SERVER_NAME vs HTTP_HOST

After modifying a working drupal installation to run on a non standard port behind a reverse proxy server (Apache), Boost cache files were no longer created.

It turns out that in checking for the domain, Boost (dev version 13-04-2011) compares the host component of $base_url to HTTP_PORT before generating the cache files. However HTTP_PORT includes the port (when it's not 80) while $parts['host'] doesn't, so the check fails. Changing HTTP_HOST to SERVER_NAME in line 457 fixes it in my case.

A more robust approach would probably be to include the port in checking for the correct domain.