127 lines
5.3 KiB
Markdown
127 lines
5.3 KiB
Markdown
# Extensible 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 in various formats.
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## Usage
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```xml
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<file-thumbnail type="proto:urn:xmpp:eft:0:blurhash" xmlns="proto:urn:xmpp:eft:0">
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<blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
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</file-thumbnail>
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```
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This example specifies a thumbnail of type `blurhash`, meaning that the child element of the
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`<file-thumbnail/>` element must contain a `<blurhash/>` element (See "Thumbnail Types").
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A `<file-thumbnail/>` element MUST only contain one child; that is the child that is specified
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by the `<file-thumbnail/>` type attribute.
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### Thumbnail Types
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#### Blurhash
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If a sender specifies the type of the `<file-thumbnail/>` element to be
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`proto:urn:xmpp:eft:0:blurhash`, then the `<blurhash/>` element's value must be interpreted
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as [Blurhash](https://github.com/woltapp/blurhash) data. As a sender, care must be taken to
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not make the Blurhash thumbnail too big as to not loose the advantages of Blurhash.
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```xml
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<file-thumbail xmlns="proto:urn:xmpp:eft:0">
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<blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
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</file-thumbnail>
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```
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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), inclusion of a
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`<thumbnail/>` element is allowed. This is to allow easy reuse of an already existent [Jingle Content Thumbnails](https://xmpp.org/extensions/xep-0264.html)
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implementation. The type of the `<file-thumbnail/>` must then be set to `proto:urn:xmpp:eft:0:base64-bob`.
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```xml
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<file-thumbail xmlns="proto:urn:xmpp:eft:0" type="proto:urn:xmpp:eft:0:base64-bob">
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<thumbnail xmlns="urn:xmpp:thumbs:1" uri="cid:sha1+...@bob.xmpp.org" media-type="image/png" width="128" height="96" />
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</file-thumbnail>
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```
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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="base64-bob" xmlns='urn:xmpp:thumbnail:0'>
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<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="proto:urn:xmpp:eft:0:blurhash" xmlns="proto:urn:xmpp:eft:0">
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<blurhash>LEHV6nWB2yk8pyoJadR*.7kCMdnj</blurhash>
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</file-thumbnail>
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<file-thumbnail type="proto:urn:xmpp:eft:0:base64-bob" xmlns="proto:urn:xmpp:eft:0">
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<thumbnail xmlns='urn:xmpp:thumbs:1'
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uri='cid:sha1+ffd7c8d28e9c5e82afea41f97108c6b4@bob.xmpp.org'
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media-type='image/png'
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width='128'
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height='96'/>
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</file-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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## Todo
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- Change XML namespace from `proto:urn:xmpp:eft:0` to `urn:xmpp:eft:0` once we submit this as an XEP
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## Changelog
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### 0.2.1
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- Remove namespacing of the `<file-thumbnail/>`'s child element
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### 0.2.0
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- Namespace the thumbnail type
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- `<file-thumbnails/>` to `<file-thumbnail/>`
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### 0.1.0
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- Remove the base64 thumbnail type
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- Namespace all thumbnail types
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- Remove the type attribute of `<file-thumbnail/>`
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- Rename `<file-thumbnail/>` to `<file-thumbnails/>`
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- Rename the namespace from file-thumbnails to eft
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- Rename from File Thumbnails to Extensible File Thumbnails
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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 | 0.2.1 |
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| Short name | eft |
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