Add noHeader function.

Which allows not adding a header where a signature declares one, making
    response headers optional.
This commit is contained in:
Julian K. Arni 2016-10-21 14:36:14 +02:00
parent 3ddf225cec
commit ed82056052
3 changed files with 44 additions and 5 deletions

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@ -75,7 +75,7 @@ import Servant.API.QueryParam (QueryFlag, QueryParam,
import Servant.API.Raw (Raw)
import Servant.API.RemoteHost (RemoteHost)
import Servant.API.ReqBody (ReqBody)
import Servant.API.ResponseHeaders (AddHeader (addHeader),
import Servant.API.ResponseHeaders (AddHeader, addHeader, noHeader,
BuildHeadersTo (buildHeadersTo),
GetHeaders (getHeaders),
HList (..), Headers (..),

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@ -23,7 +23,9 @@
-- example above).
module Servant.API.ResponseHeaders
( Headers(..)
, AddHeader(addHeader)
, AddHeader
, addHeader
, noHeader
, BuildHeadersTo(buildHeadersTo)
, GetHeaders(getHeaders)
, HeaderValMap
@ -108,17 +110,48 @@ instance OVERLAPPABLE_ ( KnownSymbol h, GetHeaders (HList rest), ToHttpApiData v
-- We need all these fundeps to save type inference
class AddHeader h v orig new
| h v orig -> new, new -> h, new -> v, new -> orig where
addHeader :: v -> orig -> new -- ^ N.B.: The same header can't be added multiple times
addHeader' :: Header h v -> orig -> new -- ^ N.B.: The same header can't be added multiple times
instance OVERLAPPING_ ( KnownSymbol h, ToHttpApiData v )
=> AddHeader h v (Headers (fst ': rest) a) (Headers (Header h v ': fst ': rest) a) where
addHeader a (Headers resp heads) = Headers resp (HCons (Header a) heads)
addHeader' hdr (Headers resp heads) = Headers resp (HCons hdr heads)
instance OVERLAPPABLE_ ( KnownSymbol h, ToHttpApiData v
, new ~ (Headers '[Header h v] a) )
=> AddHeader h v a new where
addHeader a resp = Headers resp (HCons (Header a) HNil)
addHeader' hdr resp = Headers resp (HCons hdr HNil)
-- | @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")]
--
-- 2. 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.
addHeader :: AddHeader h v orig new => v -> orig -> new
addHeader = addHeader' . Header
-- | Deliberately do not add a header to a value.
--
-- >>> let example1 = noHeader "hi" :: Headers '[Header "someheader" Int] String
-- >>> getHeaders example1
-- []
noHeader :: AddHeader h v orig new => orig -> new
noHeader = addHeader' MissingHeader
-- $setup
-- >>> import Servant.API

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@ -22,3 +22,9 @@ spec = describe "Servant.API.ResponseHeaders" $ do
it "adds headers to the front of the list" $ do
let val = addHeader 10 $ addHeader "b" 5 :: Headers '[Header "first" Int, Header "second" String] Int
getHeaders val `shouldBe` [("first", "10"), ("second", "b")]
describe "noHeader" $ do
it "does not add a header" $ do
let val = noHeader 5 :: Headers '[Header "test" Int] Int
getHeaders val `shouldBe` []