Create FeedDownloader local package.

FeedDownloader/.gitignore

@@ -0,0 +1,8 @@
+.DS_Store
+/.build
+/Packages
+xcuserdata/
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

FeedDownloader/.swiftpm/xcode/xcshareddata/xcschemes/FeedDownloader.xcscheme

@@ -0,0 +1,67 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1530"
+   version = "1.7">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES"
+      buildArchitectures = "Automatic">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "FeedDownloader"
+               BuildableName = "FeedDownloader"
+               BlueprintName = "FeedDownloader"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      shouldAutocreateTestPlan = "YES">
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "FeedDownloader"
+            BuildableName = "FeedDownloader"
+            BlueprintName = "FeedDownloader"
+            ReferencedContainer = "container:">
+         </BuildableReference>
+      </MacroExpansion>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

FeedDownloader/Package.swift

@@ -0,0 +1,32 @@
+// swift-tools-version: 5.10
+
+import PackageDescription
+
+let package = Package(
+	name: "FeedDownloader",
+	platforms: [.macOS(.v14), .iOS(.v17)],
+	products: [
+		.library(
+			name: "FeedDownloader",
+			targets: ["FeedDownloader"]),
+	],
+	dependencies: [
+		.package(path: "../Web"),
+		.package(path: "../FoundationExtras"),
+	],
+	targets: [
+		.target(
+			name: "FeedDownloader",
+			dependencies: [
+				"Web",
+				"FoundationExtras"
+			],
+			swiftSettings: [
+				.enableExperimentalFeature("StrictConcurrency")
+			]
+		),
+		.testTarget(
+			name: "FeedDownloaderTests",
+			dependencies: ["FeedDownloader"]),
+	]
+)

FeedDownloader/Sources/FeedDownloader/FeedDownloader.swift

@@ -0,0 +1,155 @@
+//
+//  FeedDownloader.swift
+//  NetNewsWire
+//
+//  Created by Brent Simmons on 5/22/24.
+//  Copyright © 2024 Brent Simmons. All rights reserved.
+//
+
+import Foundation
+import FoundationExtras
+import os
+import Web
+
+public protocol FeedDownloaderDelegate: AnyObject {
+
+	@MainActor func feedDownloader(_: FeedDownloader, requestCompletedForFeedURL: URL, response: URLResponse?, data: Data?, error: Error?)
+
+	@MainActor func feedDownloader(_: FeedDownloader, requestCanceledForFeedURL: URL, response: URLResponse?, data: Data?, error: Error?, reason: FeedDownloader.CancellationReason)
+
+	@MainActor func feedDownloaderSessionDidComplete(_: FeedDownloader)
+
+	@MainActor func feedDownloader(_: FeedDownloader, conditionalGetInfoFor: URL) -> HTTPConditionalGetInfo?
+}
+
+/// Use this to download feeds directly (local and iCloud accounts).
+@MainActor public final class FeedDownloader {
+
+	public enum CancellationReason {
+		case suspended
+		case notFeedData
+		case unexpectedResponse
+		case notModified
+	}
+
+	public weak var delegate: FeedDownloaderDelegate?
+	public var downloadProgress: DownloadProgress {
+		downloadSession.downloadProgress
+	}
+
+	private let downloadSession: DownloadSession
+	private var isSuspended = false
+
+	public init() {
+
+		self.downloadSession = DownloadSession()
+		downloadSession.delegate = self
+	}
+
+	public func downloadFeeds(_ feedURLs: Set<URL>) {
+
+		let feedIdentifiers = Set(feedURLs.map { $0.absoluteString })
+		downloadSession.download(feedIdentifiers)
+	}
+
+	public func suspend() async {
+
+		isSuspended = true
+		await downloadSession.cancelAll()
+	}
+
+	public func resume() {
+
+		isSuspended = false
+	}
+}
+
+extension FeedDownloader: DownloadSessionDelegate {
+
+	public func downloadSession(_ downloadSession: DownloadSession, requestForIdentifier identifier: String) -> URLRequest? {
+
+		guard let url = URL(string: identifier) else {
+			assertionFailure("There should be no case where identifier is not convertible to URL.")
+			return nil
+		}
+
+		var request = URLRequest(url: url)
+		if let conditionalGetInfo = delegate?.feedDownloader(self, conditionalGetInfoFor: url) {
+			conditionalGetInfo.addRequestHeadersToURLRequest(&request)
+		}
+
+		return request
+	}
+
+	public func downloadSession(_ downloadSession: DownloadSession, downloadDidCompleteForIdentifier identifier: String, response: URLResponse?, data: Data?, error: Error?) {
+
+		guard let url = URL(string: identifier) else {
+			assertionFailure("There should be no case where identifier is not convertible to URL.")
+			return
+		}
+
+		delegate?.feedDownloader(self, requestCompletedForFeedURL: url, response: response, data: data, error: error)
+	}
+
+	public func downloadSession(_ downloadSession: DownloadSession, shouldContinueAfterReceivingData data: Data, identifier: String) -> Bool {
+
+		guard let url = URL(string: identifier) else {
+			assertionFailure("There should be no case where identifier is not convertible to URL.")
+			return false
+		}
+
+		if isSuspended {
+			delegate?.feedDownloader(self, requestCanceledForFeedURL: url, response: nil, data: nil, error: nil, reason: .suspended)
+			return false
+		}
+
+		if data.isEmpty {
+			return true
+		}
+
+		if data.isNotAFeed() {
+			delegate?.feedDownloader(self, requestCanceledForFeedURL: url, response: nil, data: data, error: nil, reason: .notFeedData)
+			return false
+		}
+
+		return true
+	}
+
+	public func downloadSession(_ downloadSession: DownloadSession, didReceiveUnexpectedResponse response: URLResponse, identifier: String) {
+
+		guard let url = URL(string: identifier) else {
+			assertionFailure("There should be no case where identifier is not convertible to URL.")
+			return
+		}
+
+		delegate?.feedDownloader(self, requestCanceledForFeedURL: url, response: response, data: nil, error: nil, reason: .unexpectedResponse)
+	}
+
+	public func downloadSession(_ downloadSession: DownloadSession, didReceiveNotModifiedResponse response: URLResponse, identifier: String) {
+
+		guard let url = URL(string: identifier) else {
+			assertionFailure("There should be no case where identifier is not convertible to URL.")
+			return
+		}
+
+		delegate?.feedDownloader(self, requestCanceledForFeedURL: url, response: response,  data: nil, error: nil, reason: .notModified)
+	}
+
+	public func downloadSession(_ downloadSession: DownloadSession, didDiscardDuplicateIdentifier: String) {
+
+		// nothing to do
+	}
+
+	public func downloadSessionDidComplete(_ downloadSession: DownloadSession) {
+
+		delegate?.feedDownloaderSessionDidComplete(self)
+	}
+}
+
+extension Data {
+
+	func isNotAFeed() -> Bool {
+
+		isImage // TODO: expand this
+	}
+}

FeedDownloader/Tests/FeedDownloaderTests/FeedDownloaderTests.swift

@@ -0,0 +1,12 @@
+import XCTest
+@testable import FeedDownloader
+
+final class FeedDownloaderTests: XCTestCase {
+    func testExample() throws {
+        // XCTest Documentation
+        // https://developer.apple.com/documentation/xctest
+
+        // Defining Test Cases and Test Methods
+        // https://developer.apple.com/documentation/xctest/defining_test_cases_and_test_methods
+    }
+}

NetNewsWire.xcodeproj/project.pbxproj

@@ -1020,6 +1020,7 @@
 		8426119D1FCB6ED40086A189 /* HTMLMetadataDownloader.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = HTMLMetadataDownloader.swift; sourceTree = "<group>"; };
 		842E45CD1ED8C308000A8B52 /* AppNotifications.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AppNotifications.swift; sourceTree = "<group>"; };
 		842E45DC1ED8C54B000A8B52 /* Browser.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Browser.swift; sourceTree = "<group>"; };
+		843429CC2BFEE3B6003D6C70 /* FeedDownloader */ = {isa = PBXFileReference; lastKnownFileType = wrapper; path = FeedDownloader; sourceTree = "<group>"; };
 		843EA3EA2BFC293B003F2E97 /* Mac.xctestplan */ = {isa = PBXFileReference; lastKnownFileType = text; path = Mac.xctestplan; sourceTree = "<group>"; };
 		84411E701FE5FBFA004B527F /* SmallIconProvider.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SmallIconProvider.swift; sourceTree = "<group>"; };
 		8444C8F11FED81840051386C /* OPMLExporter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OPMLExporter.swift; sourceTree = "<group>"; };
@@ -2013,6 +2014,7 @@
 				84A699132BC34E8500605AB8 /* ArticleExtractor */,
 				84FB9FAE2BC3494B00B7AFC3 /* FeedFinder */,
 				51CD32C624D2DEF9009ABAEF /* Account */,
+				843429CC2BFEE3B6003D6C70 /* FeedDownloader */,
 				84A699182BC3524C00605AB8 /* LocalAccount */,
 				84FB9FAD2BC344F800B7AFC3 /* Feedbin */,
 				84A699192BC36EDB00605AB8 /* Feedly */,