Upload file service

The upload file service sends a post request
to the URL defined in the uploadsPath parameter
and parses the HTML response to extract
the src and canonicalSrc of the uploaded attachment

app/assets/javascripts/content_editor/services/upload_file.js

+import axios from '~/lib/utils/axios_utils';
+
+const extractAttachmentLinkUrl = (html) => {
+  const parser = new DOMParser();
+  const { body } = parser.parseFromString(html, 'text/html');
+  const link = body.querySelector('a');
+  const src = link.getAttribute('href');
+  const { canonicalSrc } = link.dataset;
+
+  return { src, canonicalSrc };
+};
+
+/**
+ * Uploads a file with a post request to the URL indicated
+ * in the uploadsPath parameter. The expected response of the
+ * uploads service is a JSON object that contains, at least, a
+ * link property. The link property should contain markdown link
+ * definition (i.e. [GitLab](https://gitlab.com)).
+ *
+ * This Markdown will be rendered to extract its canonical and full
+ * URLs using GitLab Flavored Markdown renderer in the backend.
+ *
+ * @param {Object} params
+ * @param {String} params.uploadsPath An absolute URL that points to a service
+ * that allows sending a file for uploading via POST request.
+ * @param {String} params.renderMarkdown A function that accepts a markdown string
+ * and returns a rendered version in HTML format.
+ * @param {File} params.file The file to upload
+ *
+ * @returns Returns an object with two properties:
+ *
+ * canonicalSrc: The URL as defined in the Markdown
+ * src: The absolute URL that points to the resource in the server
+ */
+export const uploadFile = async ({ uploadsPath, renderMarkdown, file }) => {
+  const formData = new FormData();
+  formData.append('file', file, file.name);
+
+  const { data } = await axios.post(uploadsPath, formData);
+  const { markdown } = data.link;
+  const rendered = await renderMarkdown(markdown);
+
+  return extractAttachmentLinkUrl(rendered);
+};

spec/frontend/content_editor/services/upload_file_spec.js

+import axios from 'axios';
+import MockAdapter from 'axios-mock-adapter';
+import { uploadFile } from '~/content_editor/services/upload_file';
+import httpStatus from '~/lib/utils/http_status';
+
+describe('content_editor/services/upload_file', () => {
+  const uploadsPath = '/uploads';
+  const file = new File(['content'], 'file.txt');
+  // TODO: Replace with automated fixture
+  const renderedAttachmentLinkFixture =
+    '<a href="/group1/project1/-/wikis/test-file.png" data-canonical-src="test-file.png"><img data-src="/group1/project1/-/wikis/test-file.png" data-canonical-src="test-file.png"></a></p>';
+  const successResponse = {
+    link: {
+      markdown: '[GitLab](https://gitlab.com)',
+    },
+  };
+  const parseHTML = (html) => new DOMParser().parseFromString(html, 'text/html');
+  let mock;
+  let renderMarkdown;
+  let renderedMarkdown;
+
+  beforeEach(() => {
+    const formData = new FormData();
+    formData.append('file', file);
+
+    renderedMarkdown = parseHTML(renderedAttachmentLinkFixture);
+
+    mock = new MockAdapter(axios);
+    mock.onPost(uploadsPath, formData).reply(httpStatus.OK, successResponse);
+    renderMarkdown = jest.fn().mockResolvedValue(renderedAttachmentLinkFixture);
+  });
+
+  afterEach(() => {
+    mock.restore();
+  });
+
+  it('returns src and canonicalSrc of uploaded file', async () => {
+    const response = await uploadFile({ uploadsPath, renderMarkdown, file });
+
+    expect(renderMarkdown).toHaveBeenCalledWith(successResponse.link.markdown);
+    expect(response).toEqual({
+      src: renderedMarkdown.querySelector('a').getAttribute('href'),
+      canonicalSrc: renderedMarkdown.querySelector('a').dataset.canonicalSrc,
+    });
+  });
+});