Add `Attachment.isFile` definition

ts/test/types/Attachment_test.ts

@@ -59,6 +59,45 @@ describe('Attachment', () => {
     });
   });
 
+  describe('isFile', () => {
+    it('should return true for JSON', () => {
+      const attachment: Attachment.Attachment = {
+        fileName: 'foo.json',
+        data: stringToArrayBuffer('{"foo": "bar"}'),
+        contentType: MIME.APPLICATION_JSON,
+      };
+      assert.isTrue(Attachment.isFile(attachment));
+    });
+
+    it('should return false for images', () => {
+      const attachment: Attachment.Attachment = {
+        fileName: 'meme.gif',
+        data: stringToArrayBuffer('gif'),
+        contentType: MIME.IMAGE_GIF,
+      };
+      assert.isFalse(Attachment.isFile(attachment));
+    });
+
+    it('should return false for videos', () => {
+      const attachment: Attachment.Attachment = {
+        fileName: 'meme.mp4',
+        data: stringToArrayBuffer('mp4'),
+        contentType: MIME.VIDEO_MP4,
+      };
+      assert.isFalse(Attachment.isFile(attachment));
+    });
+
+    it('should return false for voice message attachment', () => {
+      const attachment: Attachment.Attachment = {
+        fileName: 'Voice Message.aac',
+        flags: SignalService.AttachmentPointer.Flags.VOICE_MESSAGE,
+        data: stringToArrayBuffer('voice message'),
+        contentType: MIME.AUDIO_AAC,
+      };
+      assert.isFalse(Attachment.isFile(attachment));
+    });
+  });
+
   describe('isVoiceMessage', () => {
     it('should return true for voice message attachment', () => {
       const attachment: Attachment.Attachment = {

ts/types/Attachment.ts

@@ -41,6 +41,24 @@ export const isVisualMedia = (attachment: Attachment): boolean => {
   return MIME.isImage(contentType) || MIME.isVideo(contentType);
 };
 
+export const isFile = (attachment: Attachment): boolean => {
+  const { contentType } = attachment;
+
+  if (is.undefined(contentType)) {
+    return false;
+  }
+
+  if (isVisualMedia(attachment)) {
+    return false;
+  }
+
+  if (isVoiceMessage(attachment)) {
+    return false;
+  }
+
+  return true;
+};
+
 export const isVoiceMessage = (attachment: Attachment): boolean => {
   const flag = SignalService.AttachmentPointer.Flags.VOICE_MESSAGE;
   const hasFlag =