WizardConnect/docs/dapp.md

# Dapp integration

Dapp integration uses `@wizardconnect/dapp` (for session management and pubkey state) together
with `@wizardconnect/core` (for the relay connection and URI generation).

## DappConnectionManager

Manages a single dapp–wallet session. Handles the handshake, xpub storage, and sign request
round-trips. Most dapps only ever have one active session at a time.

```typescript
class DappConnectionManager extends EventEmitter {
  readonly pubkeyState: DappPubkeyStateManager;

  walletName: string | null;
  walletIcon: string | null;
  /** The agreed protocol name after handshake, e.g. "hdwalletv1". Null until wallet_ready. */
  protocol: string | null;

  constructor(dappName?: string, dappIcon?: string, options?: {
    /** Session persistence config. Enabled by default (key: "wizardconnect-session",
     *  storage: localStorage). Pass `false` to disable. */
    session?: DappSessionOptions | false;
  })

  /** Call from the RelayStatusCallback each time the relay status changes. */
  updateConnection(client: RelayClient | null, status: RelayStatus): void

  isWalletDiscovered(): boolean

  /** Convenience: build a full SignTransactionRequest, send it, and optionally
   *  cancel via AbortSignal. See "Sending a sign request" below. */
  signTransaction(
    request: Pick<SignTransactionRequest, "transaction" | "inputPaths">,
    options?: { signal?: AbortSignal },
  ): Promise<SignTransactionResponse>

  /** Low-level: send a fully constructed sign request. */
  sendSignRequest(request: SignTransactionRequest): Promise<SignTransactionResponse>

  /** Cancel an in-flight sign request by sequence number. Works for both
   *  sign_transaction_request and sign_message_request. */
  sendSignCancel(sequence: number, reason?: string): Promise<void>

  /** Ask the wallet to sign a plain message, proving key control. Resolves only
   *  after the result is verified. See "signMessage" below. */
  signMessage(
    request: { message: string; path?: PathName; addressIndex?: number;
               userPrompt?: string; scheme?: MessageSignatureScheme },
    options?: { signal?: AbortSignal },
  ): Promise<VerifiedMessageSignature>

  /** Whether the wallet advertised sign_message for this mode and scheme. */
  walletSupportsSignMessage(mode?: MessageSigningMode, scheme?: MessageSignatureScheme): boolean

  /** Low-level: send a sign_message request and get the raw, UNVERIFIED response. */
  sendSignMessageRequest(request: SignMessageRequest): Promise<SignMessageSuccess>

  /** Get the next sequence number (for manual request construction). */
  nextSequence(): number

  /** Send a UserDisconnect courtesy message to the wallet. */
  sendDisconnect(message?: string): Promise<void>

  /** Get raw PathXpub[] received in wallet_ready (for caching). */
  getSessionPaths(): PathXpub[]

  /** Restore cached xpub paths — enables getPubkey() without wallet_ready. */
  restoreSessionPaths(paths: PathXpub[]): void

  // Session persistence (see "Session persistence" section below)
  attachRelay(relay: DappRelayResult): void
  loadStoredSession(): StoredSession | null
  clearStoredSession(): void

  // Events
  on("walletready",     (msg: WalletReadyMessage)                                    => void)
  on("messagesent",     (msg: ProtocolMessage)                                       => void)
  on("messagereceived", (msg: ProtocolMessage)                                       => void)
  on("disconnect",      (reason: DisconnectReason, message: string | undefined)      => void)
}
```

The `"messagereceived"` event fires for **all** protocol messages, including extension-defined
actions. Use it to handle custom messages from wallet extensions. See
[extensions.md](extensions.md) for the extension system and graceful degradation patterns.

## Pubkey state — convenience delegation

`DappConnectionManager` delegates to `pubkeyState` for all pubkey operations. These methods
are also available directly on the manager:

```typescript
// Get a pubkey (derives on demand from xpub if not cached)
getPubkey(childIndex: number, index: bigint): Uint8Array | undefined

// Get all cached pubkeys for a path
getPubkeys(childIndex: number): Map<bigint, Uint8Array>

// Get/set the current address index for a path
getAddressIndex(childIndex: number): bigint
setAddressIndex(childIndex: number, index: bigint): void

// Get a smart "next index to use" (see pubkey-derivation.md)
getIndexToUse(childIndex: number, options?: { index?: bigint; reuseLast?: boolean }): bigint

// Get the min/max indices seen for a path
getIndexRange(childIndex: number): { min?: bigint; max?: bigint }

// Remove a used change address from the gap-fill queue
removeFromChangeQueue(index: bigint): void

// Get the stored xpub node (after wallet_ready)
getXpubNode(childIndex: number): HdPublicNodeValid | undefined

// Get raw PathXpub[] from wallet_ready (for caching)
getSessionPaths(): PathXpub[]

// Restore cached PathXpub[] — populates pubkeyState so getPubkey works without wallet_ready
restoreSessionPaths(paths: PathXpub[]): void
```

Child index values: `0` = receive, `1` = change, `7` = defi (Cauldron). These are
internal to the dapp layer; use `childIndexOfPathName()` to convert from `PathName` if needed.
It returns `undefined` for extension path names — callers should skip those.

## Session lifecycle

### Initial connect

```typescript
import { initiateDappRelay } from "@wizardconnect/core";
import { DappConnectionManager } from "@wizardconnect/dapp";

const dappMgr = new DappConnectionManager("My Dapp", "https://example.com/icon.png");

const relay = initiateDappRelay(
  (payload) => {
    dappMgr.updateConnection(payload.client, payload.status);
  },
);

// Persist relay credentials and auto-save walletPublicKey on key exchange
dappMgr.attachRelay(relay);

// Show relay.uri as a QR code for the wallet to scan.
console.log("Scan this URI:", relay.uri);
```

### After wallet connects

```typescript
dappMgr.on("walletready", (msg) => {
  console.log("Wallet:", msg.wallet_name);
  // pubkeyState is now populated with xpub nodes.
  // You can start deriving addresses.
});
```

### Deriving addresses

```typescript
// Get the first receive address pubkey:
const RECEIVE = 0;
const pubkey = dappMgr.getPubkey(RECEIVE, 0n);  // derives from xpub if needed
```

See [pubkey-derivation.md](pubkey-derivation.md) for full details.

### Sending a sign request

The `signTransaction` convenience method auto-fills `action`, `sequence`, and `time`:

```typescript
const response = await dappMgr.signTransaction({
  transaction: {
    transaction: txHex,
    sourceOutputs,
    userPrompt: "Confirm swap",
    broadcast: true,
  },
  inputPaths: [[0, "receive", 0], [1, "defi", 5]],  // [inputIndex, pathName, addressIndex]
});

console.log("Signed tx:", response.signedTransaction);
```

#### Cancellation via AbortSignal

Pass an `AbortSignal` to automatically cancel the request when aborted. This sends
`sign_cancel` to the wallet and rejects the promise with an `AbortError`:

```typescript
const controller = new AbortController();
cancelButton.onclick = () => controller.abort("User cancelled");

try {
  const response = await dappMgr.signTransaction(
    { transaction: { ... }, inputPaths: [...] },
    { signal: controller.signal },
  );
} catch (err) {
  if (err.name === "AbortError") {
    console.log("User cancelled the signature request");
  }
}
```

#### Low-level: sendSignRequest

For full control over the request, use `sendSignRequest` directly:

```typescript
const seq = dappMgr.nextSequence();
const request: SignTransactionRequest = {
  action: RelayMsgAction.SignTransactionRequest,
  sequence: seq,
  time: Math.floor(Date.now() / 1000),
  transaction: { ... },
  inputPaths: [[0, "receive", 0]],
};

const response = await dappMgr.sendSignRequest(request);
// Cancel with: await dappMgr.sendSignCancel(seq, "reason");
```

### Disconnecting

```typescript
// Dapp-initiated: send courtesy message, clear session, then tear down the relay
dappMgr.clearStoredSession();
await dappMgr.sendDisconnect("user closed the tab");
relay.cleanup();

// Listen for wallet-initiated disconnect or protocol mismatch:
dappMgr.on("disconnect", (reason, message) => {
  if (reason === DisconnectReason.ProtocolMismatch) {
    console.error("Protocol mismatch:", message);
  } else {
    console.log("Wallet disconnected:", reason, message);
  }
  relay.cleanup();
});
```

The `disconnect` event fires in two cases:
1. **Remote disconnect**: the wallet sent a `disconnect` message (any reason).
2. **Protocol mismatch**: `handleWalletReady` found no overlap between the dapp's and wallet's
   `supported_protocols`. The dapp automatically sends a `ProtocolMismatch` disconnect to the
   wallet before emitting the event.

### Session persistence

Session persistence is **enabled by default**. The manager automatically:

- **On construction**: restores xpub paths from storage so `getPubkey()` works immediately.
- **On `walletready`**: saves `walletName`, `walletIcon`, and xpub `paths` to storage.

The default storage key is `"wizardconnect-session"` and the default backend is `localStorage`.

#### Saving session data

Call `attachRelay()` after `initiateDappRelay()` to persist relay credentials and
automatically save the wallet public key when key exchange completes:

```typescript
const relay = initiateDappRelay(callback);
dappMgr.attachRelay(relay); // saves credentials + auto-saves walletPublicKey

// On disconnect:
dappMgr.clearStoredSession();
```

#### Loading for reconnection

Use `loadStoredSession()` on an existing manager, or the standalone `loadSession()` when
you need to read the session before creating the manager (e.g. to get relay credentials
for `initiateDappRelay`):

```typescript
import { loadSession } from "@wizardconnect/dapp";

const session = loadSession(); // uses default key and localStorage
if (session?.walletPublicKey) {
  const relay = initiateDappRelay(callback, { existingCredentials: session });
}
```

#### Configuration

```typescript
// Default: session enabled, key "wizardconnect-session", localStorage
const mgr = new DappConnectionManager("My Dapp");

// Custom key:
const mgr = new DappConnectionManager("My Dapp", undefined, {
  session: { key: "my-app-session" },
});

// Custom storage backend (e.g. for React Native or SSR):
const mgr = new DappConnectionManager("My Dapp", undefined, {
  session: { storage: myCustomStorage },
});

// Disable session persistence:
const mgr = new DappConnectionManager("My Dapp", undefined, {
  session: false,
});
```

The `SessionStorage` interface matches the Web Storage API:

```typescript
interface SessionStorage {
  getItem(key: string): string | null;
  setItem(key: string, value: string): void;
  removeItem(key: string): void;
}
```

#### Manual path management

For advanced use cases, `getSessionPaths()` and `restoreSessionPaths()` are still available:

```typescript
const paths = dappMgr.getSessionPaths();     // raw PathXpub[] from wallet_ready
dappMgr.restoreSessionPaths(paths);          // re-populate pubkeyState from cached paths
```

`restoreSessionPaths` throws if any xpub string is invalid.

### Reconnection

`updateConnection()` is called on every relay status change. When `status.status === "connected"`,
it calls `onConnected()` which waits for key exchange and then sends a fresh `dapp_ready`. The
`walletDiscovered` flag carries over reconnects (it is only reset by creating a new manager),
so the correct `wallet_discovered` value is sent on each reconnect.

When `wallet_ready` is received and there are pending (unresponded) sign requests, the manager
automatically re-sends them. This handles the case where the user triggers a signature in the
dapp before the wallet app is open — the relay's time filter would otherwise discard the
original request. Dapps do not need to handle this manually; `sendSignRequest` promises remain
valid across reconnects.

## signMessage

Proves the user controls a key, without a transaction. The signature is a standard "Bitcoin Signed
Message" signature, so anyone can verify it from the message, the signature and the address alone —
including from an OP_RETURN via a block explorer, or by pasting it into Electron Cash's Verify
Message.

```typescript
import { MODE_WALLET_CHOICE } from "@wizardconnect/core";

// 1. Check support before offering the feature.
if (!manager.walletSupportsSignMessage(MODE_WALLET_CHOICE)) {
  return; // hide the login button rather than offer one that fails
}

// 2. Get a single-use nonce from your server. See "Replay" below — this is not optional.
const nonce = await fetch("/auth/nonce").then((r) => r.text());

// 3. Ask the wallet. Omitting path/addressIndex lets the wallet pick the key,
//    so no xpub is needed.
const result = await manager.signMessage({
  message: `${location.host} wants you to sign in.\nnonce=${nonce}`,
  userPrompt: "Sign in",
});

// 4. result is already verified. Send it to your server, which retires the nonce.
await fetch("/auth/verify", { method: "POST", body: JSON.stringify(result) });
```

### What is verified before it resolves

`signMessage()` never hands back what the wallet said unchecked. It rejects unless:

1. the signature recovers over the message that was actually sent;
2. `publicKey` is the key that signed it;
3. `address` is that key's address;
4. and, when the dapp named a path it can derive, the signer is **exactly** the key it asked for.

Without (4) a wallet could answer with a signature from any key it liked and a naive dapp would
accept it as the identity it asked about. It is the library's job, not each integrator's.

### keyBinding

```typescript
type MessageKeyBinding =
  | { checked: true; path: PathName; addressIndex: number }
  | { checked: false; reason: "wallet_chose_key" | "path_not_derivable" };
```

`checked: false` does **not** mean unverified — the signature always is. It means there was no
dapp-chosen key to compare against, so the proven address is the wallet's choice rather than the
dapp's selection:

- `wallet_chose_key` — the dapp omitted `path`/`addressIndex`. Normal for identity flows; the address
  in the result *is* the identity.
- `path_not_derivable` — the dapp named an extension path (`stealth_scan`, say) that it has no
  derivation rule for.

A dapp storing an identity should care about the difference. Naming a derivable path with no xpub
available is an error, not an unchecked result — call `signMessage` after `wallet_ready`.

### Replay — your responsibility

A signature proves key control over that exact text. It has **no freshness and no audience**: it is
valid forever, to everyone, and a captured one is replayable indefinitely. Nothing in this library
can change that today.

**Use a single-use, server-issued nonce inside `message`, and retire it after one use.** A login built
without one is permanently replayable by anyone who ever sees a signature — including the relay
operator, or anyone reading it out of an OP_RETURN. Including the origin and an issued-at timestamp
is also good practice, but the nonce is the part that actually stops replay.

### Cancellation

Pass an `AbortSignal`, exactly as with `signTransaction`. There is no default timeout: a user
approving on a phone may take a while, and picking an arbitrary deadline for them is worse than
letting the dapp decide.

```typescript
const controller = new AbortController();
const promise = manager.signMessage({ message }, { signal: controller.signal });
// user closes the dialog:
controller.abort("User cancelled");
```

### Verifying elsewhere

`@wizardconnect/core` exports the verification helpers, so a server (or any third party) can check a
signature without a session:

```typescript
import {
  verifyMessageSignatureForAddress,
  messageSignatureAddress,
} from "@wizardconnect/core";

verifyMessageSignatureForAddress(message, signature, address);  // the Electron Cash-equivalent check
messageSignatureAddress(message, signature);                    // recover the address instead
```

Accepts CashAddr with or without a prefix, and legacy base58. Rejects P2SH — no message signature can
prove control of a script hash.

---

## Using initiateDappRelay without DappConnectionManager

If you need lower-level control (e.g., in the test-cli), you can work directly with the
`RelayClient` and handle `wallet_ready` manually:

```typescript
const relay = initiateDappRelay(statusCallback, options);

relay.events.on("keyexchangecomplete", async (walletPubkey) => {
  // Key exchange done — wait for relay client to be fully ready
  while (!relay.client.isKeyExchangeComplete()) {
    await sleep(50);
  }

  relay.client.on("message", (msg) => {
    if (isDappReadyMessage(msg)) { /* ... */ }
    if (isWalletReadyMessage(msg)) { /* ... */ }
  });

  await relay.client.relay({ action: RelayMsgAction.DappReady, ... });
});
```

## Using with React

For React dapps, prefer the `useWizardConnect` hook from `@wizardconnect/react` over
managing the relay lifecycle manually. The hook handles session persistence, auto-reconnect,
and relay cleanup automatically. See [react.md](react.md).

Dapps that need a custom wallet adapter (e.g. Cauldron, Moria) can use the hook and wrap
the returned `manager` in their adapter:

```typescript
const wc = useWizardConnect({ dappName: "My Dapp" });

useEffect(() => {
  if (!wc.manager) return;
  const wallet = new MyWalletAdapter(wc.manager);
  // dispatch wallet to your store
}, [wc.manager]);
```

The `DappConnectionManager` is created by the hook; the adapter receives it rather than
creating its own.