rudeshark.net/packages/backend/src/remote/webfinger.ts

import { URL } from "node:url";
import { getJson } from "@/misc/fetch.js";
import { query as urlQuery } from "@/prelude/url.js";

type ILink = {
	href: string;
	rel?: string;
};

type IWebFinger = {
	links: ILink[];
	subject: string;
};

export default async function (query: string): Promise<IWebFinger> {
	const url = genUrl(query);

	return (await getJson(
		url,
		"application/jrd+json, application/json",
	)) as IWebFinger;
}

function genUrl(query: string) {
	if (query.match(/^https?:\/\//)) {
		const u = new URL(query);
		return (
			`${u.protocol}//${u.hostname}/.well-known/webfinger?${urlQuery({ resource: query })}`
		);
	}

	const m = query.match(/^([^@]+)@(.*)/);
	if (m) {
		const hostname = m[2];
		return (
			`https://${hostname}/.well-known/webfinger?${urlQuery({ resource: `acct:${query}` })}`
		);
	}

	throw new Error(`Invalid query (${query})`);
}