val headers : req -> HTTP.headersheaders r is r's information. Initially empty it can be used be services and layers to store and share data.
val with_headers : req -> HTTP.headers -> reqwith_headers req hs is req with headers hs.
val v : ?version:HTTP.version -> HTTP.meth -> path:HTTP.path -> ?query:(string * string list) list -> HTTP.headers -> body -> reqv meth ~path headers body is an HTTP request with the given components. query defaults to None.