HTTP-4000.0.7: A library for client-side HTTP

Portabilitynon-portable (not tested)
MaintainerSigbjorn Finne <>



This module provides the data types for representing HTTP headers, and operations for looking up header values and working with sequences of header values in Requests and Responses. To avoid having to provide separate set of operations for doing so, we introduce a type class HasHeaders to facilitate writing such processing using overloading instead.



class HasHeaders x whereSource

HasHeaders is a type class for types containing HTTP headers, allowing you to write overloaded header manipulation functions for both Request and Response data types, for instance.


getHeaders :: x -> [Header]Source

setHeaders :: x -> [Header] -> xSource

data Header Source

The Header data type pairs header names & values.


Header HeaderName String 


mkHeader :: HeaderName -> String -> HeaderSource

Header constructor as a function, hiding above rep.

data HeaderName Source

HTTP HeaderName type, a Haskell data constructor for each specification-defined header, prefixed with Hdr and CamelCased, (i.e., eliding the - in the process.) Should you require using a custom header, there's the HdrCustom constructor which takes a String argument.

Encoding HTTP header names differently, as Strings perhaps, is an equally fine decidedly clear winner, but let's stick with data constructors here.

insertHeader :: HasHeaders a => HeaderSetter aSource

insertHeader hdr val x inserts a header with the given header name and value. Does not check for existing headers with same name, allowing duplicates to be introduce (use replaceHeader if you want to avoid this.)

insertHeaderIfMissing :: HasHeaders a => HeaderSetter aSource

insertHeaderIfMissing hdr val x adds the new header only if no previous header with name hdr exists in x.

insertHeaders :: HasHeaders a => [Header] -> a -> aSource

insertHeaders hdrs x appends multiple headers to x's existing set.

retrieveHeaders :: HasHeaders a => HeaderName -> a -> [Header]Source

retrieveHeaders hdrNm x gets a list of headers with HeaderName hdrNm.

replaceHeader :: HasHeaders a => HeaderSetter aSource

replaceHeader hdr val o replaces the header hdr with the value val, dropping any existing

findHeader :: HasHeaders a => HeaderName -> a -> Maybe StringSource

findHeader hdrNm x looks up hdrNm in x, returning the first header that matches, if any.

lookupHeader :: HeaderName -> [Header] -> Maybe StringSource

lookupHeader hdr hdrs locates the first header matching hdr in the list hdrs.

parseHeader :: String -> Result HeaderSource

parseHeader headerNameAndValueString tries to unscramble a header: value pairing and returning it as a Header.

parseHeaders :: [String] -> Result [Header]Source

parseHeaders hdrs takes a sequence of strings holding header information and parses them into a set of headers (preserving their order in the input argument.) Handles header values split up over multiple lines.

type HeaderSetter a = HeaderName -> String -> a -> aSource