Inline URL preview documentation. (#13261)

Inline URL preview documentation near the implementation.

1 files changed, 0 insertions, 62 deletions

diff --git a/docs/development/url_previews.md b/docs/development/url_previews.md
deleted file mode 100644
index 25f189683d..0000000000
--- a/docs/development/url_previews.md
+++ /dev/null
@@ -1,62 +0,0 @@
-URL Previews
-============
-For information on how to enable URL previews in synapse, please see the [config manual](../usage/configuration/config_documentation.md#url_preview_enabled).
-
-The `GET /_matrix/media/r0/preview_url` endpoint provides a generic preview API
-for URLs which outputs [Open Graph](https://ogp.me/) responses (with some Matrix
-specific additions).
-
-This does have trade-offs compared to other designs:
-
-* Pros:
-  * Simple and flexible; can be used by any clients at any point
-* Cons:
-  * If each homeserver provides one of these independently, all the HSes in a
-    room may needlessly DoS the target URI
-  * The URL metadata must be stored somewhere, rather than just using Matrix
-    itself to store the media.
-  * Matrix cannot be used to distribute the metadata between homeservers.
-
-When Synapse is asked to preview a URL it does the following:
-
-1. Checks against a URL blacklist (defined as `url_preview_url_blacklist` in the
-   config).
-2. Checks the in-memory cache by URLs and returns the result if it exists. (This
-   is also used to de-duplicate processing of multiple in-flight requests at once.)
-3. Kicks off a background process to generate a preview:
-   1. Checks the database cache by URL and timestamp and returns the result if it
-      has not expired and was successful (a 2xx return code).
-   2. Checks if the URL matches an [oEmbed](https://oembed.com/) pattern. If it
-      does, update the URL to download.
-   3. Downloads the URL and stores it into a file via the media storage provider
-      and saves the local media metadata.
-   4. If the media is an image:
-      1. Generates thumbnails.
-      2. Generates an Open Graph response based on image properties.
-   5. If the media is HTML:
-      1. Decodes the HTML via the stored file.
-      2. Generates an Open Graph response from the HTML.
-      3. If a JSON oEmbed URL was found in the HTML via autodiscovery:
-         1. Downloads the URL and stores it into a file via the media storage provider
-            and saves the local media metadata.
-         2. Convert the oEmbed response to an Open Graph response.
-         3. Override any Open Graph data from the HTML with data from oEmbed.
-      4. If an image exists in the Open Graph response:
-         1. Downloads the URL and stores it into a file via the media storage
-            provider and saves the local media metadata.
-         2. Generates thumbnails.
-         3. Updates the Open Graph response based on image properties.
-   6. If the media is JSON and an oEmbed URL was found:
-      1. Convert the oEmbed response to an Open Graph response.
-      2. If a thumbnail or image is in the oEmbed response:
-         1. Downloads the URL and stores it into a file via the media storage
-            provider and saves the local media metadata.
-         2. Generates thumbnails.
-         3. Updates the Open Graph response based on image properties.
-   7. Stores the result in the database cache.
-4. Returns the result.
-
-The in-memory cache expires after 1 hour.
-
-Expired entries in the database cache (and their associated media files) are
-deleted every 10 seconds. The default expiration time is 1 hour from download.