feat(iOS): Add onFileDownload callback (#1214)

`onFileDownload` is called with the URL that you can use to download the file.
When RNCWebView detects that the HTTP response should result in a file download,
`onFileDownload` is called. The client can then provide code to download
the file.

RNCWebView determines that a file download should take place if either of the
following is true:
1. The HTTP response contains a `Content-Disposition` header that is of type
  'attachment'
2. The MIME type of the response cannot be rendered by the iOS WebView

apple/RNCWebView.m

     UIScrollViewDelegate,
 #endif // !TARGET_OS_OSX
     RCTAutoInsetsProtocol>
+
+@property (nonatomic, copy) RCTDirectEventBlock onFileDownload;
 @property (nonatomic, copy) RCTDirectEventBlock onLoadingStart;
 @property (nonatomic, copy) RCTDirectEventBlock onLoadingFinish;
 @property (nonatomic, copy) RCTDirectEventBlock onLoadingError;
   decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse
                     decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler
 {
+  WKNavigationResponsePolicy policy = WKNavigationResponsePolicyAllow;
   if (_onHttpError && navigationResponse.forMainFrame) {
     if ([navigationResponse.response isKindOfClass:[NSHTTPURLResponse class]]) {
       NSHTTPURLResponse *response = (NSHTTPURLResponse *)navigationResponse.response;
       NSInteger statusCode = response.statusCode;
 
       if (statusCode >= 400) {
-        NSMutableDictionary<NSString *, id> *event = [self baseEvent];
-        [event addEntriesFromDictionary: @{
+        NSMutableDictionary<NSString *, id> *httpErrorEvent = [self baseEvent];
+        [httpErrorEvent addEntriesFromDictionary: @{
           @"url": response.URL.absoluteString,
           @"statusCode": @(statusCode)
         }];
 
-        _onHttpError(event);
+        _onHttpError(httpErrorEvent);
+      }
+
+      NSString *disposition = nil;
+      if (@available(iOS 13, *)) {
+        disposition = [response valueForHTTPHeaderField:@"Content-Disposition"];
+      }
+      BOOL isAttachment = disposition != nil && [disposition hasPrefix:@"attachment"];
+      if (isAttachment || !navigationResponse.canShowMIMEType) {
+        if (_onFileDownload) {
+          policy = WKNavigationResponsePolicyCancel;
+
+          NSMutableDictionary<NSString *, id> *downloadEvent = [self baseEvent];
+          [downloadEvent addEntriesFromDictionary: @{
+            @"downloadUrl": (response.URL).absoluteString,
+          }];
+          _onFileDownload(downloadEvent);
+        }
       }
     }
-  }  
+  }
 
-  decisionHandler(WKNavigationResponsePolicyAllow);
+  decisionHandler(policy);
 }
 
 /**

apple/RNCWebViewManager.m

 }
 
 RCT_EXPORT_VIEW_PROPERTY(source, NSDictionary)
+RCT_EXPORT_VIEW_PROPERTY(onFileDownload, RCTDirectEventBlock)
 RCT_EXPORT_VIEW_PROPERTY(onLoadingStart, RCTDirectEventBlock)
 RCT_EXPORT_VIEW_PROPERTY(onLoadingFinish, RCTDirectEventBlock)
 RCT_EXPORT_VIEW_PROPERTY(onLoadingError, RCTDirectEventBlock)

docs/Guide.md

 
 ##### iOS
 
-For iOS, all you need to do is specify the permissions in your `ios/[project]/Info.plist` file:
+On iOS, you are going to have to supply your own code to download files. You can supply an `onFileDownload` callback
+to the WebView component as a prop. If RNCWebView determines that a file download needs to take place, the URL where you can download the file
+will be given to `onFileDownload`. From that callback you can then download that file however you would like to do so.
+
+NOTE: iOS 13+ is needed for the best possible download experience. On iOS 13 Apple added an API for accessing HTTP response headers, which
+is used to determine if an HTTP response should be a download. On iOS 12 or older, only MIME types that cannot be rendered by the webview will
+trigger calls to `onFileDownload`.
+
+Example:
+```javascript
+  onFileDownload = ({ nativeEvent }) => {
+    const { downloadUrl } = nativeEvent;
+    // --> Your download code goes here <--
+  }
+```
 
-Save to gallery:
+To be able to save images to the gallery you need to specify this permission in your `ios/[project]/Info.plist` file:
 
 ```
 <key>NSPhotoLibraryAddUsageDescription</key>
 
 ##### Android
 
-Add permission in AndroidManifest.xml:
+On Android, integration with the DownloadManager is built-in.
+All you have to do to support downloads is add these permissions in AndroidManifest.xml:
 
 ```xml
 <manifest ...>

docs/Reference.md

 - [`sharedCookiesEnabled`](Reference.md#sharedCookiesEnabled)
 - [`textZoom`](Reference.md#textZoom)
 - [`ignoreSilentHardwareSwitch`](Reference.md#ignoreSilentHardwareSwitch)
+- [`onFileDownload`](Reference.md#onFileDownload)
 
 ## Methods Index
 
 | ------- | -------- | -------- |
 | boolean | No       | iOS      |
 
+### `onFileDownload`
+This property is iOS-only.
+
+Function that is invoked when the client needs to download a file.
+
+iOS 13+ only: If the webview navigates to a URL that results in an HTTP
+response with a Content-Disposition header 'attachment...', then
+this will be called.
+
+iOS 8+: If the MIME type indicates that the content is not renderable by the
+webview, that will also cause this to be called. On iOS versions before 13,
+this is the only condition that will cause this function to be called.
+
+The application will need to provide its own code to actually download
+the file.
+
+If not provided, the default is to let the webview try to render the file.
+
+Example:
+```jsx
+<WebView
+  source={{ uri: 'https://reactnative.dev' }}
+  onFileDownload={ ( { nativeEvent: { downloadUrl } } ) => {
+    // You use downloadUrl which is a string to download files however you want.
+  }}
+  />
+```
+
+| Type    | Required | Platform |
+| ------- | -------- | -------- |
+| function | No       | iOS      |
+
 ## Methods
 
 ### `extraNativeComponentConfig()`

example/App.tsx

 import Alerts from './examples/Alerts';
 import Scrolling from './examples/Scrolling';
 import Background from './examples/Background';
+import Downloads from './examples/Downloads';
 import Uploads from './examples/Uploads';
 import Injection from './examples/Injection';
 
       return <Background />;
     },
   },
+  Downloads: {
+    title: 'Downloads',
+    testId: 'downloads',
+    description: 'File downloads test',
+    render() {
+      return <Downloads />;
+    },
+  },
   Uploads: {
     title: 'Uploads',
     testId: 'uploads',
             title="Injection"
             onPress={() => this._changeTest('Injection')}
           />
+          {Platform.OS == "ios" && <Button
+            testID="testType_downloads"
+            title="Downloads"
+            onPress={() => this._changeTest('Downloads')}
+          />}
           {Platform.OS === 'android' && <Button
             testID="testType_uploads"
             title="Uploads"

example/examples/Downloads.tsx

+import React, {Component} from 'react';
+import {Alert, Platform, View} from 'react-native';
+
+import WebView, {FileDownload} from 'react-native-webview';
+
+const HTML = `
+<!DOCTYPE html>\n
+<html>
+  <head>
+    <title>Downloads</title>
+    <meta http-equiv="content-type" content="text/html; charset=utf-8">
+    <meta name="viewport" content="width=320, user-scalable=no">
+    <style type="text/css">
+      body {
+        margin: 0;
+        padding: 0;
+        font: 62.5% arial, sans-serif;
+        background: #ccc;
+      }
+    </style>
+  </head>
+  <body>
+    <a href="https://www.7-zip.org/a/7za920.zip">Example zip file download</a>
+  </body>
+</html>
+`;
+
+type Props = {};
+type State = {};
+
+export default class Downloads extends Component<Props, State> {
+  state = {};
+
+  onFileDownload = ({ nativeEvent }: { nativeEvent: FileDownload } ) => {
+    Alert.alert("File download detected", nativeEvent.downloadUrl);
+  };
+
+  render() {
+    const platformProps = Platform.select({
+      ios: {
+        onFileDownload: this.onFileDownload,
+      },
+    });
+
+    return (
+      <View style={{ height: 120 }}>
+        <WebView
+          source={{html: HTML}}
+          automaticallyAdjustContentInsets={false}
+          {...platformProps}
+        />
+      </View>
+    );
+  }
+}

example/ios/Podfile.lock

     - React-cxxreact (= 0.61.5)
     - React-jsi (= 0.61.5)
   - React-jsinspector (0.61.5)
-  - react-native-webview (8.2.0):
+  - react-native-webview (9.3.0):
     - React
   - React-RCTActionSheet (0.61.5):
     - React-Core/RCTActionSheetHeaders (= 0.61.5)
   React-jsi: cb2cd74d7ccf4cffb071a46833613edc79cdf8f7
   React-jsiexecutor: d5525f9ed5f782fdbacb64b9b01a43a9323d2386
   React-jsinspector: fa0ecc501688c3c4c34f28834a76302233e29dc0
-  react-native-webview: 1db33907230d0eb344964d6f3bb56b9ee77e25a4
+  react-native-webview: 60d883f994e96a560756c14592552e02a06d604d
   React-RCTActionSheet: 600b4d10e3aea0913b5a92256d2719c0cdd26d76
   React-RCTAnimation: 791a87558389c80908ed06cc5dfc5e7920dfa360
   React-RCTBlob: d89293cc0236d9cb0933d85e430b0bbe81ad1d72
   ReactCommon: 198c7c8d3591f975e5431bec1b0b3b581aa1c5dd
   Yoga: f2a7cd4280bfe2cca5a7aed98ba0eb3d1310f18b
 
-PODFILE CHECKSUM: 2b0bdb79b803eefe541da6f9be6b06e99063bbfd
+PODFILE CHECKSUM: c2e136f84288494fa269d79892a8a1cf7acd7c71
 
 COCOAPODS: 1.8.4

index.d.ts

 // eslint-disable-next-line
 import { IOSWebViewProps, AndroidWebViewProps } from './lib/WebViewTypes';
 
-export { WebViewMessageEvent, WebViewNavigation } from "./lib/WebViewTypes";
+export { FileDownload, WebViewMessageEvent, WebViewNavigation } from "./lib/WebViewTypes";
 
 export type WebViewProps = IOSWebViewProps & AndroidWebViewProps;
 

src/WebView.ios.tsx

         onLoadingError={this.onLoadingError}
         onLoadingFinish={this.onLoadingFinish}
         onLoadingProgress={this.onLoadingProgress}
+        onFileDownload={this.props.onFileDownload}
         onLoadingStart={this.onLoadingStart}
         onHttpError={this.onHttpError}
         onMessage={this.onMessage}

src/WebViewTypes.ts

   mainDocumentURL?: string;
 }
 
+export interface FileDownload {
+  downloadUrl: string;
+}
+
 export type DecelerationRateConstant = 'normal' | 'fast';
 
 export interface WebViewMessage extends WebViewNativeEvent {
 
 export type WebViewNavigationEvent = NativeSyntheticEvent<WebViewNavigation>;
 
+export type FileDownloadEvent = NativeSyntheticEvent<FileDownload>;
+
 export type WebViewMessageEvent = NativeSyntheticEvent<WebViewMessage>;
 
 export type WebViewErrorEvent = NativeSyntheticEvent<WebViewError>;
   onContentProcessDidTerminate?: (event: WebViewTerminatedEvent) => void;
   injectedJavaScriptForMainFrameOnly?: boolean;
   injectedJavaScriptBeforeContentLoadedForMainFrameOnly?: boolean;
+  onFileDownload?: (event: FileDownloadEvent) => void;
 }
 
 export interface MacOSNativeWebViewProps extends CommonNativeWebViewProps {
    * @platform ios
   */
   injectedJavaScriptBeforeContentLoadedForMainFrameOnly?: boolean;
+
+  /**
+   * Function that is invoked when the client needs to download a file.
+   *
+   * iOS 13+ only: If the webview navigates to a URL that results in an HTTP
+   * response with a Content-Disposition header 'attachment...', then
+   * this will be called.
+   *
+   * iOS 8+: If the MIME type indicates that the content is not renderable by the
+   * webview, that will also cause this to be called. On iOS versions before 13,
+   * this is the only condition that will cause this function to be called.
+   *
+   * The application will need to provide its own code to actually download
+   * the file.
+   *
+   * If not provided, the default is to let the webview try to render the file.
+   */
+  onFileDownload?: (event: FileDownloadEvent) => void;
 }
 
 export interface MacOSWebViewProps extends WebViewSharedProps {

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