Add web view fallback to display images

Gemini-iOS/BrowserWebViewController.swift

@@ -30,6 +30,7 @@ class BrowserWebViewController: UIViewController {
     private let renderer = GeminiHTMLRenderer()
     private(set) var document: Document?
     private var loaded = false
+    private var loadedFallback = false
     
     private var errorStack: UIStackView!
     private var errorMessageLabel: UILabel!
@@ -131,6 +132,7 @@ class BrowserWebViewController: UIViewController {
     
     func reload() {
         loaded = false
+        loadedFallback = false
         loadDocument()
     }
     
@@ -162,9 +164,13 @@ class BrowserWebViewController: UIViewController {
                             self.showError(message: "Invalid redirect URL: '\(response.meta)'")
                         }
                     }
-                } else if response.status.isSuccess,
+                } else if response.status.isSuccess {
+                    if response.mimeType == "text/gemini",
                        let text = response.bodyText {
                         self.renderDocument(GeminiParser.parse(text: text, baseURL: url))
+                    } else {
+                        self.renderFallback(response: response)
+                    }
                 } else {
                     DispatchQueue.main.async {
                         self.showError(message: "Unknown error: \(response.header)")
@@ -202,6 +208,29 @@ class BrowserWebViewController: UIViewController {
         }
     }
     
+    private func renderFallback(response: GeminiResponse) {
+        guard let body = response.body,
+              let mimeType = response.mimeType else {
+            self.showError(message: "Unknown error: \(response.header)")
+            return
+        }
+        DispatchQueue.main.async {
+            self.webView.isHidden = false
+            self.errorStack.isHidden = true
+            self.activityIndicator.isHidden = true
+            self.activityIndicator.stopAnimating()
+            
+            self.loadedFallback = true
+            
+            // todo: probably shouldn't assume this is UTF-8
+            self.webView.load(body, mimeType: mimeType, characterEncodingName: "utf-8", baseURL: self.url)
+            // When showing an image, the safe area insets seem to be ignored. This isn't perfect
+            // (there's a little extra space between the bottom of the nav bar and the top of the image),
+            // but it's better than the image being obscured.
+            self.webView.scrollView.contentInset = self.webView.safeAreaInsets
+        }
+    }
+    
     func scrollToLine(index: Int, animated: Bool) {
         if animated {
             webView.evaluateJavaScript("document.getElementById('l\(index)').getBoundingClientRect().top + window.scrollY") { (result, error) in
@@ -249,6 +278,8 @@ extension BrowserWebViewController: WKNavigationDelegate {
         let url = navigationAction.request.url!
         if url.scheme == "file" {
             decisionHandler(.allow)
+        } else if loadedFallback {
+            decisionHandler(.allow)
         } else {
             decisionHandler(.cancel)
             navigator.changeURL(url)