> ## Documentation Index
> Fetch the complete documentation index at: https://docs.stmlink.com/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> 对外开放的服务端接口有两组前缀，都用同一套鉴权：`/server/v1/...`（SRTC 与 SMeeting 的主接口）和 `/stm/srvapi/v1/...`（SMeeting 的用户体系，服务端极简对接会用到）。鉴权是 app_id + nonce + timestamp + signature 四个请求头，用 app_key 做 HMAC-SHA256 签名，只能从业务方自己的后端调用。除这两组前缀外的接口均为内部接口，不要建议客户调用。 Public server APIs use two path prefixes with the same authentication: `/server/v1/...` (the main APIs of both SRTC and SMeeting) and `/stm/srvapi/v1/...` (the SMeeting user system, used by server-side low-code integration). Authenticate with four request headers, app_id + nonce + timestamp + signature, where signature is HMAC-SHA256 keyed with app_key; call these APIs only from the customer's own backend. Any other path is internal: never suggest calling it.
> app_key 是服务端密钥，绝不能出现在客户端代码、前端配置或移动 App 里。客户端加入频道用的 token 必须由业务方后端签发后下发（SRTC 走 `/server/v1/channel/grant`，SMeeting 走 `/stm/srvapi/v1/member/grant`）。 app_key is a server-side secret and must never appear in client code, frontend config, or a mobile app. The token a client uses to join must be issued by the customer's backend and passed down to the client (SRTC: `/server/v1/channel/grant`; SMeeting: `/stm/srvapi/v1/member/grant`).
> SRTC 与 SMeeting 是上下两层不同的产品，术语不通用：SRTC 是音视频底座，说「频道 channel」「加入 / 退出」；SMeeting 建在 SRTC 之上，说「房间 room」「会议 meeting」「进入 / 退出」。回答时按用户所在的层用对应术语，不要把「房间」「会议」安到 SRTC 的接口上，也不要用「频道」「加入 / 离开」描述 SMeeting 的概念（接口标识符原样保留）。 SRTC and SMeeting are two separate layers with different terminology. SRTC is the audio/video foundation: it has channels, and users join and leave a channel. SMeeting is built on top of SRTC: it has rooms and meetings, and members enter and exit a meeting. Answer in the terms of the layer the user is working with: never apply "room" or "meeting" to SRTC APIs, and never describe SMeeting concepts in prose with "channel", "join", or "leave" (API identifiers such as `force_join` keep their literal names).
> 同一能力在各端 SDK 里的包名、类名、方法名并不相同。写示例代码时请使用文档中该端自己的 API，不要把一个端的写法套到另一个端上。苹果平台每个产品都有两套 SDK（Swift 原生与 Objective-C），两套 API 不能混用。 Package, class, and method names differ between platform SDKs for the same capability. In sample code, use the API documented for that platform; never carry one platform's code over to another. On Apple platforms each product ships two SDKs (native Swift and Objective-C) whose APIs must not be mixed.

# IM

> Use out-of-channel IM messages in the Objective-C SRTC SDK on iOS: enable IM with a token via enableImWithToken:delegate:, implement RTCEngineIMDelegate connection, reconnection, disconnection, and message callbacks, then disable IM and release resources.

### Step 1: Initialize the SDK

You must initialize the SDK before calling any other SDK function. For details, see [SDK initialization](/en/rtc/ios/quickstart#step-1-initialize-the-sdk).

### Step 2: Enable IM

#### Get a token

To enable the SDK's IM (out-of-channel messaging) service, first get an authentication token through the server API, then establish the messaging connection with the following API.

```objectivec theme={null}
RTCEngineError errorCode = [[RTCEngineKit sharedEngine] enableImWithToken:@"Your Token" delegate:self];
if (errorCode != RTCEngineErrorOK) {
    NSLog(@"Failed to establish the IM connection");
}
```

#### Set the delegate

To subscribe to delegate events, you must create an instance of `RTCEngineIMDelegate` and make your class conform to the `RTCEngineIMDelegate` protocol.

```objectivec theme={null}
@interface YourClass : NSObject <RTCEngineIMDelegate>
/// Add any of the following callbacks here as needed.
```

#### Implement the callbacks

* **Connected callback**

```objectivec theme={null}
/// Connected callback
/// You receive this event after calling enableImWithToken:() to enable IM; errors are reported through the onImDisconnected:() event.
/// - Parameters:
///   - userId: user ID
///   - sessionId: session ID
- (void)onImConnectSucceed:(NSString *)userId sessionId:(NSString *)sessionId {
    
    NSLog(@"IM connection established userId = %@, sessionId = %@", userId, sessionId);
}
```

* **Reconnecting callback**

```objectivec theme={null}
/// Reconnecting callback
/// This event means the connection has a problem, such as a network error, and the SDK is trying to reconnect.
- (void)onImReconnecting {
    
    NSLog(@"IM connection lost, the SDK is trying to reconnect.");
}
```

* **Reconnected callback**

```objectivec theme={null}
/// Reconnected callback
/// You receive this event when the connection is restored.
- (void)onImReconnected {
    
    NSLog(@"IM connection restored.");
}
```

* **Disconnected callback**

```objectivec theme={null}
/// Disconnected callback
/// Triggered by an unrecoverable error or an involuntary disconnect; if it's an error, you need to get a new token
/// @param reason leave reason
/// @param errCode error code
/// @param errMsg error message
- (void)onImDisconnected:(RTCImDisconnectReason)reason errCode:(RTCEngineError)errCode errMsg:(nullable NSString *)errMsg {
    
    NSLog(@"IM connection error or passive disconnect, please reconnect reason = %ld, errCode = %ld, errMsg = %@", reason, errCode, errMsg);
}
```

* **Message received callback**

```objectivec theme={null}
/// Message received callback
/// After a message is sent through the backend API, the specified users receive this event.
/// @param content message content
/// @param action message action
/// @param userId user ID
/// @param sessionId session ID
/// @param nickname user nickname
- (void)onImMessage:(NSString *)content action:(NSString *)action userId:(nullable NSString *)userId sessionId:(nullable NSString *)sessionId nickname:(nullable NSString *)nickname {
    
    NSLog(@"IM message received action = %@ content = %@ userId = %@", action, content, userId);
}
```

### Step 3: Disable IM

```objectivec theme={null}
[[RTCEngineKit sharedEngine] disableIm];
```

### Step 4: Release resources

```objectivec theme={null}
[[RTCEngineKit sharedEngine] destroy];
```