callWithBuffer function

Uint8List? callWithBuffer(BufferCallback fn, { int? maxSize, })

Calls a buffer callback function with dynamically sized buffers.

Starts with initialBufferSize and doubles the buffer size if the callback returns -2 (buffer too small), up to maxSize or maxBufferSize.

When maxSize is null, maxBufferSize is used. Returns the data as Uint8List on success, null on failure.

Implementation

Uint8List? callWithBuffer(BufferCallback fn, {int? maxSize}) {
  final limit = maxSize ?? maxBufferSize;
  var size = initialBufferSize;
  while (size <= limit) {
    final buf = malloc<ffi.Uint8>(size);
    final outWritten = malloc<ffi.Uint32>()..value = 0;
    try {
      final code = fn(buf, size, outWritten);
      if (code == 0) {
        final n = outWritten.value;
        if (n == 0) {
          return Uint8List(0);
        }
        return Uint8List.fromList(buf.asTypedList(n));
      }
      if (code == -2) {
        size *= 2;
        continue;
      }
      return null;
    } finally {
      malloc
        ..free(buf)
        ..free(outWritten);
    }
  }
  return null;
}