Initial support for IPP / driverless printing

Changes export logic (in sd-devices) to be able to detect IPP
printers without breaking compatibility with the old system.

To achive this, ipp-usb is used in combination with Avahi.
The former detects IPP-compatible printers and creates a local IPP
server. Avahi allows for the discovery of these printing servers
such that print dialogs can display print information.

Contrary to the legacy printer support, for driverless printing,
no print queue is setup with `lpadmin`. Printers are automatically
discovered.

debian/control

@@ -14,7 +14,8 @@ Description: securedrop client for qubes workstation
 
 Package: securedrop-export
 Architecture: all
-Depends: ${misc:Depends}, python3, udisks2, cups, printer-driver-brlaser, printer-driver-hpcups, system-config-printer, xpp, libcups2, gnome-disk-utility, libreoffice,
+Depends: ${misc:Depends}, python3, udisks2, cups, cups-ipp-utils, printer-driver-brlaser, printer-driver-hpcups,
+ avahi-daemon, system-config-printer, xpp, libcups2, gnome-disk-utility, libreoffice,
  desktop-file-utils, shared-mime-info, libfile-mimeinfo-perl
 Description: Submission export scripts for SecureDrop Workstation
  This package provides scripts used by the SecureDrop Qubes Workstation to

debian/securedrop-export.install

@@ -2,3 +2,4 @@ export/files/application-x-sd-export.xml usr/share/mime/packages
 export/files/send-to-usb.desktop usr/share/applications
 export/files/sd-logo.png usr/share/securedrop/icons
 export/files/tcrypt.conf etc/udisks2
+export/files/60-securedrop-export.preset usr/lib/systemd/system-preset

export/files/60-securedrop-export.preset

@@ -0,0 +1,4 @@
+# avahi-daemon so that driverless printers are detected when
+# plugged in via USB, overriding 75-qubes-vm.preset
+
+enable avahi-daemon.service

export/securedrop_export/print/service.py

@@ -143,32 +143,59 @@ def _check_printer_setup(self) -> None:
         Check printer setup.
         Raise ExportException if supported setup is not found.
         """
+        legacy_printers=False
         try:
             logger.info("Searching for printer")
-            output = subprocess.check_output(["sudo", "lpinfo", "-v"])
-            printers = [x for x in output.decode("utf-8").split() if "usb://" in x]
+
+            printers = self._get_printers_ipp()
             if not printers:
-                logger.info("No usb printers connected")
-                raise ExportException(sdstatus=Status.ERROR_PRINTER_NOT_FOUND)
+                # look for legacy printers after no IPP ones are detected
+                printers = self._get_printers_legacy()
+                legacy_printers=True
 
-            supported_printers = [
-                p for p in printers if any(sub in p for sub in self.SUPPORTED_PRINTERS)
-            ]
-            if not supported_printers:
-                logger.info(f"{printers} are unsupported printers")
-                raise ExportException(sdstatus=Status.ERROR_PRINTER_NOT_SUPPORTED)
+            if not printers:
+                logger.info("No supported printers connected")
+                raise ExportException(sdstatus=Status.ERROR_PRINTER_NOT_FOUND)
 
-            if len(supported_printers) > 1:
-                logger.info("Too many usb printers connected")
+            if len(printers) > 1:
+                logger.info("Too many printers connected")
                 raise ExportException(sdstatus=Status.ERROR_MULTIPLE_PRINTERS_FOUND)
 
             printer_uri = printers[0]
-            printer_ppd = self._install_printer_ppd(printer_uri)
-            self._setup_printer(printer_uri, printer_ppd)
+            if legacy_printers:  # IPP printers are auto-detected by the print dialog
+                self._setup_printer(printer_uri)
         except subprocess.CalledProcessError as e:
             logger.error(e)
             raise ExportException(sdstatus=Status.ERROR_UNKNOWN)
 
+    def _get_printers_legacy(self) -> list[str]:
+        logger.info("Searching for legacy printers")
+        output = subprocess.check_output(["sudo", "lpinfo", "-v"])
+        discovered_printers = [x for x in output.decode("utf-8").split() if "usb://" in x]
+
+        supported_printers = [
+            p for p in discovered_printers if any(sub in p for sub in self.SUPPORTED_PRINTERS)
+        ]
+        if not supported_printers:
+            logger.info(f"{discovered_printers} are unsupported printers")
+            raise ExportException(sdstatus=Status.ERROR_PRINTER_NOT_SUPPORTED)
+
+        return supported_printers
+
+    def _get_printers_ipp(self) -> list[str]:
+        logger.info("Searching for IPP printers (driverless)")
+        discovered_printers = subprocess.check_output(
+            ["ippfind"],
+            universal_newlines=True
+        ).split()
+
+        if discovered_printers:
+            logger.debug(f"Found IPP printers: {', '.join(discovered_printers)}")
+        else:
+            logger.debug(f"No IPP were found")
+
+        return discovered_printers
+
     def _get_printer_uri(self) -> str:
         """
         Get the URI via lpinfo. Only accept URIs of supported printers.
@@ -202,6 +229,9 @@ def _get_printer_uri(self) -> str:
         return printer_uri
 
     def _install_printer_ppd(self, uri):
+        """
+        Discovery and installation of PPD driver (for legacy printers)
+        """
         if not any(x in uri for x in self.SUPPORTED_PRINTERS):
             logger.error(f"Cannot install printer ppd for unsupported printer: {uri}")
             raise ExportException(sdstatus=Status.ERROR_PRINTER_NOT_SUPPORTED)