Fix error handling in pure runtimes

CHANGELOG.md

@@ -5,7 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog][chg] and this project adheres to
 [Haskell's Package Versioning Policy][pvp]
 
-## 1.0.1 - 2023-12-15
+## unreleased - 2023-11-23
+
+  - `fallibleRuntime` and `fallibleRuntimeWithContext` report errors to AWS
+    instead of returning `{"Left": "some error"}`.
+  - `fallibleRuntime` and `fallibleRuntimeWithContext` no longer wrap their
+    successful responses in `{"Right": ...}`.
+  - `pureRuntime`, `pureRuntimeWithContext`, `fallibleRuntime` and `fallibleRuntimeWithContext`
+    no longer crash the Lambda runtime if input can't be parsed from JSON.
+
+## `1.0.1` - 2023-12-15
 
   - Add support for aeson 2.2.  Users can opt in by setting the `use-aeson-2-2` flag to `true`, which for many users will be set automatically.  In a future breaking change release, this flag will default to `true`.
 

src/AWS/Lambda/Combinators.hs

@@ -13,7 +13,8 @@ They map functions (instead of values) to turn basic handlers into handlers comp
 
 module AWS.Lambda.Combinators (
     withoutContext,
-    withInfallibleParse
+    withInfallibleParse,
+    withFallibleParse
 ) where
 
 import           Data.Aeson             (FromJSON, parseJSON, Value)
@@ -70,3 +71,7 @@ withoutContext = const
 -- on a failure to convert the JSON AST sent to the Lambda.
 withInfallibleParse :: FromJSON a => (a -> b) -> Value -> b
 withInfallibleParse fn = either error fn . parseEither parseJSON
+
+-- | Like 'withInfallibleParse', but return the result in an 'Either' instead of using 'error'.
+withFallibleParse :: FromJSON a => (a -> b) -> Value -> Either String b
+withFallibleParse fn = fmap fn . parseEither parseJSON

src/AWS/Lambda/Context.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE NamedFieldPuns, OverloadedStrings #-}
+{-# LANGUAGE NamedFieldPuns #-}
 
 {-|
 Module      : AWS.Lambda.Context

src/AWS/Lambda/Runtime.hs

@@ -29,9 +29,12 @@ module AWS.Lambda.Runtime (
   mRuntimeWithContext
 ) where
 
-import           AWS.Lambda.Combinators   (withInfallibleParse)
+import           AWS.Lambda.Combinators   (withInfallibleParse,
+                                           withFallibleParse,
+                                           withoutContext)
 import           AWS.Lambda.Context       (LambdaContext(..))
 import qualified AWS.Lambda.Runtime.Value as ValueRuntime
+import           Control.Monad            (join)
 import           Control.Monad.Catch      (MonadCatch)
 import           Control.Monad.IO.Class   (MonadIO)
 import           Control.Monad.Reader     (ReaderT)
@@ -253,7 +256,7 @@ ioRuntime = ValueRuntime.ioRuntime . withInfallibleParse
 -- @
 fallibleRuntimeWithContext :: (FromJSON event, ToJSON result) =>
   (LambdaContext -> event -> Either String result) -> IO ()
-fallibleRuntimeWithContext = ValueRuntime.fallibleRuntimeWithContext . fmap withInfallibleParse
+fallibleRuntimeWithContext fn = ValueRuntime.fallibleRuntimeWithContext $ \lc -> join . withFallibleParse (fn lc)
 
 -- | For pure functions that can still fail.
 --
@@ -286,7 +289,7 @@ fallibleRuntimeWithContext = ValueRuntime.fallibleRuntimeWithContext . fmap with
 -- @
 fallibleRuntime :: (FromJSON event, ToJSON result) =>
   (event -> Either String result) -> IO ()
-fallibleRuntime = ValueRuntime.fallibleRuntime . withInfallibleParse
+fallibleRuntime = fallibleRuntimeWithContext . withoutContext
 
 -- | For pure functions that can never fail that also need access to the context.
 --
@@ -318,7 +321,7 @@ fallibleRuntime = ValueRuntime.fallibleRuntime . withInfallibleParse
 -- @
 pureRuntimeWithContext :: (FromJSON event, ToJSON result) =>
   (LambdaContext -> event -> result) -> IO ()
-pureRuntimeWithContext = ValueRuntime.pureRuntimeWithContext . fmap withInfallibleParse
+pureRuntimeWithContext = fallibleRuntimeWithContext . fmap (fmap pure)
 
 -- | For pure functions that can never fail.
 --
@@ -345,4 +348,4 @@ pureRuntimeWithContext = ValueRuntime.pureRuntimeWithContext . fmap withInfallib
 -- main = pureRuntime myHandler
 -- @
 pureRuntime :: (FromJSON event, ToJSON result) => (event -> result) -> IO ()
-pureRuntime = ValueRuntime.pureRuntime . withInfallibleParse
+pureRuntime = pureRuntimeWithContext . withoutContext

src/AWS/Lambda/Runtime/Value.hs

@@ -39,10 +39,11 @@ module AWS.Lambda.Runtime.Value (
   mRuntimeWithContext,
 ) where
 
-import           AWS.Lambda.RuntimeClient (RuntimeClientConfig, getRuntimeClientConfig,
-                                           getNextData, sendEventError, sendEventSuccess)
 import           AWS.Lambda.Combinators   (withoutContext)
 import           AWS.Lambda.Context       (LambdaContext(..))
+import           AWS.Lambda.RuntimeClient (RuntimeClientConfig, getNextData,
+                                           getRuntimeClientConfig,
+                                           sendEventError, sendEventSuccess)
 import           Control.Exception        (SomeException, displayException)
 import           Control.Monad            ((<=<), forever)
 import           Control.Monad.Catch      (MonadCatch, try)
@@ -331,7 +332,7 @@ ioRuntime = ioRuntimeWithContext . withoutContext
 -- @
 fallibleRuntimeWithContext :: ToJSON result =>
   (LambdaContext -> Value -> Either String result) -> IO ()
-fallibleRuntimeWithContext = mRuntimeWithContext . fmap (fmap pure)
+fallibleRuntimeWithContext fn = mRuntimeWithContext (\lc -> either error pure . fn lc)
 
 -- | For pure functions that can still fail.
 --