Open custom article URI schemes on iOS

Modules/RSWeb/Sources/RSWeb/URL+RSWeb.swift

@@ -17,6 +17,7 @@ private struct URLConstants {
 	static let schemeNetNewsWire = "netnewswire"
 	static let schemeFeed = "feed"
 	static let schemeFeeds = "feeds"
+	static let refusedSchemesForExternalApplications: Set<String> = [schemeHTTP, schemeHTTPS, schemeMailto, "tel", "javascript", "data", "file", "about", "blob", "vbscript"]
 #if os(macOS)
 	static let schemeMagnet = "magnet"
 	static let schemeNetNewsWireFeed = "x-netnewswire-feed"
@@ -68,6 +69,18 @@ public extension URL {
 		return components.url
 	}
 
+	// Written with the help of an LLM.
+	func preparedForOpeningInExternalApplication(excluding excludedSchemes: Set<String> = []) -> URL? {
+		guard let scheme = scheme?.lowercased(with: localeForLowercasing),
+			  !scheme.isEmpty,
+			  !URLConstants.refusedSchemesForExternalApplications.contains(scheme),
+			  !excludedSchemes.contains(where: { $0.lowercased(with: localeForLowercasing) == scheme }) else {
+			return nil
+		}
+
+		return self
+	}
+
 	func preparedForOpeningInBrowser() -> URL? {
 		guard let scheme = scheme?.lowercased(with: localeForLowercasing),
 			  URLConstants.allowedSchemesForOpening.contains(scheme) else {

Modules/RSWeb/Tests/RSWebTests/URLPreparedForOpeningTests.swift

@@ -47,6 +47,39 @@ struct URLPreparedForOpeningTests {
 		#expect(prepared.absoluteString == "http://example.com/path?q=1")
 	}
 
+	@Test func externalApplicationURLsPassThroughUnchanged() throws {
+		for string in [
+			"octal://item?id=12345678",
+			"OCTAL://item?id=1",
+			"netnewswire://theme/add?url=https://example.com/t.nnwtheme",
+			"netnewswire://theme/add",
+			"feed:https://example.com/rss.xml",
+			"feeds:https://example.com/rss.xml"
+		] {
+			let prepared = try #require(url(string).preparedForOpeningInExternalApplication())
+			#expect(prepared.absoluteString == string)
+		}
+	}
+
+	@Test func blocksNonExternalApplicationURLs() throws {
+		for string in [
+			"http://example.com/", "https://example.com/", "mailto:me@example.com", "tel:+15555555555",
+			"javascript:alert(1)", "JAVASCRIPT:alert(1)", "data:text/html,x", "file:///etc/passwd",
+			"about:blank", "blob:https://example.com/id", "vbscript:msgbox(1)", "relative/path"
+		] {
+			#expect(try url(string).preparedForOpeningInExternalApplication() == nil)
+		}
+	}
+
+	@Test func excludesInternalSchemesCaseInsensitively() throws {
+		let excludedSchemes: Set<String> = ["nnwImageIcon", "nnwArticleImage"]
+		for string in ["nnwImageIcon:abc", "nnwArticleImage:abc", "NNWIMAGEICON:abc", "NNWARTICLEIMAGE:abc"] {
+			let original = try url(string)
+			#expect(original.preparedForOpeningInExternalApplication(excluding: excludedSchemes) == nil)
+			#expect(original.preparedForOpeningInExternalApplication() != nil)
+		}
+	}
+
 	private func url(_ string: String) throws -> URL {
 		try #require(URL(string: string))
 	}

iOS/Article/WebViewController.swift

@@ -511,8 +511,11 @@ extension WebViewController: WKNavigationDelegate {
 					UIApplication.shared.open(url, options: [.universalLinksOnly: false], completionHandler: nil)
 				}
 
+			} else if let externalURL = url.preparedForOpeningInExternalApplication(excluding: [ArticleRenderer.imageIconScheme, ArticleRenderer.articleImageScheme]) {
+				decisionHandler(.cancel, preferences)
+				UIApplication.shared.open(externalURL, options: [:], completionHandler: nil)
 			} else {
-				decisionHandler(.allow, preferences)
+				decisionHandler(url.scheme == nil ? .allow : .cancel, preferences)
 			}
 		} else {
 			decisionHandler(.allow, preferences)
@@ -960,8 +963,16 @@ private extension WebViewController {
 		}
 	}
 
-	// If the resource cannot be opened with an installed app, present the web view.
+	// Web URLs fall back to the web view when no installed app opens them.
 	func openURL(_ url: URL) {
+		if let externalURL = url.preparedForOpeningInExternalApplication(excluding: [ArticleRenderer.imageIconScheme, ArticleRenderer.articleImageScheme]) {
+			UIApplication.shared.open(externalURL, options: [:], completionHandler: nil)
+			return
+		}
+		guard url.isHTTPOrHTTPSURL() || url.scheme?.lowercased() == "mailto" || url.scheme?.lowercased() == "tel" else {
+			return
+		}
+
 		UIApplication.shared.open(url, options: [.universalLinksOnly: true]) { didOpen in
 			assert(Thread.isMainThread)
 			guard didOpen == false else {