[zeromq-dev] Is ZMTP3 backwards compatibility with ZMTP1.0 broken?

Pieter Hintjens ph at imatix.com
Mon Aug 12 16:30:08 CEST 2013


OK, I've made that change. Thanks.

On Mon, Aug 12, 2013 at 3:05 PM, Merijn Verstraaten
<merijn at inconsistent.nl> wrote:
> This is not necessarily a problem, if we retroactively define ZMTP1.0 to
> ignore the more flag on identity frames, which the current C++
> implementation already seems to be doing.
>
> Cheers,
> Merijn
>
> On Aug 12, 2013, at 01:45 , KIU Shueng Chuan wrote:
>
> According to the "Backwards Interoperability" sections of RFC15 and RFC23,
> bit 0 of the flags field is used to probe whether the peer is using
> ZMTP/1.0.
> So now it needs to be left as %x7F.
>
>
>
> On Mon, Aug 12, 2013 at 7:13 AM, Pieter Hintjens <ph at imatix.com> wrote:
>>
>> On Sun, Aug 11, 2013 at 11:19 PM, Merijn Verstraaten
>> <merijn at inconsistent.nl> wrote:
>>
>> > RFC23 states that a backward compatibility detecting handshake starts as
>> > follows:
>> > "Send a 10-octet pseudo-signature consisting of "%xFF size %x7F" where
>> > 'size' is the number of octets in the sender's identity (0 or greater) plus
>> > 1. The size SHALL be 8 octets in network byte order and occupies the padding
>> > field."
>> >
>> > However, RFC13 states that ZMTP1.0 long length messages follow the
>> > format "%xFF size flags", where bit 0 of flags specifies whether there are
>> > more messages to come, which is wrong for an identity frame. Do existing
>> > ZMTP1.0 implementations simply ignore this flag on identity frames?
>>
>> Good catch. For sure ZMTP 1.0 implementations don't check this, but
>> I'm wondering why we chose %x7F. That might be a mistake, based on the
>> explanation of the flags field in RFC 13 (bit 0 is put before bits
>> 1-7). I suspect the intention was to create a valid frame, with the
>> reserved bits all set to 1. So, %xFE.
>>
>> -Pieter
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