Re: [Extra] Barry Leiba's Discuss on draft-ietf-extra-imap-fetch-preview-03: (with DISCUSS and COMMENT)

["Neil Jenkins" <[e-mail]>]

On Mon, 1 Jul 2019, at 17:29, Michael Slusarz wrote:
> A real world example - we are currently working on an initiative to push email as a chat medium (Shameless plug: https://www.coi-dev.org/). In every chat client I have ever used, sending images and/or video is an important part of conversations. When an image/video appears in a chat stream, the full contents are not generally displayed - it is a small preview of the image (or a small preview of a frame of the video). That small image that is surely a "preview" of that message. Mixed media previews are a very common paradigm in other messaging systems - why should email be any different? 
> 
> We shouldn't have to come back in a year and propose a new "FETCH IMAGEPREVIEW" standard to support this - we should instead be able to propose a simple, optional extension to the base PREVIEW behavior.

I see, thanks for providing your motivation for this, it makes it much easier to discuss. This is certainly *a* solution to this problem, but I do wonder if it's the best one. If we start with the requirement that we must use IMAP for the chat message sync protocol, which admittedly does limit the options somewhat, the other main thing I would try is fetching the body structure with the COI client when getting a message listing. You would be able to see that, for example, a message has only an image/png part and how large it is. If it's small, the client may just fetch it directly. If it's large, you want a way for the client to ask the server for this image downsampled to a particular size; the client can specify exactly what it needs to optimise bandwidth usage.

Neil.