Implement download_file in widget driver

src/stores/widgets/StopGapWidgetDriver.ts

@@ -73,6 +73,7 @@ import { navigateToPermalink } from "../../utils/permalinks/navigator";
 import { SdkContextClass } from "../../contexts/SDKContext";
 import { ModuleRunner } from "../../modules/ModuleRunner";
 import SettingsStore from "../../settings/SettingsStore";
+import { Media } from "../../customisations/Media";
 
 // TODO: Purge this from the universe
 
@@ -679,4 +680,18 @@ export class StopGapWidgetDriver extends WidgetDriver {
 
         return { contentUri: uploadResult.content_uri };
     }
+
+    /**
+     * Download a file from the media repository on the homeserver.
+     *
+     * @param contentUri - the MXC URI of the file to download
+     * @returns an object with: file - response contents as Blob
+     */
+    public async downloadFile(contentUri: string): Promise<{ file: XMLHttpRequestBodyInit }> {
+        const client = MatrixClientPeg.safeGet();
+        const media = new Media({mxc: contentUri}, client);
+        const response = await media.downloadSource();
+        const blob = await response.blob();
+        return { file:  blob };
+    }
 }

test/stores/widgets/StopGapWidgetDriver-test.ts

@@ -15,6 +15,7 @@
 */
 
 import { mocked, MockedObject } from "jest-mock";
+import fetchMockJest from "fetch-mock-jest";
 import {
     MatrixClient,
     ClientEvent,
@@ -616,4 +617,32 @@
             expect(client.uploadContent).toHaveBeenCalledWith("data");
         });
     });
+
+    describe("downloadFile", () => {
+        let driver: WidgetDriver;
+
+        beforeEach(() => {
+            driver = mkDefaultDriver();
+        });
+
+        it("should download a file and return the blob", async () => {
+            // eslint-disable-next-line no-restricted-properties
+            client.mxcUrlToHttp.mockImplementation((mxcUrl) => {
+                if (mxcUrl === "mxc://example.com/test_file") {
+                    return "https://example.com/_matrix/media/v3/download/test_file";
+                }
+
+                return null;
+            });
+
+            fetchMockJest.get("https://example.com/_matrix/media/v3/download/test_file", "test contents");
+
+            const result = await driver.downloadFile("mxc://example.com/test_file");
+            // A type test is impossible here because of
+            // https://github.com/jefflau/jest-fetch-mock/issues/209
+            // Tell TypeScript that file is a blob.
+            const file = result.file as Blob;
+            await expect(file.text()).resolves.toEqual("test contents");
+        });
+    });
 });