Add nix import and export to nncp

hosts/containers/nncp/default.nix

@@ -1,6 +1,8 @@
 { config, lib, pkgs, ... }:
 
 {
+  imports = [ ./neighbours.nix ];
+
   c3d2.mergeNncpSettings = false;
   c3d2.hq.statistics.enable = true;
   c3d2.autoUpdate = true;
@@ -27,9 +29,7 @@
         in lib.mapAttrs (name: value:
           value // {
             via = lib.lists.remove "c3d2" value.via;
-          } // (if (value.addrs or { }) == { } then
-            { }
-          else {
+          } // (lib.attrsets.optionalAttrs (value.addrs or { } != { }) {
             calls = [ nightCall ];
           })) (builtins.removeAttrs config.c3d2.nncp.neigh [ "c3d2" ]);
     };

hosts/containers/nncp/neighbours.nix

@@ -0,0 +1,19 @@
+{ config, lib, pkgs, ... }:
+
+let
+  exec = {
+    # A command to asynchronously export store paths to a remote caller.
+    nix-store-export = with pkgs;
+      [
+        (writeScript "nncp-nix-store-export.sh" ''
+          #!${bash}/bin/bash
+          set -euo pipefail
+          ${config.nix.package}/bin/nix-store --export $@ | \
+            ${config.programs.nncp.package}/bin/nncp-exec -nice $NNCP_NICE $NNCP_SENDER nix-store-import
+        '')
+      ];
+
+    # A command to import store paths from a remote caller.
+    nix-store-import = [ "${config.nix.package}/bin/nix-store" "--import" ];
+  };
+in { programs.nncp.settings.neigh = { emery = { inherit exec; }; }; }

modules/nncp.nix

@@ -8,12 +8,20 @@ let
   daemonCfg = config.services.nncp.daemon;
   settingsFormat = pkgs.formats.json { };
   jsonCfgFile = settingsFormat.generate "nncp.json" programCfg.settings;
+  pkg = programCfg.package;
 in {
   options = {
     programs.nncp = {
 
       enable = mkEnableOption "NNCP (Node to Node copy) utilities";
 
+      package = mkOption {
+        type = types.package;
+        default = pkgs.nncp;
+        defaultText = literalExpression "pkgs.nncp";
+        description = "The NNCP package to use system-wide.";
+      };
+
       secrets = mkOption {
         type = with types; listOf str;
         example = [ "/run/keys/nncp.hjson" ];
@@ -108,7 +116,7 @@ in {
     };
 
     environment = mkIf programCfg.enable {
-      systemPackages = [ pkgs.nncp ];
+      systemPackages = [ pkg ];
       etc."nncp.hjson".source = nncpCfgFile;
     };
 
@@ -121,12 +129,12 @@ in {
       nncpCfgDir=$(mktemp --directory nncp.XXXXXXXXXX)
       for f in ${jsonCfgFile} ${toString config.programs.nncp.secrets}; do
         tmpdir=$(mktemp --directory nncp.XXXXXXXXXX)
-        ${pkgs.nncp}/bin/nncp-cfgdir -cfg $f -dump $tmpdir
+        ${pkg}/bin/nncp-cfgdir -cfg $f -dump $tmpdir
         ${pkgs.findutils}/bin/find $tmpdir -size 1c -delete
         cp -a $tmpdir/* $nncpCfgDir/
         rm -rf $tmpdir
       done
-      ${pkgs.nncp}/bin/nncp-cfgdir -load $nncpCfgDir > ${nncpCfgFile}
+      ${pkg}/bin/nncp-cfgdir -load $nncpCfgDir > ${nncpCfgFile}
       rm -rf $nncpCfgDir
       chgrp uucp ${nncpCfgFile}
     '';
@@ -139,7 +147,7 @@ in {
       wantedBy = [ "multi-user.target" ];
       serviceConfig = {
         ExecStart = ''
-          ${pkgs.nncp}/bin/nncp-caller -noprogress -cfg "${nncpCfgFile}" ${
+          ${pkg}/bin/nncp-caller -noprogress -cfg "${nncpCfgFile}" ${
             lib.strings.escapeShellArgs callerCfg.extraArgs
           }'';
         Group = "uucp";
@@ -155,7 +163,7 @@ in {
       wantedBy = [ "multi-user.target" ];
       serviceConfig = {
         ExecStart = ''
-          ${pkgs.nncp}/bin/nncp-daemon -noprogress -cfg "${nncpCfgFile}" ${
+          ${pkg}/bin/nncp-daemon -noprogress -cfg "${nncpCfgFile}" ${
             lib.strings.escapeShellArgs daemonCfg.extraArgs
           }'';
         Restart = "on-failure";
@@ -170,7 +178,7 @@ in {
       after = [ "network.target" ];
       serviceConfig = {
         ExecStart = ''
-          ${pkgs.nncp}/bin/nncp-daemon -noprogress -ucspi -cfg "${nncpCfgFile}" ${
+          ${pkg}/bin/nncp-daemon -noprogress -ucspi -cfg "${nncpCfgFile}" ${
             lib.strings.escapeShellArgs daemonCfg.extraArgs
           }'';
         Group = "uucp";