Commits on Apr 25, 2024

1. Cache videos …

   This commit implements a simple but functional video cache.
   
   It works by providing a method called `maybe_cached_url`, where a video
   URL can be passed in, and this method will either return the URL of a
   cached version of this video if available, or the original URL if not. It also
   downloads new video URLs on the background into the cache folder for use
   next time.
   
   Functional testing
   -------------------
   
   PASS
   
   Device: iPhone 15 simulator
   iOS: 17.4
   Damus: Approximately this commit
   Setup:
   - Debug connection
   - Expiry time locally changed to 5 minutes
   
   Steps:
   1. Basic functionality
     1. Go to a profile with lots of videos
     2. Scroll down
     3. Filter logs to only logs that start with "Loading video with URL"
     4. Check that most videos are being loaded from external URLs. PASS
     5. Now restart the app and go to that same profile
     6. Scroll down and watch logs. Videos should now be loaded with an internal file URL. PASS
   2. Automatic cache refresh after expiry
     1. Go to the video-heavy profile, make note of the external URL.
     2. Go to a different screen and then come back to that video. Make sure the file was loaded from cache. PASS
     3. Now go to a different screen and wait 5 minutes.
     4. Come back to the same video. It should be loaded from the external URL. PASS
   3. "Clear cache" button functionality
     1. Go to the video-heavy profile, make note of the external URL.
     2. Go to a different screen and then come back to that video. Make sure the file was loaded from cache. PASS
     3. Now quit the app (to ensure file is not in use when trying to delete it)
     4. Clear cache in settings
     5. Go back to the same video. It should now be loaded from the external URL. PASS
   
   Performance testing
   -----------------------
   
   Device: iPhone 13 mini
   iOS: 17.3.1
   Damus: This commit
   Baseline: 87de88861adb3b41d73998452e7c876ab5ee06bf
   Setup:
   - Debug connection
   - Expiry time locally changed to 5 minutes
   - Running on Profile mode, with XCode Instruments
   
   Steps:
   1. Start recording network activity with XCode Instruments
   2. Go to a video-heavy profile (e.g. Julian Figueroa)
   3. Scroll down to a specific video (Make sure to scroll through at least 5 videos)
   4. Stop recording and measure the "Bytes In" from "Network connections"
   5. Repeat this for all test configurations
   
   Results:
   - Baseline (No caching support): 26.74 MiB
   - This commit (First run, cleared cache): 40.52 MiB
   - This commit (Second run, cache filled with videos): 8.13 MiB
   
   Automated test coverage
   ------------------------
   
   PASS
   
   Device: iPhone 15 simulator
   iOS: 17.4
   Damus: This commit
   Coverage:
   - Ran new automated tests multiple times. PASS 3/3 times
   - Ran all other automated tests. PASS
   
   Signed-off-by: Daniel D’Aquino <[email protected]>
   Link: [email protected]
   Signed-off-by: William Casarin <[email protected]>

   

   danieldaquino authored and jb55 committed Apr 25, 2024
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2. Custom video loader caching technique …

   This commit brings significant improvements to the video cache feature.
   
   Previously, the cache would merely download the video when requested, in
   parallel with AVPlayer which also triggers a video download.
   
   The video cache has been updated to tap into the AVPlayer loading
   process, removing the download duplication.
   
   Here is how that works:
   1. The player requests an AVAsset from the cache.
   2. The cache will return a cached asset if possible, or a special AVURLAsset with a custom `AVAssetResourceLoaderDelegate`.
   3. The video player will start sending loading requests to this loader delegate.
   4. Upon receiving the first request, the loader delegate begins to download the video data on the background.
   5. Upon receiving these requests, the loader delegate will also record the requests, so that it can serve them once possible
   6. The loader delegate keeps track of all video data chunks as it receives them from the download task, through the `URLSessionDataDelegate` and `URLSessionTaskDelegate` protocols
   7. As it receives data, it checks all pending loading requests from the AVPlayer, and fulfills them as soon as possible
   8. If the download fails (e.g. timeout errors, loss of connection), it attempts to restart the download.
   9. If the download succeeds, it saves the video to the cache on disk
   
   Closes: #1717
   Changelog-Added: Add video cache to save network bandwidth
   Signed-off-by: Daniel D’Aquino <[email protected]>
   Link: [email protected]
   Signed-off-by: William Casarin <[email protected]>

   

   danieldaquino authored and jb55 committed Apr 25, 2024
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