clanService:phonebox: fax echo feature

modules/clan/phonebox/default.nix

@@ -30,7 +30,12 @@
             ...
           }:
           let
+            asterisk = pkgs.asterisk.overrideAttrs (old: {
+              propagatedNativeBuildInputs = [ pkgs.spandsp3 ];
+            });
+
             user = "asterisk";
+            faxDir = "/run/asterisk/fax";
             rtpPortFrom = 10000;
             rtpPortTo = 20000;
             ata-interface = settings.ata-ethernet-iface;
@@ -191,6 +196,7 @@
 
             services.asterisk = {
               enable = lib.mkDefault true;
+              package = lib.mkDefault asterisk;
               confFiles =
                 let
                   machines = lib.attrNames roles.default.machines;
@@ -240,6 +246,13 @@
                     syslog.local0 => notice,warning,error
                   '';
 
+                  "modules.conf" = ''
+                    [modules]
+                    autoload=yes
+
+                    load => res_fax_spandsp.so
+                  '';
+
                   # Dial plan config
                   "extensions.conf" =
                     let
@@ -257,6 +270,16 @@
                       same  =>     n,Playback(hello-world)
                       same  =>     n,Hangup()
 
+                      exten => 000,1,Answer()
+                      same => n,ReceiveFAX(${faxDir}/echo-''${UNIQUEID}.tiff)
+                      same => n,Set(FAXFILE=${faxDir}/echo-''${UNIQUEID}.tiff)
+                      same => n,Set(FAXECHO=true)
+
+                      exten => h,1,GotoIf($[''${FAXECHO}]?sendfax)
+                      same => n,Hangup()
+                      same => n(sendfax),Originate(PJSIP/00,app,SendFAX,${faxDir}/echo-''${UNIQUEID}.tiff)
+                      same => n,Set(FAXECHO=false)
+
                     ''
                     + (genLocalExtenConf {
                       localNumber = config.clan.core.vars.generators.phonebox.files.ata-local-number.value;
@@ -318,6 +341,10 @@
                 };
             };
 
+            systemd.tmpfiles.rules = [
+              "d ${faxDir}                            0755 ${user} ${user} - -"
+            ];
+
             systemd.services.asterisk-watcher = {
               enable = true;
               description = "Asterisk Configuration files watcher";