Merge pull request #76 from dnikolovv/more-efficient-context-initialization

More efficient context initialization

Author: Nick Tchayka

aws-lambda-haskell-runtime.cabal

@@ -4,10 +4,10 @@ cabal-version: 1.12
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: c21b3c988844f7c4bfb806aff4e307c5d5dc63a7973eff4a83eb329e7bccb1c9
+-- hash: f12bd3188248690adb9f0c4972dd66cb983b9057555d14205384c600255cb999
 
 name:           aws-lambda-haskell-runtime
-version:        3.0.0
+version:        3.0.1
 synopsis:       Haskell runtime for AWS Lambda
 description:    Please see the README on GitHub at <https://github.com/theam/aws-lambda-haskell-runtime#readme>
 category:       AWS

package.yaml

@@ -1,5 +1,5 @@
 name: aws-lambda-haskell-runtime
-version: 3.0.0
+version: 3.0.1
 github: "theam/aws-lambda-haskell-runtime"
 license: Apache-2.0
 author: Nikita Tchayka

src/Aws/Lambda/Runtime.hs

@@ -1,3 +1,5 @@
+{-# OPTIONS_GHC -fno-warn-name-shadowing #-}
+
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeApplications    #-}
 
@@ -35,10 +37,13 @@ runLambda initializeCustomContext callback = do
   manager <- Http.newManager httpManagerSettings
   customContext <- initializeCustomContext
   customContextRef <- newIORef customContext
+  context   <- Context.initialize @context customContextRef `catch` errorParsing `catch` variableNotSet
   forever $ do
     lambdaApi <- Environment.apiEndpoint `catch` variableNotSet
     event     <- ApiInfo.fetchEvent manager lambdaApi `catch` errorParsing
-    context   <- Context.initialize @context customContextRef event `catch` errorParsing `catch` variableNotSet
+
+    -- Purposefully shadowing to prevent using the initial "empty" context
+    context <- Context.setEventData context event
 
     (((invokeAndRun callback manager lambdaApi event context
       `Checked.catch` \err -> Publish.parsingError err lambdaApi context manager)

src/Aws/Lambda/Runtime/Context.hs

@@ -1,6 +1,7 @@
 module Aws.Lambda.Runtime.Context
   ( Context(..)
   , initialize
+  , setEventData
   ) where
 
 import Control.Exception.Safe.Checked
@@ -29,25 +30,40 @@ initialize
   :: Throws Error.Parsing
   => Throws Error.EnvironmentVariableNotSet
   => IORef context
-  -> ApiInfo.Event
   -> IO (Context context)
-initialize customContextRef ApiInfo.Event{..} = do
+initialize customContextRef = do
   functionName          <- Environment.functionName
   version               <- Environment.functionVersion
   logStream             <- Environment.logStreamName
   logGroup              <- Environment.logGroupName
   memoryLimitInMb       <- Environment.functionMemory
 
-  Environment.setXRayTrace traceId
-  pure Context
+  pure $ Context
     { functionName       = functionName
     , functionVersion    = version
     , logStreamName      = logStream
     , logGroupName       = logGroup
     , memoryLimitInMb    = memoryLimitInMb
-    , invokedFunctionArn = invokedFunctionArn
-    , xrayTraceId        = traceId
-    , awsRequestId       = awsRequestId
-    , deadline           = deadlineMs
     , customContext      = customContextRef
+
+    -- We set those to "empty" values because they will be assigned
+    -- from the incoming event once one has been received. (see setEventData)
+    , invokedFunctionArn = mempty
+    , xrayTraceId        = mempty
+    , awsRequestId       = mempty
+    , deadline           = 0
     }
+
+-- | Sets the context's event data
+setEventData
+  :: Context context
+  -> ApiInfo.Event
+  -> IO (Context context)
+setEventData context ApiInfo.Event{..} = do
+  Environment.setXRayTrace traceId
+
+  return $ context
+    { invokedFunctionArn = invokedFunctionArn
+    , xrayTraceId        = traceId
+    , awsRequestId       = awsRequestId
+    , deadline           = deadlineMs }