lighttpd: add gitweb as a sub-service

Now you can access gitweb at http://yourserver/gitweb by simply adding
this to configuration.nix (assuming services.lighttpd.enable = true);

  services.lighttpd.gitweb.enable = true;

The path to all bare repositories served by gitweb can be set with this
option (default value below):

  services.lighttpd.gitweb.projectroot = "/srv/git";

Based on patch contributed by Bjørn Forsman.

modules/module-list.nix

@@ -186,6 +186,7 @@
   ./services/web-servers/apache-httpd/default.nix
   ./services/web-servers/jboss/default.nix
   ./services/web-servers/lighttpd/default.nix
+  ./services/web-servers/lighttpd/gitweb.nix
   ./services/web-servers/nginx/default.nix
   ./services/web-servers/tomcat.nix
   ./services/x11/desktop-managers/default.nix

modules/services/web-servers/lighttpd/gitweb.nix

@@ -0,0 +1,63 @@
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let
+  cfg = config.services.lighttpd.gitweb;
+  gitwebConfigFile = pkgs.writeText "gitweb.conf" ''
+    # path to git projects (<project>.git)
+    $projectroot = "${cfg.projectroot}";
+  '';
+in
+{
+
+  options.services.lighttpd.gitweb = {
+
+    enable = mkOption {
+      default = false;
+      type = types.uniq types.bool;
+      description = ''
+        If true, enable gitweb in lighttpd. Access it at http://yourserver/gitweb
+      '';
+    };
+
+    projectroot = mkOption {
+      default = "/srv/git";
+      type = types.uniq types.string;
+      description = ''
+        Path to git projects (bare repositories) that should be served by
+        gitweb. Must not end with a slash.
+      '';
+    };
+
+  };
+
+  config = mkIf cfg.enable {
+
+    services.lighttpd.extraConfig = ''
+      server.modules += (
+        "mod_alias",
+        "mod_cgi",
+        "mod_redirect",
+        "mod_setenv"
+      )
+      $HTTP["url"] =~ "^/gitweb" {
+          cgi.assign = (
+              ".cgi" => "${pkgs.perl}/bin/perl"
+          )
+          url.redirect = (
+              "^/gitweb$" => "/gitweb/"
+          )
+          alias.url = (
+              "/gitweb/static/" => "${pkgs.git}/share/gitweb/static/",
+              "/gitweb/"        => "${pkgs.git}/share/gitweb/gitweb.cgi"
+          )
+          setenv.add-environment = (
+              "GITWEB_CONFIG" => "${gitwebConfigFile}"
+          )
+      }
+    '';
+
+  };
+
+}