Teams App Developer

state.storage-patterns-ts

purpose

State management with IStorage interface, LocalStorage, and per-user/per-conversation state patterns in Teams bots.

rules

1. Use the IStorage interface (get/set/delete) for all state management. It supports both synchronous and async implementations, so custom backends (Redis, Cosmos DB) can return Promises. github.com/microsoft/teams.ts

2. LocalStorage from @microsoft/teams.common is an in-memory store with optional LRU eviction. Pass { max: N } to cap entries and prevent unbounded memory growth in long-running bots. github.com/microsoft/teams.ts

3. Pass storage to the App constructor via the storage option. The storage instance is then available as ctx.storage in all route handlers. github.com/microsoft/teams.ts

4. For per-user state, key on activity.from.id (or activity.from.aadObjectId for AAD-stable IDs). For per-conversation state, key on activity.conversation.id. Choose the right scope for your data. learn.microsoft.com -- Bot state

5. When combining state with ChatPrompt, pass the user's stored messages array to the prompt's messages option. This restores conversation history across handler invocations. github.com/microsoft/teams.ts

6. Initialize state lazily: check if state exists for the key, and if not, create a default state object and store it. This avoids null reference errors on first interaction. github.com/microsoft/teams.ts

7. LocalStorage is volatile -- data is lost on process restart. For production bots, implement IStorage backed by a persistent store (Azure Cosmos DB, Redis, SQL). learn.microsoft.com -- Bot state management

8. Keep state objects small. Store only what is needed (message history, preferences, session flags). Large state objects increase memory pressure and serialization cost for persistent backends. github.com/microsoft/teams.ts

9. The IStorage generic signature is IStorage<TKey, TValue>. Type both the key and value for compile-time safety. For example, new LocalStorage<IUserState>() types the value while using string keys. github.com/microsoft/teams.ts

10. Do not rely on in-memory state in multi-instance deployments (e.g., Azure App Service with multiple instances or containers). Each instance has its own LocalStorage. Use a shared persistent store instead. learn.microsoft.com -- Scale out

patterns

Per-user state with ChatPrompt message history

import { App } from '@microsoft/teams.apps';
import { ChatPrompt, LocalMemory, Message } from '@microsoft/teams.ai';
import { OpenAIChatModel } from '@microsoft/teams.openai';
import { LocalStorage, ConsoleLogger } from '@microsoft/teams.common';
import { DevtoolsPlugin } from '@microsoft/teams.dev';

const model = new OpenAIChatModel({
  apiKey: process.env.OPENAI_API_KEY,
  model: 'gpt-4o',
});

interface IUserState {
  messages: Message[];
  preferences: Record<string, any>;
}

const userStore = new LocalStorage<IUserState>({}, {
  max: 1000, // LRU eviction after 1000 users
});

const app = new App({
  logger: new ConsoleLogger('state-bot', { level: 'debug' }),
  plugins: [new DevtoolsPlugin()],
});

app.on('message', async ({ activity, send }) => {
  const userId = activity.from.id;

  // Lazy initialization: create state if it does not exist
  let state = userStore.get(userId);
  if (!state) {
    state = { messages: [], preferences: {} };
    userStore.set(userId, state);
  }

  const prompt = new ChatPrompt({
    model,
    instructions: 'You are a helpful assistant.',
    messages: state.messages, // Restore conversation history
  });

  const result = await prompt.send(activity.text);
  if (result.content) {
    await send(result.content);
  }
});

app.start(3978);

Per-conversation state with App storage

import { App } from '@microsoft/teams.apps';
import { ChatPrompt, Message } from '@microsoft/teams.ai';
import { OpenAIChatModel } from '@microsoft/teams.openai';
import { LocalStorage, ConsoleLogger } from '@microsoft/teams.common';
import { DevtoolsPlugin } from '@microsoft/teams.dev';

const model = new OpenAIChatModel({
  apiKey: process.env.OPENAI_API_KEY,
  model: 'gpt-4o',
});

interface IConversationState {
  messages: Message[];
  topicCount: number;
}

// Pass storage to App -- available as ctx.storage in handlers
const storage = new LocalStorage<IConversationState>({}, { max: 500 });

const app = new App({
  storage,
  logger: new ConsoleLogger('conv-bot'),
  plugins: [new DevtoolsPlugin()],
});

app.on('message', async ({ activity, send, storage }) => {
  const convId = activity.conversation.id;

  let state = storage.get(convId) as IConversationState | undefined;
  if (!state) {
    state = { messages: [], topicCount: 0 };
    storage.set(convId, state);
  }

  const prompt = new ChatPrompt({
    model,
    instructions: 'You are a helpful assistant. Be concise.',
    messages: state.messages,
  });

  const result = await prompt.send(activity.text);
  if (result.content) {
    state.topicCount++;
    await send(result.content);
  }
});

app.start(3978);

IStorage interface for custom backends

import { IStorage } from '@microsoft/teams.common';

// Example: custom Redis-backed storage implementing IStorage
class RedisStorage<T> implements IStorage<string, T> {
  private client: any; // Your Redis client

  constructor(redisClient: any) {
    this.client = redisClient;
  }

  async get(key: string): Promise<T | undefined> {
    const raw = await this.client.get(`bot:state:${key}`);
    return raw ? JSON.parse(raw) : undefined;
  }

  async set(key: string, value: T): Promise<void> {
    await this.client.set(`bot:state:${key}`, JSON.stringify(value));
  }

  async delete(key: string): Promise<void> {
    await this.client.del(`bot:state:${key}`);
  }
}

// Usage with App
// const storage = new RedisStorage<IConversationState>(redisClient);
// const app = new App({ storage });

pitfalls

• Unbounded LocalStorage: Not setting max on LocalStorage allows the store to grow without limit, eventually exhausting process memory. Always specify a max entry count.

• Data loss on restart: LocalStorage is in-memory only. Restarting the process loses all state. Use a persistent backend (Cosmos DB, Redis) for production bots.

• Wrong state key scope: Using activity.from.id when you want conversation-scoped state (or vice versa) causes data to bleed across contexts. Use activity.conversation.id for conversation state and activity.from.id for user state.

• Mutating state without re-setting: If your IStorage backend uses serialization (e.g., Redis), mutating the returned object does not persist changes. Call storage.set(key, state) after modifications.

• Large message history: Passing the entire message history to ChatPrompt without a max limit on LocalMemory can exceed token limits. Use LocalMemory with max and collapse for automatic summarization.

• Multi-instance deployments with LocalStorage: Each process instance has its own in-memory store. In scaled deployments, a user may hit different instances, seeing inconsistent state.

• Missing null check on get(): storage.get(key) returns undefined if the key does not exist. Always check for undefined and initialize before accessing properties.

references

• Teams AI Library v2 -- GitHub

• Bot state management concepts

• Azure Cosmos DB for state storage

• Teams bot conversation context

instructions

This expert covers state management and storage patterns for Teams bots built with the Teams AI Library v2 (@microsoft/teams.ts) in TypeScript. Use it when you need to:

• Understand the IStorage interface (get/set/delete) and implement custom backends

• Configure LocalStorage with LRU eviction limits

• Pass storage to the App constructor and access it in handlers via ctx.storage

• Implement per-user state keyed on activity.from.id

• Implement per-conversation state keyed on activity.conversation.id

• Combine stored message history with ChatPrompt for multi-turn conversations

Pair with ai.memory-localmemory-ts.md for LocalMemory (AI message memory with summarization) and auth.oauth-sso-ts.md for authenticated state patterns. Pair with ai.memory-localmemory-ts.md for combining state with AI conversation history, and runtime.app-init-ts.md for passing storage to the App constructor.

research

Deep Research prompt:

"Write a micro expert on state and storage patterns for Teams SDK v2 bots (TypeScript). Cover IStorage interface, LocalStorage with LRU eviction, per-user and per-conversation state, combining state with ChatPrompt messages, implementing custom persistent backends (Redis, Cosmos DB), and warnings about multi-instance deployments. Include 2-3 TypeScript code examples."