midnight-dapp-dev:dapp-connector

DApp Connector API v4.0.1

This skill covers the Midnight DApp Connector API for browser-based wallet integration: connecting to the Lace wallet extension, using the ConnectedAPI for transactions and balances, handling errors, and building React 19.x / Next.js 16.x DApps. For Node.js CLI deployment with WalletFacade and HD keys, see midnight-dapp-dev:midnight-sdk. For contract runtime and witness types, see compact-core:compact-witness-ts. For local development network setup, see midnight-tooling:devnet.

Connection Lifecycle

window.midnight.mnLace  ->  InitialAPI.connect(networkId)  ->  ConnectedAPI
     (injected)                                                (WalletConnectedAPI & HintUsage)

1. Detect -- Check window.midnight?.mnLace for the injected wallet object. For TypeScript window augmentation, see references/connector-api-types.md.
2. Connect -- Call connect(networkId) with the target network ("undeployed", "preview", or "preprod")
3. Interact -- Use the returned ConnectedAPI for addresses, balances, transfers, and proving

InitialAPI

The wallet extension injects an InitialAPI object at window.midnight.{walletId}. For the Lace wallet, the identifier is mnLace:

import type { InitialAPI } from "@midnight-ntwrk/dapp-connector-api";

const wallet: InitialAPI | undefined = window.midnight?.mnLace;

Property	Type	Description
name	string	Wallet display name
icon	string	Wallet icon URL
apiVersion	string	Semver version of the connector API
rdns	string	Reverse DNS identifier for the wallet
connect(networkId)	(networkId: string) => Promise<ConnectedAPI>	Initiates the connection handshake

Calling connect() triggers the Lace authorization prompt. The user chooses "Always" (persistent across sessions) or "Only once" (single-session permission).

ConnectedAPI

ConnectedAPI is the intersection of WalletConnectedAPI and HintUsage:

type ConnectedAPI = WalletConnectedAPI & HintUsage;

HintUsage

interface HintUsage {
  hintUsage(methodNames: string[]): void;
}

Call hintUsage to pre-declare which methods the DApp intends to use. This allows the wallet to optimize permission prompts.

WalletConnectedAPI (16 methods)

Method	Returns	Purpose
getConfiguration()	Configuration	indexerUri, indexerWsUri, substrateNodeUri, networkId
getConnectionStatus()	ConnectionStatus	connected or disconnected
getShieldedAddresses()	{shieldedAddress, shieldedCoinPublicKey, shieldedEncryptionPublicKey}	All Bech32m-encoded
getUnshieldedAddress()	{unshieldedAddress}	Bech32m-encoded
getDustAddress()	{dustAddress}	Bech32m-encoded
getShieldedBalances()	Record<string, bigint>	Token type to balance mapping
getUnshieldedBalances()	Record<string, bigint>	Token type to balance mapping
getDustBalance()	{balance, cap}	Current balance and max cap from NIGHT staking
getTxHistory(page, size)	HistoryEntry[]	txHash, txStatus per entry
makeTransfer(outputs, options?)	{tx}	Create a balanced transfer transaction
makeIntent(inputs, outputs, options)	{tx}	Create an unbalanced intent for swaps
balanceUnsealedTransaction(tx, options?)	{tx}	Balance a transaction from a contract call
balanceSealedTransaction(tx, options?)	{tx}	Balance a sealed transaction for swap completion
submitTransaction(tx)	void	Submit a balanced and proven transaction
signData(data, options)	Signature	Sign arbitrary data with the unshielded key
getProvingProvider(keyMaterialProvider)	ProvingProvider	Delegate ZK proving to the wallet

All WalletConnectedAPI methods are async and return Promise<...> wrappers around the types shown above.

Configuration Object

getConfiguration() returns the network endpoints the wallet is connected to:

interface Configuration {
  indexerUri: string;       // GraphQL HTTP endpoint
  indexerWsUri: string;     // GraphQL WebSocket endpoint
  substrateNodeUri: string; // Substrate node RPC
  networkId: string;        // "undeployed", "preview", or "preprod"
}

Use these values to configure SDK providers instead of hardcoding endpoints. This respects the user's network selection and is the recommended privacy-preserving approach.

Error Handling

All DApp Connector errors use a discriminated type (not class instances):

interface APIError {
  type: "DAppConnectorAPIError";
  code: ErrorCode;
  reason: string;
}

type ErrorCode =
  | "Disconnected"
  | "InternalError"
  | "InvalidRequest"
  | "PermissionRejected"
  | "Rejected";

Check errors by type field, not instanceof:

try {
  const api = await wallet.connect("preview");
} catch (error: unknown) {
  if (
    typeof error === "object" &&
    error !== null &&
    "type" in error &&
    (error as APIError).type === "DAppConnectorAPIError"
  ) {
    const apiError = error as APIError;
    switch (apiError.code) {
      case "PermissionRejected":
        console.error("User rejected the connection request");
        break;
      case "Disconnected":
        console.error("Wallet disconnected");
        break;
      case "InternalError":
        console.error("Wallet internal error:", apiError.reason);
        break;
      case "InvalidRequest":
        console.error("Invalid request:", apiError.reason);
        break;
      case "Rejected":
        console.error("Request rejected:", apiError.reason);
        break;
    }
  }
}

Never use instanceof for DApp Connector errors. The error objects are plain objects serialized across the extension boundary, so instanceof checks always fail.

Lace Wallet Setup

Installation

1. Install the Lace wallet extension from the Chrome Web Store
2. If using Brave, disable Brave Shields for the DApp origin (shields interfere with extension injection)
3. Open Lace and create a new wallet
4. Save the seed phrase securely -- this is the only way to recover the wallet
5. Set a spending password

Network Selection

Lace supports three networks:

Network	Network ID	Use Case
Undeployed	undeployed	Local development with Docker containers
Preview	preview	Public testnet for integration testing
Preprod	preprod	Pre-production testing

Select the network in Lace settings. The "Undeployed" network connects to localhost endpoints matching the local Docker stack.

Funding

1. Copy the unshielded address from Lace
2. Navigate to the network faucet (e.g., https://faucet.preview.midnight.network)
3. Request tDUST tokens
4. Delegate NIGHT tokens in Lace to begin DUST generation
5. Wait for DUST to accumulate (used for transaction fees)

Authorization Modes

When a DApp calls connect(), Lace prompts the user:

• Always -- Persistent authorization across browser sessions for this DApp origin
• Only once -- Single-session authorization; re-prompts after page refresh or browser restart

React 19.x Integration Pattern

Wallet Connection Hook

"use client";
import { useState, useCallback, useEffect } from "react";
import type { InitialAPI, ConnectedAPI } from "@midnight-ntwrk/dapp-connector-api";

interface WalletState {
  connectedApi: ConnectedAPI | null;
  isConnecting: boolean;
  error: string | null;
}

export function useWalletConnection() {
  const [state, setState] = useState<WalletState>({
    connectedApi: null,
    isConnecting: false,
    error: null,
  });

  const connect = useCallback(async (networkId: string) => {
    setState((prev) => ({ ...prev, isConnecting: true, error: null }));

    const wallet: InitialAPI | undefined = window.midnight?.mnLace;
    if (!wallet) {
      setState((prev) => ({
        ...prev,
        isConnecting: false,
        error: "Lace wallet extension not found. Install it from the Chrome Web Store.",
      }));
      return;
    }

    try {
      const api = await wallet.connect(networkId);
      setState({ connectedApi: api, isConnecting: false, error: null });
    } catch (err: unknown) {
      const message =
        typeof err === "object" && err !== null && "reason" in err
          ? (err as { reason: string }).reason
          : "Failed to connect to wallet";
      setState((prev) => ({ ...prev, isConnecting: false, error: message }));
    }
  }, []);

  const disconnect = useCallback(() => {
    setState({ connectedApi: null, isConnecting: false, error: null });
  }, []);

  return { ...state, connect, disconnect };
}

Wallet Balance Component

"use client";
import { useState, useEffect } from "react";
import type { ConnectedAPI } from "@midnight-ntwrk/dapp-connector-api";

export function WalletBalances({ api }: { api: ConnectedAPI }) {
  const [shielded, setShielded] = useState<Record<string, bigint>>({});
  const [unshielded, setUnshielded] = useState<Record<string, bigint>>({});

  useEffect(() => {
    const fetchBalances = async () => {
      const [s, u] = await Promise.all([
        api.getShieldedBalances(),
        api.getUnshieldedBalances(),
      ]);
      setShielded(s);
      setUnshielded(u);
    };
    fetchBalances();
  }, [api]);

  return (
    <div>
      <h3>Shielded</h3>
      {Object.entries(shielded).map(([token, balance]) => (
        <p key={token}>{token}: {balance.toString()}</p>
      ))}
      <h3>Unshielded</h3>
      {Object.entries(unshielded).map(([token, balance]) => (
        <p key={token}>{token}: {balance.toString()}</p>
      ))}
    </div>
  );
}

Next.js 16.x Patterns

Client-Only Wallet Access

The window object is undefined during server-side rendering. All wallet access must be in Client Components:

"use client";

import { useEffect, useState } from "react";

function WalletDetector() {
  const [walletAvailable, setWalletAvailable] = useState(false);

  useEffect(() => {
    // window.midnight is only available in the browser
    setWalletAvailable(window.midnight?.mnLace !== undefined);
  }, []);

  if (!walletAvailable) {
    return <p>Install the Lace wallet extension to continue.</p>;
  }

  return <p>Lace wallet detected.</p>;
}

Dynamic Import for Wallet Modules

For modules that reference window at import time, use next/dynamic with SSR disabled:

import dynamic from "next/dynamic";

const WalletPanel = dynamic(() => import("./WalletPanel"), { ssr: false });

Using getConfiguration() for Provider Endpoints

Instead of hardcoding network endpoints, read them from the wallet's configuration. This ensures the DApp uses the same network the user selected in Lace:

"use client";

import type { ConnectedAPI } from "@midnight-ntwrk/dapp-connector-api";
import { indexerPublicDataProvider } from "@midnight-ntwrk/midnight-js-indexer-public-data-provider";

async function createProvidersFromWallet(api: ConnectedAPI) {
  const config = await api.getConfiguration();

  const publicDataProvider = indexerPublicDataProvider(
    config.indexerUri,
    config.indexerWsUri,
  );

  // Use config.substrateNodeUri for node connections
  // Use config.networkId for setNetworkId()
  return { publicDataProvider, networkId: config.networkId };
}

Building MidnightProviders from DApp Connector

In the browser, the DApp Connector replaces the Node.js WalletFacade. The ConnectedAPI provides the wallet and midnight provider capabilities:

import type { WalletProvider, MidnightProvider } from "@midnight-ntwrk/midnight-js-types";
import type { ConnectedAPI } from "@midnight-ntwrk/dapp-connector-api";

async function createWalletProvider(api: ConnectedAPI): Promise<WalletProvider> {
  const { shieldedCoinPublicKey, shieldedEncryptionPublicKey } =
    await api.getShieldedAddresses();

  return {
    getCoinPublicKey: () => shieldedCoinPublicKey,
    getEncryptionPublicKey: () => shieldedEncryptionPublicKey,
    balanceTx: async (tx, newCoins, ttl) => {
      const result = await api.balanceUnsealedTransaction(tx, { newCoins, ttl });
      return result.tx;
    },
  };
}

function createMidnightProvider(api: ConnectedAPI): MidnightProvider {
  return {
    submitTx: async (tx) => {
      await api.submitTransaction(tx);
      return tx.txId;
    },
  };
}

For the complete browser provider assembly including FetchZkConfigProvider and in-memory private state, see references/browser-providers.md. For the full type reference of all DApp Connector interfaces, see references/connector-api-types.md.

Common Mistakes

Mistake	Fix
Accessing window.midnight during SSR	Guard with "use client" directive and useEffect or typeof window !== "undefined" checks
Using instanceof for error checking	Check error.type === "DAppConnectorAPIError" instead
Hardcoding network endpoints	Use getConfiguration() to read the wallet's active endpoints
Not handling PermissionRejected	Users can deny the connection prompt; always handle this error code
Forgetting to fund the wallet	Transfer tDUST from faucet and delegate NIGHT for DUST generation before transacting
Using Brave without disabling shields	Brave Shields blocks extension injection; disable for the DApp origin

Reference Files

Topic	Reference File
Complete type definitions for InitialAPI, ConnectedAPI, WalletConnectedAPI, all method signatures, Configuration, ErrorCode	references/connector-api-types.md
Full browser provider assembly pattern, FetchZkConfigProvider, in-memory private state, wallet-to-SDK bridge	references/browser-providers.md