This code doesn't compile when bzip2 is installed but zlib is not. Regardless is it not correct to use Z_BUF_ERROR here.

see http://www.bzip.org/1.0.3/html/low-level.html

int old_sz =0, new_sz =0;
while(_stream.next_in != nullptr && _stream.avail_in != 0) {
int st = BZ2_bzCompress(&_stream, BZ_FINISH);
switch (st) {
case BZ_STREAM_END:
break;
case BZ_FINISH_OK:
// No output space. Increase the output space by 20%.
// (Should we fail the compression since it expands the size?)
old_sz = output->size();
new_sz = (int)(output->size() * 1.2);
output->resize(new_sz);
// Set more output.
_stream.next_out = (char _)&(_output)[old_sz];
_stream.avail_out = new_sz - old_sz;
break;
case Z_BUF_ERROR:
default:
BZ2_bzCompressEnd(&_stream);
return false;
}
}