407 lines
20 KiB
TypeScript
407 lines
20 KiB
TypeScript
// STUN and TURN for screen sharing between browser users (RFC 5389, RFC 5766).
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// STUN tells a browser its public address so two of them can connect directly. Where that is
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// not possible (mobile carriers, company networks, browsers that forbid direct UDP such as
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// Vanadium) the stream goes through this relay instead: the browser reaches it over UDP or
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// TCP, and the relay passes the packets on over UDP. Credentials are short-lived and come
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// from the proxy's API, so only people using this site can relay through it.
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import dgram from 'node:dgram';
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import net from 'node:net';
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import os from 'node:os';
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import { createHash, createHmac, randomBytes, timingSafeEqual } from 'node:crypto';
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const COOKIE = 0x2112a442;
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const REALM = 'mumh5';
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// Message types: request, with success (| 0x100) and error (| 0x110) answers
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const BINDING = 0x0001, ALLOCATE = 0x0003, REFRESH = 0x0004, SEND = 0x0016, DATA = 0x0017, CREATE_PERMISSION = 0x0008, CHANNEL_BIND = 0x0009;
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const A = {
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USERNAME: 0x0006, MESSAGE_INTEGRITY: 0x0008, ERROR_CODE: 0x0009, CHANNEL_NUMBER: 0x000c, LIFETIME: 0x000d, XOR_PEER_ADDRESS: 0x0012,
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DATA: 0x0013, REALM: 0x0014, NONCE: 0x0015, XOR_RELAYED_ADDRESS: 0x0016, REQUESTED_ADDRESS_FAMILY: 0x0017, REQUESTED_TRANSPORT: 0x0019,
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XOR_MAPPED_ADDRESS: 0x0020
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};
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const LIFETIME = 600; // an allocation, unless refreshed
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const PERMISSION = 300; // a peer address may send for this long after CreatePermission
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const CHANNEL = 600;
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const NONCE_AGE = 3600;
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export const CREDENTIAL_TTL = 12 * 3600;
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export interface TurnOptions {
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port: number;
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bind: string;
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// false: answer STUN binding requests only
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relay: boolean;
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// Address announced for relayed traffic; found from the connection or the network interfaces when unset
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publicIp: string | null;
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// UDP ports used for relaying, so a firewall can open exactly these
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minPort: number;
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maxPort: number;
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maxAllocations: number;
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maxPerAddress: number;
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// Peers the relay may talk to; keeps it from being used to reach private networks
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peerAllowed: (ip: string) => boolean;
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// One line per relay event, for finding out why someone cannot connect
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log?: (line: string) => void;
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}
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// Loopback, private, link-local and other addresses that are not on the public internet
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export function isPrivateAddress(address: string): boolean {
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if (net.isIPv4(address)) {
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const [a, b] = address.split('.').map(Number);
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return a === 0 || a === 10 || a === 127 || (a === 100 && b >= 64 && b <= 127) || (a === 169 && b === 254) ||
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(a === 172 && b >= 16 && b <= 31) || (a === 192 && b === 168) || a >= 224;
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}
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const v6 = address.toLowerCase();
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const mapped = /^::ffff:(\d+\.\d+\.\d+\.\d+)$/.exec(v6);
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if (mapped) return isPrivateAddress(mapped[1]);
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return v6 === '::' || v6 === '::1' || /^f[cd]/.test(v6) || /^fe[89ab]/.test(v6) || /^ff/.test(v6);
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}
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const v4 = (address: string) => address.replace(/^::ffff:(\d+\.\d+\.\d+\.\d+)$/i, '$1');
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function ipBytes(address: string): number[] | null {
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const a = v4(address);
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if (net.isIPv4(a)) return a.split('.').map(Number);
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if (!net.isIPv6(a)) return null;
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const [head, tail = ''] = a.split('%')[0].split('::');
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const h = head ? head.split(':') : [], t = tail ? tail.split(':') : [];
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const groups = a.includes('::') ? [...h, ...new Array(8 - h.length - t.length).fill('0'), ...t] : h;
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return groups.flatMap(g => { const n = parseInt(g, 16); return [n >> 8, n & 255]; });
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}
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// Address attribute value, masked with the cookie and (for IPv6) the transaction id
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export function xorAddress(address: string, port: number, header: Uint8Array): Uint8Array | null {
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const bytes = ipBytes(address);
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if (!bytes) return null;
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const out = new Uint8Array(4 + bytes.length);
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out[1] = bytes.length === 4 ? 1 : 2;
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out[2] = (port >> 8) ^ 0x21;
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out[3] = (port & 255) ^ 0x12;
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for (let i = 0; i < bytes.length; i++) out[4 + i] = bytes[i] ^ header[4 + i];
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return out;
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}
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export function unxorAddress(value: Uint8Array, header: Uint8Array): { ip: string; port: number } | null {
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if (value.length !== 8 && value.length !== 20) return null;
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const port = ((value[2] ^ 0x21) << 8) | (value[3] ^ 0x12);
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const raw = [...value.subarray(4)].map((b, i) => b ^ header[4 + i]);
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if (raw.length === 4) return { ip: raw.join('.'), port };
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const groups: string[] = [];
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for (let i = 0; i < 16; i += 2) groups.push(((raw[i] << 8) | raw[i + 1]).toString(16));
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return { ip: groups.join(':'), port };
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}
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interface Stun { type: number; header: Uint8Array; attrs: { type: number; value: Uint8Array; offset: number }[]; raw: Uint8Array }
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export function parse(msg: Uint8Array): Stun | null {
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if (msg.length < 20) return null;
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const view = new DataView(msg.buffer, msg.byteOffset, msg.byteLength);
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if (view.getUint32(4) !== COOKIE || view.getUint16(2) !== msg.length - 20) return null;
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const attrs: Stun['attrs'] = [];
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for (let at = 20; at + 4 <= msg.length;) {
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const type = view.getUint16(at), length = view.getUint16(at + 2);
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if (at + 4 + length > msg.length) return null;
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attrs.push({ type, value: msg.subarray(at + 4, at + 4 + length), offset: at });
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at += 4 + ((length + 3) & ~3);
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}
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return { type: view.getUint16(0), header: msg.subarray(0, 20), attrs, raw: msg };
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}
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// Builds a message; with a key it is signed (MESSAGE-INTEGRITY), which browsers check on answers
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export function build(type: number, header: Uint8Array, attrs: [number, Uint8Array][], key?: Buffer): Uint8Array {
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const body = attrs.reduce((n, [, v]) => n + 4 + ((v.length + 3) & ~3), 0);
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const out = new Uint8Array(20 + body + (key ? 24 : 0));
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const view = new DataView(out.buffer);
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view.setUint16(0, type);
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out.set(header.subarray(4, 20), 4);
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let at = 20;
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for (const [t, v] of attrs) {
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view.setUint16(at, t);
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view.setUint16(at + 2, v.length);
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out.set(v, at + 4);
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at += 4 + ((v.length + 3) & ~3);
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}
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// The length field counts the integrity attribute while it is being computed
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view.setUint16(2, out.length - 20);
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if (key) {
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view.setUint16(at, A.MESSAGE_INTEGRITY);
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view.setUint16(at + 2, 20);
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out.set(createHmac('sha1', key).update(out.subarray(0, at)).digest(), at + 4);
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}
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return out;
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}
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const text = (s: string) => new TextEncoder().encode(s);
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const u32 = (n: number) => { const b = new Uint8Array(4); new DataView(b.buffer).setUint32(0, n); return b; };
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const errorCode = (code: number, reason: string) => Uint8Array.from([0, 0, Math.floor(code / 100), code % 100, ...text(reason)]);
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// Binding answer on its own, for the STUN-only case and the tests
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export function stunResponse(msg: Uint8Array, address: string, port: number): Uint8Array | null {
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const m = parse(msg);
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if (!m || m.type !== BINDING) return null;
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const mapped = xorAddress(address, port, m.header);
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return mapped && build(BINDING | 0x100, m.header, [[A.XOR_MAPPED_ADDRESS, mapped]]);
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}
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// The password that goes with a username, as handed out by the API and checked here
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export function turnCredential(secret: string, username: string): string {
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return createHmac('sha1', secret).update(username).digest('base64');
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}
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interface Client { key: string; ip: string; port: number; send(bytes: Uint8Array): void; local: string | null }
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interface Allocation {
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client: Client;
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authKey: Buffer;
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relay: dgram.Socket;
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relayIp: string;
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permissions: Map<string, number>;
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channels: Map<number, { ip: string; port: number; expires: number }>;
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byPeer: Map<string, number>;
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expires: number;
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}
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export async function startTurn(opts: TurnOptions, secret: string): Promise<{ port: number; close(): void }> {
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const allocations = new Map<string, Allocation>();
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const now = () => Math.floor(Date.now() / 1000);
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const nonce = () => { const t = String(now()); return `${t}-${createHmac('sha1', secret).update(`nonce:${t}`).digest('hex').slice(0, 24)}`; };
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const nonceValid = (n: string) => {
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const [t, mac] = n.split('-');
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return !!mac && now() - Number(t) < NONCE_AGE && mac === createHmac('sha1', secret).update(`nonce:${t}`).digest('hex').slice(0, 24);
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};
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function free(a: Allocation): void {
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if (allocations.get(a.client.key) === a) allocations.delete(a.client.key);
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try { a.relay.close(); } catch { /* already closed */ }
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}
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const sweep = setInterval(() => { for (const a of allocations.values()) if (a.expires < now()) free(a); }, 15000);
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sweep.unref();
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// The address peers must send to. Behind a 1:1 NAT (many cloud hosts) it has to be configured.
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function relayAddress(family: 4 | 6, local: string | null): string | null {
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if (opts.publicIp && (net.isIPv4(opts.publicIp) ? 4 : 6) === family) return opts.publicIp;
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if (local && (net.isIPv4(local) ? 4 : 6) === family && !/^(0\.0\.0\.0|::)$/.test(local)) return local;
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const want = family === 4 ? 'IPv4' : 'IPv6';
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const found = Object.values(os.networkInterfaces()).flat().filter(i => i && i.family === want && !i.address.startsWith('fe80'));
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// A public address first; Docker bridges and the like come before loopback only
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return (found.find(i => !isPrivateAddress(i!.address)) ?? found.find(i => !i!.internal) ?? found[0])?.address ?? null;
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}
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async function bindRelay(family: 4 | 6): Promise<dgram.Socket | null> {
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const span = opts.maxPort - opts.minPort + 1;
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const start = Math.floor(Math.random() * span);
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for (let i = 0; i < Math.min(span, 64); i++) {
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const socket = dgram.createSocket({ type: family === 4 ? 'udp4' : 'udp6', ipv6Only: family === 6 });
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const ok = await new Promise<boolean>(resolve => {
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socket.once('error', () => resolve(false));
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socket.bind(opts.minPort + ((start + i) % span), () => resolve(true));
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});
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if (ok) { socket.removeAllListeners('error'); socket.on('error', () => {}); return socket; }
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try { socket.close(); } catch { /* never opened */ }
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}
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return null;
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}
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// Checks the credentials of a request; answers with the right error and returns null otherwise
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function authenticate(m: Stun, client: Client): Buffer | null {
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const get = (t: number) => m.attrs.find(a => a.type === t);
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const fail = (code: number, reason: string) => {
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client.send(build(m.type | 0x110, m.header, [[A.ERROR_CODE, errorCode(code, reason)], [A.REALM, text(REALM)], [A.NONCE, text(nonce())]]));
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return null;
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};
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const integrity = get(A.MESSAGE_INTEGRITY);
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// The first request always comes without credentials; that is how a client learns the realm
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if (!integrity) return fail(401, 'Unauthorized');
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opts.log?.(`relay: ${client.key} sent credentials`);
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const username = get(A.USERNAME), n = get(A.NONCE);
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if (!username || !n || integrity.value.length !== 20) return fail(400, 'Bad Request');
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if (!nonceValid(new TextDecoder().decode(n.value))) return fail(438, 'Stale Nonce');
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const user = new TextDecoder().decode(username.value);
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// The username is the time the credential runs out
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if (!(Number(user.split(':')[0]) > now())) return fail(401, 'Unauthorized');
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const key = createHash('md5').update(`${user}:${REALM}:${turnCredential(secret, user)}`).digest();
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const signed = Uint8Array.from(m.raw.subarray(0, integrity.offset));
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new DataView(signed.buffer).setUint16(2, integrity.offset + 24 - 20);
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const expected = createHmac('sha1', key).update(signed).digest();
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if (!timingSafeEqual(expected, integrity.value)) return fail(401, 'Unauthorized');
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return key;
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}
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// Two clients of this relay reach each other at its announced address. Behind a 1:1 NAT that
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// address is not on this machine and the router will not turn the packet around, so such
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// traffic stays on loopback and is presented as coming from the announced address.
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const loopback = (ip: string) => ip === '127.0.0.1' || ip === '::1';
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function toPeer(a: Allocation, data: Uint8Array, ip: string, port: number): void {
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a.relay.send(data, port, ip === a.relayIp ? (net.isIPv4(ip) ? '127.0.0.1' : '::1') : ip);
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}
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function fromPeer(a: Allocation, data: Buffer, peerIp: string, peerPort: number): void {
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const seen = v4(peerIp);
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const ip = loopback(seen) && !loopback(a.relayIp) ? a.relayIp : seen;
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if ((a.permissions.get(ip) ?? 0) < now()) return;
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const channel = a.byPeer.get(`${ip}:${peerPort}`);
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if (channel != null && (a.channels.get(channel)?.expires ?? 0) >= now()) {
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const out = new Uint8Array(4 + data.length);
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new DataView(out.buffer).setUint16(0, channel);
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new DataView(out.buffer).setUint16(2, data.length);
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out.set(data, 4);
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return a.client.send(out);
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}
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const header = new Uint8Array(20);
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new DataView(header.buffer).setUint32(4, COOKIE);
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header.set(randomBytes(12), 8);
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const peer = xorAddress(ip, peerPort, header);
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if (peer) a.client.send(build(DATA, header, [[A.XOR_PEER_ADDRESS, peer], [A.DATA, data]]));
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}
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async function handle(msg: Uint8Array, client: Client): Promise<void> {
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// ChannelData: channel number, length, payload
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if (msg.length >= 4 && (msg[0] & 0xc0) === 0x40) {
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const a = allocations.get(client.key);
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const view = new DataView(msg.buffer, msg.byteOffset, msg.byteLength);
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const bound = a?.channels.get(view.getUint16(0));
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const length = view.getUint16(2);
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if (a && bound && bound.expires >= now() && 4 + length <= msg.length) toPeer(a, msg.subarray(4, 4 + length), bound.ip, bound.port);
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return;
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}
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const m = parse(msg);
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if (!m) return;
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if (m.type === BINDING) {
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const mapped = xorAddress(client.ip, client.port, m.header);
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if (mapped) client.send(build(BINDING | 0x100, m.header, [[A.XOR_MAPPED_ADDRESS, mapped]]));
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return;
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}
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if (!opts.relay) return;
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const get = (t: number) => m.attrs.find(a => a.type === t);
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const existing = allocations.get(client.key);
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if (m.type === SEND) {
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const peer = get(A.XOR_PEER_ADDRESS), data = get(A.DATA);
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const to = peer && unxorAddress(peer.value, m.header);
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if (existing && to && data && (existing.permissions.get(to.ip) ?? 0) >= now()) toPeer(existing, data.value, to.ip, to.port);
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return;
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}
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if (![ALLOCATE, REFRESH, CREATE_PERMISSION, CHANNEL_BIND].includes(m.type)) return;
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const key = authenticate(m, client);
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if (!key) return;
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const ok = (attrs: [number, Uint8Array][] = []) => client.send(build(m.type | 0x100, m.header, attrs, key));
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const error = (code: number, reason: string) => {
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opts.log?.(`relay: ${client.key} refused, ${code} ${reason}`);
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client.send(build(m.type | 0x110, m.header, [[A.ERROR_CODE, errorCode(code, reason)]], key));
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};
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if (m.type === ALLOCATE) {
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if (existing) return error(437, 'Allocation Mismatch');
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if (get(A.REQUESTED_TRANSPORT)?.value[0] !== 17) return error(442, 'Unsupported Transport Protocol');
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const family: 4 | 6 = get(A.REQUESTED_ADDRESS_FAMILY)?.value[0] === 2 ? 6 : 4;
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const mine = [...allocations.values()].filter(a => a.client.ip === client.ip).length;
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if (allocations.size >= opts.maxAllocations || mine >= opts.maxPerAddress) return error(486, 'Allocation Quota Reached');
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const relayIp = relayAddress(family, client.local);
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const relay = relayIp ? await bindRelay(family) : null;
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if (!relay || !relayIp) return error(508, 'Insufficient Capacity');
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// Another request for the same client may have won while the port was being opened
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if (allocations.has(client.key)) { relay.close(); return error(437, 'Allocation Mismatch'); }
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const a: Allocation = { client, authKey: key, relay, relayIp, permissions: new Map(), channels: new Map(), byPeer: new Map(), expires: now() + LIFETIME };
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allocations.set(client.key, a);
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relay.on('message', (data, from) => fromPeer(a, data, from.address, from.port));
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opts.log?.(`relay: ${client.key} got ${relayIp}:${relay.address().port} (${allocations.size} in use)`);
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return ok([
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[A.XOR_RELAYED_ADDRESS, xorAddress(relayIp, relay.address().port, m.header)!],
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[A.LIFETIME, u32(LIFETIME)],
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[A.XOR_MAPPED_ADDRESS, xorAddress(client.ip, client.port, m.header)!]
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]);
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}
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if (!existing) return error(437, 'Allocation Mismatch');
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if (m.type === REFRESH) {
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const wanted = get(A.LIFETIME);
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const seconds = wanted ? Math.min(new DataView(wanted.value.buffer, wanted.value.byteOffset).getUint32(0), LIFETIME) : LIFETIME;
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if (seconds === 0) free(existing);
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else existing.expires = now() + seconds;
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return ok([[A.LIFETIME, u32(seconds)]]);
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}
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const peers = m.attrs.filter(a => a.type === A.XOR_PEER_ADDRESS).map(a => unxorAddress(a.value, m.header));
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if (!peers.length || peers.some(p => !p)) return error(400, 'Bad Request');
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// Other clients of this relay are reached at its own address
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if (peers.some(p => p!.ip !== existing.relayIp && !opts.peerAllowed(p!.ip))) return error(403, 'Forbidden');
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if (m.type === CREATE_PERMISSION) {
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for (const p of peers) existing.permissions.set(p!.ip, now() + PERMISSION);
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return ok();
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}
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// ChannelBind
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const number = get(A.CHANNEL_NUMBER);
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const channel = number ? new DataView(number.value.buffer, number.value.byteOffset).getUint16(0) : 0;
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const peer = peers[0]!;
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const peerKey = `${peer.ip}:${peer.port}`;
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if (channel < 0x4000 || channel > 0x7ffe) return error(400, 'Bad Request');
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const boundTo = existing.channels.get(channel), boundAs = existing.byPeer.get(peerKey);
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if ((boundTo && `${boundTo.ip}:${boundTo.port}` !== peerKey) || (boundAs != null && boundAs !== channel)) return error(400, 'Bad Request');
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existing.channels.set(channel, { ...peer, expires: now() + CHANNEL });
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existing.byPeer.set(peerKey, channel);
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existing.permissions.set(peer.ip, now() + PERMISSION);
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return ok();
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}
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// UDP: one message per packet
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const udp = dgram.createSocket(net.isIPv4(opts.bind) ? 'udp4' : 'udp6');
|
|
udp.on('message', (msg, from) => {
|
|
const ip = v4(from.address);
|
|
handle(msg, { key: `udp:${ip}:${from.port}`, ip, port: from.port, local: null, send: bytes => udp.send(bytes, from.port, from.address) }).catch(() => {});
|
|
});
|
|
const port = await new Promise<number>((resolve, reject) => {
|
|
udp.once('error', reject);
|
|
udp.bind(opts.port, opts.bind, () => { udp.removeAllListeners('error'); udp.on('error', () => {}); resolve(udp.address().port); });
|
|
});
|
|
|
|
// TCP, for browsers and networks that allow no UDP: the same messages, one after another, padded to 4 bytes
|
|
const tcp = net.createServer(socket => {
|
|
const ip = v4(socket.remoteAddress ?? ''), remotePort = socket.remotePort ?? 0;
|
|
const client: Client = {
|
|
key: `tcp:${ip}:${remotePort}`, ip, port: remotePort, local: socket.localAddress ? v4(socket.localAddress) : null,
|
|
send: bytes => {
|
|
if (socket.destroyed) return;
|
|
// A slow reader must not grow our memory; it loses packets instead, like on UDP
|
|
if (socket.writableLength > 4 * 1024 * 1024) return;
|
|
const padded = (bytes.length + 3) & ~3;
|
|
socket.write(padded === bytes.length ? bytes : Buffer.concat([bytes, Buffer.alloc(padded - bytes.length)]));
|
|
}
|
|
};
|
|
let pending: Buffer = Buffer.alloc(0);
|
|
socket.setNoDelay(true);
|
|
socket.setTimeout(LIFETIME * 1000, () => socket.destroy());
|
|
socket.on('data', (chunk: Buffer) => {
|
|
pending = pending.length ? Buffer.concat([pending, chunk]) : chunk;
|
|
while (pending.length >= 4) {
|
|
const kind = pending[0] & 0xc0;
|
|
if (kind !== 0x00 && kind !== 0x40) return socket.destroy();
|
|
const length = (kind === 0x00 ? 20 : 4) + pending.readUInt16BE(2);
|
|
const framed = (length + 3) & ~3;
|
|
if (length > 65536) return socket.destroy();
|
|
if (pending.length < framed) break;
|
|
handle(Uint8Array.from(pending.subarray(0, length)), client).catch(() => {});
|
|
pending = pending.subarray(framed);
|
|
}
|
|
});
|
|
socket.on('error', () => {});
|
|
socket.on('close', () => { const a = allocations.get(client.key); if (a) free(a); });
|
|
});
|
|
if (opts.relay) {
|
|
await new Promise<void>(resolve => {
|
|
// Relaying over UDP still works without the TCP port
|
|
tcp.once('error', () => resolve());
|
|
tcp.listen({ port, host: opts.bind }, () => { tcp.removeAllListeners('error'); tcp.on('error', () => {}); resolve(); });
|
|
});
|
|
}
|
|
|
|
return {
|
|
port,
|
|
close() {
|
|
clearInterval(sweep);
|
|
for (const a of [...allocations.values()]) free(a);
|
|
try { udp.close(); } catch { /* already closed */ }
|
|
tcp.close();
|
|
}
|
|
};
|
|
}
|