libhttp-message-perl 6.13-1 (amd64 binary) in ubuntu bionic

 The HTTP::Message distribution contains classes useful for representing the
 messages passed in HTTP style communication. These are classes representing
 requests, responses and the headers contained within them.
 .
 The HTTP::Headers class encapsulates HTTP-style message headers. The headers
 consist of attribute-value pairs also called fields, which may be repeated,
 and which are printed in a particular order. The field names are cases
 insensitive.
 .
 Instances of this class are usually created as member variables of the
 HTTP::Request and HTTP::Response classes, internal to the library.