Add a tweak telling the content server to give the client a path computed from a template (the value of the tweak). This can happen only if the client sets the device_compatible flag.

resources/default_tweaks.py

@@ -572,3 +572,14 @@ restrict_output_formats = None
 # numbers.
 # The value can be between 50 and 99
 content_server_thumbnail_compression_quality = 75
+
+#: Set the template for the file name supplied by the content server
+# Setting this tweak will make the content server supply the template's value
+# when a book's metadata is requested in "device compatible" mode. The client
+# can use this value as part of the path for the book when downloaded. Note
+# that the save_template_title_series_sorting tweak is used to control title
+# and series values.
+# Examples:
+#  content_server_path_for_client = "{title}-{author}"
+#  content_server_path_for_client = "{title_sort}-{:'series_sort()'||-}{author_sort}"
+content_server_path_for_client = ''

src/calibre/library/server/ajax.py

@@ -191,7 +191,14 @@ class AjaxServer(object):
             else:
                 series = ''
             data['_series_sort_'] = series
-
+            if tweaks['content_server_path_for_client']:
+                import posixpath
+                from calibre.devices.utils import create_upload_path
+                from calibre.utils.filenames import ascii_filename as sanitize
+                data['_filename_'] = create_upload_path(mi, '',
+                                tweaks['content_server_path_for_client'],
+                                sanitize, path_type=posixpath)
+                print('filename', data['_filename_'])
         return data, mi.last_modified
 
     @Endpoint(set_last_modified=False)