[zeromq-dev] STREAM sockets merge two chunks of data on a single recv

[Amr Ali]

When you say "chunks", do you mean parts of a multi-part message being 
sent using send_multipart with the MORE flag set?

On 03/04/2015 12:12 AM, André Caron wrote:
> Stream sockets are basically glorified TCP sockets.  They don't have any
> framing, which means that there is no way to guarantee the receiving
> peer will receive the same number of chunks you send.  Some things that
> can happen:
> - peer receives chunks as sent (likely if chunks are small AND there is
> enough time between sends);
> - peer receives all data in fewer, but larger chunks;
> - peer receives all data in more, but smaller chunks;
> - peer receives part of one chunk before a disconnection.
>
> In order to make sure the peer is atomically delivered each chunk you
> send, you need framing support in the protocol.
>
> André
>
> On Tue, Mar 3, 2015 at 4:09 PM, Amr Ali <amr.ali.cc at gmail.com
> <mailto:amr.ali.cc at gmail.com>> wrote:
>
>     While testing an API implementation where I use 0MQ STREAM socket to
>     send data to a server that uses vanilla TCP socket to receive the data I
>     noticed something peculiar that failed my tests.
>
>     In my tests I use a 0MQ STREAM socket to mock the service's server TCP
>     socket.
>
>     So my API function does multiple consecutive `send()`s (exactly 3), and
>     in my unit test function I do 4 `recv()`s (the first is to get the
>     client identity). The 3rd `recv()` returns the data both the 2nd and 3rd
>     `send()` sent, and the 4th `recv()` times out.
>
>     API sends:
>
>     [First Message]
>     +++ some code +++
>     [Second Message]
>     +++ some code +++
>     [Third Message]
>
>     Test Receives:
>
>     [Client Identity -- no data]
>     +++ some asserts +++
>     [First Message]
>     +++ some asserts +++
>     [Second Message + Third Message]
>     +++ some asserts +++
>     [This recv raises EAGAIN]
>
>     Does libzmq internally make sure to flush data on a STREAM socket before
>     other `send()` calls?
>     --
>     Amr
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>
>
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-- 
Amr