Goal

When a FileTransformer changes the file format (e.g. DNG to JPEG), the uploaded attachment still describes the original file: it is sent as type: image, mime_type: image/x-adobe-dng, image_url: null, and the message list shows a placeholder.

Closes AND-1630

Port of #6792 to develop.

Implementation

• AttachmentUploader runs the transformer first and resolves the MIME type, attachment type and upload endpoint from the transformed file, then uploads it without transforming it again.
• mimeType, imageUrl, name and fileSize describe the uploaded file. A changed extension keeps the original base name (photo.dng becomes photo.jpg).
• When the transformed file's extension says nothing about its format (e.g. .tmp), the type falls back to the original file, as before.
• The internal ChatClient.sendFile/sendImage overloads (and ChatApi) get a transform flag, which AttachmentUploader sets to false so the file isn't transformed twice. The public ChatClient.sendFile/sendImage still transform. No public API changes.
• FileTransformer KDoc: a transformer that changes the format must return a file with a matching extension.

Testing

AttachmentUploaderTests cover a format-changing transform, the .tmp fallback and a failed transform. MoshiChatApiTest covers uploads that skip the transformer, and ChatClientChannelFileUploaderTests that the public upload methods still transform.

Verified on an emulator on v6 (#6792): with a transformer turning .dng into .jpg, v6 sends image/x-adobe-dng with no image_url and shows a placeholder, while the fix sends image/jpeg with image_url set and renders the image (re-run on the latest commit). The port only needed a trivial conflict resolution in the ChatClient constructor.

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Summary by CodeRabbit

• New Features
  • Files and images can now be transformed before upload, with the option to upload an already transformed file without applying the transformation again.
  • Attachment filenames and MIME types reflect the transformed file’s format when it can be identified. Existing attachment details are retained when the transformed format is unknown.
• Documentation
  • Clarified that file transformers should return filenames with extensions matching the transformed format.