[Experimental] Custom scheme

[kuenishi]

When a configuration file $XDG_CONFIG_HOME/pfio.ini is placed, it provides an injection point to customize FS resolution from scheme ( s3 part of s3://some/path/to/file ). It lets us configure endpoint, secret, arbitrary configurations that's available at the kwargs of each FSes. If you have some s3-compat storage system which is not S3, the configuration file would be like:

[foobar]
scheme = s3
endpoint = https://your-s3-endpoint.example.com

And apps will code like this:

  fs = pfio.v2.from_url('foobar://path/to/a')
  with fs.open('filename') as fp:
      fp.read()

Possible discussions:

• The configuration object will be static and unchanged during the process. It can be a global configuration variable
• Configuration file name and path (make it configurable with env string?)

TODOs

• [x] tests
• [x] docs

[kuenishi]

Let us load secrets via environmental variables e.g.

[foobar]
scheme = s3
endpoint = https://foobar.example.com/
aws access_key_id = $CUSTOM_ACCESS_KEY
aws_secret_access_key = $CUSTOM_ACCESS_SECRET

Other discussions:

• won't do the global configuration variable as like an API
• no need for configurable config path

[kuenishi]

Assigned to 2.5.1 instead as it's yet an experimental feature.