Thanks.  Also I meant to have said, "...to terminate only on a *blank* non-header non-comment line, in accordance with RFC 2616 (and 7230)."

I note that the RFCs require CRLF to terminate but in my experience you can get all manner of "blank" lines, so accepting len(line.strip())==0 is going to accommodate servers that give CRCR or LFLF or (and I have seen this) LFCRLF.