/**
   * Returns a {@code ByteSource} that reads base-encoded bytes from the specified {@code
   * CharSource}.
   */
  @J2ktIncompatible
  @GwtIncompatible // ByteSource,CharSource
  public final ByteSource decodingSource(CharSource encodedSource) {
    checkNotNull(encodedSource);
    return new ByteSource() {
      @Override
      public InputStream openStream() throws IOException {