Streams an OpenAI response, compatible with Next.js

stream.ts

/**
 * Usage:
 *
 * export const config = {
 *   runtime: "edge",
 * };
 *
 * const stream = await streamFromResponse(await openai.complete({
 *    model: 'gpt-3.5-turbo',
 *    prompt: 'this is a test',
 *    stream: true
 *  })
 *
 * return new Response(stream);
 */

import {
  createParser,
  ParsedEvent,
  ReconnectInterval,
} from "eventsource-parser";

export const streamFromResponse = (response: any): ReadableStream => {
  const encoder = new TextEncoder();
  const decoder = new TextDecoder();

  return new ReadableStream({
    async start(controller) {
      const onParse = (event: ParsedEvent | ReconnectInterval) => {
        if (event.type === "event") {
          const data = event.data;

          if (data === "[DONE]") {
            controller.close();
            return;
          }

          try {
            const json = JSON.parse(data);
            const text = json.choices[0].delta.content;
            const queue = encoder.encode(text);
            controller.enqueue(queue);
          } catch (e) {
            controller.error(e);
          }
        }
      };

      const parser = createParser(onParse);

      for await (const chunk of response.body as any) {
        parser.feed(decoder.decode(chunk));
      }
    },
  });
};