Nodejs and Mailgun: Send generated attachment *not* from file system - node.js

Question

I generate attachments in a node app and would like to send them using Mailgun. I have no access to the file system (Netlify functions).
Is there an easy way to accomplish that?
The hole picture
It's a Jamstack (Gatsby/React, Netlify, Mailgun) web app. Customers configure and request offers. Browser generates and posts offers and images to a Netlify function (fetch api). The function send the offer mail with the PDF-offer and images attached.
Code I tested (edit: 02/25)
const path = require('path');
const fs = require('fs');
const mailgun = require('mailgun-js')
const FormData = require('form-data');
const { Readable } = require('stream');
const API_KEY = 'SECRET';
const DOMAIN = 'brasilius.de';
const mg = mailgun({apiKey: API_KEY, domain: DOMAIN, host: "api.eu.mailgun.net"});
const stream = fs.createReadStream('test.txt'); // This works
/* {
id: '<20210225115125.1.BF14CC322F8E0DAC#brasilius.de>',
message: 'Queued. Thank you.'
} */
/*
const stream = Readable.from(["Send this text as attachment."]) // Won't work
{ message: "'from' parameter is missing" }
*/
const data = {
from: 'Excited User <me#brasilius.de>',
to: 'test#user.de',
subject: 'Hello',
text: 'Testing some Mailgun awesomeness!',
attachment: stream
};
mg.messages().send(data, (error, body) => {
console.log(body);
});

Answer 1

The simplest solution I found here
// https://thecodebarbarian.com/sending-emails-using-the-mailgun-api.html
const mailgun = require('mailgun-js')
const mg = mailgun({apiKey: process.env.API_KEY, domain: process.env.DOMAIN, host: "api.eu.mailgun.net"});
const filename = 'test.txt';
const text = "Example test content."
const attch = new mg.Attachment({data: Buffer.from(text), filename: filename})
const data = {
from: process.env.FROM,
to: process.env.TO,
subject: 'Hello',
text: 'Testing Mailgun attachments.',
attachment: attch
};
mg.messages().send(data, (error, body) => {
console.log(body);
});
As #Joe recommended, a solution with Nodemailers Mailcomposer:
// See: https://documentation.mailgun.com/en/latest/api-sending.html#examples
// See: http://nodemailer.com/extras/mailcomposer/#attachments
const mailgun = require('mailgun-js')
const MailComposer = require('nodemailer/lib/mail-composer');
const mg = mailgun({apiKey: process.env.API_KEY, domain: process.env.DOMAIN, host: "api.eu.mailgun.net"});
const mailOptions = {
from: process.env.FROM,
subject: 'Hello',
text: 'Testing Mailgun attachments.',
attachments: [
{ // utf-8 string as an attachment
filename: 'text.txt',
content: 'For testing just a text file. This could be a ReadStream, Buffer or other.'
}
]
};
const mail = new MailComposer(mailOptions);
mail.compile().build(function(mailBuildError, message) {
var dataToSend = {
to: process.env.TO,
message: message.toString('ascii')
};
mg.messages().sendMime(dataToSend, function(sendError, body) {
if (sendError) {
console.log(sendError);
return;
}
});
});