fix: Accept empty result from sd-devices during export for backwards compatibility

securedrop_client/export.py

@@ -117,7 +117,7 @@ def connect_signals(
                 self.run_printer_preflight, type=Qt.QueuedConnection
             )
 
-    def _export_archive(cls, archive_path: str) -> ExportStatus:
+    def _export_archive(cls, archive_path: str) -> Optional[ExportStatus]:
         """
         Make the subprocess call to send the archive to the Export VM, where the archive will be
         processed.
@@ -152,7 +152,14 @@ def _export_archive(cls, archive_path: str) -> ExportStatus:
                 ],
                 stderr=subprocess.STDOUT,
             )
-            return ExportStatus(output.decode("utf-8").strip())
+            result = output.decode("utf-8").strip()
+
+            # No status is returned for successful `disk`, `printer-test`, and `print` calls.
+            # This will change in a future release of sd-export.
+            if result:
+                return ExportStatus(result)
+            else:
+                return None
         except ValueError as e:
             logger.debug(f"Export subprocess returned unexpected value: {e}")
             raise ExportError(ExportStatus.UNEXPECTED_RETURN_STATUS)
@@ -241,7 +248,7 @@ def _run_usb_test(self, archive_dir: str) -> None:
         """
         archive_path = self._create_archive(archive_dir, self.USB_TEST_FN, self.USB_TEST_METADATA)
         status = self._export_archive(archive_path)
-        if status != ExportStatus.USB_CONNECTED:
+        if status and status != ExportStatus.USB_CONNECTED:
             raise ExportError(status)
 
     def _run_disk_test(self, archive_dir: str) -> None:
@@ -257,7 +264,7 @@ def _run_disk_test(self, archive_dir: str) -> None:
         archive_path = self._create_archive(archive_dir, self.DISK_TEST_FN, self.DISK_TEST_METADATA)
 
         status = self._export_archive(archive_path)
-        if status != ExportStatus.DISK_ENCRYPTED:
+        if status and status != ExportStatus.DISK_ENCRYPTED:
             raise ExportError(status)
 
     def _run_disk_export(self, archive_dir: str, filepaths: List[str], passphrase: str) -> None:

tests/test_export.py

@@ -408,7 +408,7 @@ def test__export_archive_with_evil_command(mocker):
     Ensure shell command is shell-escaped.
     """
     export = Export()
-    check_output = mocker.patch("subprocess.check_output", return_value=b"")
+    check_output = mocker.patch("subprocess.check_output", return_value=b"ERROR_FILE_NOT_FOUND")
 
     with pytest.raises(ExportError, match="UNEXPECTED_RETURN_STATUS"):
         export._export_archive("somefile; rm -rf ~")
@@ -426,3 +426,33 @@ def test__export_archive_with_evil_command(mocker):
         ],
         stderr=-2,
     )
+
+
+def test__export_archive_success_on_empty_return_value(mocker):
+    """
+    Ensure an error is not raised when qrexec call returns empty string,
+    (success state for `disk`, `print`, `printer-test`).
+
+    When export behaviour changes so that all success states return a status
+    string, this test will no longer pass and should be rewritten.
+    """
+    export = Export()
+    check_output = mocker.patch("subprocess.check_output", return_value=b"")
+
+    result = export._export_archive("somefile.sd-export")
+
+    check_output.assert_called_once_with(
+        [
+            "qrexec-client-vm",
+            "--",
+            "sd-devices",
+            "qubes.OpenInVM",
+            "/usr/lib/qubes/qopen-in-vm",
+            "--view-only",
+            "--",
+            "somefile.sd-export",
+        ],
+        stderr=-2,
+    )
+
+    assert result is None