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

This example specifies a thumbnail of type blurhash, meaning that the child element of the <file-thumbnail/> element must contain a <blurhash/> element (See "Thumbnail Types").

A <file-thumbnail/> element MUST only contain one child; that is the child that is specified by the <file-thumbnail/> type attribute.

Thumbnail Types

Blurhash

If a sender specifies the type of the <file-thumbnail/> element to be proto:urn:xmpp:eft:0:blurhash, then the <blurhash/> element's value 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-thumbail xmlns="proto:urn:xmpp:eft:0">
	<blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
</file-thumbnail>

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. The type of the <file-thumbnail/> must then be set to proto:urn:xmpp:eft:0:base64-bob.

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

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-thumbnail type="proto:urn:xmpp:eft:0:blurhash" xmlns="proto:urn:xmpp:eft:0">
                    <blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
                </file-thumbnail>
                <file-thumbnail type="proto:urn:xmpp:eft:0:base64-bob" xmlns="proto:urn:xmpp:eft:0">
                    <thumbnail xmlns='urn:xmpp:thumbs:1'
                            uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org'
                            media-type='image/png'
                            width='128'
                            height='96'/>
                </file-thumbnail>
            </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 we submit this as an XEP

Changelog

0.2.1

Remove namespacing of the <file-thumbnail/>'s child element

0.2.0

Namespace the thumbnail type
<file-thumbnails/> to <file-thumbnail/>

0.1.0

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

Info

Key	Value
Author	PapaTutuWawa
Version	0.2.1
Short name	eft

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