Servant.API.ResponseHeaders

This module provides facilities for adding headers to a response.

>>> let headerVal = addHeader "some-url" 5 :: Headers '[Header "Location" String] Int

The value is added to the header specified by the type (Location in the example above).

Documentation

data Headers ls a

Response Header objects. You should never need to construct one directly. Instead, use addOptionalHeader.

Constructors

Headers

Fields

• getResponse :: a

  The underlying value of a Headers

• getHeadersHList :: HList ls

  HList of headers.

Instances

(KnownSymbol h, ToHttpApiData v) => AddHeader h v (Headers (fst ': rest) a) (Headers (Header h v ': (fst ': rest)) a)

Defined in Servant.API.ResponseHeaders

Methods

addOptionalHeader :: ResponseHeader h v -> Headers (fst ': rest) a -> Headers (Header h v ': (fst ': rest)) a

Functor (Headers ls)

Defined in Servant.API.ResponseHeaders

Methods

fmap :: (a -> b) -> Headers ls a -> Headers ls b

(<$) :: a -> Headers ls b -> Headers ls a

(NFDataHList ls, NFData a) => NFData (Headers ls a)

Defined in Servant.API.ResponseHeaders

Methods

rnf :: Headers ls a -> ()

GetHeaders' hs => GetHeaders (Headers hs a)

Defined in Servant.API.ResponseHeaders

Methods

getHeaders :: Headers hs a -> [Header]

data ResponseHeader (sym :: Symbol) a

Constructors

Header a

MissingHeader

UndecodableHeader ByteString

Instances

Functor (ResponseHeader sym)

Defined in Servant.API.ResponseHeaders

Methods

fmap :: (a -> b) -> ResponseHeader sym a -> ResponseHeader sym b

(<$) :: a -> ResponseHeader sym b -> ResponseHeader sym a

Eq a => Eq (ResponseHeader sym a)

Defined in Servant.API.ResponseHeaders

Methods

(==) :: ResponseHeader sym a -> ResponseHeader sym a -> Bool

(/=) :: ResponseHeader sym a -> ResponseHeader sym a -> Bool

Show a => Show (ResponseHeader sym a)

Defined in Servant.API.ResponseHeaders

Methods

showsPrec :: Int -> ResponseHeader sym a -> ShowS

show :: ResponseHeader sym a -> String

showList :: [ResponseHeader sym a] -> ShowS

NFData a => NFData (ResponseHeader sym a)

Defined in Servant.API.ResponseHeaders

Methods

rnf :: ResponseHeader sym a -> ()

class AddHeader h v orig new | h v orig -> new, new -> h, new -> v, new -> orig

Minimal complete definition

addOptionalHeader

Instances

(KnownSymbol h, ToHttpApiData v, new ~ Headers '[Header h v] a) => AddHeader h v a new

Defined in Servant.API.ResponseHeaders

Methods

addOptionalHeader :: ResponseHeader h v -> a -> new

(KnownSymbol h, ToHttpApiData v) => AddHeader h v (Headers (fst ': rest) a) (Headers (Header h v ': (fst ': rest)) a)

Defined in Servant.API.ResponseHeaders

Methods

addOptionalHeader :: ResponseHeader h v -> Headers (fst ': rest) a -> Headers (Header h v ': (fst ': rest)) a

addHeader :: AddHeader h v orig new => v -> orig -> new

addHeader adds a header to a response. Note that it changes the type of the value in the following ways:

1. A simple value is wrapped in "Headers '[hdr]":

>>> let example1 = addHeader 5 "hi" :: Headers '[Header "someheader" Int] String;
>>> getHeaders example1
[("someheader","5")]

1. A value that already has a header has its new header *prepended* to the existing list:

>>> let example1 = addHeader 5 "hi" :: Headers '[Header "someheader" Int] String;
>>> let example2 = addHeader True example1 :: Headers '[Header "1st" Bool, Header "someheader" Int] String
>>> getHeaders example2
[("1st","true"),("someheader","5")]

Note that while in your handlers type annotations are not required, since the type can be inferred from the API type, in other cases you may find yourself needing to add annotations.

noHeader :: AddHeader h v orig new => orig -> new

Deliberately do not add a header to a value.

>>> let example1 = noHeader "hi" :: Headers '[Header "someheader" Int] String
>>> getHeaders example1
[]

class HasResponseHeader h a headers

Minimal complete definition

hlistLookupHeader

Instances

HasResponseHeader h a rest => HasResponseHeader h a (first ': rest)

Defined in Servant.API.ResponseHeaders

Methods

hlistLookupHeader :: HList (first ': rest) -> ResponseHeader h a

HasResponseHeader h a (Header h a ': rest)

Defined in Servant.API.ResponseHeaders

Methods

hlistLookupHeader :: HList (Header h a ': rest) -> ResponseHeader h a

lookupResponseHeader :: HasResponseHeader h a headers => Headers headers r -> ResponseHeader h a

Look up a specific ResponseHeader, without having to know what position it is in the HList.

>>> let example1 = addHeader 5 "hi" :: Headers '[Header "someheader" Int] String
>>> let example2 = addHeader True example1 :: Headers '[Header "1st" Bool, Header "someheader" Int] String
>>> lookupResponseHeader example2 :: ResponseHeader "someheader" Int
Header 5

>>> lookupResponseHeader example2 :: ResponseHeader "1st" Bool
Header True

Usage of this function relies on an explicit type annotation of the header to be looked up. This can be done with type annotations on the result, or with an explicit type application. In this example, the type of header value is determined by the type-inference, we only specify the name of the header:

>>> :set -XTypeApplications
>>> case lookupResponseHeader @"1st" example2 of { Header b -> b ; _ -> False }
True

Since: 0.15

class BuildHeadersTo hs where

Methods

buildHeadersTo :: [Header] -> HList hs

Note: if there are multiple occurrences of a header in the argument, the values are interspersed with commas before deserialization (see RFC2616 Sec 4.2)

Instances

BuildHeadersTo ('[] :: [Type])

Defined in Servant.API.ResponseHeaders

Methods

buildHeadersTo :: [Header] -> HList '[]

(FromHttpApiData v, BuildHeadersTo xs, KnownSymbol h) => BuildHeadersTo (Header h v ': xs)

Defined in Servant.API.ResponseHeaders

Methods

buildHeadersTo :: [Header0] -> HList (Header h v ': xs)

class GetHeaders ls where

Methods

getHeaders :: ls -> [Header]

Instances

GetHeadersFromHList hs => GetHeaders (HList hs)

Defined in Servant.API.ResponseHeaders

Methods

getHeaders :: HList hs -> [Header]

GetHeaders' hs => GetHeaders (Headers hs a)

Defined in Servant.API.ResponseHeaders

Methods

getHeaders :: Headers hs a -> [Header]

class GetHeaders' hs

Auxiliary class for GetHeaders (Headers hs a) instance

Minimal complete definition

getHeaders'

Instances

GetHeaders' ('[] :: [Type])

This instance is an optimisation

Defined in Servant.API.ResponseHeaders

Methods

getHeaders' :: Headers '[] a -> [Header]

(KnownSymbol h, GetHeadersFromHList rest, ToHttpApiData v) => GetHeaders' (Header h v ': rest)

Defined in Servant.API.ResponseHeaders

Methods

getHeaders' :: Headers (Header h v ': rest) a -> [Header0]

type family HeaderValMap (f :: * -> *) (xs :: [*]) where ...

Equations

HeaderValMap f '[] = '[]

HeaderValMap f (Header h x ': xs) = Header h (f x) ': HeaderValMap f xs

data HList a where

Constructors

HNil :: HList '[]

HCons :: ResponseHeader h x -> HList xs -> HList (Header h x ': xs)

Instances

NFDataHList xs => NFData (HList xs)

Defined in Servant.API.ResponseHeaders

Methods

rnf :: HList xs -> ()

GetHeadersFromHList hs => GetHeaders (HList hs)

Defined in Servant.API.ResponseHeaders

Methods

getHeaders :: HList hs -> [Header]