looksLikeBinary function

bool looksLikeBinary(Uint8List bytes)

Whether bytes look like a binary file rather than text (for example a binary file renamed .txt or .csv).

A cheap heuristic, not a content-type sniffer: a NUL byte, or more than 5% non-whitespace control bytes in the first 8000 bytes, means binary. UTF-16 text with a byte order mark is text, whatever its NUL bytes.

Implementation

bool looksLikeBinary(Uint8List bytes) {
  if (bytes.isEmpty || hasUtf16Bom(bytes)) return false;
  final sampleSize = bytes.length < 8000 ? bytes.length : 8000;
  var controlCount = 0;
  for (var i = 0; i < sampleSize; i++) {
    final b = bytes[i];
    if (b == 0) return true;
    final isCommonWhitespace = b == 0x09 || b == 0x0A || b == 0x0D;
    if (!isCommonWhitespace && b < 0x20) controlCount++;
  }
  return controlCount / sampleSize > 0.05;
}