it-tools/src/composable/downloadBase64.test.ts

import { describe, expect, it } from 'vitest';
import { getMimeTypeFromBase64 } from './downloadBase64';

describe('downloadBase64', () => {
  describe('getMimeTypeFromBase64', () => {
    it('when the base64 string has a data URI, it returns the mime type', () => {
      expect(getMimeTypeFromBase64({ base64String: 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA' })).to.deep.equal({ mimeType: 'image/png' });
      expect(getMimeTypeFromBase64({ base64String: 'data:image/jpg;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA' })).to.deep.equal({ mimeType: 'image/jpg' });
    });

    it('when the base64 string has no data URI, it try to infer the mime type from the signature', () => {
      // https://en.wikipedia.org/wiki/List_of_file_signatures

      // PNG
      expect(getMimeTypeFromBase64({ base64String: 'iVBORw0KGgoAAAANSUhEUgAAAAUA' })).to.deep.equal({ mimeType: 'image/png' });

      // GIF
      expect(getMimeTypeFromBase64({ base64String: 'R0lGODdh' })).to.deep.equal({ mimeType: 'image/gif' });
      expect(getMimeTypeFromBase64({ base64String: 'R0lGODlh' })).to.deep.equal({ mimeType: 'image/gif' });

      // JPG
      expect(getMimeTypeFromBase64({ base64String: '/9j/' })).to.deep.equal({ mimeType: 'image/jpg' });

      // PDF
      expect(getMimeTypeFromBase64({ base64String: 'JVBERi0' })).to.deep.equal({ mimeType: 'application/pdf' });
    });

    it('when the base64 string has no data URI and no signature, it returns an undefined mimeType', () => {
      expect(getMimeTypeFromBase64({ base64String: 'JVBERi' })).to.deep.equal({ mimeType: undefined });
    });
  });
});