Initial commit for proxy support

[gareth-ellis]

Initial support for proxies.

The aim is to rely on existing support from requests or aiohttp.

Next steps:

• more thorough testing
• documentation

[pquentin]

Have you considered using requests inconditionally here? Without any proxy tests, requests support could be subtly broken.

[gareth-ellis]

I considered it - my aim here though was to try and retain as much current behaviour when not using proxies as possible. I was aiming to get in a set of proxy tests to cover the proxy use case.

[fressi-elastic]

What would happen with any of these variables set to empty value? Example:

http_proxy=

[gareth-ellis]

requests would be used, but requests likely would not use the proxy. Requests actually looks at any env var ending with _proxy - we can check if there is a value if you feel that is necessary, though i don't want to start doing any other validation on the input, since that will automatically be up to the client that we are using (requests for synchronus, aiohttp for async).

[fressi-elastic]

Please add unit test(s) for this fix so we can test it without having to deal with actually making requests to a server. Also please validate what would happen with any of these variables set as an empty value.

[fressi-elastic]

What would happen with any of these variables set to empty value? Example:

http_proxy=

[fressi-elastic]

If kwargs already contains "node_class" key, then this would raise an exception. I think you should add node_class as an expecific parameter at the beginning of this method so that in case is None then we can replace its value. Example:

def __init__(self, node_class = None, **kwargs):
   
   # ...
  if node_class is None and any(x in os.environ for x in proxy_env_vars):
      node_class = RequestsHttpNode
  super().__init__(*args, node_class=node_class, **kwargs)