

Starlette itself is anyio-compatible. However, underlying implementations of low-level libraries are mostly not.

• With current scheme, SQLAlchemy is main core part, which is not anyio-compatible.
• Anyio-compatible websockets are available, if using hypercorn (beta, as of right now) + anysocks/asyncwebsockets. However, so far these are less reliable/feature-complete than asyncio implementation.
• There is no DB engines (at least for Postgres) with anyio, but there are separate implementations for asyncio and trio
  • pg-purepy exists, but it is not feature-complete
  • trio-pg is just wrapper around asyng pg
• Same for redis / mqtt / rmq
• There is anyio implementation for SMTP https://pypi.org/project/smtpproto/

Desireable contrib libraries to have around for production

• MongoDB driver, apparently easy to impement via https://github.com/mongodb/motor
• Elasticsearch driver, should be easy to implement with httpx
• aioftp/aiosftp => anyio - seems moderately difficult
• aiortc => anyio - seems very difficult
• aiozmq => anyio - seems very difficult, also see: zmq support python-trio/trio#116
• aiobotocore for S3 file storage - pending issue support pluggable http clients/coroutine frameworks (anyio/httpx) aio-libs/aiobotocore#749