[zeromq-dev] Raw protocol spec for REQ/REP socket?

[Gary Shi]

I want to implement part of the ZeroMQ protocol so I can write
programs interact with it, on platforms where ZeroMQ is not available.
And I found REQ/REP
packets different with 2/SPB: both side make a first connection,
sending 1 packet of \x01\x00; close it then send REQ/REP messages, but
all messages are prefixed by \x01\x01. What's the use of them?

I also checked PUB messages, they're not prefixed. Is it safe to just
append \x01\x01 in front of the SPB messages to talk to a ZeroMQ REP
server?

I noticed the source code called xreq_t::xsend and xrep_t::xrecv for a
empty message with ZMQ_MSG_MORE flag turned on, for the first message.
And the comment mentioned "backtrace stack", but I have no idea about it.

-- 
regards,
Gary Shi