fix(openai): parsing of streaming completions

ihp-openai/IHP/OpenAI.hs

@@ -120,45 +120,56 @@ streamCompletion secretKey completionRequest' onStart callback = do
 
 streamCompletionWithoutRetry :: ByteString -> CompletionRequest -> IO () -> (Text -> IO ()) -> IO (Either Text Text)
 streamCompletionWithoutRetry secretKey completionRequest' onStart callback = do
-        let completionRequest = enableStream completionRequest'
-        modifyContextSSL (\context -> do
-                SSL.contextSetVerificationMode context SSL.VerifyNone
-                pure context
-            )
-        withOpenSSL do
-            withConnection (establishConnection "https://api.openai.com/v1/chat/completions") \connection -> do
-                    let q = buildRequest1 do
-                                http POST "/v1/chat/completions"
-                                setContentType "application/json"
-                                Network.Http.Client.setHeader "Authorization" ("Bearer " <> secretKey)
-
-                    sendRequest connection q (jsonBody completionRequest)
+    let completionRequest = enableStream completionRequest'
+    modifyContextSSL (\context -> do
+            SSL.contextSetVerificationMode context SSL.VerifyNone
+            pure context
+        )
+    withOpenSSL do
+        withConnection (establishConnection "https://api.openai.com/v1/chat/completions") \connection -> do
+            let q = buildRequest1 do
+                    http POST "/v1/chat/completions"
+                    setContentType "application/json"
+                    Network.Http.Client.setHeader "Authorization" ("Bearer " <> secretKey)
+            sendRequest connection q (jsonBody completionRequest)
+            onStart
+            receiveResponse connection handler
 
-                    let handler = \p i -> do
-                            let status = getStatusCode p
-                            if status == 200
-                                then do
-                                    x <- Streams.foldM (parseResponseChunk callback) ("", "") i
-                                    return (Right (snd x))
-                                else do
-                                    x <- Streams.fold mappend mempty i
-                                    return (Left $ "an error happend: " <> Text.pack (show x))
-
-                    onStart
-                    receiveResponse connection handler
     where
-        parseResponseChunk :: (Text -> IO ()) -> (ByteString, Text) -> ByteString -> IO (ByteString, Text)
-        parseResponseChunk callback (curBuffer, chunk) input = do
-            case ByteString.stripPrefix "data: " (ByteString.strip (curBuffer <> input)) of
-                Just json -> do
-                    case decodeStrict json of
-                        Just CompletionResult { choices } -> do
-                            let tokens :: Text = mconcat $ map (.text) choices
-                            callback tokens
-                            pure ("", chunk <> tokens)
-                        otherwise -> do
-                            pure (curBuffer <> json, chunk)
-                Nothing -> pure (curBuffer <> input, chunk)
+        handler :: Response -> Streams.InputStream ByteString -> IO (Either Text Text)
+        handler response stream = do
+            let status = getStatusCode response
+            if status == 200
+                then do
+                    {-
+                    parse stream line by line as event stream format according to API spec:
+                    https://platform.openai.com/docs/api-reference/chat/create#chat/create-stream
+                    https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format
+                    -}
+                    (_, _, output) <- Streams.lines stream >>= Streams.foldM (parseResponseChunk callback) ("", False, "")
+                    return (Right output)
+                else do
+                    x :: ByteString <- Streams.fold mappend mempty stream
+                    return (Left $ "an error happend: " <> Text.pack (show x))
+
+        parseResponseChunk :: (Text -> IO ()) -> (ByteString, Bool, Text) -> ByteString -> IO (ByteString, Bool, Text)
+        parseResponseChunk callback (curBuffer, emptyLineFound, chunk) input
+            -- input line is empty, but previous was not, append newline to buffer
+            | ByteString.null input && not emptyLineFound = pure (curBuffer <> "\n", True, chunk)
+            -- input line is empty, previous line was already empty: message ended, clear buffer
+            | ByteString.null input && emptyLineFound = pure ("", True, chunk)
+            -- lines starting with : are comments, ignore
+            | ":" `ByteString.isPrefixOf` input = pure (curBuffer, False, chunk)
+            -- try to parse line together with buffer otherwise
+            | otherwise = case ByteString.stripPrefix "data: " (ByteString.strip (curBuffer <> input)) of
+                    Just json -> do
+                        case eitherDecodeStrict json of
+                            Right CompletionResult { choices } -> do
+                                let tokens :: Text = mconcat $ map (.text) choices
+                                callback tokens
+                                pure ("", False, chunk <> tokens)
+                            Left err -> pure (curBuffer <> json, False, chunk)
+                    Nothing -> pure (curBuffer <> input, False, chunk)
 
 
 fetchCompletion :: ByteString -> CompletionRequest -> IO Text
@@ -192,4 +203,4 @@ fetchCompletionWithoutRetry secretKey completionRequest = do
                     pure (mconcat $ map (.text) completionResult.choices)
 
 enableStream :: CompletionRequest -> CompletionRequest
-enableStream completionRequest = completionRequest { stream = True }
+enableStream completionRequest = completionRequest { stream = True }