encodeHeader method

@override String encodeHeader(String text, { int nameLength = 0, bool fromStart = false, })

Encodes the header text in base64 only if required. text specifies the text to be encoded. codec the optional codec, which defaults to utf8. Set the optional fromStart to true in case the encoding should start at the beginning of the text and not in the middle.

Implementation

@override
String encodeHeader(String text,
    {int nameLength = 0, bool fromStart = false}) {
  var runes = List.from(text.runes, growable: false);
  var numberOfRunesAbove7Bit = 0;
  var startIndex = -1;
  var endIndex = -1;
  for (var runeIndex = 0; runeIndex < runes.length; runeIndex++) {
    var rune = runes[runeIndex];
    if (rune > 128) {
      numberOfRunesAbove7Bit++;
      if (startIndex == -1) {
        startIndex = runeIndex;
        endIndex = runeIndex;
      } else {
        endIndex = runeIndex;
      }
    }
  }
  if (numberOfRunesAbove7Bit == 0) {
    return text;
  } else {
    // TODO Set the correct encoding
    final qpWordHead = '=?utf8?B?';
    final qpWordTail = '?=';
    final qpWordDelimSize = qpWordHead.length + qpWordTail.length;
    if (fromStart) {
      startIndex = 0;
      endIndex = text.length - 1;
    }
    // Available space for the current encoded word
    var qpWordSize = MailConventions.encodedWordMaxLength -
        qpWordDelimSize -
        startIndex -
        (nameLength + 2);
    var buffer = StringBuffer();
    if (startIndex > 0) {
      buffer.write(text.substring(0, startIndex));
    }
    var textToEncode =
        fromStart ? text : text.substring(startIndex, endIndex + 1);
    var encoded = encodeText(textToEncode, wrap: false);
    buffer.write(qpWordHead);
    if (encoded.length < qpWordSize) {
      buffer.write(encoded);
    } else {
      // Reuses startIndex for folding
      startIndex = 0;
      while (startIndex < encoded.length) {
        var chunk = startIndex + qpWordSize > encoded.length
            ? encoded.substring(startIndex)
            : encoded.substring(startIndex, startIndex + qpWordSize);
        buffer.write(chunk);
        startIndex += qpWordSize;
        if (startIndex < encoded.length) {
          buffer
            ..write(qpWordTail)
            // NOTE Per specification, a CRLF should be inserted here,
            // but the folding occurs on the rendering function.
            // Here we leave only the WSP marker to separate each q-encode word.
            // ..writeCharCode(AsciiRunes.runeCarriageReturn)
            // ..writeCharCode(AsciiRunes.runeLineFeed)
            // Assumes per default a single leading space for header folding
            ..writeCharCode(AsciiRunes.runeSpace);
          buffer.write(qpWordHead);
          qpWordSize =
              MailConventions.encodedWordMaxLength - qpWordDelimSize - 1;
        }
      }
    }
    buffer.write(qpWordTail);
    if (endIndex < text.length - 1) {
      buffer.write(text.substring(endIndex + 1));
    }
    return buffer.toString();
  }
}