Header Contract Audit

Audit one set of response headers against a contract the caller states: headers that must be present, headers that must not be, and exact, prefix or substring rules on values. Also reports a header repeated with different values, where which one a client uses varies; an absent Content-Type, which forces a client to sniff; and a textual Content-Type with no charset. Optionally reports absent cache directives and no validator at all, which makes a conditional request impossible.