HTTP-4000.3.7: A library for client-side HTTP

CopyrightSee LICENSE file
MaintainerGanesh Sittampalam <>
Portabilitynon-portable (not tested)
Safe HaskellSafe



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 where #

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.

Minimal complete definition

getHeaders, setHeaders


getHeaders :: x -> [Header] #

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


data Header #

The Header data type pairs header names & values.


Header HeaderName String 


mkHeader :: HeaderName -> String -> Header #

Header constructor as a function, hiding above rep.

data HeaderName #

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 a #

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 a #

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

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

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

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

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

replaceHeader :: HasHeaders a => HeaderSetter a #

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

findHeader :: HasHeaders a => HeaderName -> a -> Maybe String #

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

lookupHeader :: HeaderName -> [Header] -> Maybe String #

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

parseHeader :: String -> Result Header #

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

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

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.

headerMap :: [(String, HeaderName)] #

headerMap is a straight assoc list for translating between header names and values.

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