Add support for download function in web

dio/lib/src/options.dart

@@ -41,6 +41,10 @@ enum ResponseType {
 
   /// Get the original bytes, the [Response.data] will be [List<int>].
   bytes,
+
+  /// Get blob url.
+  /// Only work in web.
+  blobUrl,
 }
 
 /// {@template dio.options.ListFormat}

plugins/web_adapter/lib/src/html/adapter.dart

@@ -38,7 +38,8 @@ class BrowserHttpClientAdapter implements HttpClientAdapter {
     xhrs.add(xhr);
     xhr
       ..open(options.method, '${options.uri}')
-      ..responseType = 'arraybuffer';
+      ..responseType =
+          options.responseType == ResponseType.blobUrl ? 'blob' : 'arraybuffer';
 
     final withCredentialsOption = options.extra['withCredentials'];
     if (withCredentialsOption != null) {
@@ -65,18 +66,35 @@ class BrowserHttpClientAdapter implements HttpClientAdapter {
     final completer = Completer<ResponseBody>();
 
     xhr.onLoad.first.then((_) {
-      final Uint8List body = (xhr.response as ByteBuffer).asUint8List();
-      completer.complete(
-        ResponseBody.fromBytes(
-          body,
-          xhr.status!,
-          headers: xhr.responseHeaders.map((k, v) => MapEntry(k, v.split(','))),
-          statusMessage: xhr.statusText,
-          isRedirect: xhr.status == 302 ||
-              xhr.status == 301 ||
-              options.uri.toString() != xhr.responseUrl,
-        ),
-      );
+      if (options.responseType == ResponseType.blobUrl) {
+        completer.complete(
+          ResponseBody.fromString(
+            Url.createObjectUrl(xhr.response),
+            xhr.status!,
+            headers:
+                xhr.responseHeaders.map((k, v) => MapEntry(k, v.split(','))),
+            statusMessage: xhr.statusText,
+            isRedirect: xhr.status == 302 ||
+                xhr.status == 301 ||
+                options.uri.toString() != xhr.responseUrl,
+          ),
+        );
+      } else {
+        final Uint8List body = (xhr.response as ByteBuffer).asUint8List();
+        completer.complete(
+          ResponseBody.fromBytes(
+            body,
+            xhr.status!,
+            headers: xhr.responseHeaders.map(
+              (k, v) => MapEntry(k, v.split(',')),
+            ),
+            statusMessage: xhr.statusText,
+            isRedirect: xhr.status == 302 ||
+                xhr.status == 301 ||
+                options.uri.toString() != xhr.responseUrl,
+          ),
+        );
+      }
     });
 
     Timer? connectTimeoutTimer;

plugins/web_adapter/lib/src/html/dio_impl.dart

@@ -1,5 +1,7 @@
 // export '../js_interop/dio_impl.dart';
 
+import 'dart:async';
+
 import 'package:dio/dio.dart';
 
 import 'adapter.dart';
@@ -27,9 +29,24 @@ class DioForBrowser with DioMixin implements Dio {
     String lengthHeader = Headers.contentLengthHeader,
     Object? data,
     Options? options,
-  }) {
-    throw UnsupportedError(
-      'The download method is not available in the Web environment.',
+  }) async {
+    final Response response = await fetch(
+      RequestOptions(
+        baseUrl: urlPath,
+        data: data,
+        method: 'GET',
+        responseType: ResponseType.blobUrl,
+        queryParameters: queryParameters,
+        cancelToken: cancelToken,
+        onReceiveProgress: onReceiveProgress,
+      ),
     );
+
+    final completer = Completer<Response>();
+
+    // Set response in Completer
+    completer.complete(response);
+
+    return DioMixin.listenCancelForAsyncTask(cancelToken, completer.future);
   }
 }