Send Email via GMail with correct encoding of German umlauts in Subject

import { encode as base64UrlEncode } from "https://deno.land/[email protected]/encoding/base64url.ts";

/**

 * @param user_id User's email address. The special value `me` can be used to indicate the authenticated user.

 */

type Gmail = {

  token: string;

};

// Helper function to Base64-encode UTF-8 strings

function base64EncodeUTF8(str) {

  // Encode string as UTF-8 then convert to base64

  return btoa(unescape(encodeURIComponent(str)));

}

export async function main(

  gmail_auth: Gmail,

  to_email: string,

  subject: string,

  message: string,

  user_id: string = "me",

) {

  const token = gmail_auth["token"];

  if (!token) {

    throw Error(`

    No authentication token was found.

    Go to "https://app.windmill.dev/resources?connect_app=gmail" to connect Gmail, 

    then select your token from the dropdown in the arguments window.

    (Click "Refresh" if you don't see your resource in the list.)\n`);

  }

  // This breaks subject encoding of umlauts:

  //const text =

  //  `From: <${user_id}>\nTo: <${to_email}>\nSubject: ${subject}\nContent-Type: text/html; charset="UTF-8"\n\r <p>${message}</p>`;

  //const textEncoder = new TextEncoder();

  //const email = base64UrlEncode(textEncoder.encode(text));

  //const body = JSON.stringify({

  //  raw: email,

  //});

  // Instead: wrap the encoded subject in RFC 2047 format

  const encodedSubject = `=?UTF-8?B?${base64EncodeUTF8(subject)}?=`;

  // Build the raw email string with the encoded subject header

  const text = `From: <${user_id}>\n` +

    `To: <${to_email}>\n` +

    `Subject: ${encodedSubject}\n` +

    `Content-Type: text/html; charset="UTF-8"\n\n` +

    `<p>${message}</p>`;

  // Convert the email string into a Uint8Array and then Base64url encode it

  const textEncoder = new TextEncoder();

  const emailBytes = textEncoder.encode(text);

  const email = base64UrlEncode(emailBytes);

  // Prepare the request body for the Gmail API

  const body = JSON.stringify({

    raw: email,

  });

  const SEND_URL =

    `https://gmail.googleapis.com/gmail/v1/users/${user_id}/messages/send`;

  const response = await fetch(SEND_URL, {

    method: "POST",

    headers: { Authorization: "Bearer " + token },

    body,

  });

  const result = await handleSendEmailResult(await response.json(), to_email);

  return result;

}

async function handleSendEmailResult(result: object, to_email: string) {

  if (Object.keys(result).includes("error")) {

    return Promise.reject({ wm_to_email: to_email, ...result });

  }

  return result;

}