import express from "express"; import { SMTPServer } from "smtp-server"; import mailparser from "mailparser"; import { promises as fs } from "fs"; import * as entities from "entities"; import { JSDOM } from "jsdom"; import * as sanitizeXMLString from "sanitize-xml-string"; import writeFileAtomic from "write-file-atomic"; import cryptoRandomString from "crypto-random-string"; export const WEB_PORT = process.env.WEB_PORT ?? 8000; export const EMAIL_PORT = process.env.EMAIL_PORT ?? 2525; export const BASE_URL = process.env.BASE_URL ?? "http://localhost:8000"; export const EMAIL_DOMAIN = process.env.EMAIL_DOMAIN ?? "localhost"; export const ISSUE_REPORT = process.env.ISSUE_REPORT ?? "mailto:kill-the-newsletter@leafac.com"; export const webServer = express() .use(express.static("static")) .use(express.urlencoded({ extended: true })) .get("/", (req, res) => res.send( layout(`

`) ) ) .post("/", async (req, res, next) => { try { const { name } = req.body; const identifier = createIdentifier(); await writeFileAtomic(feedPath(identifier), feed(X(name), identifier)); res.send( layout(`

“${H(name)}” Inbox Created

${created(identifier)} `) ); } catch (error) { console.error(error); next(error); } }) .get("/alternate", (req, res) => res.send( layout(`

Typically each entry in a feed includes a link
to an online version of the same content,
but the content from the entries in a Kill the Newsletter!
feed come from emails—an online version may not even exist—
so you’re reading this instead.

Create an Inbox

`) ) ) .listen(WEB_PORT); export const emailServer = new SMTPServer({ disabledCommands: ["AUTH", "STARTTLS"], async onData(stream, session, callback) { try { const email = await mailparser.simpleParser(stream); const newEntry = entry( X(email.subject ?? ""), X(email.from?.text ?? ""), X(typeof email.html === "string" ? email.html : email.textAsHtml ?? "") ); for (const { address } of session.envelope.rcptTo) { const match = address.match( new RegExp(`^(?\\w+)@${EMAIL_DOMAIN}$`) ); if (match?.groups === undefined) continue; const path = feedPath(match.groups.identifier); const xmlText = await fs.readFile(path, "utf8").catch(() => null); if (xmlText === null) continue; const xml = new JSDOM(xmlText, { contentType: "text/xml" }); const document = xml.window.document; const updated = document.querySelector("feed > updated"); if (updated === null) throw new Error(`Can’t find ‘updated’ field in feed at ‘${path}’.`); updated.textContent = now(); const firstEntry = document.querySelector("feed > entry:first-of-type"); if (firstEntry !== null) firstEntry.insertAdjacentHTML("beforebegin", newEntry); else document .querySelector("feed")! .insertAdjacentHTML("beforeend", newEntry); while ( document.querySelector("feed > entry") !== null && xml.serialize().length > 500_000 ) document.querySelector("feed > entry:last-of-type")!.remove(); await writeFileAtomic( path, `${xml.serialize()}` ); } callback(); } catch (error) { console.error( `Error receiving email: ${JSON.stringify(session, null, 2)}` ); console.error(error); stream.resume(); callback(new Error("Failed to receive message. Please try again.")); } }, }).listen(EMAIL_PORT); function layout(content: string): string { return ` Kill the Newsletter!

Kill the Newsletter!

Convert email newsletters into Atom feeds

Convert email newsletters into Atom feeds

${content}
`; } function created(identifier: string): string { return `

Sign up for the newsletter with
${feedEmail( identifier )}

Subscribe to the Atom feed at
${feedURL(identifier)}

Don’t share these addresses.
They contain an identifier that other people could use
to send you spam and to control your newsletter subscriptions.

Enjoy your readings!

Create Another Inbox

`.trim(); } function feed(name: string, identifier: string): string { return ` ${urn(identifier)} ${name} Kill the Newsletter! Inbox: ${feedEmail( identifier )} → ${feedURL(identifier)} ${now()} Kill the Newsletter! ${entry( `“${name}” Inbox Created`, "Kill the Newsletter!", X(created(identifier)) )} `; } function entry(title: string, author: string, content: string): string { return ` ${urn(createIdentifier())} ${title} ${author} ${now()} ${content} `.trim(); } function createIdentifier(): string { return cryptoRandomString({ length: 20, characters: "1234567890qwertyuiopasdfghjklzxcvbnm", }); } function now(): string { return new Date().toISOString(); } function feedPath(identifier: string): string { return `static/feeds/${identifier}.xml`; } function feedURL(identifier: string): string { return `${BASE_URL}/feeds/${identifier}.xml`; } function feedEmail(identifier: string): string { return `${identifier}@${EMAIL_DOMAIN}`; } function urn(identifier: string): string { return `urn:kill-the-newsletter:${identifier}`; } function X(string: string): string { return entities.encodeXML(sanitizeXMLString.sanitize(string)); } function H(string: string): string { return entities.encodeHTML(sanitizeXMLString.sanitize(string)); }