Minimal example for the servant-pagination Next-Range issue

Main.hs

{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE DeriveGeneric    #-}
{-# LANGUAGE DataKinds    #-}
{-# LANGUAGE TypeOperators    #-}
{-# LANGUAGE MultiParamTypeClasses    #-}
{-# LANGUAGE TypeFamilies    #-}

module Main where

import           Data.Aeson   (ToJSON)
import           GHC.Generics (Generic)
import qualified Data.Aeson   as Aeson
import           Data.Maybe               (fromMaybe)
import           Data.Proxy               (Proxy (..))
import           Servant
import           Servant.Pagination
import qualified Network.Wai.Handler.Warp as Warp

data Color = Color
  { name :: String
  , rgb  :: [Int]
  , hex  :: String
  } deriving (Eq, Show, Generic)

instance ToJSON Color where
  toJSON =
    Aeson.genericToJSON Aeson.defaultOptions

colors :: [Color]
colors =
  [ Color "Aqua" [0, 255, 255] "#00ffff"
  , Color "Black" [0, 0, 0] "#000000"
  , Color "Blue" [0, 0, 255] "#0000ff"
  ]

instance HasPagination Color "name" where
  type RangeType Color "name" = String
  getFieldValue _ = name

type API =
  "colors"
    :> Header "Range" (Ranges '["name"] Color)
    :> GetPartialContent '[JSON] (Headers (PageHeaders '["name"] Color) [Color])

defaultRange :: Range "name" String
defaultRange =
  getDefaultRange (Proxy @Color)

server :: Server API
server mrange = do
  let range =
        fromMaybe defaultRange (mrange >>= extractRange)
  returnRange range (applyRange range colors)

main :: IO ()
main =
  Warp.run 1337 (serve (Proxy :: Proxy API) server)