After such positive reception of our SaasKit last month, we’ve teamed up with Supabase to bring you yet another Deno Fresh starter. This time, we’ve created a custom ChatGPT-style doc search using the OpenAI Text Completion API.

A screenshot of the demo hosted on Deno Deploy, based off Supabase’s docs.

Supabase’s free, hosted PostgresDB is perfect to use with OpenAI’s GPT-3, since the database comes with the extension pgvector, allowing you to store embeddings and perform vector similarity search. Both of those are required for building GPT-3 apps.

If you want to dive into more details, check out this blogpost. Or you can dive right in and start building your own custom ChatGPT doc search.

Let’s start coding!

Technical Details

Building your own custom ChatGPT involves four steps:

1. ⚡️ GitHub Action Pre-process the knowledge base (your .mdx files in your docs folder).
2. ⚡️ GitHub Action Store embeddings in Postgres with pgvector.
3. 🏃 Runtime Perform vector similarity search to find the content that’s relevant to the question.
4. 🏃 Runtime Inject content into OpenAI GPT-3 text completion prompt and stream response to the client.

⚡️ GitHub Action

Step 1. and 2. happen via a GitHub Action anytime we make changes to the main branch.

When main is merged, this generate-embeddings script is executed, which performs the following tasks:

1. Pre-process the knowledge base with the .mdx files
2. Generate embeddings with OpenAI
3. Store the embedding in Supabase

Here’s a workflow diagram of what happens:

We can use the setup-deno GitHub Action to execute TypScript scripts via Deno in GitHub Actions. This action allows us to also use npm specifiers.

Here’s the GitHub Action yml file:

name: Generate Embeddings

on:
  push:
    branches:
      - main
  workflow_dispatch:

jobs:
  generate-embeddings:
    runs-on: ubuntu-latest

    env:
      SUPABASE_URL: ${{ secrets.SUPABASE_URL }}
      SUPABASE_SERVICE_ROLE_KEY: ${{ secrets.SUPABASE_SERVICE_ROLE_KEY }}
      OPENAI_KEY: ${{ secrets.OPENAI_KEY }}

    steps:
      - uses: actions/checkout@v3

      - uses: denoland/setup-deno@v1
        with:
          deno-version: v1.x

      - run: deno task embeddings

In addition to storing the embeddings, this script generates a checksum for each of your .mdx files and stores this in another database table to make sure the embeddings are only regenerated when the file has changed.

🏃 Runtime

Step 3. and 4. happen at runtime, anytime the user submits a question. When this happens, the following sequence of tasks is performed:

1. Edge function receives the query and generates an embedding for the query with OpenAI
2. The embedding vector is used to perform a vector similarity search on Supabase with pgvector, which returns the relevant docs
3. The docs and query is sent to OpenAI and the response is streamed to the client

Here’s a workflow diagram describing the steps in further detail:

In the code, the user prompt begins with the SearchDialog island.

Then, the vector-search API endpoint generates the embedding, then performs the vector search on Supabase. When it gets the response with relevant docs, it assembles the prompt for OpenAI:

const prompt = codeBlock`
${oneLine`
  You are a very enthusiastic Supabase representative who loves
  to help people! Given the following sections from the Supabase
  documentation, answer the question using only that information,
  outputted in markdown format. If you are unsure and the answer
  is not explicitly written in the documentation, say
  "Sorry, I don't know how to help with that."
`}

Context sections:
${contextText}

Question: """
${sanitizedQuery}
"""

Answer as markdown (including related code snippets if available):
`;

const completionOptions: CreateCompletionRequest = {
  model: "text-davinci-003",
  prompt,
  max_tokens: 512,
  temperature: 0,
  stream: true,
};


const response = await fetch("https://api.openai.com/v1/completions", {
  headers: {
    Authorization: `Bearer ${OPENAI_KEY}`,
    "Content-Type": "application/json",
  },
  method: "POST",
  body: JSON.stringify(completionOptions),
});


return new Response(response.body, {
  headers: {
    ...corsHeaders,
    "Content-Type": "text/event-stream",
  },
});

Finally, the SearchDialog island uses the EventSource web API to process server-sent events that are returned from the OpenAI API. This is what allows us to stream the response to the client as it is being generated from OpenAI:

const onSubmit = (e: Event) => {
  e.preventDefault();
  answer.value = "";
  isLoading.value = true;

  const query = new URLSearchParams({ query: inputRef.current!.value });
  const eventSource = new EventSource(`api/vector-search?${query}`);

  eventSource.addEventListener("error", (err) => {
    isLoading.value = false;
    console.error(err);
  });
  eventSource.addEventListener("message", (e: MessageEvent) => {
    isLoading.value = false;

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

    const completionResponse: CreateCompletionResponse = JSON.parse(e.data);
    const text = completionResponse.choices[0].text;

    answer.value += text;
  });

  isLoading.value = true;
};

What’s next?

This is the full power of open source and the modern web coming together right here at your fingertips. Try it out now, we can’t wait to see what you will build!

Here are additional resources to learn about building with OpenAI and ChatGPT.

• Read the blogpost on how we built ChatGPT for the Supabase Docs.
• [Docs] pgvector: Embeddings and vector similarity
• Watch Greg’s “How I built this” video on the Rabbit Hole Syndrome YouTube Channel.

Finally, we’d like to thank Asher Gomez for his contribution on this project.

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