Merge pull request #1882 from cheahjs/feat/harden-streaming-parser

feat: use spec compliant SSE parser for OpenAI responses

package-lock.json

@@ -12,6 +12,7 @@
 				"async": "^3.2.5",
 				"bits-ui": "^0.19.7",
 				"dayjs": "^1.11.10",
+				"eventsource-parser": "^1.1.2",
 				"file-saver": "^2.0.5",
 				"highlight.js": "^11.9.0",
 				"i18next": "^23.10.0",
@@ -3167,6 +3168,14 @@
 			"integrity": "sha512-tYUSVOGeQPKt/eC1ABfhHy5Xd96N3oIijJvN3O9+TsC28T5V9yX9oEfEK5faP0EFSNVOG97qtAS68GBrQB2hDg==",
 			"dev": true
 		},
+		"node_modules/eventsource-parser": {
+			"version": "1.1.2",
+			"resolved": "https://registry.npmjs.org/eventsource-parser/-/eventsource-parser-1.1.2.tgz",
+			"integrity": "sha512-v0eOBUbiaFojBu2s2NPBfYUoRR9GjcDNvCXVaqEf5vVfpIAh9f8RCo4vXTP8c63QRKCFwoLpMpTdPwwhEKVgzA==",
+			"engines": {
+				"node": ">=14.18"
+			}
+		},
 		"node_modules/execa": {
 			"version": "4.1.0",
 			"resolved": "https://registry.npmjs.org/execa/-/execa-4.1.0.tgz",

package.json

@@ -49,6 +49,7 @@
 		"async": "^3.2.5",
 		"bits-ui": "^0.19.7",
 		"dayjs": "^1.11.10",
+		"eventsource-parser": "^1.1.2",
 		"file-saver": "^2.0.5",
 		"highlight.js": "^11.9.0",
 		"i18next": "^23.10.0",

src/lib/apis/streaming/index.ts

+import { EventSourceParserStream } from 'eventsource-parser/stream';
+import type { ParsedEvent } from 'eventsource-parser';
+
 type TextStreamUpdate = {
 	done: boolean;
 	value: string;
 };
 
-// createOpenAITextStream takes a ReadableStreamDefaultReader from an SSE response,
+// createOpenAITextStream takes a responseBody with a SSE response,
 // and returns an async generator that emits delta updates with large deltas chunked into random sized chunks
 export async function createOpenAITextStream(
-	messageStream: ReadableStreamDefaultReader,
+	responseBody: ReadableStream<Uint8Array>,
 	splitLargeDeltas: boolean
 ): Promise<AsyncGenerator<TextStreamUpdate>> {
-	let iterator = openAIStreamToIterator(messageStream);
+	const eventStream = responseBody
+		.pipeThrough(new TextDecoderStream())
+		.pipeThrough(new EventSourceParserStream())
+		.getReader();
+	let iterator = openAIStreamToIterator(eventStream);
 	if (splitLargeDeltas) {
 		iterator = streamLargeDeltasAsRandomChunks(iterator);
 	}
@@ -17,7 +24,7 @@ export async function createOpenAITextStream(
 }
 
 async function* openAIStreamToIterator(
-	reader: ReadableStreamDefaultReader
+	reader: ReadableStreamDefaultReader<ParsedEvent>
 ): AsyncGenerator<TextStreamUpdate> {
 	while (true) {
 		const { value, done } = await reader.read();
@@ -25,31 +32,22 @@ async function* openAIStreamToIterator(
 			yield { done: true, value: '' };
 			break;
 		}
-		const lines = value.split('\n');
-		for (let line of lines) {
-			if (line.endsWith('\r')) {
-				// Remove trailing \r
-				line = line.slice(0, -1);
-			}
-			if (line !== '') {
-				console.log(line);
-				if (line === 'data: [DONE]') {
-					yield { done: true, value: '' };
-				} else if (line.startsWith(':')) {
-					// Events starting with : are comments https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format
-					// OpenRouter sends heartbeats like ": OPENROUTER PROCESSING"
-					continue;
-				} else {
-					try {
-						const data = JSON.parse(line.replace(/^data: /, ''));
-						console.log(data);
+		if (!value) {
+			continue;
+		}
+		const data = value.data;
+		if (data.startsWith('[DONE]')) {
+			yield { done: true, value: '' };
+			break;
+		}
 
-						yield { done: false, value: data.choices?.[0]?.delta?.content ?? '' };
-					} catch (e) {
-						console.error('Error extracting delta from SSE event:', e);
-					}
-				}
-			}
+		try {
+			const parsedData = JSON.parse(data);
+			console.log(parsedData);
+
+			yield { done: false, value: parsedData.choices?.[0]?.delta?.content ?? '' };
+		} catch (e) {
+			console.error('Error extracting delta from SSE event:', e);
 		}
 	}
 }

src/lib/stores/index.ts

@@ -78,6 +78,7 @@ type Settings = {
 	saveChatHistory?: boolean;
 	notificationEnabled?: boolean;
 	title?: TitleSettings;
+	splitLargeDeltas?: boolean;
 
 	system?: string;
 	requestFormat?: string;

src/routes/(app)/+page.svelte

@@ -605,14 +605,8 @@
 
 		scrollToBottom();
 
-		if (res && res.ok) {
-			const reader = res.body
-				.pipeThrough(new TextDecoderStream())
-				.pipeThrough(splitStream('\n'))
-				.getReader();
-
-			const textStream = await createOpenAITextStream(reader, $settings.splitLargeChunks);
-			console.log(textStream);
+		if (res && res.ok && res.body) {
+			const textStream = await createOpenAITextStream(res.body, $settings.splitLargeChunks);
 
 			for await (const update of textStream) {
 				const { value, done } = update;

src/routes/(app)/c/[id]/+page.svelte

@@ -617,14 +617,8 @@
 
 		scrollToBottom();
 
-		if (res && res.ok) {
-			const reader = res.body
-				.pipeThrough(new TextDecoderStream())
-				.pipeThrough(splitStream('\n'))
-				.getReader();
-
-			const textStream = await createOpenAITextStream(reader, $settings.splitLargeChunks);
-			console.log(textStream);
+		if (res && res.ok && res.body) {
+			const textStream = await createOpenAITextStream(res.body, $settings.splitLargeChunks);
 
 			for await (const update of textStream) {
 				const { value, done } = update;