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 <daniel@daquino.me> Link: 20240411004129.84436-3-daniel@daquino.me Signed-off-by: William Casarin <jb55@jb55.com>
This commit is contained in:
Daniel D’Aquino
committed by
William Casarin
William Casarin
parent
c2918aaf16
commit
26d2627a1c
114
damus/Models/VideoCache.swift
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114
damus/Models/VideoCache.swift
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//
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// VideoCache.swift
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// damus
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//
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// Created by Daniel D'Aquino on 2024-04-01.
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//
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import Foundation
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import CryptoKit
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// Default expiry time of only 1 day to prevent using too much storage
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fileprivate let DEFAULT_EXPIRY_TIME: TimeInterval = 60*60*24
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// Default cache directory is in the system-provided caches directory, so that the operating system can delete files when it needs storage space
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// (https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html)
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fileprivate let DEFAULT_CACHE_DIRECTORY_PATH: URL? = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first?.appendingPathComponent("video_cache")
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struct VideoCache {
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private let cache_url: URL
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private let expiry_time: TimeInterval
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static let standard: VideoCache? = try? VideoCache()
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init?(cache_url: URL? = nil, expiry_time: TimeInterval = DEFAULT_EXPIRY_TIME) throws {
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guard let cache_url_to_apply = cache_url ?? DEFAULT_CACHE_DIRECTORY_PATH else { return nil }
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self.cache_url = cache_url_to_apply
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self.expiry_time = expiry_time
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// Create the cache directory if it doesn't exist
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do {
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try FileManager.default.createDirectory(at: self.cache_url, withIntermediateDirectories: true, attributes: nil)
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} catch {
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Log.error("Could not create cache directory: %s", for: .storage, error.localizedDescription)
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throw error
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}
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}
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/// Checks for a cached video and returns its URL if available, otherwise downloads and caches the video.
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func maybe_cached_url_for(video_url: URL) throws -> URL {
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let cached_url = url_to_cached_url(url: video_url)
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if FileManager.default.fileExists(atPath: cached_url.path) {
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// Check if the cached video has expired
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let file_attributes = try FileManager.default.attributesOfItem(atPath: cached_url.path)
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if let modification_date = file_attributes[.modificationDate] as? Date, Date().timeIntervalSince(modification_date) <= expiry_time {
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// Video is not expired
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return cached_url
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} else {
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Task {
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// Video is expired, delete and re-download on the background
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try FileManager.default.removeItem(at: cached_url)
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return try await download_and_cache_video(from: video_url)
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}
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return video_url
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}
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} else {
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Task {
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// Video is not cached, download and cache on the background
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return try await download_and_cache_video(from: video_url)
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}
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return video_url
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}
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}
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/// Downloads video content using URLSession and caches it to disk.
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private func download_and_cache_video(from url: URL) async throws -> URL {
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let (data, response) = try await URLSession.shared.data(from: url)
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guard let http_response = response as? HTTPURLResponse,
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200..<300 ~= http_response.statusCode else {
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throw URLError(.badServerResponse)
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}
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let destination_url = url_to_cached_url(url: url)
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try data.write(to: destination_url)
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return destination_url
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}
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func url_to_cached_url(url: URL) -> URL {
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let hashed_url = hash_url(url)
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let file_extension = url.pathExtension
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return self.cache_url.appendingPathComponent(hashed_url + "." + file_extension)
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}
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/// Deletes all cached videos older than the expiry time.
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func periodic_purge(completion: ((Error?) -> Void)? = nil) {
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DispatchQueue.global(qos: .background).async {
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Log.info("Starting periodic video cache purge", for: .storage)
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let file_manager = FileManager.default
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do {
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let cached_files = try file_manager.contentsOfDirectory(at: self.cache_url, includingPropertiesForKeys: [.contentModificationDateKey], options: .skipsHiddenFiles)
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for file in cached_files {
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let attributes = try file.resourceValues(forKeys: [.contentModificationDateKey])
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if let modification_date = attributes.contentModificationDate, Date().timeIntervalSince(modification_date) > self.expiry_time {
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try file_manager.removeItem(at: file)
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}
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}
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DispatchQueue.main.async {
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completion?(nil)
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}
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} catch {
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DispatchQueue.main.async {
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completion?(error)
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}
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}
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}
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}
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/// Hashes the URL using SHA-256
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private func hash_url(_ url: URL) -> String {
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let data = Data(url.absoluteString.utf8)
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let hashed_data = SHA256.hash(data: data)
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return hashed_data.compactMap { String(format: "%02x", $0) }.joined()
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}
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}
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