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# File Thumbnails
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## 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 ](https://xmpp.org/extensions/xep-0264.html ).
However, this protocol requires that the thumbnail is a base64-encoded image published using
[Bits of Binary ](https://xmpp.org/extensions/xep-0231.html ). This prevents clients from implementing newer technologies, such as
[Blurhash ](https://github.com/woltapp/blurhash ).
This document specifies are more general and extensible element for specifiying thumbnails.
## Usage
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```xml
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< file-thumbnail type = "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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In this example, the thumbnail is specified of type `proto:urn:xmpp:file-thumbnails:0:blurhash` , which means that a supporting
client should decode the `<blurhash/>` element using the [Blurhash ](https://github.com/woltapp/blurhash ) algorithm.
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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 />` element.
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### Thumbnail Types
#### Blurhash
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If a sender specifies the type to be of `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
the blurhash data from growing to large in order to prevent hitting the stanza size limit.
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```xml
< file-thumbail xmlns = "proto:urn:xmpp:file-thumbnails:0" type = "blurhash" >
< blurhash > LEHV6nWB2yk8pyoJadR*.7kCMdnj< / blurhash >
< / file-thumbnail >
```
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#### Jingle Content Thumbnail Compatability
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In order to enable a pseudo-interoperability with [Jingle Content Thumbnails ](https://xmpp.org/extensions/xep-0264.html ), a type
`base64-bob` is defined.
If a sender specified the type to be of `base64-bob` , then the `<file-thumbnail />`
element must contain exactly one `<base64-bob />` element. The attributes of the element are the same
as the `<thumbnail />` element specified in [Jingle Content Thumbnails ](https://xmpp.org/extensions/xep-0264.html ).
```xml
< file-thumbail xmlns = "proto:urn:xmpp:file-thumbnails:0" type = "base64-bob" >
< base64-bob uri = "cid:sha1+...@bob.xmpp.org" media-type = "image/png" width = "128" height = "96" / >
< / file-thumbnail >
```
This allows clients that already support [Jingle Content Thumbnails ](https://xmpp.org/extensions/xep-0264.html ) to reuse
the same logic they use for retrieving thumbnail data.
#### Base64 Data
If a sender specified the type to be of `base64` , then the `<file-thumbnail />` element must
contain exactly one `<base64 />` element. The element must posess an `media-type` attribute, whose value
contains the mime type of the thumbnail data, while the inner text of the element contains the base64-encoded
binary thumbnail data.
```xml
< file-thumbail xmlns = "proto:urn:xmpp:file-thumbnails:0" type = "base64" >
< base64 media-type = "image/png" width = "128" height = "96" >
[base64 data]
< / base64 >
< / file-thumbnail >
```
Note that this thumbnail type is essentially the same as the `base64-bob` type, but allowing the thumbnail to be used even if
the sender is not available on a server that does not cache [Bits of Binary ](https://xmpp.org/extensions/xep-0231.html ) data or has it otherwise not available.
If using this thumbnail type, care has to be taken in order to not hit any existing stanza size limits.
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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' >
< 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 >
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< 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" / >
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< / thumbnail >
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< file-thumbnail type = "blurhash" xmlns = "proto:urn:xmpp:file-thumbnails:0" >
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< blurhash > LEHV6nWB2yk8pyoJadR*.7kCMdnj< / blurhash >
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< / 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 ](https://xmpp.org/extensions/xep-0264.html ).
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## Info
| Key | Value |
| --- | --- |
| Author | PapaTutuWawa |
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| Version | 0.0.3 |
