code-pairing.ts

1// Device pairing over a code — the PAIR_IDENTITY half.2//3// The dialling half (decode the code, connect, plaintext hello, Noise NK) lives4// in `shared/pairing-dial.ts` and is shared with vault adoption, which speaks5// ADOPT_* frames over the same channel instead. This module is only what6// happens once that channel is open:7//8//   1. exchange PAIR_IDENTITY (send ours incl. vault_id, then read theirs)9//   2. derive the SAS, surface it for user confirmation10//   3. on confirm -> persist the PairedDevice; on reject -> abort without11//      persisting12//13// Two code forms reach here. A pairing code (`A74H-48J3-KI32-OEP4`) is the14// primary path: the phone listens and the code carries its address. A legacy15// 6-digit helper code has no address, so the host is probed for.1617import { dialPairingChannel, type PairingDialDeps } from "../shared/pairing-dial";18import type { LocalIdentity } from "../shared/pairing-handshake";19import { parsePairingCode } from "../shared/pairing-code";20import type { DeviceType, PairedDevice } from "../shared/sync-types";2122/** Default sync port a peer announces; used when ws_port is absent. */23const DEFAULT_SYNC_PORT = 8765;2425export type CodePairingError =26  | "invalid_code"      // socket closed before PEACH_HELLO_ACK (wrong/expired)27  | "no_host_found"     // nothing answered at the endpoint28  | "handshake_failed"  // Noise NK / PAIR_IDENTITY decode failed29  | "sas_mismatch"      // user rejected the SAS30  | "vault_locked";     // no master key available3132export interface CodePairingDeps extends PairingDialDeps {33  /** Public identity for our outbound PAIR_IDENTITY (incl. vaultId). */34  getLocalIdentity(): Promise<LocalIdentity>;35  /** Persist on user confirm. */36  persistDevice(device: PairedDevice): Promise<void>;37  /** Optional fast-path cache for the next sync round. */38  cacheLastKnownIp?(pubkeyHex: string, ip: string): Promise<void>;39}4041export interface CodePairingCallbacks {42  /** Show the 6-digit SAS; the popup must compare it against the peer's. */43  onSasReady(sas: string): void;44  /** Pairing succeeded and the device was persisted. */45  onComplete(device: PairedDevice): void;46  /** Pairing failed at some stage. */47  onError(error: CodePairingError): void;48}4950interface PairingFrame {51  type: "PAIR_IDENTITY";52  device_id: string;53  device_name: string;54  device_type: DeviceType;55  long_term_public_key_hex: string;56  signing_public_key_hex?: string;57  ws_port?: number;58  vault_id?: string; // Change 1 — additive, optional59}6061function encodeJson(obj: unknown): Uint8Array {62  return new TextEncoder().encode(JSON.stringify(obj));63}6465function decodePairIdentity(bytes: Uint8Array): PairingFrame {66  const p = JSON.parse(new TextDecoder().decode(bytes)) as Record<string, unknown>;67  if (p?.type !== "PAIR_IDENTITY") throw new Error("expected PAIR_IDENTITY");68  if (typeof p.device_id !== "string" || !p.device_id) throw new Error("device_id missing");69  if (typeof p.device_name !== "string") throw new Error("device_name missing");70  if (typeof p.device_type !== "string") throw new Error("device_type missing");71  if (typeof p.long_term_public_key_hex !== "string" ||72      !/^[0-9a-f]{64}$/.test(p.long_term_public_key_hex)) {73    throw new Error("long_term_public_key_hex is not 32-byte hex");74  }75  return p as unknown as PairingFrame;76}7778/**79 * Drive a complete code pairing.80 *81 * `confirm` is a function the caller resolves AFTER the user has compared the82 * SAS shown here against the SAS the peer displays. Resolving false (or83 * rejecting) aborts before any device is persisted — this is the out-of-band84 * MITM defence (see the SECURITY note in pairing-handshake.ts), and it, not the85 * pairing token, is what actually authenticates the peer.86 */87export async function pairWithCode(88  code: string,89  cb: CodePairingCallbacks,90  deps: CodePairingDeps,91  confirm: (sas: string) => Promise<boolean>,92): Promise<void> {93  let identity: LocalIdentity;94  try {95    identity = await deps.getLocalIdentity();96  } catch {97    cb.onError("vault_locked");98    return;99  }100101  const dial = await dialPairingChannel(code, deps);102  if (!dial.ok) {103    cb.onError(dial.error);104    return;105  }106  const { channel, sas, host, socket } = dial.dialled;107108  try {109    // Initiator (browser) sends its identity FIRST, then reads the peer's.110    const ourFrame: PairingFrame = {111      type: "PAIR_IDENTITY",112      device_id: identity.deviceId,113      device_name: identity.deviceName,114      device_type: identity.deviceType,115      long_term_public_key_hex: identity.longTermPublicKeyHex,116      signing_public_key_hex: identity.signingPublicKeyHex,117      ws_port: identity.wsPort,118      vault_id: identity.vaultId, // Change 1119    };120    await channel.send(encodeJson(ourFrame));121122    const theirFrame = decodePairIdentity(await channel.receive());123124    cb.onSasReady(sas);125    const confirmed = await confirm(sas);126    if (!confirmed) {127      cb.onError("sas_mismatch");128      return;129    }130131    // ws_port comes from the peer frame, defaulting to 8765 (both peers132    // announce it, but guard it). The device-type fallback follows the code133    // form so a phone never lands in the registry labelled "desktop".134    const device: PairedDevice = {135      deviceId: theirFrame.device_id,136      deviceName: theirFrame.device_name,137      deviceType:138        (theirFrame.device_type as DeviceType) ||139        (parsePairingCode(code) ? "android" : "desktop"),140      longTermPublicKeyHex: theirFrame.long_term_public_key_hex,141      signingPublicKeyHex: theirFrame.signing_public_key_hex,142      trustSource: "direct",143      wsPort: typeof theirFrame.ws_port === "number" ? theirFrame.ws_port : DEFAULT_SYNC_PORT,144      pairedAt: Date.now(),145    };146    await deps.persistDevice(device);147    if (deps.cacheLastKnownIp && device.longTermPublicKeyHex) {148      await deps.cacheLastKnownIp(device.longTermPublicKeyHex, host).catch(() => undefined);149    }150    cb.onComplete(device);151  } catch (err) {152    if (typeof console !== "undefined") console.error("[desktop-pairing] handshake failed:", err);153    cb.onError("handshake_failed");154  } finally {155    socket.close();156  }157}