shadowfacts.net/lib/activitypub/federate.ts

import { promises as fs } from "fs";
import crypto from "crypto";
import uuidv4 from "uuid/v4";
import request from "request";
import { Database } from "sqlite3";
import { Activity, Article, Create, Actor, Follow, Accept } from "./activity";
import { URL } from "url";

const domain = process.env.DOMAIN;

function createActivity(article: Article): Create {
	const uuid = uuidv4();
	const createObject = {
		"@context": [
			"https://www.w3.org/ns/activitystreams"
		],
		"type": "Create",
		"id": `https://${domain}/ap/${uuid}`,
		"actor": `https://${domain}/ap/actor`,
		"to": article.to,
		"cc": article.cc,
		"object": article
	};
	return createObject;
}

export async function fetchActor(url: string): Promise<Actor> {
	return new Promise((resolve, reject) => {
		request({
			url,
			headers: {
				"Accept": "application/activity+json"
			},
			method: "GET",
			json: true
		}, (err, res) => {
			if (err) reject(err);
			else resolve(<Actor>res.body);
		});
	});
}

export async function signAndSend(activity: Activity, inbox: string) {
	const targetDomain = new URL(inbox).hostname;
	const inboxFragment = inbox.replace("https://" + targetDomain, "");
	const date = new Date();
	const privKey = (await fs.readFile(process.env.PRIV_KEY_PEM!)).toString();
	const signer = crypto.createSign("sha256");
	const stringToSign = `(request-target): post ${inboxFragment}\nhost: ${targetDomain}\ndate: ${date.toUTCString()}`;
	signer.update(stringToSign);
	signer.end();
	const signature = signer.sign(privKey, "base64");
	const header = `keyId="https://${domain}/ap/actor#main-key",headers="(request-target) host date",signature="${signature}"`;
	console.log("Sending:", activity);
	console.log("stringToSign:", stringToSign);
	console.log("Signature: " + header);
	request({
		url: inbox,
		headers: {
			"Host": targetDomain,
			"Date": date.toUTCString(),
			"Signature": header,
			"Accept": "application/activity+json, application/json"
		},
		method: "POST",
		json: true,
		body: activity
	}, (err, res) => {
		console.log("Sent message to inbox at", targetDomain);
		console.log("Response status code", res.statusCode);
		console.log(res.body);
		if (err) console.log("Error:", err, res);
	});
}

async function sendToFollowers(activity: Create, db: Database) {
	db.each("SELECT inbox FROM followers", (err, result) => {
		if (err) {
			console.log("Error getting followers: ", err);
			return;
		}
		const inbox = "https://" + new URL(result.inbox).host + "/inbox";
		console.log(`Federating ${activity.object.id} to ${inbox}`);
		signAndSend(activity, inbox);
	});
}

export default function federate(toFederate: [string, Article][], db: Database) {
	for (const [id, article] of toFederate) {
		
		sendToFollowers(createActivity(article), db);
		db.run("UPDATE articles SET has_federated = 1 WHERE id = $id", {
			$id: id
		});
		break;
	}
}