table.lookup_regex

# Here we allow a different set of extensions per-path in the url.
# For example:
#   /articles/abc.png - wrong extension for the dirname
#   /images/abc.png   - this extension is allowed for /images
table t REGEX {
  "/images": "^(?:jpe?g|png)$",
  "/articles": "^md$",
}

sub vcl_recv {
  declare local var.re REGEX;
  set var.re = table.lookup_regex(t, req.url.dirname);
  if (req.url.ext !~ var.re) {
    error 403; # unexpected file extension
  }

  error 200;
}