Implement `Attachment.save`

ts/test/types/Attachment_test.ts

@@ -0,0 +1,60 @@
+/**
+ * @prettier
+ */
+import 'mocha';
+import { assert } from 'chai';
+
+import * as Attachment from '../../types/Attachment';
+import { MIMEType } from '../../types/MIME';
+// @ts-ignore
+import { stringToArrayBuffer } from '../../../js/modules/string_to_array_buffer';
+
+describe('Attachment', () => {
+  describe('getFileExtension', () => {
+    it('should return file extension from content type', () => {
+      const input: Attachment.Attachment = {
+        data: stringToArrayBuffer('foo'),
+        contentType: 'image/gif' as MIMEType,
+      };
+      assert.strictEqual(Attachment.getFileExtension(input), 'gif');
+    });
+
+    it('should return file extension for QuickTime videos', () => {
+      const input: Attachment.Attachment = {
+        data: stringToArrayBuffer('foo'),
+        contentType: 'video/quicktime' as MIMEType,
+      };
+      assert.strictEqual(Attachment.getFileExtension(input), 'mov');
+    });
+  });
+
+  describe('getSuggestedFilename', () => {
+    context('for attachment with filename', () => {
+      it('should return existing filename if present', () => {
+        const attachment: Attachment.Attachment = {
+          fileName: 'funny-cat.mov',
+          data: stringToArrayBuffer('foo'),
+          contentType: 'video/quicktime' as MIMEType,
+        };
+        const actual = Attachment.getSuggestedFilename({ attachment });
+        const expected = 'funny-cat.mov';
+        assert.strictEqual(actual, expected);
+      });
+    });
+    context('for attachment without filename', () => {
+      it('should generate a filename based on timestamp', () => {
+        const attachment: Attachment.Attachment = {
+          data: stringToArrayBuffer('foo'),
+          contentType: 'video/quicktime' as MIMEType,
+        };
+        const timestamp = new Date(new Date(0).getTimezoneOffset() * 60 * 1000);
+        const actual = Attachment.getSuggestedFilename({
+          attachment,
+          timestamp,
+        });
+        const expected = 'signal-attachment-1970-01-01-000000.mov';
+        assert.strictEqual(actual, expected);
+      });
+    });
+  });
+});

ts/types/Attachment.ts

@@ -2,8 +2,10 @@
  * @prettier
  */
 import is from '@sindresorhus/is';
+import moment from 'moment';
 
 import * as GoogleChrome from '../util/GoogleChrome';
+import { arrayBufferToObjectURL } from '../util/arrayBufferToObjectURL';
 import { MIMEType } from './MIME';
 
 export interface Attachment {
@@ -23,6 +25,8 @@ export interface Attachment {
   // flags?: number;
 }
 
+const SAVE_CONTENT_TYPE = 'application/octet-stream' as MIMEType;
+
 export const isVisualMedia = (attachment: Attachment): boolean => {
   const { contentType } = attachment;
 
@@ -34,3 +38,55 @@ export const isVisualMedia = (attachment: Attachment): boolean => {
   const isSupportedVideoType = GoogleChrome.isVideoTypeSupported(contentType);
   return isSupportedImageType || isSupportedVideoType;
 };
+
+export const save = ({
+  attachment,
+  timestamp,
+}: {
+  attachment: Attachment;
+  timestamp?: number;
+}): void => {
+  const url = arrayBufferToObjectURL({
+    data: attachment.data,
+    type: SAVE_CONTENT_TYPE,
+  });
+  const anchorElement = document.createElement('a');
+  anchorElement.href = url;
+  anchorElement.download = getSuggestedFilename({ attachment, timestamp });
+  anchorElement.click();
+  URL.revokeObjectURL(url);
+};
+
+export const getSuggestedFilename = ({
+  attachment,
+  timestamp,
+}: {
+  attachment: Attachment;
+  timestamp?: number | Date;
+}): string => {
+  if (attachment.fileName) {
+    return attachment.fileName;
+  }
+
+  const prefix = 'signal-attachment';
+  const suffix = timestamp
+    ? moment(timestamp).format('-YYYY-MM-DD-HHmmss')
+    : '';
+  const fileType = getFileExtension(attachment);
+  const extension = fileType ? `.${fileType}` : '';
+  return `${prefix}${suffix}${extension}`;
+};
+
+export const getFileExtension = (attachment: Attachment): string | null => {
+  if (!attachment.contentType) {
+    return null;
+  }
+
+  switch (attachment.contentType) {
+    case 'video/quicktime':
+      return 'mov';
+    default:
+      // TODO: Use better MIME --> file extension mapping:
+      return attachment.contentType.split('/')[1];
+  }
+};