Revert "Merge master into staging-next"

I merged master into staging-next but accidentally pushed it to master.
This should get us back to 87a19e9048.

This reverts commit ac241fb7a5, reversing
changes made to 76a439239e.

nixos/modules/services/networking/kresd.nix

@@ -3,34 +3,12 @@
 with lib;
 
 let
+
   cfg = config.services.kresd;
-
-  # Convert systemd-style address specification to kresd config line(s).
-  # On Nix level we don't attempt to precisely validate the address specifications.
-  mkListen = kind: addr: let
-    al_v4 = builtins.match "([0-9.]\+):([0-9]\+)" addr;
-    al_v6 = builtins.match "\\[(.\+)]:([0-9]\+)" addr;
-    al_portOnly = builtins.match "()([0-9]\+)" addr;
-    al = findFirst (a: a != null)
-      (throw "services.kresd.*: incorrect address specification '${addr}'")
-      [ al_v4 al_v6 al_portOnly ];
-    port = last al;
-    addrSpec = if al_portOnly == null then "'${head al}'" else "{'::', '127.0.0.1'}";
-    in # freebind is set for compatibility with earlier kresd services;
-       # it could be configurable, for example.
-      ''
-        net.listen(${addrSpec}, ${port}, { kind = '${kind}', freebind = true })
-      '';
-
-  configFile = pkgs.writeText "kresd.conf" (
-    optionalString (cfg.listenDoH != []) ''
-      modules.load('http')
-    ''
-    + concatMapStrings (mkListen "dns") cfg.listenPlain
-    + concatMapStrings (mkListen "tls") cfg.listenTLS
-    + concatMapStrings (mkListen "doh") cfg.listenDoH
-    + cfg.extraConfig
-  );
+  configFile = pkgs.writeText "kresd.conf" ''
+    ${optionalString (cfg.listenDoH != []) "modules.load('http')"}
+    ${cfg.extraConfig};
+  '';
 
   package = pkgs.knot-resolver.override {
     extraFeatures = cfg.listenDoH != [];
@@ -47,7 +25,6 @@ in {
           value
       )
     )
-    (mkRemovedOptionModule [ "services" "kresd" "cacheDir" ] "Please use (bind-)mounting instead.")
   ];
 
   ###### interface
@@ -58,8 +35,8 @@ in {
       description = ''
         Whether to enable knot-resolver domain name server.
         DNSSEC validation is turned on by default.
-        You can run <literal>sudo nc -U /run/knot-resolver/control/1</literal>
-        and give commands interactively to kresd@1.service.
+        You can run <literal>sudo nc -U /run/kresd/control</literal>
+        and give commands interactively to kresd.
       '';
     };
     extraConfig = mkOption {
@@ -69,10 +46,16 @@ in {
         Extra lines to be added verbatim to the generated configuration file.
       '';
     };
+    cacheDir = mkOption {
+      type = types.path;
+      default = "/var/cache/kresd";
+      description = ''
+        Directory for caches.  They are intended to survive reboots.
+      '';
+    };
     listenPlain = mkOption {
       type = with types; listOf str;
       default = [ "[::1]:53" "127.0.0.1:53" ];
-      example = [ "53" ];
       description = ''
         What addresses and ports the server should listen on.
         For detailed syntax see ListenStream in man systemd.socket.
@@ -92,54 +75,91 @@ in {
       default = [];
       example = [ "198.51.100.1:443" "[2001:db8::1]:443" "443" ];
       description = ''
-        Addresses and ports on which kresd should provide DNS over HTTPS (see RFC 8484).
+        Addresses and ports on which kresd should provide DNS over HTTPS (see RFC 7858).
         For detailed syntax see ListenStream in man systemd.socket.
       '';
     };
-    instances = mkOption {
-      type = types.ints.unsigned;
-      default = 1;
-      description = ''
-        The number of instances to start.  They will be called kresd@{1,2,...}.service.
-        Knot Resolver uses no threads, so this is the way to scale.
-        You can dynamically start/stop them at will, so this is just system default.
-      '';
-    };
     # TODO: perhaps options for more common stuff like cache size or forwarding
   };
 
   ###### implementation
   config = mkIf cfg.enable {
-    environment.etc."knot-resolver/kresd.conf".source = configFile; # not required
+    environment.etc."kresd.conf".source = configFile; # not required
 
-    users.users.knot-resolver =
-      { isSystemUser = true;
-        group = "knot-resolver";
+    users.users.kresd =
+      { uid = config.ids.uids.kresd;
+        group = "kresd";
         description = "Knot-resolver daemon user";
       };
-    users.groups.knot-resolver.gid = null;
+    users.groups.kresd.gid = config.ids.gids.kresd;
 
-    systemd.packages = [ package ]; # the units are patched inside the package a bit
-
-    systemd.targets.kresd = { # configure units started by default
-      wantedBy = [ "multi-user.target" ];
-      wants = [ "kres-cache-gc.service" ]
-        ++ map (i: "kresd@${toString i}.service") (range 1 cfg.instances);
-    };
-    systemd.services."kresd@".serviceConfig = {
-      ExecStart = "${package}/bin/kresd --noninteractive "
-        + "-c ${package}/lib/knot-resolver/distro-preconfig.lua -c ${configFile}";
-      # Ensure correct ownership in case UID or GID changes.
-      CacheDirectory = "knot-resolver";
-      CacheDirectoryMode = "0750";
+    systemd.sockets.kresd = rec {
+      wantedBy = [ "sockets.target" ];
+      before = wantedBy;
+      listenStreams = cfg.listenPlain;
+      socketConfig = {
+        ListenDatagram = listenStreams;
+        FreeBind = true;
+        FileDescriptorName = "dns";
+      };
     };
 
-    environment.etc."tmpfiles.d/knot-resolver.conf".source =
-      "${package}/lib/tmpfiles.d/knot-resolver.conf";
+    systemd.sockets.kresd-tls = mkIf (cfg.listenTLS != []) rec {
+      wantedBy = [ "sockets.target" ];
+      before = wantedBy;
+      partOf = [ "kresd.socket" ];
+      listenStreams = cfg.listenTLS;
+      socketConfig = {
+        FileDescriptorName = "tls";
+        FreeBind = true;
+        Service = "kresd.service";
+      };
+    };
 
-    # Try cleaning up the previously default location of cache file.
-    # Note that /var/cache/* should always be safe to remove.
-    # TODO: remove later, probably between 20.09 and 21.03
-    systemd.tmpfiles.rules = [ "R /var/cache/kresd" ];
+    systemd.sockets.kresd-doh = mkIf (cfg.listenDoH != []) rec {
+      wantedBy = [ "sockets.target" ];
+      before = wantedBy;
+      partOf = [ "kresd.socket" ];
+      listenStreams = cfg.listenDoH;
+      socketConfig = {
+        FileDescriptorName = "doh";
+        FreeBind = true;
+        Service = "kresd.service";
+      };
+    };
+
+    systemd.sockets.kresd-control = rec {
+      wantedBy = [ "sockets.target" ];
+      before = wantedBy;
+      partOf = [ "kresd.socket" ];
+      listenStreams = [ "/run/kresd/control" ];
+      socketConfig = {
+        FileDescriptorName = "control";
+        Service = "kresd.service";
+        SocketMode = "0660"; # only root user/group may connect and control kresd
+      };
+    };
+
+    systemd.tmpfiles.rules = [ "d '${cfg.cacheDir}' 0770 kresd kresd - -" ];
+
+    systemd.services.kresd = {
+      description = "Knot-resolver daemon";
+
+      serviceConfig = {
+        User = "kresd";
+        Type = "notify";
+        WorkingDirectory = cfg.cacheDir;
+        Restart = "on-failure";
+        Sockets = [ "kresd.socket" "kresd-control.socket" ]
+          ++ optional (cfg.listenTLS != []) "kresd-tls.socket";
+      };
+
+      # Trust anchor goes from dns-root-data by default.
+      script = ''
+        exec '${package}/bin/kresd' --config '${configFile}' --forks=1
+      '';
+
+      requires = [ "kresd.socket" ];
+    };
   };
 }