### Content repository The content repository (or "media repository") allows users to upload files to their homeserver for later use. For example, files which the user wants to send to a room would be uploaded here, as would an avatar the user wants to use. Uploads are POSTed to a resource on the user's local homeserver which returns an `mxc://` URI which can later be used to GET the download. Content is downloaded from the recipient's local homeserver, which must first transfer the content from the origin homeserver using the same API (unless the origin and destination homeservers are the same). When serving content, the server SHOULD provide a `Content-Security-Policy` header. The recommended policy is `sandbox; default-src 'none'; script-src 'none'; plugin-types application/pdf; style-src 'unsafe-inline'; object-src 'self';`. {{% boxes/added-in-paragraph %}} {{< added-in v="1.4" >}} The server SHOULD additionally provide `Cross-Origin-Resource-Policy: cross-origin` when serving content to allow (web) clients to access restricted APIs such as `SharedArrayBuffer` when interacting with the media repository. {{% /boxes/added-in-paragraph %}} {{% boxes/added-in-paragraph %}} {{< changed-in v="1.11" >}} The unauthenticated download endpoints have been deprecated in favour of newer, authenticated, ones. This change includes updating the paths of all media endpoints from `/_matrix/media/*` to `/_matrix/client/{version}/media/*`, with the exception of the `/upload` and `/create` endpoints. The upload/create endpoints are expected to undergo a similar transition in a later version of the specification. {{% /boxes/added-in-paragraph %}} #### Matrix Content (`mxc://`) URIs Content locations are represented as Matrix Content (`mxc://`) URIs. They look like: ``` mxc:/// : The name of the homeserver where this content originated, e.g. matrix.org : An opaque ID which identifies the content. ``` #### Client behaviour {id="content-repo-client-behaviour"} Clients can access the content repository using the following endpoints. {{% boxes/added-in-paragraph %}} {{< changed-in v="1.11" >}} Clients SHOULD NOT use the deprecated media endpoints described below. Instead, they SHOULD use the new endpoints which require authentication. {{% /boxes/added-in-paragraph %}} {{% boxes/warning %}} By Matrix 1.12, servers SHOULD "freeze" the deprecated, unauthenticated, endpoints to prevent newly-uploaded media from being downloaded. This SHOULD mean that any media uploaded *before* the freeze remains accessible via the deprecated endpoints, and any media uploaded *after* (or *during*) the freeze SHOULD only be accessible through the new, authenticated, endpoints. For remote media, "newly-uploaded" is determined by the date the cache was populated. This may mean the media is older than the freeze, but because the server had to re-download it, it is now considered "new". Clients SHOULD update to support the authenticated endpoints before servers freeze unauthenticated access. Servers SHOULD consider their local ecosystem impact before enacting a freeze. This could mean ensuring their users' typical clients support the new endpoints when available, or updating bridges to start using media proxies. In addition to the above, servers SHOULD exclude [IdP icons used in the `m.login.sso` flow](/client-server-api/#definition-mloginsso-flow-schema) from the freeze. See the `m.login.sso` flow schema for details. An *example* timeline for a server may be: * Matrix 1.11 release: Clients begin supporting authenticated media. * Matrix 1.12 release: Servers freeze unauthenticated media access. * Media uploaded prior to this point still works with the deprecated endpoints. * Newly uploaded (or cached) media *only* works on the authenticated endpoints. Matrix 1.12 is expected to be released in the July-September 2024 calendar quarter. {{% /boxes/warning %}} {{% http-api spec="client-server" api="authed-content-repo" %}} {{% http-api spec="client-server" api="content-repo" %}} ##### Thumbnails The homeserver SHOULD be able to supply thumbnails for uploaded images and videos. The exact file types which can be thumbnailed are not currently specified - see [Issue \#1938](https://github.com/matrix-org/matrix-doc/issues/1938) for more information. The thumbnail methods are "crop" and "scale". "scale" tries to return an image where either the width or the height is smaller than the requested size. The client should then scale and letterbox the image if it needs to fit within a given rectangle. "crop" tries to return an image where the width and height are close to the requested size and the aspect matches the requested size. The client should scale the image if it needs to fit within a given rectangle. The dimensions given to the thumbnail API are the minimum size the client would prefer. Servers must never return thumbnails smaller than the client's requested dimensions, unless the content being thumbnailed is smaller than the dimensions. When the content is smaller than the requested dimensions, servers should return the original content rather than thumbnail it. Servers SHOULD produce thumbnails with the following dimensions and methods: - 32x32, crop - 96x96, crop - 320x240, scale - 640x480, scale - 800x600, scale In summary: - "scale" maintains the original aspect ratio of the image - "crop" provides an image in the aspect ratio of the sizes given in the request - The server will return an image larger than or equal to the dimensions requested where possible. Servers MUST NOT upscale thumbnails under any circumstance. Servers MUST NOT return a smaller thumbnail than requested, unless the original content makes that impossible. #### Security considerations The HTTP GET endpoint does not require any authentication. Knowing the URL of the content is sufficient to retrieve the content, even if the entity isn't in the room. `mxc://` URIs are vulnerable to directory traversal attacks such as `mxc://127.0.0.1/../../../some_service/etc/passwd`. This would cause the target homeserver to try to access and return this file. As such, homeservers MUST sanitise `mxc://` URIs by allowing only alphanumeric (`A-Za-z0-9`), `_` and `-` characters in the `server-name` and `media-id` values. This set of whitelisted characters allows URL-safe base64 encodings specified in RFC 4648. Applying this character whitelist is preferable to blacklisting `.` and `/` as there are techniques around blacklisted characters (percent-encoded characters, UTF-8 encoded traversals, etc). Homeservers have additional content-specific concerns: - Clients may try to upload very large files. Homeservers should not store files that are too large and should not serve them to clients, returning a HTTP 413 error with the `M_TOO_LARGE` code. - Clients may try to upload very large images. Homeservers should not attempt to generate thumbnails for images that are too large, returning a HTTP 413 error with the `M_TOO_LARGE` code. - Remote homeservers may host very large files or images. Homeservers should not proxy or thumbnail large files or images from remote homeservers, returning a HTTP 502 error with the `M_TOO_LARGE` code. - Clients may try to upload a large number of files. Homeservers should limit the number and total size of media that can be uploaded by clients, returning a HTTP 403 error with the `M_FORBIDDEN` code. - Clients may try to access a large number of remote files through a homeserver. Homeservers should restrict the number and size of remote files that it caches. - Clients or remote homeservers may try to upload malicious files targeting vulnerabilities in either the homeserver thumbnailing or the client decoders.