Keep looking for a favicon when the home page can't be read

Modules/HTMLMetadata/Sources/HTMLMetadata/HTMLMetadataDownloader.swift

@@ -31,6 +31,9 @@ nonisolated public final class HTMLMetadataDownloader: Sendable {
 	/// while its lookup runs, or after it found nothing, until `cache` is emptied.
 	private let urlsLookedUp = Mutex(Set<String>())
 
+	/// URLs whose last fetch failed and that aren’t due for a retry yet.
+	private let unavailableURLs = Mutex(Set<String>())
+
 	init() {
 		NotificationCenter.default.addObserver(self, selector: #selector(handleAppDidGoToBackground(_:)), name: .appDidGoToBackground, object: nil)
 		NotificationCenter.default.addObserver(self, selector: #selector(handleLowMemory(_:)), name: .lowMemory, object: nil)
@@ -59,6 +62,11 @@ nonisolated public final class HTMLMetadataDownloader: Sendable {
 		return nil
 	}
 
+	/// True when the last fetch failed and no retry is pending, so there is no point waiting for
+	/// metadata. Callers that can proceed without it — a `/favicon.ico` guess, say — should.
+	public func metadataIsUnavailable(for url: String) -> Bool {
+		unavailableURLs.withLock { $0.contains(url) }
+	}
 }
 
 // MARK: - Private
@@ -88,6 +96,7 @@ nonisolated private extension HTMLMetadataDownloader {
 			}
 
 			if await HTMLMetadataDatabase.shared.recentlyFailed(for: url) {
+				markUnavailable(url)
 				return
 			}
 
@@ -117,6 +126,20 @@ nonisolated private extension HTMLMetadataDownloader {
 
 	func cacheRecord(_ record: HTMLMetadataRecord) {
 		cache.withLock { $0[record.url] = record }
+		unavailableURLs.withLock { _ = $0.remove(record.url) }
+	}
+
+	/// Marked before any stale record is returned, so a usable record still wins.
+	func markUnavailable(_ url: String) {
+		guard unavailableURLs.withLock({ $0.insert(url).inserted }) else {
+			return
+		}
+		// Observers re-query on this Notification, and metadataIsUnavailable then tells them
+		// not to keep waiting. There is no record to send.
+		let userInfo: [String: Any] = [HTMLMetadataUserInfoKey.url: url]
+		NotificationCenter.default.postOnMainThread(
+			name: .htmlMetadataAvailable, object: self, userInfo: userInfo
+		)
 	}
 
 	func downloadMetadataIfNeeded(_ url: String) {
@@ -180,6 +203,7 @@ nonisolated private extension HTMLMetadataDownloader {
 					await HTMLMetadataDatabase.shared.noteFailure(url: url, statusCode: statusCode)
 				}
 
+				markUnavailable(url)
 				// Download failed — try returning stale cached data.
 				await returnStaleCacheIfAvailable(url)
 
@@ -190,6 +214,7 @@ nonisolated private extension HTMLMetadataDownloader {
 			} catch {
 				// Pre-response failure (DNS, TLS, network).
 				await HTMLMetadataDatabase.shared.noteTransientFailure(url: url)
+				markUnavailable(url)
 				await returnStaleCacheIfAvailable(url)
 
 				activityLog.didFail(.htmlMetadataDownloader, kind: kind, error: error)

Modules/Images/Sources/Images/FaviconDownloader.swift

@@ -226,24 +226,38 @@ private extension FaviconDownloader {
 		}
 		let faviconURLs = htmlMetadata.usableFaviconURLs() ?? [String]()
 
-		guard let scheme = url.scheme, let host = url.host else {
+		guard let defaultFaviconURL = Self.defaultFaviconURL(for: url) else {
 			return faviconURLs.isEmpty ? nil : faviconURLs
 		}
-
-		let defaultFaviconURL = "\(scheme)://\(host)/favicon.ico".lowercased(with: FaviconDownloader.localeForLowercasing)
 		return faviconURLs + [defaultFaviconURL]
 	}
 
+	/// `/favicon.ico` needs no HTML, so it’s still worth a try when the home page can’t be read.
+	func faviconURLsWithoutMetadata(homePageURL: String) -> [String]? {
+		guard HTMLMetadataDownloader.shared.metadataIsUnavailable(for: homePageURL), let url = URL(string: homePageURL), let defaultFaviconURL = Self.defaultFaviconURL(for: url) else {
+			return nil
+		}
+		return [defaultFaviconURL]
+	}
+
+	static func defaultFaviconURL(for url: URL) -> String? {
+		guard let scheme = url.scheme, let host = url.host else {
+			return nil
+		}
+		return "\(scheme)://\(host)/favicon.ico".lowercased(with: localeForLowercasing)
+	}
+
 	func homePageURLsSearching(with faviconURL: String) -> [String] {
 		searches.filter { $0.value.faviconURL == faviconURL }.map { $0.key }
 	}
 
-	/// Without the home page’s metadata in memory, the search starts when `.htmlMetadataAvailable` arrives.
+	/// Without the home page’s metadata in memory, the search starts when `.htmlMetadataAvailable` arrives,
+	/// or tries only `/favicon.ico` if the metadata isn’t coming.
 	func searchForFavicon(homePageURL: String) {
 		guard searches[homePageURL] == nil else {
 			return
 		}
-		guard let faviconURLs = findFaviconURLs(with: homePageURL) else {
+		guard let faviconURLs = findFaviconURLs(with: homePageURL) ?? faviconURLsWithoutMetadata(homePageURL: homePageURL) else {
 			homePagesAwaitingMetadataForSearch.insert(homePageURL)
 			return
 		}