Add a cache to HTMLMetadataDownloader; do all parsing off the main thread, for better UI performance. Also: make FaviconURLFinder use HTMLMetadataDownloader, as it should have in the first place.

Evergreen/HTMLMetadata/HTMLMetadataDownloader.swift

@@ -12,6 +12,9 @@ import RSParser
 
 struct HTMLMetadataDownloader {
 
+	static var metadataCache = [String: RSHTMLMetadata]()
+	static let serialDispatchQueue = DispatchQueue(label: "HTMLMetadataDownloader")
+
 	static func downloadMetadata(for url: String, _ callback: @escaping (RSHTMLMetadata?) -> Void) {
 
 		guard let actualURL = URL(string: url) else {
@@ -25,8 +28,7 @@ struct HTMLMetadataDownloader {
 
 				let urlToUse = response.url ?? actualURL
 				let parserData = ParserData(url: urlToUse.absoluteString, data: data)
-				let metadata = RSHTMLMetadataParser.htmlMetadata(with: parserData)
-				callback(metadata)
+				parseMetadata(with: parserData, callback)
 				return
 			}
 
@@ -37,4 +39,27 @@ struct HTMLMetadataDownloader {
 			callback(nil)
 		}
 	}
+
+	private static func parseMetadata(with parserData: ParserData, _ callback: @escaping (RSHTMLMetadata?) -> Void) {
+
+		serialDispatchQueue.async {
+
+			let md5String = (parserData.data as NSData).rs_md5HashString()
+			if let md5String = md5String, let cachedMetadata = metadataCache[md5String] {
+				DispatchQueue.main.async {
+					callback(cachedMetadata)
+				}
+				return
+			}
+
+			let htmlMetadata = RSHTMLMetadataParser.htmlMetadata(with: parserData)
+			if let md5String = md5String {
+				metadataCache[md5String] = htmlMetadata
+			}
+
+			DispatchQueue.main.async {
+				callback(htmlMetadata)
+			}
+		}
+	}
 }