[zeromq-dev] ZeroMQ STREAM Socket Type

Doron Somech somdoron at gmail.com
Wed May 25 11:41:02 CEST 2016


1. Doesn't matter
2. Yes, first part is the identity, then the data.
3. I'm not sure multipart is even working with STREAM socket.

On Tue, May 24, 2016 at 6:43 PM, Peter Witkowski <pwitkowski at gmail.com>
wrote:

> Thanks for the reply.
>
> First, I think the diagram below (please forgive my poor ASCII art) shows
> what I was trying to explain.
>
> Original (working code):
> PUSH (three part message) -----------TCP--------------> PULL (three part
> message)
>
> Currently Planned Implementation:
> STREAM Client  (PUSH replacement)------TCP--------> Data Link Server
> ---------MAGIC?-------> Data Link Client------TCP------>STREAM Server (PULL
> replacement)
>
> Each STREAM socket must talk to the data link's TCP service (and this is
> "regular" TCP) which then forwards the sender's data across the link.  No
> data from the PULL replacement will be able to make it back due to
> limitations with the physical layer on the data link (labeled "MAGIC?").
>
> I still have a few questions left:
> 1. Does it matter what I set the ZMQ_CONNECT_RID to?  I'm assuming the
> STREAM Server isn't looking for this.
> 2. How does the receive side look like?  Do I get a identity from the Data
> Link Client after I bind?  Do I read this out each time before I read the
> actual data?
> 3. I'm assuming it's best to now NOT use the three part message (have to
> check each zmq_send() call for the number of bytes sent).  Instead, I'm
> planning on serializing and ensuring that all the bytes make it across.
>
> Thanks again for the help.
>
> On Tue, May 24, 2016 at 3:00 AM, Doron Somech <somdoron at gmail.com> wrote:
>
>> Ok, you have an option called ZMQ_CONNECT_RID, when you set it in a
>> STREAM socket is set the identity of the first peer, so instead of what you
>> are doing now, do:
>>
>> 1. Set the socket CONNECT RID  to "C" (or whatever)
>> 2. Connect the socket (RID MUST BE BEFORE CONNECT)
>> 3. Send identity"C"
>> 4. Send message
>>
>> Regarding atomic send, it wont, STREAM will send any bytes arrive, but it
>> should not matter as TCP is stream protocol snd don't have the notion of
>> messages.
>>
>> Zero length message is not flushing the data, is just closing the tcp
>> socket. You can also just close the socket.
>> On May 24, 2016 09:52, "Doron Somech" <somdoron at gmail.com> wrote:
>>
>>> It seems what you are doing won't work as currently it is hard to use
>>> STREAM as the first sender, as you don't know the identity if the peer. I
>>> think someone added notify option, worth to check it out. Are you using
>>> STREAM at both sides?
>>> On May 24, 2016 00:04, "Peter Witkowski" <pwitkowski at gmail.com> wrote:
>>>
>>>> Sorry to spam everyone, but just to clarify, when I say that PUSH-PULL
>>>> doesn't work because of handshaking, I'm speaking about the ZeroMQ
>>>> handshake (greetings, etc.).  The data link handles the TCP connection
>>>> stuff.
>>>>
>>>> On Mon, May 23, 2016 at 4:58 PM, Peter Witkowski <pwitkowski at gmail.com>
>>>> wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> Long story short, I have code that works that I now need to refactor.
>>>>> The networking for my application has changed and I need to push my ZeroMQ
>>>>> messages over a half-duplex (i.e., one way) wireless data link.  The data
>>>>> link is looking for raw TCP on either end and specifies what side is the
>>>>> client and server.  You can think of this data link as a one way bridge,
>>>>> with a TCP endpoint on either end that I need to talk to.  The data link
>>>>> then forwards the TCP traffic in some weird protocol to the other side.
>>>>>
>>>>> The code I have written is a PUSH-PULL pattern, which doesn't work due
>>>>> to the handshaking involved at the socket's start-up (I'm assuming there's
>>>>> no way to disable this).  The code sends and receives a three-part message
>>>>> (the third message part is large, about 65KB).  I need to refactor this
>>>>> into two STREAM sockets, but I'm having problems (conceptually) with
>>>>> sending and receiving.
>>>>>
>>>>> Here's some pseudo code for the sender (which is the client per the
>>>>> data link):
>>>>>
>>>>>    - Set-up context, open socket, call connect.
>>>>>    - Get ZMQ_IDENTITY using zmq_getsockopt()
>>>>>    - Send identity
>>>>>    - Send message part 1 (assuming that this is an atomic send and
>>>>>    won't only send N bytes)
>>>>>    - Send identity
>>>>>    - Send message part 2 (see previous assumption about atomic)
>>>>>    - Send identity
>>>>>    - Send message part 3 (see previous assumption about atomic)
>>>>>    - When I'm ready to close, I send the identity followed by a zero
>>>>>    length packet
>>>>>
>>>>> The receiver (TCP server per the data link) is basically the opposite,
>>>>> but here I'm a bit confused.  Namely, is each receive call atomic, or is
>>>>> there a chance that the data gets chunked up into multiple messages?  Also,
>>>>> do I need to read off the identifier each time or does the library only
>>>>> forward the message parts?
>>>>>
>>>>> Also, in general, are there any issues with using ZeroMQ (even STREAM
>>>>> sockets) with this set-up?  Note that my assumption is that the receiver
>>>>> never needs to send data and the sender never needs to receive data.
>>>>>
>>>>> Thanks in advance for the help.
>>>>> --
>>>>> Peter Witkowski
>>>>> pwitkowski at gmail.com
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Peter Witkowski
>>>> pwitkowski at gmail.com
>>>>
>>>> _______________________________________________
>>>> zeromq-dev mailing list
>>>> zeromq-dev at lists.zeromq.org
>>>> http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>>>
>>>
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>
>
>
> --
> Peter Witkowski
> pwitkowski at gmail.com
>
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