[zeromq-dev] Can I make a ROUTER ignore a client's ZMQ_IDENTITY?

[Pieter Hintjens]

OK, I've logged an issue for this: https://github.com/zeromq/libzmq/issues/801

The first problem is that the actual behavior is undocumented. Since
3.2 stable, router sockets *reject* clients with duplicate identities.
There was a brief period where they accepted them and gave them
anonymous identities. That isn't how it works since 2012-04-02.

I've fixed the documentation to at least document existing behavior so
that applications can depend on it. Next step is to decide if we want
other behavior, and how to make that happen.

-Pieter

On Wed, Jan 1, 2014 at 1:03 PM, Pieter Hintjens <ph at imatix.com> wrote:
> Indeed, I've reproduced this. Seems the second duplicate identity is
> rejected. This is a change of behavior. I'll investigate... thanks for
> reporting it.
>
> On Sat, Dec 28, 2013 at 10:40 AM, Tom Nakamura <tnakamura at eml.cc> wrote:
>>
>>
>> On Sat, Dec 28, 2013, at 12:02 AM, Pieter Hintjens wrote:
>>> On Sat, Dec 28, 2013 at 12:32 AM, Tom Nakamura <tnakamura at eml.cc> wrote:
>>>
>>> If I expose
>>> > a ROUTER socket to unknown/untrusted clients, then the router may get
>>> > multiple connections with the same identity by accident or malice
>>> > resulting in a denial of service.  Or am I missing something in the way
>>> > routers work?
>>>
>>> You can't ignore identities. However duplicate clients with the same
>>> ID will be treated as anonymous (their ID will be ignored) so there is
>>> no risk of a denial of service. You can switch off that behavior using
>>> ZMQ_ROUTER_HANDOVER, which lets clients "steal" connections by
>>> specifying an already-used ID.
>>>
>>> -Pieter
>>
>> Wait, so what am I doing wrong below? I create two detached threads
>> which creates a DEALER socket (same thing happens with REQ but DEALER
>> makes it shorter) that sends a message every second (and printf()s a
>> debug message, see code), and receives those messages on a ROUTER in the
>> main thread and calls zmsg_dump().
>>
>>     #include <stdio.h>
>>     #include <stdlib.h>
>>     #include <assert.h>
>>     #include <zmq.h>
>>     #include <czmq.h>
>>
>>     // connection point does not seem to make a difference
>>     //#define ENDPOINT "tcp://127.0.0.1:8888"
>>     #define ENDPOINT "ipc://myipc.ipc"
>>
>>     void * client_thread(void * args){
>>         zctx_t * context = zctx_new();
>>         void * client = zsocket_new (context, ZMQ_DEALER);
>>
>>         zsocket_set_identity(client, "CUSTOMID");
>>
>>         int rc = zsocket_connect(client, ENDPOINT); assert(rc != -1);
>>
>>         while (! zctx_interrupted){
>>             // i'm just using the context address as an id to
>>             // differentiate the two client's printfs
>>             printf("> %p sent msg\n", context);
>>             zstr_send(client, "SOMEMSG");
>>             zclock_sleep(1000);
>>         }
>>
>>         zsocket_destroy(context, client);
>>         zctx_destroy(&context);
>>         return NULL;
>>     }
>>
>>     int main(int argc, char * argv[]) {
>>         int rc;
>>
>>         rc = zthread_new (client_thread, NULL); assert(rc == 0);
>>         rc = zthread_new (client_thread, NULL); assert(rc == 0);
>>
>>         zctx_t * context = zctx_new();
>>         assert(context);
>>
>>         void * server = zsocket_new (context, ZMQ_ROUTER);
>>         assert(server);
>>
>>         rc = zsocket_bind(server, ENDPOINT); assert(rc != -1);
>>
>>         while (!zctx_interrupted){
>>             zmsg_t * msg = zmsg_recv(server);
>>             if (!msg)
>>                 break;
>>             zmsg_dump(msg);
>>         }
>>
>>         zsocket_destroy(context, server);
>>         zctx_destroy(&context);
>>
>>         return 0;
>>     }
>>
>> By setting the client identity, I only get one reply for each time the
>> clients both send a message:
>>
>>     > 0x7f77380008c0 sent msg
>>     > 0x7f77300008c0 sent msg
>>     --------------------------------------
>>     [008] CUSTOMID
>>     [007] SOMEMSG
>>     > 0x7f77380008c0 sent msg
>>     > 0x7f77300008c0 sent msg
>>     --------------------------------------
>>     [008] CUSTOMID
>>     [007] SOMEMSG
>>     > 0x7f77380008c0 sent msg
>>     > 0x7f77300008c0 sent msg
>>     --------------------------------------
>>     [008] CUSTOMID
>>     [007] SOMEMSG
>>
>> But if I comment out the zsocket_set_identity() call, I get what one
>> would expect (a response to each):
>>
>>     > 0x7f44e80008c0 sent msg
>>     > 0x7f44e00008c0 sent msg
>>     --------------------------------------
>>     [005] 006B8B4567
>>     [007] SOMEMSG
>>     --------------------------------------
>>     [005] 006B8B4568
>>     [007] SOMEMSG
>>     > 0x7f44e00008c0 sent msg
>>     > 0x7f44e80008c0 sent msg
>>     --------------------------------------
>>     [005] 006B8B4568
>>     [007] SOMEMSG
>>     --------------------------------------
>>     [005] 006B8B4567
>>     [007] SOMEMSG
>>     > 0x7f44e80008c0 sent msg
>>     > 0x7f44e00008c0 sent msg
>>     --------------------------------------
>>     [005] 006B8B4567
>>     [007] SOMEMSG
>>     --------------------------------------
>>     [005] 006B8B4568
>>     [007] SOMEMSG
>>
>> I am using zeromq 4.0.3 and czmq 2.0.3 on Linux Mint 15 64 bit.
>> Thank you,
>> Tom
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