feat: Add option for custom error page

android/capacitor/src/main/java/com/getcapacitor/Bridge.java

@@ -1,5 +1,6 @@
 package com.getcapacitor;
 
+import android.annotation.SuppressLint;
 import android.app.Activity;
 import android.content.ActivityNotFoundException;
 import android.content.Context;
@@ -10,6 +11,7 @@
 import android.content.pm.PackageManager;
 import android.content.res.Configuration;
 import android.net.Uri;
+import android.os.Build;
 import android.os.Bundle;
 import android.os.Handler;
 import android.os.HandlerThread;
@@ -73,6 +75,8 @@ public class Bridge {
     private static final String BUNDLE_PLUGIN_CALL_BUNDLE_KEY = "capacitorLastPluginCallBundle";
     private static final String LAST_BINARY_VERSION_CODE = "lastBinaryVersionCode";
     private static final String LAST_BINARY_VERSION_NAME = "lastBinaryVersionName";
+    private final int MINIMUM_ANDROID_WEBVIEW_VERSION = 60;
+    private static final String MINIMUM_ANDROID_WEBVIEW_ERROR = "System WebView is not supported";
 
     // The name of the directory we use to look for index.html and the rest of our web assets
     public static final String DEFAULT_WEB_ASSET_DIR = "public";
@@ -257,10 +261,60 @@ private void loadWebView() {
                 setServerBasePath(path);
             }
         }
+
+        if (!this.isMinimumWebViewInstalled()) {
+            String errorUrl = this.getErrorUrl();
+            if (errorUrl != null) {
+                webView.loadUrl(errorUrl);
+                return;
+            } else {
+                Logger.error(MINIMUM_ANDROID_WEBVIEW_ERROR);
+            }
+        }
+
         // Get to work
         webView.loadUrl(appUrl);
     }
 
+    @SuppressLint("WebViewApiAvailability")
+    private boolean isMinimumWebViewInstalled() {
+        PackageManager pm = getContext().getPackageManager();
+
+        // Check getCurrentWebViewPackage() directly if above Android 8
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            PackageInfo info = WebView.getCurrentWebViewPackage();
+            String majorVersionStr = info.versionName.split("\\.")[0];
+            int majorVersion = Integer.parseInt(majorVersionStr);
+            return majorVersion >= MINIMUM_ANDROID_WEBVIEW_VERSION;
+        }
+
+        // Otherwise manually check WebView versions
+        try {
+            String webViewPackage = "com.google.android.webview";
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+                webViewPackage = "com.android.chrome";
+            }
+            PackageInfo info = pm.getPackageInfo(webViewPackage, 0);
+            String majorVersionStr = info.versionName.split("\\.")[0];
+            int majorVersion = Integer.parseInt(majorVersionStr);
+            return majorVersion >= MINIMUM_ANDROID_WEBVIEW_VERSION;
+        } catch (Exception ex) {
+            Logger.warn("Unable to get package info for 'com.google.android.webview'" + ex.toString());
+        }
+
+        try {
+            PackageInfo info = pm.getPackageInfo("com.android.webview", 0);
+            String majorVersionStr = info.versionName.split("\\.")[0];
+            int majorVersion = Integer.parseInt(majorVersionStr);
+            return majorVersion >= MINIMUM_ANDROID_WEBVIEW_VERSION;
+        } catch (Exception ex) {
+            Logger.warn("Unable to get package info for 'com.android.webview'" + ex.toString());
+        }
+
+        // Could not detect any webview, return false
+        return false;
+    }
+
     public boolean launchIntent(Uri url) {
         /*
          * Give plugins the chance to handle the url
@@ -408,6 +462,20 @@ public String getServerUrl() {
         return this.config.getServerUrl();
     }
 
+    public String getErrorUrl() {
+        String errorPath = this.config.getErrorPath();
+
+        if (errorPath != null && !errorPath.trim().isEmpty()) {
+            return appUrl + errorPath;
+        }
+
+        return null;
+    }
+
+    public String getAppUrl() {
+        return appUrl;
+    }
+
     public CapConfig getConfig() {
         return this.config;
     }

android/capacitor/src/main/java/com/getcapacitor/BridgeWebViewClient.java

@@ -56,6 +56,15 @@ public void onReceivedError(WebView view, WebResourceRequest request, WebResourc
                 listener.onReceivedError(view);
             }
         }
+
+        String errorPath = bridge.getErrorUrl();
+        String appUrl = bridge.getAppUrl();
+        if (appUrl.charAt(appUrl.length() - 1) != '/') {
+            appUrl += "/";
+        }
+        if (errorPath != null && request.getUrl().toString().equals(appUrl)) {
+            view.loadUrl(errorPath);
+        }
     }
 
     @Override

android/capacitor/src/main/java/com/getcapacitor/CapConfig.java

@@ -43,6 +43,7 @@ public class CapConfig {
     private boolean webContentsDebuggingEnabled = false;
     private boolean loggingEnabled = true;
     private boolean initialFocus = true;
+    private String errorPath;
 
     // Embedded
     private String startPath;
@@ -124,6 +125,7 @@ private CapConfig(Builder builder) {
         this.webContentsDebuggingEnabled = builder.webContentsDebuggingEnabled;
         this.loggingEnabled = builder.loggingEnabled;
         this.initialFocus = builder.initialFocus;
+        this.errorPath = builder.errorPath;
 
         // Embedded
         this.startPath = builder.startPath;
@@ -156,6 +158,7 @@ private void deserializeConfig(@Nullable Context context) {
         html5mode = JSONUtils.getBoolean(configJSON, "server.html5mode", html5mode);
         serverUrl = JSONUtils.getString(configJSON, "server.url", null);
         hostname = JSONUtils.getString(configJSON, "server.hostname", hostname);
+        errorPath = JSONUtils.getString(configJSON, "server.errorPath", null);
 
         String configSchema = JSONUtils.getString(configJSON, "server.androidScheme", androidScheme);
         if (this.validateScheme(configSchema)) {
@@ -224,6 +227,10 @@ public String getServerUrl() {
         return serverUrl;
     }
 
+    public String getErrorPath() {
+        return errorPath;
+    }
+
     public String getHostname() {
         return hostname;
     }
@@ -415,6 +422,7 @@ public static class Builder {
         // Server Config Values
         private boolean html5mode = true;
         private String serverUrl;
+        private String errorPath;
         private String hostname = "localhost";
         private String androidScheme = CAPACITOR_HTTP_SCHEME;
         private String[] allowNavigation;
@@ -472,6 +480,11 @@ public Builder setServerUrl(String serverUrl) {
             return this;
         }
 
+        public Builder setErrorUPath(String errorPath) {
+            this.errorPath = errorPath;
+            return this;
+        }
+
         public Builder setHostname(String hostname) {
             this.hostname = hostname;
             return this;

cli/src/declarations.ts

@@ -443,6 +443,14 @@ export interface CapacitorConfig {
      * @default []
      */
     allowNavigation?: string[];
+
+    /**
+     * Specify path to a local html page to display in case of errors.
+     *
+     * @since 4.0.0
+     * @default null
+     */
+    errorPath?: string;
   };
 
   cordova?: {

ios/Capacitor/Capacitor/CAPInstanceConfiguration.h

@@ -13,6 +13,7 @@ NS_SWIFT_NAME(InstanceConfiguration)
 @property (nonatomic, readonly, nonnull) NSArray<NSString*> *allowedNavigationHostnames;
 @property (nonatomic, readonly, nonnull) NSURL *localURL;
 @property (nonatomic, readonly, nonnull) NSURL *serverURL;
+@property (nonatomic, readonly, nullable) NSString *errorPath;
 @property (nonatomic, readonly, nonnull) NSDictionary *pluginConfigurations;
 @property (nonatomic, readonly) BOOL loggingEnabled;
 @property (nonatomic, readonly) BOOL scrollingEnabled;

ios/Capacitor/Capacitor/CAPInstanceConfiguration.m

@@ -46,6 +46,7 @@ - (instancetype)initWithDescriptor:(CAPInstanceDescriptor *)descriptor isDebug:(
         else {
             _serverURL = _localURL;
         }
+        _errorPath = descriptor.errorPath;
         // extract the one value we care about from the cordova configuration
         _cordovaDeployDisabled = [descriptor cordovaDeployDisabled];
     }
@@ -60,6 +61,7 @@ - (instancetype)initWithConfiguration:(CAPInstanceConfiguration*)configuration a
         _allowedNavigationHostnames = [[configuration allowedNavigationHostnames] copy];
         _localURL = [[configuration localURL] copy];
         _serverURL = [[configuration serverURL] copy];
+        _errorPath = [[configuration errorPath] copy];
         _pluginConfigurations = [[configuration pluginConfigurations] copy];
         _loggingEnabled = configuration.loggingEnabled;
         _scrollingEnabled = configuration.scrollingEnabled;

ios/Capacitor/Capacitor/CAPInstanceConfiguration.swift

@@ -15,6 +15,14 @@ extension InstanceConfiguration {
         return serverURL
     }
 
+    @objc var errorPathURL: URL? {
+        guard let errorPath = errorPath else {
+            return nil
+        }
+
+        return appStartServerURL.appendingPathComponent(errorPath)
+    }
+
     @available(*, deprecated, message: "Use getPluginConfig")
     @objc public func getPluginConfigValue(_ pluginId: String, _ configKey: String) -> Any? {
         return (pluginConfigurations as? JSObject)?[keyPath: KeyPath("\(pluginId).\(configKey)")]

ios/Capacitor/Capacitor/CAPInstanceDescriptor.h

@@ -53,6 +53,11 @@ NS_SWIFT_NAME(InstanceDescriptor)
  @discussion Defaults to @c capacitor. Set by @c server.iosScheme in the configuration file.
  */
 @property (nonatomic, copy, nullable) NSString *urlScheme;
+/**
+ @brief The path to a local html page to display in case of errors.
+ @discussion Defaults to nil.
+ */
+@property (nonatomic, copy, nullable) NSString *errorPath;
 /**
  @brief The hostname that will be used for the server URL.
  @discussion Defaults to @c localhost. Set by @c server.hostname in the configuration file.

ios/Capacitor/Capacitor/CAPInstanceDescriptor.swift

@@ -96,6 +96,9 @@ internal extension InstanceDescriptor {
             if let urlString = config[keyPath: "server.url"] as? String {
                 serverURL = urlString
             }
+            if let errorPathString = (config[keyPath: "server.errorPath"] as? String) {
+                errorPath = errorPathString
+            }
             if let insetBehavior = config[keyPath: "ios.contentInset"] as? String {
                 let availableInsets: [String: UIScrollView.ContentInsetAdjustmentBehavior] = ["automatic": .automatic,
                                                                                               "scrollableAxes": .scrollableAxes,

ios/Capacitor/Capacitor/WebViewDelegationHandler.swift

@@ -132,13 +132,22 @@ internal class WebViewDelegationHandler: NSObject, WKNavigationDelegate, WKUIDel
             webView.isOpaque = isOpaque
             webViewLoadingState = .subsequentLoad
         }
+
+        if let errorURL = bridge?.config.errorPathURL {
+            webView.load(URLRequest(url: errorURL))
+        }
+
         CAPLog.print("⚡️  WebView failed to load")
         CAPLog.print("⚡️  Error: " + error.localizedDescription)
     }
 
     // The force unwrap is part of the protocol declaration, so we should keep it.
     // swiftlint:disable:next implicitly_unwrapped_optional
     public func webView(_ webView: WKWebView, didFailProvisionalNavigation navigation: WKNavigation!, withError error: Error) {
+        if let errorURL = bridge?.config.errorPathURL {
+            webView.load(URLRequest(url: errorURL))
+        }
+
         CAPLog.print("⚡️  WebView failed provisional navigation")
         CAPLog.print("⚡️  Error: " + error.localizedDescription)
     }