Refactor oEmbed previews (#10814)

The major change is moving the decision of whether to use oEmbed
further up the call-stack. This reverts the _download_url method to
being a "dumb" functionwhich takes a single URL and downloads it
(as it was before #7920).

This also makes more minor refactorings:

* Renames internal variables for clarity.
* Factors out shared code between the HTML and rich oEmbed
  previews.
* Fixes tests to preview an oEmbed image.
This commit is contained in:
Patrick Cloke 2021-09-21 12:09:57 -04:00 committed by GitHub
parent 2843058a8b
commit ba7a91aea5
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5 changed files with 299 additions and 220 deletions

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@ -25,16 +25,14 @@ When Synapse is asked to preview a URL it does the following:
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 pattern. If it does, fetch the oEmbed
response. If this is an image, replace the URL to fetch and continue. If
if it is HTML content, use the HTML as the document and continue.
3. If it doesn't match an oEmbed pattern, downloads the URL and stores it
into a file via the media storage provider and saves the local media
metadata.
5. If the media is an image:
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.
6. If the media is HTML:
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 an image exists in the Open Graph response:
@ -42,6 +40,13 @@ When Synapse is asked to preview a URL it does the following:
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.