v2ray: add v2ray service

nixos/modules/module-list.nix

@@ -724,6 +724,7 @@
   ./services/networking/tvheadend.nix
   ./services/networking/unbound.nix
   ./services/networking/unifi.nix
+  ./services/networking/v2ray.nix
   ./services/networking/vsftpd.nix
   ./services/networking/wakeonlan.nix
   ./services/networking/websockify.nix

nixos/modules/services/networking/v2ray.nix

@@ -0,0 +1,81 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  options = {
+
+    services.v2ray = {
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether to run v2ray server.
+
+          Either `configFile` or `config` must be specified.
+        '';
+      };
+
+      configFile = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        example = "/etc/v2ray/config.json";
+        description = ''
+          The absolute path to the configuration file.
+
+          Either `configFile` or `config` must be specified.
+
+          See <link xlink:href="https://v2ray.com/en/configuration/overview.html"/>.
+        '';
+      };
+
+      config = mkOption {
+        type = types.nullOr (types.attrsOf types.unspecified);
+        default = null;
+        example = {
+          inbounds = [{
+            port = 1080;
+            listen = "127.0.0.1";
+            protocol = "http";
+          }];
+          outbounds = [{
+            protocol = "freedom";
+          }];
+        };
+        description = ''
+          The configuration object.
+
+          Either `configFile` or `config` must be specified.
+
+          See <link xlink:href="https://v2ray.com/en/configuration/overview.html"/>.
+        '';
+      };
+    };
+
+  };
+
+  config = let
+    cfg = config.services.v2ray;
+    configFile = if cfg.configFile != null
+      then cfg.configFile
+      else (pkgs.writeText "v2ray.json" (builtins.toJSON cfg.config));
+
+  in mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = (cfg.configFile == null) != (cfg.config == null);
+        message = "Either but not both `configFile` and `config` should be specified for v2ray.";
+      }
+    ];
+
+    systemd.services.v2ray = {
+      description = "v2ray Daemon";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+      path = [ pkgs.v2ray ];
+      script = ''
+        exec v2ray -config ${configFile}
+      '';
+    };
+  };
+}