Privnote + AWS Lambda

index.mjs

import { S3Client, PutObjectCommand, GetObjectCommand, DeleteObjectCommand } from "@aws-sdk/client-s3";

const s3Client = new S3Client({ region: "us-east-1" });

const Bucket = "BUCKET_NAME_GOES_HERE";

export const handler = async (event) => {
  let statusCode = 200;
  let body = ``;
  if (event.requestContext.http.method === "POST") {
    // POST /
    const buff = Buffer.from(event.body ?? "", "base64");
    const eventBody = buff.toString("UTF-8");
    const params = new URLSearchParams(eventBody);
    const uuid = params.get("uuid");
    const note = params.get("ciphered");
    const bytes = Buffer.byteLength(note);
    // Only allow to save notes below 1MB
    if (bytes < 1048577) {
      const bucketParams = {
        Bucket,
        ACL: "private",
        ServerSideEncryption: "AES256",
        // Do not store the last part of the key
        Key: uuid?.split("-")?.splice(0, 4)?.join("-"),
        Body: `${note}`,
      };
      try {
        // Save note
        await s3Client.send(new PutObjectCommand(bucketParams));
        body = `<div>
  <p>
    <label for="note" class="w-100 alert alert-warning fw-light fst-italic py-1">The note will self-destruct after reading it.</label>
    <input type="text" class="form-control shadow-sm" id="link" value="https://biubkhqe6zz3hypoitljy2vqti0yyvbn.lambda-url.us-east-1.on.aws/${uuid}" onClick="this.select()" readonly />
  </p>
</div>`;
      } catch (error) {
        console.log(error);
        statusCode = 500;
        body = `<div class="alert alert-danger">Error: saving</div>`;
      }
    } else {
      statusCode = 500;
      body = `<div class="alert alert-danger">Error: too big</div>`;
    }
  } else {
    // GET /:uuid
    const uuid = `${event.requestContext.http.path}`.replaceAll("/", "");
    if (uuid !== "") {
      const bucketParams = { Bucket, Key: uuid?.split("-")?.splice(0, 4)?.join("-") };
      try {
        // Load note
        const data = await s3Client.send(new GetObjectCommand(bucketParams));
        const streamToString = await data.Body?.transformToString();
        try {
          // Delete note
          await s3Client.send(new DeleteObjectCommand(bucketParams));
          // Show note to the user
          body = `<form id="noteForm">
  <div class="col-12">
    <label for="note" class="w-100 alert alert-warning fw-light fst-italic py-1">This note was destroyed. If you need to keep it, copy it before closing this window.</label>
    <textarea class="form-control shadow-sm" id="note" name="note" rows="10" required></textarea>
  </div>
</form>
<script type="text/javascript" src="https://unpkg.com/crypto-js/crypto-js.js"></script>
<script type="text/javascript">
  const formEl = document.getElementById("noteForm");
  document.addEventListener("DOMContentLoaded", () => {
    // Decrypt in the browser
    const bytes  = CryptoJS.AES.decrypt("${streamToString}", "${uuid}");
    const originalText = bytes.toString(CryptoJS.enc.Utf8);
    formEl.elements.note.value = originalText;
  });
</script>`;
        } catch (error) {
          console.log(error);
          statusCode = 500;
          body = `<div class="alert alert-danger">Error: deleting</div>`;
        }
      } catch (error) {
        console.log(error);
        statusCode = 404;
        body = `<div class="alert alert-danger">Error 404: not found</div>`;
      }
    } else {
      // Default GET /
      body = `<form id="noteForm" class="row g-3 mx-auto" method="POST">
  <div class="col-12">
    <label for="note" class="form-label">New note:</label>
    <textarea class="form-control shadow-sm" id="note" name="note" rows="10" required></textarea>
  </div>
  <div class="col-12 mt-4">
    <button type="submit" name="submitButton" class="btn btn-primary shadow">Create note</button>
  </div>
</form>
<script type="text/javascript" src="https://unpkg.com/crypto-js/crypto-js.js"></script>
<script type="text/javascript">
  const formEl = document.getElementById("noteForm");
  formEl.addEventListener("submit", (event) => {
    formEl.elements.submitButton.disabled = true;
    event.preventDefault();
    // Generate uuid in the browser
    const uuid = crypto.randomUUID();
    // Cipher text
    const ciphertext = CryptoJS.AES.encrypt(formEl.elements.note.value, uuid).toString();
    // Add a hidden input to the form with the ciphered text
    const cipheredEl = document.createElement('input');
    cipheredEl.type = "hidden";
    cipheredEl.name = "ciphered";
    cipheredEl.value = ciphertext;
    formEl.appendChild(cipheredEl);
    // Add a hidden input with the uuid
    const uuidEl = document.createElement('input');
    uuidEl.type = "hidden";
    uuidEl.name = "uuid";
    uuidEl.value = uuid;
    formEl.appendChild(uuidEl);
    // Submit form
    formEl.submit();
  });
</script>`;
    }
  }
  const html = `<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Private Note</title>
    <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0-alpha1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-GLhlTQ8iRABdZLl6O3oVMWSktQOp6b7In1Zl3/Jr59b6EGGoI1aFkw7cmDA6j6gD" crossorigin="anonymous" />
  </head>
  <body class="bg-body-tertiary">
    <nav class="navbar navbar-dark bg-dark">
      <div class="container-fluid" style="max-width:720px">
        <a class="navbar-brand" href="/">🔒 Private Note</a>
      </div>
    </nav>
    <main class="container my-3" style="max-width:720px">
      ${body}
    </main>
  </body>
</html>`;
  const response = {
    statusCode,
    headers: { "Content-Type": "text/html" },
    body: html,
  };
  return response;
};

This is my Privnote clone in a single AWS Lambda.

Permissions required:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:PutObject",
        "s3:PutObjectAcl",
        "s3:GetObject",
        "s3:GetObjectAcl",
        "s3:DeleteObject"
      ],
      "Resource": [
        "arn:aws:s3:::BUCKET_NAME_GOES_HERE",
        "arn:aws:s3:::BUCKET_NAME_GOES_HERE/*"
      ]
    }
  ]
}