Option for proxy usage in Nix daemon

svn path=/nixos/trunk/; revision=13689

system/options.nix

@@ -2682,6 +2682,16 @@ in
       ";
     };
 
+    proxy = mkOption {
+        default = "";
+	description = "
+	  This option specifies the proxy to use for fetchurl. The real effect 
+	  is just exporting http_proxy, https_proxy and ftp_proxy with that
+	  value.
+	";
+	example = "http://127.0.0.1:3128";
+    };
+
   };
 
 

system/system.nix

@@ -103,7 +103,15 @@ rec {
         export NIX_REMOTE_SYSTEMS=/etc/nix.machines
         export NIX_CURRENT_LOAD=/var/run/nix/current-load
       ''
-    else "");
+    else "")
+    +
+    (if config.nix.proxy != "" then
+    ''
+        export http_proxy=${config.nix.proxy}
+        export https_proxy=${config.nix.proxy}
+        export ftp_proxy=${config.nix.proxy}
+    '' else "")
+    ;
 
               
   # The services (Upstart) configuration for the system.