Attachments and Links

Terminology

Attachment : Anything that can be attached to a note
Link : Anything remote linked to in a note
AttachmentThumbnail : The thumbnail of an attachment

Not every Link has an attachment. An attachment is created for a link when it becomes something attachable. So happens when additional information on a link's URL becomes available.

Following how it is done with Links, anything with a thumbnail in GNU social must have an attachment as only attachments can have a thumbnail.

This design prevents file and thumbnail duplication, thus saving storage.

An example of a module making use of this system is the Avatar component. It creates an attachment and uses the thumbnail route to access different avatar sizes via the AttachmentThumbnail controller.

Migrating data from v2

File to Attachment

Direct transformation:

id => id
filehash => filehash
mimetype => mimetype
size => size
modified => modified

Requires computation:

filename => {if file is in storage then filename, else null}
width => {if file is known by V3, re-compute then width, else null}
height => {if file is known by V3, re-compute then height, else null}
Count references and fill lives

File to Link

Only if url and urlhash are not null.

Direct transformation:

id => id
url => url
urlhash => url_hash

File and File_to_post to AttachmentToNote

Direct transformation by joining File f and File_to_post fp on id = file_id with fp.file_id, fp.post_id, f.title, f.filename, fp.modified:

file_id => attachment_id
post_id => note_id
modified => modified

Requires computation:

title ?? filename => title

File_thumbnail to AttachmentThumbnail

For every attachment where we have the original (filename not null), just let them be regenerated on request. For all the others, compute the mime-type and rescale to the new default sizes.

The field url from File_thumbnail has duplicated information that was already migrated in the tables above and can, therefore, be safely ignored now.

Embed and StoreRemoteMedia

// TODO

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