Session Management & Persistence (NDK Mobile)

@nostr-dev-kit/mobile builds upon the session management provided by @nostr-dev-kit/react by adding persistent storage for user sessions and signers using expo-secure-store. This allows your mobile application to remember logged-in users across restarts.

Core Concepts Recap

• Session State: Managed by useNDKSessions in ndk-hooks (in-memory).
• Persistence: Handled by ndk-mobile using secure storage.

Automatic Persistence with useSessionMonitor

The easiest way to enable session persistence is by using the useSessionMonitor hook provided by ndk-mobile.

• Purpose: Automatically loads saved sessions on app startup and saves changes to the active session whenever it's updated in the useNDKSessions store.
• Usage: Call this hook once near the root of your application, typically within a component that also initializes NDK (e.g., using NDKProvider). It automatically uses the NDK instance provided by the context. You can optionally pass SessionInitOptions to customize how sessions are initialized when loaded from storage.

import React, { useEffect, useState } from 'react';
import NDK from '@nostr-dev-kit/ndk';
import { NDKProvider, useNDKStore } from '@nostr-dev-kit/mobile';
import { useSessionMonitor, NDKCacheAdapterSqlite, bootNDK } from '@nostr-dev-kit/mobile';

const cacheAdapter = new NDKCacheAdapterSqlite('your-app');
cacheAdapter.initialize();

function initializeNDK() {
    const opts: Record<string, unknown> = {}; // Use a more specific type than any

    const ndk = new NDK({
        cacheAdapter,
        explicitRelayUrls: [ /* your default relays */ ],
        clientName: 'your-app',
    });

    // Boot NDK with the most logged-in accounts that ndk-mobile saves for you
    bootNDK(ndk); // Call synchronous boot function

    ndk.connect();

    return ndk;
}

const ndk = initializeNDK();

function AppRoot() {
    const { setNDK } = useNDKStore();

    useEffect(() => setNDK(ndk), []);
    // Optionally pass options to control how restored sessions are initialized
    useSessionMonitor({
        // Example: Don't automatically fetch profiles for restored sessions
        // profile: false,
        // follows: false,
        // muteList: false,
    });

    return (
        <NDKProvider ndk={ndk}>
            {/* Your App Components */}
        </NDKProvider>
    );
}

How it works:

1. On Mount: useSessionMonitor retrieves the ndk instance using the useNDK hook. It then calls loadSessionsFromStorage (asynchronously) to retrieve saved sessions.
2. It iterates through the stored sessions (most recent first):
   • Gets the NDKUser instance using ndk.getUser().
   • If a signerPayload exists, it calls ndkSignerFromPayload (asynchronously) to deserialize the signer.
   • Calls initSession (from ndk-hooks) for each user, passing the ndk instance, user, optional signer, and merging any provided sessionInitOptions with the default autoSetActive: isFirst logic. This populates the useNDKSessions store.
3. On Active Session Change: The hook subscribes to changes in useNDKSessions.activeSessionPubkey. When the active session changes:
   • It retrieves the full active session data using getActiveSession().
   • It accesses the signer directly from the session data.
   • It serializes the signer using signer.toPayload().
   • It calls addOrUpdateStoredSession (asynchronously) to save the pubkey, serialized signerPayload, and update the lastActive timestamp in secure storage.
4. On Session Removal: The hook monitors the sessions map from useNDKSessions. When a session is detected as removed (comparing current vs. previous state), it calls removeStoredSession (asynchronously) to delete the session from secure storage.

Logging In / Starting a New Session

This is the standard method for logging a user into your application and establishing their active session. It's typically performed after a successful login event, such as obtaining credentials via NIP-07, NIP-46 (Nostr Connect), or directly using a private key. This involves:

1. Getting the NDKUser: Obtain the NDKUser object for the logged-in user, usually via ndk.getUser({ npub }) or ndk.getUser({ hexpubkey }).
2. Getting the NDKSigner: Obtain the appropriate NDKSigner instance (e.g., Nip07Signer, Nip46Signer, PrivateKeySigner).
3. Calling initSession: Use the initSession function exported from @nostr-dev-kit/react (and re-exported by ndk-mobile) to add the user and signer to the session store.

import { useNDK } from "@nostr-dev-kit/react";
import { useNDKSessions } from "@nostr-dev-kit/react";
import { NDKUser, NDKPrivateKeySigner } from "@nostr-dev-kit/ndk";
import React from 'react';

// Assume you have obtained the user's private key after login
const userPrivateKey = "nsec..."; // Replace with actual private key logic

function LoginButton() {
    const { ndk } = useNDK();
    const { initSession, setActiveSession } = useNDKSessions();

    const handleLogin = async () => {
        if (!ndk || !userPrivateKey) return;

        try {
            // 1. Create the signer
            const signer = new NDKPrivateKeySigner(userPrivateKey);

            // 2. Get the NDKUser associated with the signer
            const user: NDKUser = await signer.user();
            await user.fetchProfile(); // Optional: Fetch profile details

            // 3. Initialize the session in the store
            //    - Pass ndk, user, and signer.
            //    - Set autoSetActive to true if you want this to be the main session immediately.
            initSession(ndk, user, signer, true);

            // Alternatively, if you initSession with autoSetActive: false,
            // you can activate it later:
            // setActiveSession(user.pubkey);

            console.log(`Session initialized for user: ${user.npub}`);

            // If useSessionMonitor is active, this session will now be persisted.

        } catch (error) {
            console.error("Failed to initialize session:", error);
            // Handle login error
        }
    };

    return <button onClick={handleLogin}>Login with Private Key</button>;
}

Important Notes:

• If you are using useSessionMonitor, calling initSession will trigger the monitor to persist the newly added session automatically.
• Ensure you handle signer creation securely, especially when dealing with private keys.
• The ndk instance must be available when calling initSession. Make sure your component is within the NDKProvider context or has access to the initialized NDK instance.