Treat an empty http_proxy mean "Don't use proxy" and skip parsing it

[ikedam]

Replaces #21570

An empty value for http_proxy results error messages like this, as described in #17631 :

E1230 02:42:28.834924400       1 uri_parser.cc:46]           bad uri.scheme: ''
E1230 02:42:28.835090500       1 uri_parser.cc:52]                            ^ here
E1230 02:42:28.835106400       1 http_proxy.cc:63]           cannot parse value of 'http_proxy' env var

You can see this by simply running

$ http_proxy= bins/opt/h2_local_ipv4_test no_logging

I want to suppress this error as:

• I pass empty http_proxy with following docker-compose.yaml to have it work on environments both with proxies and without proxies:

  environment:
      http_proxy: ${http_proxy}
      https_proxy: ${https_proxy}
  

  • I created a repository to demonstrate that situation: https://github.com/ikedam/grpcio-httpproxy-demo .
• Allowing empty grpc_proxy can be useful as a way to have grpc not to use http_proxy
  • Refer https_proxy environment variable is ignored when empty rubygems/rubygems#1706
• It's useless to let users know that an empty string is invalid as a URL.

This change only suppress the error message and doesn't change the actual communication behavior.

@nicolasnoble

[ikedam]

To have new goto not cross the initialization.

[markdroth]

This looks good to me. I've triggered the tests to run. I'll let Yash do the second review and merge when ready.

[yashykt]

EasyCLA has not passed yet. @ikedam have you signed the cla?

[ikedam]

I signed it.

[ikedam]

I believe the above comment will proceed the check according to FAQ ( https://identity.linuxfoundation.org/projects/cncf ).

[ikedam]

Hmm... the status doesn’t seem changed from “Expected — Waiting for status to be reported”.

I’ve already singed the CLA in #21570 .
I might need to sign again for each pull requests, but I haven’t received any Emails requesting that and I don’t know how to do that...

[yashykt]

Closing and reopening the PR did the trick

[yashykt]

Unrelated interop build failures and other test issues - #19726, #21627

[ikedam]

Thanks!