Fix: Respect no_proxy in proxies dictionary and NO_PROXY env var

[cjac]

This PR addresses issue #5000 by ensuring that proxy bypass directives are respected, whether provided directly within the proxies dictionary passed to request functions or set via environment variables.

Previously, bypass rules in the proxies dictionary were not fully honored, and the NO_PROXY environment variable was not always checked when a proxies dictionary was provided.

This change includes:

1. src/requests/sessions.py:

   • Modified Session.send to check both no_proxy and no keys in the proxies dictionary. If the request URL matches any pattern in the list, proxies are cleared for that request.
   • Updated merge_environment_settings to check both no_proxy and no keys when merging environment proxies.
   • Updated Session.request docstring to clarify no and no_proxy key support.

2. src/requests/utils.py:

   • Updated select_proxy to evaluate bypass rules before selecting a proxy.
   • Refined select_proxy to respect standard precedence for environment variables (preferring lowercase no_proxy over NO_PROXY).
   • Updated resolve_proxies to check both no_proxy and no keys.

3. src/requests/api.py:

   • Updated requests.request docstring to clarify no and no_proxy key support in the proxies dictionary.

4. tests/test_requests.py:

   • Added new test cases (test_no_proxy_in_proxies_dict, test_no_proxy_star_in_proxies_dict, test_no_proxy_not_matching_in_proxies_dict) to verify that bypass rules within the proxies dictionary work as expected.

5. tests/test_utils.py:

   • Added new test cases (test_select_proxy_with_no_proxy) to ensure proxy bypass rules and environment variables are correctly handled by select_proxy.

These changes ensure consistent behavior for proxy bypass logic, regardless of how the proxy settings are configured.

Closes #5000

[hajo-m]

Regarding #5000 (comment)

[Mukller]

The
o_proxy handling in send() and select_proxy() looks correct. However, est_rewind_body_no_seek (line ~2004 in test_requests.py) has its body replaced with pass, which breaks the original test. This needs to be restored before merge.

Also, select_proxy now returns None when NO_PROXY matches — callers of select_proxy should be checked to ensure they handle None gracefully (currently merge_environment_settings and send both use the return value as a dict key or proxy URL).

Fix the broken test and this should be good.

[cjac]

Thank you for the review. I have addressed the issues raised:

• Missing test_rewind_body_no_seek: This test has been restored to its original implementation with BadFileObj and the UnrewindableBodyError assertion. The new tests have been moved out of this function.

• Handling of None from select_proxy: Callers in HTTPAdapter have been checked. They use truthiness evaluations (if proxy:) and treat None safely as bypassing the proxy setup, proceeding to standard connection Pool Manager invocation.

• Dictionary Key and Environment Precedence: Addressed concerns regarding key naming ('no' vs 'no_proxy') by checking both in the proxies dictionary. Refined select_proxy to explicitly respect both no_proxy and NO_PROXY environment variables, prioritizing the lowercase version to maintain consistency with urllib and other standard HTTP clients.

[cjac]

now possible to accurately specify using environment variables which hosts should skip proxy and go direct

[cjac]

rebased onto orgin's main