Introduce a dedicated networking.proxy option

Following the discussion NixOS#5021:
- obsolete the nix.proxy option
- add the networking.proxy option
- open a default no_proxy environment variable
- add a rsync option
- Manual tests ok.
- Automatic tests ok.

Amended by lethalman to simplify the option descriptions.

nixos/tests/networking-proxy.nix

@@ -0,0 +1,109 @@
+# Test whether `networking.proxy' work as expected.
+
+# TODO: use a real proxy node and put this test into networking.nix
+# TODO: test whether nix tools work as expected behind a proxy
+
+let default-config = {
+        imports = [ ./common/user-account.nix ];
+
+        services.xserver.enable = false;
+
+        virtualisation.memorySize = 128;
+      };
+in import ./make-test.nix {
+  name = "networking-proxy";
+
+  nodes = {
+    # no proxy
+    machine =
+      { config, pkgs, ... }:
+
+      default-config;
+
+    # proxy default
+    machine2 =
+      { config, pkgs, ... }:
+
+      default-config // {
+        networking.proxy.default = "http://user:pass@host:port";
+      };
+
+    # specific proxy options
+    machine3 =
+      { config, pkgs, ... }:
+
+      default-config //
+      {
+        networking.proxy = {
+          # useless because overriden by the next options
+          default = "http://user:pass@host:port";
+          # advanced proxy setup
+          httpProxy = "123-http://user:pass@http-host:port";
+          httpsProxy = "456-http://user:pass@https-host:port";
+          rsyncProxy = "789-http://user:pass@rsync-host:port";
+          ftpProxy = "101112-http://user:pass@ftp-host:port";
+          noProxy = "131415-127.0.0.1,localhost,.localdomain";
+        };
+      };
+
+    # mix default + proxy options
+    machine4 =
+      { config, pkgs, ... }:
+
+      default-config // {
+        networking.proxy = {
+          # open for all *_proxy env var
+          default = "000-http://user:pass@default-host:port";
+          # except for those 2
+          rsyncProxy = "123-http://user:pass@http-host:port";
+          noProxy = "131415-127.0.0.1,localhost,.localdomain";
+        };
+      };
+    };
+
+  testScript =
+    ''
+      startAll;
+
+      # no proxy at all
+      print $machine->execute("env | grep -i proxy");
+      print $machine->execute("su - alice -c 'env | grep -i proxy'");
+      $machine->mustFail("env | grep -i proxy");
+      $machine->mustFail("su - alice -c 'env | grep -i proxy'");
+
+      # Use a default proxy option
+      print $machine2->execute("env | grep -i proxy");
+      print $machine2->execute("su - alice -c 'env | grep -i proxy'");
+      $machine2->mustSucceed("env | grep -i proxy");
+      $machine2->mustSucceed("su - alice -c 'env | grep -i proxy'");
+
+      # explicitly set each proxy option
+      print $machine3->execute("env | grep -i proxy");
+      print $machine3->execute("su - alice -c 'env | grep -i proxy'");
+      $machine3->mustSucceed("env | grep -i http_proxy | grep 123");
+      $machine3->mustSucceed("env | grep -i https_proxy | grep 456");
+      $machine3->mustSucceed("env | grep -i rsync_proxy | grep 789");
+      $machine3->mustSucceed("env | grep -i ftp_proxy | grep 101112");
+      $machine3->mustSucceed("env | grep -i no_proxy | grep 131415");
+      $machine3->mustSucceed("su - alice -c 'env | grep -i http_proxy | grep 123'");
+      $machine3->mustSucceed("su - alice -c 'env | grep -i https_proxy | grep 456'");
+      $machine3->mustSucceed("su - alice -c 'env | grep -i rsync_proxy | grep 789'");
+      $machine3->mustSucceed("su - alice -c 'env | grep -i ftp_proxy | grep 101112'");
+      $machine3->mustSucceed("su - alice -c 'env | grep -i no_proxy | grep 131415'");
+
+      # set default proxy option + some other specifics
+      print $machine4->execute("env | grep -i proxy");
+      print $machine4->execute("su - alice -c 'env | grep -i proxy'");
+      $machine4->mustSucceed("env | grep -i http_proxy | grep 000");
+      $machine4->mustSucceed("env | grep -i https_proxy | grep 000");
+      $machine4->mustSucceed("env | grep -i rsync_proxy | grep 123");
+      $machine4->mustSucceed("env | grep -i ftp_proxy | grep 000");
+      $machine4->mustSucceed("env | grep -i no_proxy | grep 131415");
+      $machine4->mustSucceed("su - alice -c 'env | grep -i http_proxy | grep 000'");
+      $machine4->mustSucceed("su - alice -c 'env | grep -i https_proxy | grep 000'");
+      $machine4->mustSucceed("su - alice -c 'env | grep -i rsync_proxy | grep 123'");
+      $machine4->mustSucceed("su - alice -c 'env | grep -i ftp_proxy | grep 000'");
+      $machine4->mustSucceed("su - alice -c 'env | grep -i no_proxy | grep 131415'");
+    '';
+
+}