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Get rid of eitherDecodeLenient
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maksbotan committed Jul 11, 2023
1 parent 942c7e2 commit 160bf12
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Showing 3 changed files with 4 additions and 55 deletions.
19 changes: 2 additions & 17 deletions doc/tutorial/Server.lhs
Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,6 @@ import System.Directory
import Text.Blaze
import Text.Blaze.Html.Renderer.Utf8
import Servant.Types.SourceT (source)
import qualified Data.Aeson.Parser
import qualified Text.Blaze.Html
```
Expand Down Expand Up @@ -431,25 +430,11 @@ class Accept ctype => MimeUnrender ctype a where
mimeUnrender :: Proxy ctype -> ByteString -> Either String a
```
We don't have much work to do there either, `Data.Aeson.eitherDecode` is
precisely what we need. However, it only allows arrays and objects as toplevel
JSON values and this has proven to get in our way more than help us so we wrote
our own little function around **aeson** and **attoparsec** that allows any type of
JSON value at the toplevel of a "JSON document". Here's the definition in case
you are curious.
``` haskell
eitherDecodeLenient :: FromJSON a => ByteString -> Either String a
eitherDecodeLenient input = do
v :: Value <- parseOnly (Data.Aeson.Parser.value <* endOfInput) (cs input)
parseEither parseJSON v
```
This function is exactly what we need for our `MimeUnrender` instance.
As with `MimeRender`, we can use a function already available in `aeson`: `Data.Aeson.eitherDecode`.
``` haskell ignore
instance FromJSON a => MimeUnrender JSON a where
mimeUnrender _ = eitherDecodeLenient
mimeUnrender _ = eitherDecode
```
And this is all the code that lets you use `JSON` with `ReqBody`, `Get`,
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30 changes: 2 additions & 28 deletions servant/src/Servant/API/ContentTypes.hs
Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,6 @@ module Servant.API.ContentTypes
, AllMime(..)
, AllMimeRender(..)
, AllMimeUnrender(..)
, eitherDecodeLenient
, canHandleAcceptH
) where

Expand All @@ -75,13 +74,7 @@ import Control.Monad.Compat
import Control.DeepSeq
(NFData)
import Data.Aeson
(FromJSON (..), ToJSON (..), encode)
import Data.Aeson.Parser
(value)
import Data.Aeson.Types
(parseEither)
import Data.Attoparsec.ByteString.Char8
(endOfInput, parseOnly, skipSpace, (<?>))
(FromJSON (..), ToJSON (..), encode, eitherDecode)
import Data.Bifunctor
(bimap)
import qualified Data.ByteString as BS
Expand Down Expand Up @@ -371,28 +364,9 @@ instance NFData NoContent
--------------------------------------------------------------------------
-- * MimeUnrender Instances

-- | Like 'Data.Aeson.eitherDecode' but allows all JSON values instead of just
-- objects and arrays.
--
-- Will handle trailing whitespace, but not trailing junk. ie.
--
-- >>> eitherDecodeLenient "1 " :: Either String Int
-- Right 1
--
-- >>> eitherDecodeLenient "1 junk" :: Either String Int
-- Left "trailing junk after valid JSON: endOfInput"
eitherDecodeLenient :: FromJSON a => ByteString -> Either String a
eitherDecodeLenient input =
parseOnly parser (cs input) >>= parseEither parseJSON
where
parser = skipSpace
*> Data.Aeson.Parser.value
<* skipSpace
<* (endOfInput <?> "trailing junk after valid JSON")

-- | `eitherDecode`
instance FromJSON a => MimeUnrender JSON a where
mimeUnrender _ = eitherDecodeLenient
mimeUnrender _ = eitherDecode

-- | @urlDecodeAsForm@
-- Note that the @mimeUnrender p (mimeRender p x) == Right x@ law only
Expand Down
10 changes: 0 additions & 10 deletions servant/test/Servant/API/ContentTypesSpec.hs
Original file line number Diff line number Diff line change
Expand Up @@ -219,16 +219,6 @@ spec = describe "Servant.API.ContentTypes" $ do
handleCTypeH (Proxy :: Proxy '[JSONorText]) "image/jpeg"
"foobar" `shouldBe` (Nothing :: Maybe (Either String Int))

-- aeson >= 0.9 decodes top-level strings
describe "eitherDecodeLenient" $ do

it "parses top-level strings" $ do
let toMaybe = either (const Nothing) Just
-- The Left messages differ, so convert to Maybe
property $ \x -> toMaybe (eitherDecodeLenient x)
`shouldBe` (decode x :: Maybe String)


data SomeData = SomeData { record1 :: String, record2 :: Int }
deriving (Generic, Eq, Show)

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