anchor.diff:    /// // Generate an HmacSecretKey.
     /// final key = await HmacSecretKey.generateKey(sha256);
     ///
  -  /// // Function that creates a stream of data from our string-to-sign:
     /// String stringToSign = 'example-string-to-signed';
  -  /// Stream<List<int>> dataStream() async* {
  -  ///   yield utf8.encode(stringToSign);
  -  /// }
     ///
     /// // Compute signature.
  -  /// final signature = await key.sign(dataStream());
  +  /// final signature = await key.sign(Stream.fromIterable([
  +  ///   utf8.encode(stringToSign),
  +  /// ]));
     ///
     /// // Print as base64
     /// print(base64.encode(signature));
  
positive.code:   ///
    /// // Create a signature for UTF-8 encoded message
    /// final message = 'hello world';
    /// final signature = await privateKey.sign(() async* {
    ///   yield utf8.encode(message);
    /// }());
    /// print('signature: ${base64.encode(signature)}');
    /// ```
    Future<Uint8List> sign(Stream<List<int>> data);
  
negative.code:   /// // Generate an HmacSecretKey.
    /// final key = await HmacSecretKey.generateKey(sha256);
    ///
    /// String stringToSign = 'example-string-to-signed';
    ///
    /// // Compute signature.
    /// final signature = await key.sign(Stream.fromIterable([
    ///   utf8.encode(stringToSign),
    /// ]));
    ///
    /// // Verify signature.
    /// final result = await key.verify(signature, Stream.fromIterable([
    ///   utf8.encode(stringToSign),
    /// ]));
    /// assert(result == true, 'this signature should be valid');
    /// ```
    Future<bool> verify(List<int> signature, Stream<List<int>> data);
  