Providers

The Midnight SDK requires six providers to deploy and interact with a contract. Kosh configures them in src/dapp/providers.ts with two separate factory functions: one for the browser (backed by the Lace wallet) and one for Node.js scripts.

The Six Providers

Provider	Interface	Purpose
privateStateProvider	PrivateStateProvider	Reads/writes member secrets
publicDataProvider	PublicDataProvider	Queries ledger state via Indexer GraphQL
zkConfigProvider	ZKConfigProvider	Loads ZK circuit keys
proofProvider	ProofProvider	Sends circuit inputs to the remote proof server
walletProvider	WalletProvider	Balances and signs transactions via Lace
midnightProvider	MidnightProvider	Submits signed transactions to the node

The first four are infrastructure providers. The last two are backed by the user's connected Lace wallet and are required for any operation that moves funds or modifies on-chain state.

Browser Providers

In the browser, all six providers are created by createBrowserProviders():

import { createBrowserProviders } from '@/dapp/providers';
import type { ConnectedAPI } from '@midnight-ntwrk/dapp-connector-api';

const providers = await createBrowserProviders(connectedApi);

This calls createAllBrowserProviders() from src/dapp/lace-providers.ts, which wraps the Lace ConnectedAPI into the SDK provider interfaces:

• walletProvider — delegates balanceTx to api.balanceUnsealedTransaction()
• midnightProvider — delegates submitTx to api.submitTransaction()
• zkConfigProvider — fetches ZK keys from /build/keys/ and /build/zkir/ (served statically)
• proofProvider — sends proof requests to https://proof-server.preprod.midnight.network
• publicDataProvider — reads state from the preprod Indexer GraphQL endpoint
• privateStateProvider — stores member secrets in-memory during the browser session

// src/dapp/lace-providers.ts (simplified)
export async function createAllBrowserProviders(
  connectedApi: ConnectedAPI,
  indexerUri: string,
): Promise<KoshProviders> {
  return {
    walletProvider:       createWalletProvider(connectedApi),
    midnightProvider:     createMidnightProvider(connectedApi),
    zkConfigProvider:     createBrowserZkConfigProvider('/build'),
    proofProvider:        createBrowserProofProvider(ENV.PROOF_SERVER_URL),
    publicDataProvider:   createBrowserPublicDataProvider(indexerUri),
    privateStateProvider: createInMemoryPrivateStateProvider(),
  };
}

Node.js Providers (Local Dev)

For deploy scripts and integration tests, createProviders() returns Node.js-compatible providers:

import { createProviders } from '@/dapp/providers';

const providers = await createProviders(
  './build',          // Path to Compact compiler output
  '~/.kosh/state',    // LevelDB path for private state
);

These use:

• levelPrivateStateProvider — LevelDB on the local filesystem
• NodeZkConfigProvider — loads keys from build/keys/ and build/zkir/
• HttpClientProofProvider — HTTP client to the proof server (local Docker at :6300 or remote)
• IndexerPublicDataProvider — GraphQL client to the Indexer

The Node.js providers do not include walletProvider or midnightProvider — these must be supplied separately when running against a real network.

Environment Variables

All endpoint URLs are configurable via .env.local:

NEXT_PUBLIC_INDEXER_URL=https://indexer.preprod.midnight.network/api/v3/graphql
NEXT_PUBLIC_INDEXER_WS_URL=wss://indexer.preprod.midnight.network/api/v3/graphql/ws
NEXT_PUBLIC_NODE_URL=https://rpc.preprod.midnight.network
NEXT_PUBLIC_PROOF_SERVER_URL=https://proof-server.preprod.midnight.network
NEXT_PUBLIC_NETWORK_ID=preprod

If no .env.local is present, these preprod network defaults are used. For local Docker dev, override with localhost URLs and set NEXT_PUBLIC_NETWORK_ID=undeployed.

Lace Wallet Config

On wallet connect, Kosh saves the wallet's own endpoint configuration to sessionStorage:

const cfg = await api.getConfiguration();
sessionStorage.setItem('kosh:wallet:config', JSON.stringify(cfg));

getLaceConfig() reads this to ensure publicDataProvider uses the same Indexer endpoint as the wallet — keeping them in sync regardless of .env.local.

Network ID

The network ID must be set once before any SDK calls:

import { setNetworkId } from '@midnight-ntwrk/midnight-js-network-id';

setNetworkId('preprod');  // Set at module load time in providers.ts

The network ID affects shielded address encoding and is validated by the Lace wallet. Use preprod for the beta testnet, undeployed for local Docker dev.