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Add short-lived cache to Downloader.

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This commit is contained in:
Brent Simmons
2025-05-07 20:07:15 -07:00
parent 1c7578b8ac
commit 3785df268c
1 changed files with 52 additions and 21 deletions
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73
Modules/RSWeb/Sources/RSWeb/Downloader.swift
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@@ -8,19 +8,24 @@
import Foundation
import os
import RSCore
public typealias DownloadCallback = @MainActor (Data?, URLResponse?, Error?) -> Swift.Void
/// Simple downloader, for a one-shot download like an image
/// or a web page. For a download-feeds session, see DownloadSession.
/// Caches response for a short time for GET requests. May return cached response.
@MainActor public final class Downloader {
public static let shared = Downloader()
private let urlSession: URLSession
private var callbacks = [URL: [DownloadCallback]]()
private static let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category: "Downloader")
private static let debugLoggingEnabled = true
// Cache — short-lived
private let cache = Cache<DownloaderRecord>(timeToLive: 60 * 3, timeBetweenCleanups: 60 * 2)
nonisolated private static let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category: "Downloader")
nonisolated private static let debugLoggingEnabled = true
private init() {
let sessionConfiguration = URLSessionConfiguration.ephemeral
@@ -41,11 +46,12 @@ public typealias DownloadCallback = @MainActor (Data?, URLResponse?, Error?) ->
urlSession.invalidateAndCancel()
}
public func download(_ url: URL, _ completion: @escaping DownloadCallback) {
download(URLRequest(url: url), completion)
public func download(_ url: URL, _ callback: @escaping DownloadCallback) {
assert(Thread.isMainThread)
download(URLRequest(url: url), callback)
}
public func download(_ urlRequest: URLRequest, _ completion: @escaping DownloadCallback) {
public func download(_ urlRequest: URLRequest, _ callback: @escaping DownloadCallback) {
assert(Thread.isMainThread)
guard let url = urlRequest.url else {
@@ -53,25 +59,20 @@ public typealias DownloadCallback = @MainActor (Data?, URLResponse?, Error?) ->
return
}
addCallback(url: url, callback: completion)
let isCacheableRequest = urlRequest.httpMethod == HTTPMethod.get
var urlRequestToUse = urlRequest
urlRequestToUse.addSpecialCaseUserAgentIfNeeded()
let task = urlSession.dataTask(with: urlRequestToUse) { (data, response, error) in
Task { @MainActor in
self.callAndReleaseCallbacks(url, data, response, error)
// Return cached record if available.
if isCacheableRequest {
if let cachedRecord = cache[url.absoluteString] {
if Self.debugLoggingEnabled {
Self.logger.debug("Downloader: returning cached record for \(url)")
}
callback(cachedRecord.data, cachedRecord.response, cachedRecord.error)
return
}
}
task.resume()
}
}
private extension Downloader {
func addCallback(url: URL, callback: @escaping DownloadCallback) {
assert(Thread.isMainThread)
// Add callback. If there is already a download in progress for this URL, return early.
if callbacks[url] == nil {
if Self.debugLoggingEnabled {
Self.logger.debug("Downloader: downloading \(url)")
@@ -86,7 +87,29 @@ private extension Downloader {
callbacks[url]?.append(callback)
return
}
var urlRequestToUse = urlRequest
urlRequestToUse.addSpecialCaseUserAgentIfNeeded()
let task = urlSession.dataTask(with: urlRequestToUse) { (data, response, error) in
if isCacheableRequest {
if Self.debugLoggingEnabled {
Self.logger.debug("Downloader: caching record for \(url)")
}
let cachedRecord = DownloaderRecord(data: data, response: response, error: error)
self.cache[url.absoluteString] = cachedRecord
}
Task { @MainActor in
self.callAndReleaseCallbacks(url, data, response, error)
}
}
task.resume()
}
}
private extension Downloader {
func callAndReleaseCallbacks(_ url: URL, _ data: Data? = nil, _ response: URLResponse? = nil, _ error: Error? = nil) {
assert(Thread.isMainThread)
@@ -115,3 +138,11 @@ private extension Downloader {
}
}
}
struct DownloaderRecord: CacheRecord, Sendable {
let dateCreated = Date()
let data: Data?
let response: URLResponse?
let error: Error?
}