# Stream channels (/en/realtime-media/rtm/build/work-with-channels/stream-channel/ios)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

Stream channels are based on the room model. In Signaling, communication through stream channels requires use of specific APIs. This page shows you how to join, leave, and send messages in stream channels.

    ## Understand the tech [#understand-the-tech-2]

    To use stream channels, you first create a stream channel object instance. The channel instance gives you access to all stream channel management methods. Use the stream channel instance to:

    * Join and leave a channel
    * Join and leave topics
    * Subscribe to and unsubscribe from topics
    * Send messages
    * Destroy the channel instance

    After joining a stream channel, you listen to event notifications in the channel. To send and receive messages in the channel, you use [topics](topics). Signaling allows thousands of stream channels to exist simultaneously in your app. However, due to client-side performance and bandwidth limitations, a single client may only join a limited number of channels concurrently. For details, see [API usage restrictions](../../reference/limitations).

    ## Prerequisites [#prerequisites-2]

    Ensure that you have:

    * Integrated the Signaling SDK in your project, and implemented the framework functionality from the [SDK quickstart](../../quickstart) page.

    * Activated the stream channel capability.

      <CalloutContainer type="warning">
        <CalloutTitle>
          Important
        </CalloutTitle>

        <CalloutDescription>
          **Stream channel activation requirements**

          Please note that the activation of Stream Channel functionality in Signaling directly depends on the activation of the 128-host feature in Real-Time Communication (RTC). To ensure proper activation:

          * Submit a formal request to [support@agora.io](mailto\:support@agora.io).
          * Specifically request activation of the 128-host feature.
          * Wait for confirmation before implementing Stream Channel features.

          For further assistance or questions regarding this requirement, please contact [Agora Support](mailto\:support@agora.io).
        </CalloutDescription>
      </CalloutContainer>

    ## Implement communication in a stream channel [#implement-communication-in-a-stream-channel-2]

    This section shows you how to use the Signaling SDK to implement stream channel communication in your app.

    ### Create a stream channel [#create-a-stream-channel-2]

    To use stream channel functionality, call `createStreamChannel` to create a `AgoraRtmStreamChannel` object instance.

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        ```swift
        do {
            let streamChannel = try rtmClient.createStreamChannel("exampleChannel")
            print("Stream channel created successfully: \\(streamChannel)")
            // You can now use the streamChannel instance
        } catch {
            print("Failed to create stream channel: \\(error)")
        }
        ```
      </CodeBlockTab>

      <CodeBlockTab value="Objective-C">
        ```objc
        NSError* create_error = nil;
        AgoraRtmStreamChannel* stream_channel = [rtm createStreamChannel:@"your_channel" error:&create_error];
        ```
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    This method creates only one `AgoraRtmStreamChannel` instance at a time. If you need to create multiple instances, call the method multiple times.

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        ```swift
        do {
            let stream_channel = try RtmClient?.createStreamChannel(channelName1)
            if stream_channel != nil {
                print("create stream channel success");
            }
         } catch let error {
            print("error\\(error)")
        }

        do {
            let stream_channel = try RtmClient?.createStreamChannel(channelName2)
            if stream_channel != nil {
                print("create stream channel success");
            }
         } catch let error {
            print("error\\(error)")
        }
        ```
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        ```objc
        NSError* create_error = nil;
        // Create the first instance
        AgoraRtmStreamChannel* stream_channel1 = [rtm createStreamChannel:@"your_channel1" error:&create_error];
        // Create the second instance
        AgoraRtmStreamChannel* stream_channel2 = [rtm createStreamChannel:@"your_channel2" error:&create_error];
        ```
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    </CodeBlockTabs>

    <CalloutContainer type="info">
      <CalloutDescription>
        Signaling enables you to create unlimited stream channel instances in a single app. However, best practice is to create channels based on your actual requirements to maintain optimal client-side performance. For instance, if you hold multiple stream channel instances, destroy the ones that are no longer in use to prevent resource blocking, and recreate them when they are needed again.
      </CalloutDescription>
    </CalloutContainer>

    ### Join a stream channel [#join-a-stream-channel-2]

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        Call the `join` method on the `AgoraRtmStreamChannel` instance with appropriate options as follows:

        ```swift
        let join_option = AgoraRtmJoinChannelOption();
        join_option.token = "your_token"
        stream_channel.join(join_option, completion: { (res, error) in
            if error != nil {
                print("\\(error?.operation) failed! error reason is \\(error?.reason)")
            } else {
                print("success")
            }
            })
        ```
      </TabsContent>

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        Call the `joinWithOption` method on the `AgoraRtmStreamChannel` instance with appropriate options as follows:

        ```objc
        AgoraRtmJoinChannelOption* join_opt =  [[AgoraRtmJoinChannelOption alloc] init];
        join_opt.token =  @"your_token";
        [stream_channel joinWithOption:join_opt completion:^(AgoraRtmCommonResponse * _Nullable response, AgoraRtmErrorInfo * _Nullable errorInfo) {
            if (errorInfo == nil) {
                NSLog(@"join channel success!!");
            } else {
                NSLog(@"join channel failed, errorCode %d, reason %@", errorInfo.errorCode, errorInfo.reason);
            }
        }];
        ```
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    When joining a channel, set the `token` parameter in `AgoraRtmJoinChannelOption` to a valid temporary token string. For testing purposes, use the [Token Builder ](https://agora-token-generator-demo.vercel.app/).

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        ```swift
        let join_option = AgoraRtmJoinChannelOption();
        join_option.token = "your_token"
        join_option.features = [.presence, .storage]
        stream_channel.join(join_option, completion: { (res, error) in
            if error != nil {
                print("\\(error?.operation) failed! error reason is \\(error?.reason)")
            } else {
                print("success")
            }
            })
        ```
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      <CodeBlockTab value="Objective-C">
        ```objc
        AgoraRtmJoinChannelOption* join_opt =  [[AgoraRtmJoinChannelOption alloc] init];
        join_opt.token =  @"your_token";
        join_opt.features = join_opt.features | AgoraRtmJoinChannelFeatureLock;
        [stream_channel joinWithOption:join_opt completion:^(AgoraRtmCommonResponse * _Nullable response, AgoraRtmErrorInfo * _Nullable errorInfo) {
            if (errorInfo == nil) {
                NSLog(@"join channel success!!");
            } else {
                NSLog(@"join channel failed, errorCode %d, reason %@", errorInfo.errorCode, errorInfo.reason);
            }
        }];
        ```
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    In stream channels, message flow is managed using topics. Even if you configure a global message listener, you must still join a topic to send messages. Similarly, to receive messages you must subscribe to a topic. See [Topics](topics) for more information.

    ### Send a message [#send-a-message-2]

    To send a message to a stream channel:

    * Create an `AgoraRtmStreamChannel` instance.
    * Join a stream channel.
    * Call `joinTopic` to register as a message publisher for the specified topic. See [Topics](topics).

    Call `publishTopicMessage` to publish a message to a topic. This method sends a message to a single topic at a time. To deliver messages to multiple topics, call the method separately for each topic.

    Refer to the following sample code for sending messages:

    * String message

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        ```swift
        let message = "Hello Agora!"

            streamChannel.publishTopicMessage("your_topic", message: message, option: nil) { response, errorInfo in
                if errorInfo == nil {
                    print("publish success!!")
                } else {
                    print("publish failed, errorCode \\(errorInfo!.errorCode), reason \\(errorInfo!.reason)")
                }
            }
        ```
      </CodeBlockTab>

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        ```objc
        // Send a string message
            NSString* message = @"Hello Agora!"; // Message content
            [stream_channel publishTopicMessage:@"your_topic" message:message option:nil completion:^(AgoraRtmCommonResponse * _Nullable response, AgoraRtmErrorInfo * _Nullable errorInfo) {
                if (errorInfo == nil) {
                    NSLog(@"publish success!!");
                } else {
                    NSLog(@"publish failed, errorCode %d, reason %@", errorInfo.errorCode, errorInfo.reason);
                }
            }];
        ```
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    </CodeBlockTabs>

    * Binary message

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        ```swift
        let bytes: [UInt8] = [ /* your raw values */ ]
            let rawMessage = Data(bytes: bytes, count: bytes.count)

            streamChannel.publishTopicMessage("your_topic", data: rawMessage, option: nil) { response, errorInfo in
                if errorInfo == nil {
                    print("publish success!!")
                } else {
                    print("publish failed, errorCode \\(errorInfo!.errorCode), reason \\(errorInfo!.reason)")
                }
            }
        ```
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        ```objc
        // Send a binary message
            unsigned char bytes[32] = { /* your raw values */ }; // Binary message content
            NSData* raw_message = [[NSData alloc] initWithBytes:bytes length:32]; // Creating NSData object with binary message
            [stream_channel publishTopicMessage:@"your_topic" data:raw_message option:nil completion:^(AgoraRtmCommonResponse * _Nullable response, AgoraRtmErrorInfo * _Nullable errorInfo) {
                if (errorInfo == nil) {
                    NSLog(@"publish success!!");
                } else {
                    NSLog(@"publish failed, errorCode %d, reason %@", errorInfo.errorCode, errorInfo.reason);
                }
            }];
        ```
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    In Signaling, a user may register as a message publisher for up to 8 topics concurrently. However, there is no limit on the number of users a single topic can accommodate. You can achieve a message transmission frequency to a topic of up to 120 QPS. This capability is useful in use-cases that demand high-frequency and high-concurrency data processing, such as Metaverse location status synchronization, collaborative office sketchpad applications, and parallel control operation-instructions transmission.

    ### Leave a stream channel [#leave-a-stream-channel-2]

    To leave a channel, call the `leave` method on the `AgoraRtmStreamChannel` instance:

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        ```swift
        stream_channel.leave({ res, error in
            if error != nil {
                print("\\(error?.operation) failed! error reason is \\(error?.reason)")
            } else {
                print("success")
            }
        })
        ```

        To rejoin a stream channel, call the `join` method again. You can join and leave as long as the corresponding `AgoraRtmStreamChannel` instance remains active and is not destroyed.
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        ```objc
        [stream_channel leave:^(AgoraRtmCommonResponse * _Nullable response, AgoraRtmErrorInfo * _Nullable errorInfo) {
            if (errorInfo == nil) {
                NSLog(@"leave channel success!!");
            } else {
                NSLog(@"leave channel failed, errorCode %d, reason %@", errorInfo.errorCode, errorInfo.reason);
            }
        }];
        ```

        To rejoin a stream channel, call the `joinWithOption` method again. You can join and leave as long as the corresponding `AgoraRtmStreamChannel` instance remains active and has not been destroyed.
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    ### Destroy the stream channel instance [#destroy-the-stream-channel-instance-1]

    To destroy the stream channel instance, call `destroy`:

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        ```swift
        stream_channel.destroy();
        stream_channel = nil;
        ```
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        ```objc
        [stream_channel destroy];
        stream_channel = nil;
        ```
      </CodeBlockTab>
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    <CalloutContainer type="info">
      <CalloutDescription>
        Destroying a stream channel removes the `AgoraRtmStreamChannel` instance from your app. This action is local to your app and does not affect other users or the Signaling channel.
      </CalloutDescription>
    </CalloutContainer>

    ## Reference [#reference-2]

    This section contains content that completes the information on this page, or points you to documentation that explains other aspects to this product.

    ### Message packet size [#message-packet-size-2]

    Signaling SDK imposes size limits on message payload packets sent in Message channels and Stream channels. The limit is 32 KB for Message channels and 1 KB for Stream channels. The message payload packet size includes the message payload itself plus the size of the `customType` field. If the message payload package size exceeds the limit, you receive an error message.

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        ```objc
        // errorInfo
        {
            errorInfo.errorCode = .channelMessageLengthExceedLimitation
            errorInfo.reason = "Publish too long message."
            errorInfo.operation = "publish"; // or "publishTopicMessage
        }
        ```
      </CodeBlockTab>

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        ```objc
        // errorInfo
        {
            errorInfo.errorCode = AgoraRtmErrorChannelMessageLengthExceedLimitation;
            errorInfo.reason = @"Publish too long message.";
            errorInfo.Operation = @"publish"; // or "publishTopicMessage"
        }
        ```
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    To avoid sending failure due to message payload packet size exceeding the limit, check the packet size before sending.

    ### API reference [#api-reference-2]

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        * [`createStreamChannel`](/en/api-reference/api-ref/signaling?platform=ios\&tab=swift#channelcreatepropsag_platform)
        * [`join`](/en/api-reference/api-ref/signaling?platform=ios\&tab=swift#channeljoinpropsag_platform)
        * [`publishTopicMessage`](/en/api-reference/api-ref/signaling?platform=ios\&tab=swift#topicpublishpropsag_platform)
        * [`leave`](/en/api-reference/api-ref/signaling?platform=ios\&tab=swift#channelleavepropsag_platform)
        * [`destroy`](/en/api-reference/api-ref/signaling?platform=ios\&tab=swift#channelreleasepropsag_platform)
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        * [`createStreamChannel`](/en/api-reference/api-ref/signaling?platform=ios\&tab=objc#channelcreatepropsag_platform)
        * [`joinWithOption`](/en/api-reference/api-ref/signaling?platform=ios\&tab=objc#channeljoinpropsag_platform)
        * [`publishTopicMessage`](/en/api-reference/api-ref/signaling?platform=ios\&tab=objc#topicpublishpropsag_platform)
        * [`leave`](/en/api-reference/api-ref/signaling?platform=ios\&tab=objc#channelleavepropsag_platform)
        * [`destroy`](/en/api-reference/api-ref/signaling?platform=ios\&tab=objc#channelreleasepropsag_platform)
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