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, PAIRING_PORT, 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. Same23 *  fixed port pairing dials — SyncReconnectListener.SYNC_PORT on Android. */24const DEFAULT_SYNC_PORT = PAIRING_PORT;2526export type CodePairingError =27  | "invalid_code"      // socket closed before PEACH_HELLO_ACK (wrong/expired)28  | "no_host_found"     // nothing answered at the endpoint29  | "handshake_failed"  // Noise NK / PAIR_IDENTITY decode failed30  | "sas_mismatch"      // user rejected the SAS31  | "vault_locked";     // no master key available3233export interface CodePairingDeps extends PairingDialDeps {34  /** Public identity for our outbound PAIR_IDENTITY (incl. vaultId). */35  getLocalIdentity(): Promise<LocalIdentity>;36  /** Persist on user confirm. */37  persistDevice(device: PairedDevice): Promise<void>;38  /** Optional fast-path cache for the next sync round. */39  cacheLastKnownIp?(pubkeyHex: string, ip: string): Promise<void>;40}4142export interface CodePairingCallbacks {43  /** Show the 6-digit SAS; the popup must compare it against the peer's. */44  onSasReady(sas: string): void;45  /** Pairing succeeded and the device was persisted. */46  onComplete(device: PairedDevice): void;47  /** Pairing failed at some stage. */48  onError(error: CodePairingError): void;49}5051interface PairingFrame {52  type: "PAIR_IDENTITY";53  device_id: string;54  device_name: string;55  device_type: DeviceType;56  long_term_public_key_hex: string;57  signing_public_key_hex?: string;58  ws_port?: number;59  vault_id?: string; // Change 1 — additive, optional60}6162function encodeJson(obj: unknown): Uint8Array {63  return new TextEncoder().encode(JSON.stringify(obj));64}6566function decodePairIdentity(bytes: Uint8Array): PairingFrame {67  const p = JSON.parse(new TextDecoder().decode(bytes)) as Record<string, unknown>;68  if (p?.type !== "PAIR_IDENTITY") throw new Error("expected PAIR_IDENTITY");69  if (typeof p.device_id !== "string" || !p.device_id) throw new Error("device_id missing");70  if (typeof p.device_name !== "string") throw new Error("device_name missing");71  if (typeof p.device_type !== "string") throw new Error("device_type missing");72  if (typeof p.long_term_public_key_hex !== "string" ||73      !/^[0-9a-f]{64}$/.test(p.long_term_public_key_hex)) {74    throw new Error("long_term_public_key_hex is not 32-byte hex");75  }76  return p as unknown as PairingFrame;77}7879/**80 * Drive a complete code pairing.81 *82 * `confirm` is a function the caller resolves AFTER the user has compared the83 * SAS shown here against the SAS the peer displays. Resolving false (or84 * rejecting) aborts before any device is persisted — this is the out-of-band85 * MITM defence (see the SECURITY note in pairing-handshake.ts), and it, not the86 * pairing token, is what actually authenticates the peer.87 */88export async function pairWithCode(89  code: string,90  cb: CodePairingCallbacks,91  deps: CodePairingDeps,92  confirm: (sas: string) => Promise<boolean>,93): Promise<void> {94  let identity: LocalIdentity;95  try {96    identity = await deps.getLocalIdentity();97  } catch {98    cb.onError("vault_locked");99    return;100  }101102  const dial = await dialPairingChannel(code, deps);103  if (!dial.ok) {104    cb.onError(dial.error);105    return;106  }107  const { channel, sas, host, socket } = dial.dialled;108109  try {110    // Initiator (browser) sends its identity FIRST, then reads the peer's.111    const ourFrame: PairingFrame = {112      type: "PAIR_IDENTITY",113      device_id: identity.deviceId,114      device_name: identity.deviceName,115      device_type: identity.deviceType,116      long_term_public_key_hex: identity.longTermPublicKeyHex,117      signing_public_key_hex: identity.signingPublicKeyHex,118      ws_port: identity.wsPort,119      vault_id: identity.vaultId, // Change 1120    };121    await channel.send(encodeJson(ourFrame));122123    const theirFrame = decodePairIdentity(await channel.receive());124125    cb.onSasReady(sas);126    const confirmed = await confirm(sas);127    if (!confirmed) {128      cb.onError("sas_mismatch");129      return;130    }131132    // ws_port comes from the peer frame, defaulting to 8765 (both peers133    // announce it, but guard it). The device-type fallback follows the code134    // form so a phone never lands in the registry labelled "desktop".135    const device: PairedDevice = {136      deviceId: theirFrame.device_id,137      deviceName: theirFrame.device_name,138      deviceType:139        (theirFrame.device_type as DeviceType) ||140        (parsePairingCode(code) ? "android" : "desktop"),141      longTermPublicKeyHex: theirFrame.long_term_public_key_hex,142      signingPublicKeyHex: theirFrame.signing_public_key_hex,143      trustSource: "direct",144      wsPort: typeof theirFrame.ws_port === "number" ? theirFrame.ws_port : DEFAULT_SYNC_PORT,145      pairedAt: Date.now(),146    };147    await deps.persistDevice(device);148    if (deps.cacheLastKnownIp && device.longTermPublicKeyHex) {149      await deps.cacheLastKnownIp(device.longTermPublicKeyHex, host).catch(() => undefined);150    }151    cb.onComplete(device);152  } catch (err) {153    if (typeof console !== "undefined") console.error("[desktop-pairing] handshake failed:", err);154    cb.onError("handshake_failed");155  } finally {156    socket.close();157  }158}