> ## 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.

# RTCEngineIMDelegate

> iOS (Objective-C) callback protocol for IM (out-of-channel messaging): connection success, reconnecting, reconnected, disconnect, and incoming IM messages. Read when handling IM connection state or messages on iOS.

## Connection callbacks

### onImConnectSucceed:sessionId:()

`- (void)onImConnectSucceed:(NSString *)userId sessionId:(NSString *)sessionId`

Called when the connection succeeds.

After you call `enableImWithToken:()` to enable IM (out-of-channel messaging), you receive this event once the connection succeeds. If an error occurs, the SDK fires the `onImDisconnected:errCode:errMsg:()` callback.

**Parameters**

| userId | User ID |
| - | - |
| sessionId | Session ID |

### onImReconnecting()

`- (void)onImReconnecting`

Called when reconnection starts.

Triggered when the connection drops and reconnection begins. If an error occurs, the SDK fires the `onImDisconnected:errCode:errMsg:()` callback.

### onImReconnected()

`- (void)onImReconnected`

Called when reconnection succeeds.

Triggered after the connection is restored. If an error occurs, the SDK fires the `onImDisconnected:errCode:errMsg:()` callback.

### onImDisconnected:errCode:errMsg:()

`- (void)onImDisconnected:(RTCImDisconnectReason)reason errCode:(RTCEngineError)errCode errMsg:(nullable NSString *)errMsg`

Called when the connection drops or is closed involuntarily.

When the reason is `RTCImDisconnectReasonError`, the SDK has hit an unrecoverable error, such as an authentication failure. You need to get a new token before enabling the IM service again. For error codes, see [Error codes](/en/rtc/ios/error-codes).

When the reason is anything other than `RTCImDisconnectReasonError`, the connection was closed involuntarily. For the specific reasons, see [RTCImDisconnectReason](/en/rtc/ios/types#rtcimdisconnectreason).

**Parameters**

| reason | Disconnect reason |
| - | - |
| errCode | Error code |
| errMsg | Error message |

## Message callbacks

### onImMessage:action:userId:sessionId:nickname:()

`- (void)onImMessage:(NSString *)content action:(NSString *)action userId:(nullable NSString *)userId sessionId:(nullable NSString *)sessionId nickname:(nullable NSString *)nickname`

Called when a message arrives.

When your app's business features send a message through the backend API, the SDK notifies you through this callback.

**Parameters**

| content | Message content |
| - | - |
| action | Message action |
| userId | User ID |
| sessionId | Session ID |
| nickname | User nickname |