session: Cache http requests to trusted hosts

Author: Noah Gorny

news/9498.feature.rst

@@ -0,0 +1 @@
+If a host is explicitly specified as trusted by the user (via the --trusted-host option), cache HTTP responses from it in addition to HTTPS ones.

src/pip/_internal/network/session.py

@@ -358,8 +358,15 @@ def add_trusted_host(
         if host_port not in self.pip_trusted_origins:
             self.pip_trusted_origins.append(host_port)
 
+        self.mount(
+            build_url_from_netloc(host, scheme="http") + "/", self._trusted_host_adapter
+        )
         self.mount(build_url_from_netloc(host) + "/", self._trusted_host_adapter)
         if not host_port[1]:
+            self.mount(
+                build_url_from_netloc(host, scheme="http") + ":",
+                self._trusted_host_adapter,
+            )
             # Mount wildcard ports for the same host.
             self.mount(build_url_from_netloc(host) + ":", self._trusted_host_adapter)