[zeromq-dev] Binding to TCP port 0

[AJ Lewis]

On Thu, Jan 26, 2012 at 03:57:37PM +0100, Martin Lucina wrote:
> aj.lewis at quantum.com said:
> > On Thu, Jan 26, 2012 at 07:53:06AM -0600, Pieter Hintjens wrote:
> > > On Thu, Jan 26, 2012 at 2:17 AM, Ian Barber <ian.barber at gmail.com>
> > > wrote:
> > Forgive me if I'm being dense, but couldn't the N case work if you
> > made sure to do the getsockopt() call after each zmq_bind()?
> > 
> > zmq_bind(foo, "tcp://XXXX:0") zmq_getsockopt(foo,
> > GET_LAST_BOUND_PORT, &port1, sizeof(port1)) zmq_bind(foo,
> > "tcp://YYYY:0") zmq_getsockopt(foo, GET_LAST_BOUND_PORT, &port2,
> > sizeof(port2))
> 
> Yup, that would work. Sorry for missing the point about zmq_bind()
> being synchronous.
> 
> Ian also made a great point that this can be extended to "bind to
> unnamed endpoint" (for want of a better name) for all transports. So,
> what I think we want is that the getsockopt API should return a string
> (so as to be usable for multiple transports, plus returning a
> different-data-type-per-transport is a PITA).
> 
> It'd also be nice to define a consistent way to specify this "unnamed
> endpoint" for all transports that might want to provide such
> functionality.  ":0" happens to work for the tcp:// case, but does not
> really make sense for inproc:// or ipc://.
> 
> This leaves us with something like this proposal:
> 
> zmq_bind(foo, "tcp://XXXX:*");    // "tcp://*:*" if you want
> INADDR_ANY char endpoint [ZMQ_ENDPOINT_MAX]; zmq_getsockopt(foo,
> ZMQ_GET_ENDPOINT, endpoint, sizeof endpoint);
> 
> => endpoint is filled as "tcp://XXXX:12345".
> 
> zmq_bind(foo, "ipc://*"); char endpoint [ZMQ_ENDPOINT_MAX];
> zmq_getsockopt(foo, ZMQ_GET_ENDPOINT, endpoint, sizeof endpoint);
> 
> => endpoint is filled as "ipc:///tmp/Xyz358hfA7".
> 
> inproc:// semantics would be identical to ipc:// (w/o the /tmp/ prefix
> obviously).
> 
> The use of "*" seems fairly uncontroversial -- note that this means an
> ipc:// endpoint cannot therefore contain "*" which is an (albeit
> niche) backward-incompatible change.

I think the "*" is fine, and it makes sense to me to extend it to all
endpoint types.  I'm a bit concerned about having the full
${transport}://${path/port} string passed back.  That means that the app
needs to parse that string out to get what it needs, when what it really
wants is just the ${path/port} depending on the transport.  Is there a
reason to include more than the part of the transport string that was
wildcarded?

> Thoughts? I'll ping Martin Sustrik tomorrow to see if he thinks
> there's any reason why this wouldn't work; I believe he's ignoring
> this thread as TL;DR :-)

Thanks,
-- 
AJ Lewis
Software Engineer
Quantum Corporation

Work:    651 688-4346

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