A REST API for fetching the repsponse from a custom GPT assistant via the OpenAI API. Runs as a Cloudflare Worker.

open-ai-assistant.js

/**
 * A REST API for fetching the repsponse from
 * a custom GPT assistant via the OpenAI API
 * Deployed as a simple Cloudflare Worker
 * Licensed under MIT (C) Alicia Sykes 2024
 */

(() => {
  addEventListener("fetch", (event) => {
    event.respondWith(handleRequest(event.request));
  });
  async function fetchOpenAI(url, options) {
    const response = await fetch(url, options);
    if (!response.ok) {
      throw new Error(`OpenAI API request failed: ${response.statusText}`);
    }
    return response.json();
  }
  async function handleRequest(request) {
    const allowedOrigins = JSON.parse(ALLOWED_ORIGINS || "[]")
    const origin = request.headers.get("Origin");
    let responseHeaders = {
      "Content-Type": "application/json",
      "Access-Control-Allow-Origin": "null",
      "Access-Control-Allow-Methods": "GET, POST, OPTIONS",
      "Access-Control-Allow-Headers": "Content-Type, Authorization"
    };
    if (allowedOrigins.length <1 || allowedOrigins.includes(origin)) {
      responseHeaders["Access-Control-Allow-Origin"] = origin;
    }
    if (!OPENAI_API_KEY) {
      throw new Error("OPENAI_API_KEY is required");
    }
    if (!ASSISTANT_ID) {
      throw new Error("ASSISTANT_ID is required");
    }
    const assistantId = ASSISTANT_ID;
    const headers = {
      "Authorization": `Bearer ${OPENAI_API_KEY}`,
      "Content-Type": "application/json",
      "OpenAI-Beta": "assistants=v1"
    };
    const thread = await fetchOpenAI(`https://api.openai.com/v1/threads`, {
      method: "POST",
      headers
    });
    const url = new URL(request.url);
    const pathSegments = url.pathname.split("/");
    const userPrompt = pathSegments[pathSegments.length - 1];
    const isValidInput = typeof userPrompt === "string" && userPrompt.length > 0 && userPrompt.length <= 200;
    if (!isValidInput) {
      return new Response("[]", { status: 400 });
    }
    await fetchOpenAI(`https://api.openai.com/v1/threads/${thread.id}/messages`, {
      method: "POST",
      headers,
      body: JSON.stringify({ role: "user", content: userPrompt })
    });
    const run = await fetchOpenAI(`https://api.openai.com/v1/threads/${thread.id}/runs`, {
      method: "POST",
      headers,
      body: JSON.stringify({ assistant_id: assistantId })
    });
    let runStatus = run.status;
    while (runStatus !== "completed" && runStatus !== "failed") {
      await new Promise((resolve) => setTimeout(resolve, 10));
      console.log("wating");
      const updatedRun = await fetchOpenAI(`https://api.openai.com/v1/threads/${thread.id}/runs/${run.id}`, {
        method: "GET",
        headers
      });
      runStatus = updatedRun.status;
    }
    const messages = await fetchOpenAI(`https://api.openai.com/v1/threads/${thread.id}/messages`, {
      method: "GET",
      headers
    });

    const assistantMessages = messages.data
      .filter((message) => message.role === "assistant")
      .map((message) => message.content);
    
    const theEnd = assistantMessages?.[0]?.[0]?.text?.value ?? "[]";
    return new Response(JSON.stringify(theEnd), {
      headers: { "Content-Type": "application/json", ...responseHeaders }
    });
  }
})();

About
You can use a custom GPT programmatically by creating an Assistant through the OpenAI dashboard (platform.openai.com/assistants).
Passing a message, and getting a response from such an assistant requires several steps, and as such it makes sense to create a little micro-service to handle these interactions. This is especially true if you plan on using this through a frontend application, as it wouldn't be secure to directly make requests to OpenAI, as your API key would be out in the clear.

The above script is just an example, to get you started. You'll likely need to modify it to fit your requirements.

---

Deployment

1. Setup Node.js, if you haven't already done so, then install wrangler, npm i -g wrangler
2. Create a new worker project, with wrangler init sponsors-api
3. Navigate into your project, and install deps with cd sponsors-api and npm install
4. In your wrangler.toml add your API key to the GITHUB_TOKEN env var
5. Start the development server, and test everything's working with wrangler dev
6. Finally, run wrangler deploy to deploy your app to the world!

Alternatively, just log in to Cloudflare, GO to "Workers" then "New" / "Quick Edit".
And then paste the above script in, and then hit "Save & Deploy". Done :)

The following environmental variables will be required:

• OPENAI_API_KEY - Your OpenAI API key
• ASSISTANT_ID - The ID of the assistant you've created

You can now make requests to https://[project-name].workers.dev/[users-question] 🚀

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License
Licensed under MIT, © Alicia Sykes 2024