Handle HTTP status in index lookup

src/Main.purs

@@ -53,6 +53,7 @@ data AviaryError
     | StrangeIndex
     | IndexMissingField String
     | ImageNotFound
+    | IndexNotFound
 
 type Image =
     { key :: Aff CryptoKey
@@ -77,6 +78,7 @@ instance showAviaryError :: Show AviaryError where
     show StrangeIndex = "The gallery index matched with the provided key, but was in a strange format.  This could indicate a severe version mismatch, or that the gallery was created by a malfunctioning client."
     show (IndexMissingField f) = "The gallery index was missing the crucial field " <> f <> ".  This is almost certainly the result of a version mismatch or that the creator's client was not fully up-to-spec."
     show ImageNotFound = "The image was not found, likely indicating that it expired"
+    show IndexNotFound = "The index was not found, likely indicating that the gallery never existed or expired"
     show (UnexpectedStatusCode status) = "Server returned an unexpected status code: " <> (show status)
 
 type UrlInfo =
@@ -173,14 +175,18 @@ main_aff = do
         Right keyBuffer -> do
             cryptoKey <- importKey keyBuffer
             { status, arrayBuffer } <- fetch (urlInfo.server <> "/" <> urlInfo.fileId <> ".bin") {}
-            encryptedIndex <- arrayBuffer
-            serializedIndex <- try $ decryptBlob cryptoKey encryptedIndex urlInfo.nonce
-            case serializedIndex of
-                Left err -> do
-                    _ <- liftEffect $ log $ message err
-                    pure $ Left $ DecryptFailed
-                Right serializedIndex' -> do
-                    liftEffect $ parseIndex serializedIndex'
+            case status of
+                200 -> do
+                    encryptedIndex <- arrayBuffer
+                    serializedIndex <- try $ decryptBlob cryptoKey encryptedIndex urlInfo.nonce
+                    case serializedIndex of
+                        Left err -> do
+                            _ <- liftEffect $ log $ message err
+                            pure $ Left $ DecryptFailed
+                        Right serializedIndex' -> do
+                            liftEffect $ parseIndex serializedIndex'
+                404 -> pure $ Left ImageNotFound
+                s -> pure $ Left $ if s / 100 == 5 then ServerError else UnexpectedStatusCode s
     maybeUrls <- case maybeIndex of
         Left err -> pure $ Left err
         Right index -> Right <$> parTraverse (fetchImageAsBlobUrl urlInfo.nonce) index.images