recoll is a local search engine based on Xapian:
   http://www.lesbonscomptes.com/recoll/

   By itself recoll does not offer web or API access,
   this can be achieved using recoll-webui:
   https://github.com/koniu/recoll-webui

   As recoll-webui by default does not support paged JSON
   results it is advisable to use a patched version which does:
   https://github.com/Yetangitu/recoll-webui/tree/jsonpage
   A pull request was sent upstream, if this is merged the patched
   version is no longer needed

   This engine uses a custom 'files' result template

   set base_url to the location where recoll-webui can be reached
   set dl_prefix to a location where the file hierarchy as indexed by recoll can be reached
   set search_dir to the part of the indexed file hierarchy to be searched, use an empty string to search the entire search domain