Check NO_PROXY env to disable proxy settings

news/5378.bugfix.rst

@@ -0,0 +1 @@
+Check ``NO_PROXY`` env variable to disable proxy settings.

src/pip/_internal/cli/req_command.py

@@ -143,7 +143,9 @@ def _build_session(
             session.timeout = timeout if timeout is not None else options.timeout
 
         # Handle configured proxies
-        if options.proxy:
+        if "no_proxy" in os.environ or "NO_PROXY" in os.environ:
+            session.proxies["no_proxy"] = "*"
+        elif options.proxy:
             session.proxies = {
                 "http": options.proxy,
                 "https": options.proxy,

tests/functional/test_proxy.py

@@ -0,0 +1,34 @@
+from pathlib import Path
+from typing import Any, Dict
+
+import proxy
+import pytest
+from proxy.http.proxy import HttpProxyBasePlugin
+
+from tests.lib import PipTestEnvironment
+
+
+class AccessLogPlugin(HttpProxyBasePlugin):
+    def on_access_log(self, context: Dict[str, Any]) -> None:
+        print(context)
+
+
+@pytest.mark.network
+def test_no_proxy(
+    script: PipTestEnvironment, capfd: pytest.CaptureFixture[str]
+) -> None:
+    with proxy.Proxy(port=8888, num_acceptors=1, plugins=[AccessLogPlugin]):
+        script.environ["no_proxy"] = "1"
+        result = script.pip(
+            "download",
+            "--proxy",
+            "http://127.0.0.1:8888",
+            "--trusted-host",
+            "127.0.0.1",
+            "-d",
+            "pip_downloads",
+            "INITools==0.1",
+        )
+        result.did_create(Path("scratch") / "pip_downloads" / "INITools-0.1.tar.gz")
+        out, _ = capfd.readouterr()
+        assert "CONNECT" not in out

tests/requirements.txt

@@ -11,3 +11,4 @@ virtualenv < 20.0
 werkzeug
 wheel
 tomli-w
+proxy.py