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# File Thumbnails
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## Introduction
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When sending media, it is often helpful for users when a thumbnail can be shown before the
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actual file is finished downloading.
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XMPP already has a protocol for specifying thumbails, [Jingle Content Thumbnails](https://xmpp.org/extensions/xep-0264.html).
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However, this protocol requires that the thumbnail is a base64-encoded image published using
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[Bits of Binary](https://xmpp.org/extensions/xep-0231.html). This prevents clients from implementing newer technologies, such as
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[Blurhash](https://github.com/woltapp/blurhash).
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This document specifies are more general and extensible element for specifiying thumbnails.
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## Usage
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```xml
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<file-thumbnail type="proto:urn:xmpp:file-thumbnails:0:blurhash" xmlns="proto:urn:xmpp:file-thumbnails:0">
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<blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
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</thumbnail>
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```
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In this example, the thumbnail is specified of type `proto:urn:xmpp:file-thumbnails:0:blurhash`, which means that a supporting
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client should decode the `<blurhash/>` element using the [Blurhash](https://github.com/woltapp/blurhash) algorithm.
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In order to enable a sort-of interoperability with [Jingle Content Thumbnails](https://xmpp.org/extensions/xep-0264.html), a type
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`proto:urn:xmpp:file-thumbnails:0:jct` is defined.
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```xml
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<file-thumbnail type="proto:urn:xmpp:file-thumbnails:0:jct" xmlns="proto:urn:xmpp:file-thumbnails:0">
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<thumbnail xmlns="urn:xmpp:thumbs:1" uri="..." media-type="image/png" width="128" height="96" />
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</thumbnail>
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```
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In the case of [Jingle Content Thumbnails](https://xmpp.org/extensions/xep-0264.html) compatibility,
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the `<file-thumbnail />` element must contain exactly one `<thumbnail xmlns="urn:xmpp:thumbs:1" />` element.
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Other extensions may define similar types. Note that the content of the `<file-thumbnail />` element
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is dependent on the type specified in the `<file-thumbnail xmlns="proto:urn:xmpp:file-thumbnails:0" />`
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element.
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### Thumbnail Types
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#### Blurhash
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If a sender specifies the type to be of `proto:urn:xmpp:file-thumbnails:0:blurhash`, then the `<file-thumbnail />` element must contain the
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image data as specified by the [Blurhash](https://github.com/woltapp/blurhash) algorithm. Care should be taken to prevent
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the blurhash data from growing to large in order to prevent hitting the stanza size limit.
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### Jingle Content Thumbnail Compatability
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If a sender specified the type to be of `proto:urn:xmpp:file-thumbnails:0:jct`, then the `<file-thumbnail />`
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element must contain exactly one `<thumbnail xmlns="urn:xmpp:thumbs:1" />` element.
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## Usage Example with Stateless Inline Media Sharing
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NOTE: This example is taken from [Stateless Inline Media Sharing](https://xmpp.org/extensions/xep-0385.html) and modified for this protocol.
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```xml
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<message to='julient@shakespeare.lit' from='romeo@montague.lit'>
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<body>Look at the nice view from the summit.</body>
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<reference xmlns='urn:xmpp:reference:0' begin='17' end='20' type='data'>
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<media-sharing xmlns='urn:xmpp:sims:1'>
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<file xmlns='urn:xmpp:jingle:apps:file-transfer:5'>
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<media-type>image/jpeg</media-type>
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<name>summit.jpg</name>
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<size>3032449</size>
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<hash xmlns='urn:xmpp:hashes:2' algo='sha3-256'>2XarmwTlNxDAMkvymloX3S5+VbylNrJt/l5QyPa+YoU=</hash>
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<hash xmlns='urn:xmpp:hashes:2' algo='id-blake2b256'>2AfMGH8O7UNPTvUVAM9aK13mpCY=</hash>
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<desc>Photo from the summit.</desc>
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<file-thumbnail type="proto:proto:urn:xmpp:file-thumbnails:0:jct" xmlns='urn:xmpp:thumbnail:0'>
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<thumbnail xmlns='urn:xmpp:thumbs:1'uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org' media-type='image/png' width='128' height='96'/>
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</thumbnail>
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<file-thumbnail type="proto:urn:xmpp:file-thumbnails:0:blurhash" xmlns='proto:urn:xmpp:file-thumbnails:0'>
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<blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
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</thumbnail>
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</file>
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<sources>
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<reference xmlns='urn:xmpp:reference:0' type='data' uri='https://download.montague.lit/4a771ac1-f0b2-4a4a-9700-f2a26fa2bb67/summit.jpg' />
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<reference xmlns='urn:xmpp:reference:0' type='data' uri='xmpp:romeo@montague.lit/resource?jingle;id=9559976B-3FBF-4E7E-B457-2DAA225972BB' />
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</sources>
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</media-sharing>
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</reference>
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</message>
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```
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## Security Considerations
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The same considerations apply as specified by [Jingle Content Thumbnails](https://xmpp.org/extensions/xep-0264.html).
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## Info
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| Key | Value |
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| --- | --- |
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| Author | PapaTutuWawa |
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| Version | 0.0.2 |
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