Extensible File Thumbnails

Introduction

When sending media, it is often helpful for users when a thumbnail can be shown before the actual file is finished downloading.

XMPP already has a protocol for specifying thumbails, Jingle Content Thumbnails. However, this protocol requires that the thumbnail is a base64-encoded image published using Bits of Binary. This prevents clients from implementing newer technologies, such as Blurhash.

This document specifies are more general and extensible element for specifiying thumbnails in various formats.

Usage

<file-thumbnails xmlns="proto:urn:xmpp:eft:0">
	<blurhash xmlns="proto:urn:xmpp:eft:blurhash">LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
</file-thumbnails>

In this example, the thumbnail contains only a blurhash thumbnail, indicated by the <blurhash/> element, but an implementation may add more versions of the same thumbnail, i.e. another <base64-bob/> element as a fallback if a client does not support blurhash. To prevent confusion in the display of a thumbnail, all children of <file-thumbnail /> must describe a thumbnail for the same file.

Thumbnail Types

Blurhash

If a sender includes a <blurhash/> inside the <file-thumbnail/> element, then it must be interpreted as Blurhash data. As a sender, care must be taken to not make the Blurhash thumbnail too big as to not loose the advantages of blurhash.

<file-thumbails xmlns="proto:urn:xmpp:eft:0">
	<blurhash xmlns="proto:urn:xmpp:eft:blurhash">LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
</file-thumbnails>

Jingle Content Thumbnail Compatability

In order to enable a pseudo-interoperability with Jingle Content Thumbnails, inclusion of a <thumbnail/> element is allowed. This is to allow easy reuse of an already existent Jingle Content Thumbnails implementation.

<file-thumbails xmlns="proto:urn:xmpp:eft:0" type="base64-bob">
	<thumbnail xmlns="urn:xmpp:thumbs:1" uri="cid:sha1+...@bob.xmpp.org" media-type="image/png" width="128" height="96" />
</file-thumbnails>

NOTE: This example is taken from Stateless Inline Media Sharing and modified for this protocol.

<message to='julient@shakespeare.lit' from='romeo@montague.lit'>
  <body>Look at the nice view from the summit.</body>
  <reference xmlns='urn:xmpp:reference:0' begin='17' end='20' type='data'>
    <media-sharing xmlns='urn:xmpp:sims:1'>
      <file xmlns='urn:xmpp:jingle:apps:file-transfer:5'>
        <media-type>image/jpeg</media-type>
        <name>summit.jpg</name>
        <size>3032449</size>
        <hash xmlns='urn:xmpp:hashes:2' algo='sha3-256'>2XarmwTlNxDAMkvymloX3S5+VbylNrJt/l5QyPa+YoU=</hash>
        <hash xmlns='urn:xmpp:hashes:2' algo='id-blake2b256'>2AfMGH8O7UNPTvUVAM9aK13mpCY=</hash>
        <desc>Photo from the summit.</desc>
        <file-thumbnail type="base64-bob" xmlns='urn:xmpp:thumbnail:0'>
			<base64-bob uri="cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org" media-type="image/png" width="128" height="96" />
		</thumbnail>
        <file-thumbnails xmlns="proto:urn:xmpp:eft:0">
		  	<blurhash xmlns="proto:urn:xmpp:eft:blurhash">LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
			<thumbnail xmlns='urn:xmpp:thumbs:1'
                       uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org'
                       media-type='image/png'
                       width='128'
                       height='96'/>
		</file-thumbnails>
      </file>
      <sources>
        <reference xmlns='urn:xmpp:reference:0' type='data' uri='https://download.montague.lit/4a771ac1-f0b2-4a4a-9700-f2a26fa2bb67/summit.jpg' />
        <reference xmlns='urn:xmpp:reference:0' type='data' uri='xmpp:romeo@montague.lit/resource?jingle;id=9559976B-3FBF-4E7E-B457-2DAA225972BB' />
      </sources>
    </media-sharing>
  </reference>
</message>

Security Considerations

The same considerations apply as specified by Jingle Content Thumbnails.

Todo

Change XML namespace from proto:urn:xmpp:eft:0 to urn:xmpp:eft:0 once accepted as an experimental XEP

Changelog

0.1.0

Remove the base64 thumbnail type
Namespace all thumbnail types
Remove the type attribute of
Rename to
Rename the namespace from file-thumbnails to eft
Rename from File Thumbnails to Extensible File Thumbnails

Info

Key	Value
Author	PapaTutuWawa
Version	0.1.0
Short name	eft

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