Resolving Cross-Origin Resource Access

Background

For security purposes, the ArkWeb kernel does not allow the file and resource protocols to access cross-origin requests. As such, the Web component blocks such requests when loading local offline resources. To allow cross-origin requests using the file, you can use method 2 to set a path list. When Web components cannot access local cross-origin resources, the DevTools console displays the following error message:

Access to script at 'xxx' from origin 'xxx' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, arkweb, data, chrome-extension, chrome, https, chrome-untrusted.

Solutions to Local Cross-Origin Resource Access

Method 1

Use HTTP or HTTPS instead of the file or resource protocol to enable Web components to successfully access cross-origin resources. Customize URL domain names for individuals or organizations to prevent conflicts with actual domain names on the Internet. You also need to use the onInterceptRequest API of the Web component to intercept and replace local resources.

The following uses an example to describe how to use HTTP or HTTPS to access local cross-origin resources. the index.html and js/script.js files are stored in the rawfile folder of the project directory. When the resource protocol is used to access the index.html file, the js/script.js file is intercepted due to cross-origin access and cannot be loaded. In the example, the domain name https://www.example.com/ is used to replace the original resource protocol, and the onInterceptRequest API is used to replace the resource to ensure that the js/script.js file can be successfully loaded. In this way, the cross-origin interception problem is solved.

import { webview } from '@kit.ArkWeb';

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';
  webviewController: webview.WebviewController = new webview.WebviewController();
  // Construct a mapping table between domain names and local files.
  schemeMap = new Map([
    ['https://www.example.com/index.html', 'index.html'],
    ['https://www.example.com/js/script.js', 'js/script.js'],
  ]);
  // Construct the local file and construct the return value format mimeType.
  mimeTypeMap = new Map([
    ['index.html', 'text/html'],
    ['js/script.js', 'text/javascript']
  ]);

  build() {
    Row() {
      Column() {
        // For the local index.html file, use HTTP or HTTPS in place of file or resource as the protocol and construct a custom domain name.
        // In this example, www.example.com is constructed.
        Web({ src: 'https://www.example.com/index.html', controller: this.webviewController })
          .javaScriptAccess(true)
          .fileAccess(true)
          .domStorageAccess(true)
          .geolocationAccess(true)
          .width('100%')
          .height('100%')
          .onInterceptRequest((event) => {
            if (!event) {
              return;
            }
            // Search for the local offline resource to be loaded, and then intercept and replace the resource.
            if (this.schemeMap.has(event.request.getRequestUrl())) {
              let rawfileName: string = this.schemeMap.get(event.request.getRequestUrl())!;
              let mimeType = this.mimeTypeMap.get(rawfileName);
              if (typeof mimeType === 'string') {
                let response = new WebResourceResponse();
                // Construct the response data. If the local file is in rawfile, you can set the response data as follows:
                response.setResponseData($rawfile(rawfileName));
                response.setResponseEncoding('utf-8');
                response.setResponseMimeType(mimeType);
                response.setResponseCode(200);
                response.setReasonMessage('OK');
                response.setResponseIsReady(true);
                return response;
              }
            }
            return null;
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}

LocCrossOriginResAccSol_one.ets

<!-- main/resources/rawfile/index.html -->
<html>
<head>
	<meta name="viewport" content="width=device-width,initial-scale=1">
</head>
<body>
<script crossorigin src="./js/script.js"></script>
</body>
</html>

const body = document.body;
const element = document.createElement('div');
element.textContent = 'success';
body.appendChild(element);

script.js

Method 2

Use setPathAllowingUniversalAccess to set a path list for allowing cross-origin access to local files using the file protocol. Note that only the resources in the path list can be accessed by the file protocol when this method is used. In this case, the behavior of fileAccess is overwritten. The paths in the list should be any of the following directories:

The application file directory and its subdirectories, which can be obtained through Context.filesDir, such as:

/data/storage/el2/base/files/example
/data/storage/el2/base/haps/entry/files/example

The application resource directory and its subdirectories, which can be obtained through Context.resourceDir, such as:

/data/storage/el1/bundle/entry/resources/resfile
/data/storage/el1/bundle/entry/resources/resfile/example

Since API version 21, the application cache directory is obtained through Context.cacheDir. Example subdirectories are as follows:

/data/storage/el2/base/cache
/data/storage/el2/base/haps/entry/cache/example
The cache/web directory is not allowed. If it is included, an exception with the code 401 will be thrown. If the cache directory is set, cache/web cannot be accessed.

Since API version 21, the application temporary directory is obtained through Context.tempDir. Example subdirectories are as follows:

/data/storage/el2/base/temp
/data/storage/el2/base/haps/entry/temp/example

If a path is not any of the preceding paths, an error code 401 is reported and the path list fails to be set. If the path list is empty, the access scope of the file protocol complies with the fileAccess rule. The following is an example:

import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: WebviewController = new webview.WebviewController();
  uiContext: UIContext = this.getUIContext();

  build() {
    Row() {
      Web({ src: '', controller: this.controller })
        .onControllerAttached(() => {
          try {
            // Set the list of paths that allow cross-domain access.
            this.controller.setPathAllowingUniversalAccess([
              this.uiContext.getHostContext()!.resourceDir,
              this.uiContext.getHostContext()!.filesDir + '/example'
              ]);
            this.controller.loadUrl('file://' + this.uiContext.getHostContext()!.resourceDir + '/index.html');
          } catch (error) {
            console.error(
              `ErrorCode: ${(error as BusinessError).code},  Message: ${(error as   BusinessError).message}`);
          }
        })
        .javaScriptAccess(true)
        .fileAccess(true)
        .domStorageAccess(true)
    }
  }
}

LocCrossOriginResAccSol_two.ets

<!-- main/resources/resfile/index.html -->
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title>Demo</title>
    <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no,   viewport-fit=cover">
    <script>
		function getFile() {
			var file = "file:///data/storage/el1/bundle/entry/resources/resfile/js/script.js";
      // Use the file protocol to access the local JS file through XMLHttpRequest.
			var xmlHttpReq = new XMLHttpRequest();
			xmlHttpReq.onreadystatechange = function(){
			    console.info("readyState:" + xmlHttpReq.readyState);
			    console.info("status:" + xmlHttpReq.status);
				if(xmlHttpReq.readyState == 4){
				    if (xmlHttpReq.status == 200) {
                // If the path list is set on eTS, resources can be obtained.
				        const element = document.getElementById('text');
                        element.textContent = "load " + file + " success";
				    } else {
                // If the path list is not set on eTS, a CORS error is triggered.
				        const element = document.getElementById('text');
                        element.textContent = "load " + file + " failed";
				    }
				}
			}
			xmlHttpReq.open("GET", file);
			xmlHttpReq.send(null);
		}
    </script>
</head>

<body>
<div class="page">
    <button id="example" onclick="getFile()">loadFile</button>
</div>
<div id="text"></div>
</body>

</html>

const body = document.body;
const element = document.createElement('div');
element.textContent = 'success';
body.appendChild(element);

script.js