feat: split large openai responses into smaller chunkers

src/lib/apis/streaming/index.ts

@@ -0,0 +1,65 @@
+type TextStreamUpdate = {
+	done: boolean;
+	value: string;
+};
+
+// createOpenAITextStream takes a ReadableStreamDefaultReader from an 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
+): Promise<AsyncGenerator<TextStreamUpdate>> {
+	return streamLargeDeltasAsRandomChunks(openAIStreamToIterator(messageStream));
+}
+
+async function* openAIStreamToIterator(
+	reader: ReadableStreamDefaultReader
+): AsyncGenerator<TextStreamUpdate> {
+	while (true) {
+		const { value, done } = await reader.read();
+		if (done) {
+			yield { done: true, value: '' };
+			break;
+		}
+		const lines = value.split('\n');
+		for (const line of lines) {
+			if (line !== '') {
+				console.log(line);
+				if (line === 'data: [DONE]') {
+					yield { done: true, value: '' };
+				} else {
+					const data = JSON.parse(line.replace(/^data: /, ''));
+					console.log(data);
+
+					yield { done: false, value: data.choices[0].delta.content ?? '' };
+				}
+			}
+		}
+	}
+}
+
+// streamLargeDeltasAsRandomChunks will chunk large deltas (length > 5) into random sized chunks between 1-3 characters
+// This is to simulate a more fluid streaming, even though some providers may send large chunks of text at once
+async function* streamLargeDeltasAsRandomChunks(
+	iterator: AsyncGenerator<TextStreamUpdate>
+): AsyncGenerator<TextStreamUpdate> {
+	for await (const textStreamUpdate of iterator) {
+		if (textStreamUpdate.done) {
+			yield textStreamUpdate;
+			return;
+		}
+		let content = textStreamUpdate.value;
+		if (content.length < 5) {
+			yield { done: false, value: content };
+			continue;
+		}
+		while (content != '') {
+			const chunkSize = Math.min(Math.floor(Math.random() * 3) + 1, content.length);
+			const chunk = content.slice(0, chunkSize);
+			yield { done: false, value: chunk };
+			await sleep(5);
+			content = content.slice(chunkSize);
+		}
+	}
+}
+
+const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));