# When we get URIs with %20s or other escaped characters in them,
# a simple RedirectMatch won't do because in the query string
# DESCRIBE query, the escaped characters will be unescaped at
# some point during processing. So this is bad:
#
# RedirectMatch 303 (/rdf/.*) http://rdfabout.com/sparql?query=DESCRIBE+%3Chttp://www.rdfabout.com$1%3E
#
# Instead, we need to double-escape the characters: The percent
# signs should ultimately be escaped so the processor gets back
# the original escaping when unescaping is applied.
#
# To do this, we need to use mod_rewrite. However, mod_rewrite is
# operating on the unescaped URI, so we need the 'escape' mapping
# function, which needs to be activated in httpd.conf with:
#     RewriteMap esc int:escape
# The rewrite rule below re-escapes the unescaped URI (getting back
# the problematic URL we started with), and then mod_rewrite
# escapes it again when it sends the redirect, finally achieving
# the double-escape.

RewriteEngine on
RewriteBase "/"
RewriteRule ^(rdf/.*) http://%{HTTP_HOST}/sparql?query=DESCRIBE+<http://%{HTTP_HOST}/${esc:$1}> [R=303]