[zeromq-dev] XPUB/XSUB subscriptions and protocol differences between 3.0 and 3.1

[Julien Kauffmann]

Hi,

I've been working on a Python asyncio-native implementation of ZMTP 
during the past weeks. So far everything is going great, but as I wrote 
interoperability tests with pyzmq, I stumbled on a question for which I 
couldn't find an answer in the various RFCs/documentations.

I've implemented ZMTP 3.1 (http://rfc.zeromq.org/spec:37/) and wish to 
also support 3.0 (http://rfc.zeromq.org/spec:23/ZMTP/).

 From what I understand, the main (only ?) difference in the 3.1 version 
is the addition of the PING/PONG, SUBSCRIBE/UNSUBSCRIBE commands and 
endpoint resources.

The SUBSCRIBE/UNSUBSCRIBE part is where I think lies an ambiguity. ZMTP 
3.1 removed from the protocol specification the subscription messages in 
that format:

|subscribe = %x00 short-size %d1 subscription|

And replaced those with:

|subscribe = command-size %d9 "SUBSCRIBE" subscription |

The new RFC makes no reference to the old format whatsoever and so I 
assume this is because this "old" format is no longer supported in ZMTP 
3.1. Put otherwise, the new RFC dictates the use of commands instead of 
messages and from my understanding, commands are not visible to the 
application.

This is fine, except the PUBSUB RFC (http://rfc.zeromq.org/spec:29/), in 
the XSUB/XPUB section does not describe what kind of subscription frame 
is expected from/to be sent to the application. And since the new 
protocol uses commands and not frames anymore, there is no obvious way 
to pass those to/retrieve those from the application layer.

My questions are :
- Should an implementation for ZMTP 3.1 still support the "old" 
subscription format ? I'm asking in the case where the remote peer 
claims it uses 3.1 as well.
- Should an implementation for ZMTP 3.1 convert subscription commands 
to/from the "old" subscription format in XPUB/XSUB messages ? Is this 
documented anywhere ?

Thanks !

Julien.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.zeromq.org/pipermail/zeromq-dev/attachments/20160601/7e67cec0/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4269 bytes
Desc: Signature cryptographique S/MIME
URL: <https://lists.zeromq.org/pipermail/zeromq-dev/attachments/20160601/7e67cec0/attachment.bin>