autossh.nix: add the module, which run autossh sessions as systemd services

nixos/modules/module-list.nix

@@ -263,6 +263,7 @@
   ./services/networking/atftpd.nix
   ./services/networking/avahi-daemon.nix
   ./services/networking/bind.nix
+  ./services/networking/autossh.nix
   ./services/networking/bird.nix
   ./services/networking/bitlbee.nix
   ./services/networking/btsync.nix

nixos/modules/services/networking/autossh.nix

@@ -0,0 +1,124 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.autossh;
+
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    services.autossh = {
+
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether to enable the AutoSSH, the SSH sessions manager
+        '';
+      };
+
+      sessions = mkOption {
+        type = types.listOf (types.submodule {
+          options = {
+            name = mkOption {
+              type = types.string;
+              example = "socks-peer";
+              description = "Name of the local AutoSSH session";
+            };
+            user = mkOption {
+              type = types.string;
+              example = "bill";
+              description = "Name of the user the AutoSSH session should run as";
+            };
+            monitoringPort = mkOption {
+              type = types.int;
+              default = 0;
+              example = 20000;
+              description = ''
+                Port to be used by AutoSSH for peer monitoring. Note, that
+                AutoSSH also uses mport+1. Value of 0 disables the keep-alive
+                style monitoring
+              '';
+            };
+            extraArguments = mkOption {
+              type = types.string;
+              example = "-N -D4343 bill@socks.host.net";
+              description = ''
+                Arguments to be passed to AutoSSH and retransmitted to SSH
+                process. Some meaningful options include -N (don't run remote
+                command), -D (open SOCKS proxy on local port), -R (forward
+                remote port), -L (forward local port), -v (Enable debug). Check
+                ssh manual for the complete list.
+              '';
+            };
+          };
+        });
+
+        default = [];
+        description = ''
+          List of AutoSSH sessions to start as systemd services. Each service is
+          named 'autossh-{session.name}'.
+        '';
+
+        example = [
+          {
+            name="socks-peer";
+            user="bill";
+            monitoringPort = 20000;
+            extraArguments="-N -D4343 billremote@socks.host.net";
+          }
+        ];
+
+      };
+    };
+
+  };
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+
+    systemd.services =
+
+      lib.fold ( s : acc : acc //
+        {
+          "autossh-${s.name}" =
+            let
+              mport = if s ? monitoringPort then s.monitoringPort else 0;
+            in
+            {
+              description = "AutoSSH session (" + s.name + ")";
+
+              after = [ "network.target" ];
+              wantedBy = [ "multi-user.target" ];
+
+              # To be able to start the service with no network connection
+              environment.AUTOSSH_GATETIME="0";
+
+              # How often AutoSSH checks the network, in seconds
+              environment.AUTOSSH_POLL="30";
+
+              serviceConfig = {
+                  User = "${s.user}";
+                  PermissionsStartOnly = true;
+                  # AutoSSH may exit with 0 code if the SSH session was
+                  # gracefully terminated by either local or remote side.
+                  Restart = "on-success";
+                  ExecStart = "${pkgs.autossh}/bin/autossh -M ${toString mport} ${s.extraArguments}";
+              };
+            };
+        }) {} cfg.sessions;
+
+    environment.systemPackages = [ pkgs.autossh ];
+
+  };
+}
+
+