Add support for transforming Messages and Channels

[nuno-vieira]

🔗 Issue Links

TODO

🎯 Goal

Add support for transforming Messages and Channels. This will allow changing some of the data of these models at run time.

The most common use case for this feature is to easily allow E2EE encryption of Channels and Messages.

📝 Summary

A new StreamModelsTransformer protocol is added and can be implemented by customers. Currently, only Channels and Messages are transformable, with limited data that can be changed.

Example usage:

class CustomStreamModelsTransformer: StreamModelsTransformer {
    func transform(channel: ChatChannel) -> ChatChannel {
        channel.replacing(
            name: "Hey!",
            imageURL: channel.imageURL,
            extraData: channel.extraData
        )
    }

    func transform(message: ChatMessage) -> ChatMessage {
        message.replacing(
            text: "Yo",
            extraData: message.extraData,
            attachments: message.allAttachments
        )
    }

    func transform(newMessageInfo: NewMessageTransformableInfo) -> NewMessageTransformableInfo {
        newMessageInfo.replacing(
            text: "Changed",
            attachments: newMessageInfo.attachments,
            extraData: newMessageInfo.extraData
        )
    }
}

With the replacing function, if customers want to only change the data of a specific controller, they can do it like so:

let transformedChannels = controller.channels.map {
    $0.replacing(name: "YO", imageURL: $0.imageURL, extraData: $0.extraData)
}

// with combine:
controller.observableObject
      .channels
      .publisher
      .map {
         $0.replacing(name: "YO", imageURL: $0.imageURL, extraData: $0.extraData)
      }
      .sink(receiveValue: { transformedChannel in
         print(transformedChannel)
      })

🛠 Implementation

The way it works is that we pass the transformer to our DTO -> Mapping, and right before creating the models, we pass it to the transformer so that a new Message/Channel can be returned.

For now, the models from events are not mapped since they are not rendered in the UI. We can add them in the future if needed.

🧪 Manual Testing Notes

N/A

☑️ Contributor Checklist

• I have signed the Stream CLA (required)
• This change should be manually QAed
• Changelog is updated with client-facing changes
• Changelog is updated with new localization keys
• New code is covered by unit tests
• Documentation has been updated in the docs-content repo

[Stream-SDK-Bot]

SDK Size

title	develop	branch	diff	status
StreamChat	7.0 MB	7.02 MB	+18 KB	🟢
StreamChatUI	4.77 MB	4.77 MB	0 KB	🟢

[github-actions]

	1 Message
📖	Skipping Danger since the Pull Request is classed as Draft/Work In Progress

Generated by 🚫 Danger

[laevandus]

When thinking ahead to cleaning up deletedMessagesVisibility and others then that would require to have an access to ChatConfig within asModel(). Therefore, should we just pass in the config here and read the transformer within the asModel implementation?

[nuno-vieira]

Yeah I'm not sure how that will look like, but we can improve it once we work on that 👍 But I don't think we need to pass the whole config to the asModel though 🤔

[laevandus]

Sure, can be changed later if needed. When I briefly checked it then ChannelDTO.asModel requires multiple values from the config.

[nuno-vieira]

I see, in that case I will probably change this yet 👍

[laevandus]

StateLayer needs also this.

[nuno-vieira]

@laevandus I've add it to the state layer already 🤔

[martinmitrevski]

Looks great, I like this approach more! Few more finishing touches (docs, tests) and we're good to 🚢

[martinmitrevski]

Nit: maybe just uppercase all the letter of the channel name? Would feel weird otherwise to see only "Hey!" everywhere.
Same for messages, some small transformation of the original text would be nice.

[martinmitrevski]

we need to document this one (and the one below)