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watcha-synapse/docs/media_repository.md

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Media Repository

Synapse implementation-specific details for the media repository

The media repository

  • stores avatars, attachments and their thumbnails for media uploaded by local users.
  • caches avatars, attachments and their thumbnails for media uploaded by remote users.
  • caches resources and thumbnails used for URL previews.

All media in Matrix can be identified by a unique MXC URI, consisting of a server name and media ID:

mxc://<server-name>/<media-id>

Local Media

Synapse generates 24 character media IDs for content uploaded by local users. These media IDs consist of upper and lowercase letters and are case-sensitive. Other homeserver implementations may generate media IDs differently.

Local media is recorded in the local_media_repository table, which includes metadata such as MIME types, upload times and file sizes. Note that this table is shared by the URL cache, which has a different media ID scheme.

Paths

A file with media ID aabbcccccccccccccccccccc and its 128x96 image/jpeg thumbnail, created by scaling, would be stored at:

local_content/aa/bb/cccccccccccccccccccc
local_thumbnails/aa/bb/cccccccccccccccccccc/128-96-image-jpeg-scale

Remote Media

When media from a remote homeserver is requested from Synapse, it is assigned a local filesystem_id, with the same format as locally-generated media IDs, as described above.

A record of remote media is stored in the remote_media_cache table, which can be used to map remote MXC URIs (server names and media IDs) to local filesystem_ids.

Paths

A file from matrix.org with filesystem_id aabbcccccccccccccccccccc and its 128x96 image/jpeg thumbnail, created by scaling, would be stored at:

remote_content/matrix.org/aa/bb/cccccccccccccccccccc
remote_thumbnail/matrix.org/aa/bb/cccccccccccccccccccc/128-96-image-jpeg-scale

Older thumbnails may omit the thumbnailing method:

remote_thumbnail/matrix.org/aa/bb/cccccccccccccccccccc/128-96-image-jpeg

Note that remote_thumbnail/ does not have an s.

URL Previews

When generating previews for URLs, Synapse may download and cache various resources, including images. These resources are assigned temporary media IDs of the form yyyy-mm-dd_aaaaaaaaaaaaaaaa, where yyyy-mm-dd is the current date and aaaaaaaaaaaaaaaa is a random sequence of 16 case-sensitive letters.

The metadata for these cached resources is stored in the local_media_repository and local_media_repository_url_cache tables.

Resources for URL previews are deleted after a few days.

Paths

The file with media ID yyyy-mm-dd_aaaaaaaaaaaaaaaa and its 128x96 image/jpeg thumbnail, created by scaling, would be stored at:

url_cache/yyyy-mm-dd/aaaaaaaaaaaaaaaa
url_cache_thumbnails/yyyy-mm-dd/aaaaaaaaaaaaaaaa/128-96-image-jpeg-scale