Support for Content-Type: application/msgpack header

[astephon88]

As evidenced by msgpack/msgpack#194, there still is no clear answer on the "proper" MIME type for msgpack. Fluent-bit's HTTP output plugin uses application/msgpack for the content-type instead of aapplication/x-msgpack, so the msgpack-asgi middleware doesn't attempt to unpack requests from fluent-bit POST's

[astephon88]

source for fluent-bit's usage of application/msgpack https://github.com/fluent/fluent-bit/blob/251bd6815fdd197a09cfc1655834cf157f1e697d/plugins/out_http/http.h#L28

[florimondmanca]

👍 Sounds like a fair improvement to welcome in here. Might be worth an update to the README too if we're already discussing content types there.

[astephon88]

Just an update as I've done a bit more research...I still believe supporting both content types would be a useful improvement, but data coming from fluent-bit still will be problematic. The msgpack messages they are sending is list of a timestamp and a dict. The timestamp is a msgpack ExtType, so, barring some extra logic to only extract JSON compatible data (which probably would be out of place here), the fluent-bit messages would still fail to parse.