The existing IDENTITY socket option is useless for your purpose because
it is transmitted at the end of the handcheck in the metadata. When a
ROUTER receives a new connection, it assigns to it a own forged identity
(random for the first peer and then incremented for the next ones). It
is a 5 bytes blob, the first one is always zero, the 4 others are mapped
to a int.
So, when the peer reconnects, it is seen as a new peer and the handcheck
is reprocessed, whatever you do with the IDENTITY option. IMHO, I don't
see any use case for this option.
So, the only way I foresee is to have the ROUTER transmit to its peer
the identity it has assigned to it. The best place I think is in the
greeting's feeler: 31 bytes available not used (cf ZMTP). On the peer
side, before it reconnects, it shall set a new identity option you shall
add to libzmq, with the value previously retrieved.
So, you should have one option used by the ROUTER, both to transmit the
assign 5 bytes identity to the peer in the greeting's filler, and to get
the one transmitted by the peer To have it work, use 6 bytes in the
filler, one would be a validity flag, because it wouldn't be a good idea
that the peer transmit an identity of its own, to avoid collisions. So
first time it connects, the blob is {0, 0, 0, 0, 0, 0}. ROUTER will send
say {1, 0, 5, 240, 72, 13}. Peer will have to send {2, 0, 5, 240, 72,
13}when it reconnects. It is better to differentiate how the blob has to
be interpreted. 0: not valid, do nothing, 1: here is how I have
identified you, 2: I reconnect, please use this to identify me. This
would be necessary in the case of ROUTER-ROUTER, and ease greatly the
use of this architecture.
And you should have one option to be used by the peer to retrieve and
resend the identity at the next connexion.
Hope it helps,
Laurent.
Le 13/02/2014 23:51, Justin Karneges a écrit :
I'd like to move forward with fixing this. Can I get a confirmation that
I should proceed? Basically I want to make it so if a connection
reconnects, and an explicit identity is received from the peer, then it
should overwrite any previously set identity for that peer.
Also I tried to log an item in the Jira but I'm not sure how. Maybe I
need special access rights? I created an account at least. Also, I see
issues in github too. Which is the right place to log things?
Thanks.
On 02/08/2014 11:53 AM, Justin Karneges wrote:
Here's an even simpler example using REQ/ROUTER:
https://gist.github.com/jkarneges/1fa64e9763561f53daef
It doesn't demonstrate the routing problem but it does demonstrate the
identity binding oddity. You can see the ROUTER side that the envelope
id is always the first id it has ever seen, even if the id printed by
the REQ side is different every time.
On 02/07/2014 02:33 PM, Justin Karneges wrote:
Here's some small sample code to reproduce the issue:
https://gist.github.com/jkarneges/ab2b1abea1ee4cfc1332
A (ztest1.py) creates REQ and ROUTER sockets. B (ztest2.py) creates REP
and ROUTER sockets. B binds and provides a random identity to its ROUTER
socket. A connects its sockets to B. A queries for B's id using the REQ
socket, and then attempts to send a message via the ROUTER socket right
after that. This is repeated every 2 seconds.
A and B can be started in any order. A can be restarted and things will
still work. If B is restarted, then A's ROUTER socket will never work
again until A is restarted also.
A uses ZMQ_ROUTER_MANDATORY to show that the failures are on A's side.
On 02/07/2014 02:16 PM, Justin Karneges wrote:
It is my understanding that being able to route requires the socket to
have an identity mapping in its routing table for the peer.
For peers that do not explicitly specify their own identity, then I
believe you are correct that routing is not possible until at least one
message has been received from the peer. It is at this point that the
ROUTER socket will make up an identity for this peer and store it in its
routing table.
However, for peers that *do* explicitly specify their own identity (as I
am doing), then this identity information is delivered immediately after
the connection is established, allowing routing to the peer even if the
peer has not sent a message yet.
I should have been more clear in my original message. The B program is
explicitly specifying a random UUID as the identity of its socket before
binding.
On 02/07/2014 02:06 PM, Panu Wetterstrand wrote:
I did not quite get the problem but could this be because (I think)
router is not able to route messages to socket from which it has not
reveived data first...
7.2.2014 22.51 kirjoitti "Justin Karneges" <jus...@affinix.com
<mailto:jus...@affinix.com>>:
Hi,
1) ROUTER in program A is set to connect to a bind socket in program B.
2) Both programs are started, and the connection is established.
3) A determines B's socket identity out-of-band, and is able to send
messages to B.
3) B is terminated and the connection is lost.
4) B is started again, and the connection is re-established.
5) A determines B's socket identity out-of-band, and is no longer able
to send messages to B.
It seems this problem does not happen if B retains the same socket
identity across reconnects. However, if it uses a random identity (to
be
discovered out-of-band by A), then routing will never work again after
the first restart of B. The A program must be restarted in order to
make
things right again.
My guess is that each connect queue on a ROUTER socket is somehow bound
for life against the first identity it sees. Is this intentional
behavior?
Thanks,
Justin
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