feat(users/Profpatsch/whatcd-resolver): show json val on parse err

The json parsing library gives us an error path where the parse
failed, which means we can index into the path to show the json value
that failed us.

This can be quite expensive (and large!) of course, but the error
message clarity is worth it methinks.

Change-Id: Icacbd799254aaecd4a939ca13e6070d68a78138d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12952
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>

users/Profpatsch/whatcd-resolver/src/Http.hs

@@ -19,6 +19,7 @@ module Http
 where
 
 import AppT
+import Data.Aeson qualified as Json
 import Data.Aeson.BetterErrors qualified as Json
 import Data.CaseInsensitive (CI (original))
 import Data.Char qualified as Char
@@ -93,12 +94,18 @@ httpJson opts parser req = inSpan' "HTTP Request (JSON)" $ \span -> do
                 Left [fmt|Server returned a body with unspecified content type|]
             | code <- statusCode -> Left $ AppExceptionPretty [[fmt|Server returned an non-200 error code, code {code}:|], pretty resp]
       )
-    >>= assertM
-      span
-      ( \body ->
-          Json.parseStrict parser body
-            & first (AppExceptionTree . Json.parseErrorTree "could not parse HTTP response")
-      )
+    >>= \body -> do
+      val <-
+        Json.eitherDecodeStrict body
+          & first (\err -> AppExceptionTree $ nestedError "HTTP response was not valid JSON" (err & stringToText & newError & singleError))
+          & orAppThrow span
+
+      let res = Json.parseValue parser val
+      case res of
+        Left e -> do
+          let prettyErr = Json.parseErrorTreeValCtx "could not parse HTTP response" val e
+          appThrow span (AppExceptionTree prettyErr)
+        Right a -> pure a
 
 doRequestJson ::
   (MonadOtel m) =>