From b04876185ddc36010dde97a96007dc10616dafdd Mon Sep 17 00:00:00 2001
From: Brent Simmons <brent@ranchero.com>
Date: Wed, 13 Dec 2017 21:18:20 -0800
Subject: [PATCH] =?UTF-8?q?Clean=20up=20DownloadWithCacheManager=E2=80=99s?=
 =?UTF-8?q?=20cache=20at=20most=20every=20five=20minutes=20=E2=80=94=C2=A0?=
 =?UTF-8?q?it=E2=80=99s=20very=20expensive=20to=20do=20it=20on=20every=20r?=
 =?UTF-8?q?equest.=20This=20dramatically=20helps=20sidebar=20scrolling=20p?=
 =?UTF-8?q?erformance=20when=20you=20have=20a=20couple=20thousand=20feeds?=
 =?UTF-8?q?=20all=20trying=20to=20get=20their=20favicons.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 Frameworks/RSWeb/RSWeb/OneShotDownload.swift | 30 ++++++++------------
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/Frameworks/RSWeb/RSWeb/OneShotDownload.swift b/Frameworks/RSWeb/RSWeb/OneShotDownload.swift
index fd3beed24..455e94d65 100755
--- a/Frameworks/RSWeb/RSWeb/OneShotDownload.swift
+++ b/Frameworks/RSWeb/RSWeb/OneShotDownload.swift
@@ -65,11 +65,6 @@ private struct WebCacheRecord {
     let dateDownloaded: Date
     let data: Data
     let response: URLResponse
-    
-    func isExpired(_ timeToLive: TimeInterval) -> Bool {
-        
-        return Date().timeIntervalSince(dateDownloaded) > timeToLive
-    }
 }
 
 private final class WebCache {
@@ -77,18 +72,19 @@ private final class WebCache {
     private var cache = [URL: WebCacheRecord]()
     
     func cleanup(_ cleanupInterval: TimeInterval) {
-        
+
+		let cutoffDate = Date(timeInterval: -cleanupInterval, since: Date())
         cache.keys.forEach { (key) in
             let cacheRecord = self[key]!
-            if shouldDelete(cacheRecord, cleanupInterval) {
+            if shouldDelete(cacheRecord, cutoffDate) {
                 cache[key] = nil
             }
         }
      }
     
-    private func shouldDelete(_ cacheRecord: WebCacheRecord, _ cleanupInterval: TimeInterval) -> Bool {
+    private func shouldDelete(_ cacheRecord: WebCacheRecord, _ cutoffDate: Date) -> Bool {
         
-        return Date().timeIntervalSince(cacheRecord.dateDownloaded) > cleanupInterval
+        return cacheRecord.dateDownloaded < cutoffDate
     }
     
     subscript(_ url: URL) -> WebCacheRecord? {
@@ -115,26 +111,24 @@ private final class DownloadWithCacheManager {
 	static let shared = DownloadWithCacheManager()
 	private var cache = WebCache()
 	private static let timeToLive: TimeInterval = 10 * 60 // 10 minutes
-	private static let cleanupInterval: TimeInterval = 30 * 60 // 30 minutes
+	private static let cleanupInterval: TimeInterval = 5 * 60 // clean up the cache at most every 5 minutes
+	private var lastCleanupDate = Date()
 
 	func download(_ url: URL, _ callback: @escaping OneShotDownloadCallback) {
 
-		cache.cleanup(DownloadWithCacheManager.cleanupInterval)
+		if lastCleanupDate.timeIntervalSinceNow < -(5 * 60) {
+			lastCleanupDate = Date()
+			cache.cleanup(DownloadWithCacheManager.timeToLive)
+		}
 
 		let cacheRecord: WebCacheRecord? = cache[url]
-		if let cacheRecord = cacheRecord, !cacheRecord.isExpired(DownloadWithCacheManager.timeToLive) {
+		if let cacheRecord = cacheRecord {
 			callback(cacheRecord.data, cacheRecord.response, nil)
 			return
 		}
 
 		OneShotDownloadManager.shared.download(url) { (data, response, error) in
 
-			if let _ = error, let cacheRecord = cacheRecord {
-				// In the case where a cache record has expired, but the download returned an error, we use the cache record anyway. By design.
-				callback(cacheRecord.data, cacheRecord.response, nil)
-				return
-			}
-
 			if let data = data, let response = response, response.statusIsOK, error == nil {
 				let cacheRecord = WebCacheRecord(url: url, dateDownloaded: Date(), data: data, response: response)
 				self.cache[url] = cacheRecord