Define retry strategy

Kingfisher.xcodeproj/project.pbxproj

@@ -24,6 +24,7 @@
 		4BE688F722FD513100B11168 /* NSButton+Kingfisher.swift in Sources */ = {isa = PBXBuildFile; fileRef = D12AB6AD215D2BB50013BA68 /* NSButton+Kingfisher.swift */; };
 		4BE688F822FD513700B11168 /* WKInterfaceImage+Kingfisher.swift in Sources */ = {isa = PBXBuildFile; fileRef = D12AB6AF215D2BB50013BA68 /* WKInterfaceImage+Kingfisher.swift */; };
 		C9286407228584EB00257182 /* ImageProgressive.swift in Sources */ = {isa = PBXBuildFile; fileRef = C9286406228584EB00257182 /* ImageProgressive.swift */; };
+		D11D9B72245FA6F700C5A0AE /* RetryStrategy.swift in Sources */ = {isa = PBXBuildFile; fileRef = D11D9B71245FA6F700C5A0AE /* RetryStrategy.swift */; };
 		D12AB6C0215D2BB50013BA68 /* RequestModifier.swift in Sources */ = {isa = PBXBuildFile; fileRef = D12AB69D215D2BB50013BA68 /* RequestModifier.swift */; };
 		D12AB6C4215D2BB50013BA68 /* Resource.swift in Sources */ = {isa = PBXBuildFile; fileRef = D12AB69E215D2BB50013BA68 /* Resource.swift */; };
 		D12AB6C8215D2BB50013BA68 /* ImageDownloader.swift in Sources */ = {isa = PBXBuildFile; fileRef = D12AB69F215D2BB50013BA68 /* ImageDownloader.swift */; };
@@ -142,6 +143,7 @@
 		4BD821662189FD330084CC21 /* SessionDataTask.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SessionDataTask.swift; sourceTree = "<group>"; };
 		C9286406228584EB00257182 /* ImageProgressive.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ImageProgressive.swift; sourceTree = "<group>"; };
 		C959EEE7228940FE00467A10 /* QuartzCore.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = QuartzCore.framework; path = System/Library/Frameworks/QuartzCore.framework; sourceTree = SDKROOT; };
+		D11D9B71245FA6F700C5A0AE /* RetryStrategy.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RetryStrategy.swift; sourceTree = "<group>"; };
 		D12AB69D215D2BB50013BA68 /* RequestModifier.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = RequestModifier.swift; sourceTree = "<group>"; };
 		D12AB69E215D2BB50013BA68 /* Resource.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Resource.swift; sourceTree = "<group>"; };
 		D12AB69F215D2BB50013BA68 /* ImageDownloader.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ImageDownloader.swift; sourceTree = "<group>"; };
@@ -338,6 +340,7 @@
 				4B10480C216F157000300C61 /* ImageDataProcessor.swift */,
 				D12AB6A0215D2BB50013BA68 /* ImageModifier.swift */,
 				D12AB6A1215D2BB50013BA68 /* ImagePrefetcher.swift */,
+				D11D9B71245FA6F700C5A0AE /* RetryStrategy.swift */,
 			);
 			path = Networking;
 			sourceTree = "<group>";
@@ -822,6 +825,7 @@
 				4B10480D216F157000300C61 /* ImageDataProcessor.swift in Sources */,
 				D12AB72C215D2BB50013BA68 /* Indicator.swift in Sources */,
 				D12AB6C8215D2BB50013BA68 /* ImageDownloader.swift in Sources */,
+				D11D9B72245FA6F700C5A0AE /* RetryStrategy.swift in Sources */,
 				D1A37BE3215D359F009B39B7 /* ImageFormat.swift in Sources */,
 				D12AB714215D2BB50013BA68 /* ImageCache.swift in Sources */,
 				D12AB6D0215D2BB50013BA68 /* ImagePrefetcher.swift in Sources */,

Sources/Networking/RetryStrategy.swift

@@ -0,0 +1,72 @@
+//
+//  RetryStrategy.swift
+//  Kingfisher
+//
+//  Created by onevcat on 2020/05/04.
+//
+//  Copyright (c) 2020 Wei Wang <onevcat@gmail.com>
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in
+//  all copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+//  THE SOFTWARE.
+
+import Foundation
+
+struct RetryContext {
+
+    let source: Source
+
+    let error: KingfisherError
+    let retriedCount: Int
+
+    let userInfo: Any?
+}
+
+enum RetryPolicy {
+    case retry
+    case stop
+}
+
+protocol RetryStrategy {
+    func retry(context: RetryContext, retryHandler: @escaping (RetryPolicy) -> Void)
+}
+
+class SimpleRetryPolicy: RetryStrategy {
+    let maxRetryCount: Int
+    let retryInterval: TimeInterval
+
+    init(maxRetryCount: Int, retryInterval: TimeInterval = 3.0) {
+        self.maxRetryCount = maxRetryCount
+        self.retryInterval = retryInterval
+    }
+
+    func retry(context: RetryContext, retryHandler: @escaping (RetryPolicy) -> Void) {
+        guard context.retriedCount < maxRetryCount else {
+            retryHandler(.stop)
+            return
+        }
+
+        guard !context.error.isTaskCancelled else {
+            retryHandler(.stop)
+            return
+        }
+
+        DispatchQueue.main.asyncAfter(deadline: .now() + self.retryInterval) {
+            retryHandler(.retry)
+        }
+    }
+}