[zeromq-dev] Router Example & questions

Troy Settle troy.settle at gmail.com
Sun Mar 9 20:20:09 CET 2014


I've been digging around 0MQ for a short time now, and one of the things
that is not discussed heavily in the guide, is the ROUTER to ROUTER pair,
which would be highly useful in a completely decentralized P2P network.  So,
after working through some of the examples in the Guide, I came up with this
code.  It's in PHP, and if nobody takes my fun away, I'll write it also in C
and/or C++ (assuming I can get back up to speed in them).  Please feel free
to use this in the 0MQ Guide (with or without cleanup).

http://pastebin.com/zW548wpN

I called it node.php.  There's probably a better name as a piece of example
code.

$ php node.php <port> <peers>

It will fork out as many peers as you want (at least 2), each binding to
<port>+n and connecting to each previous node that's already bound.  What
you end up with, is any number of nodes, all connected (in some way) to all
the other nodes.  If you launch a few nodes, all messages will be received.
If you launch many nodes, messages will dropped, as the oldest and youngest
nodes don't overlap quite enough.  You can play with the sleep on line 60 to
have some fun.  Comment out the printf() and echo statements in the loop if
you want to reduce the noise.  The zhelpers.php include isn't necessary, it
was left over from a previous experiment.

My test machine is a single CPU VM running FreeBSD 10 and PHP 5.5.9.  The
largest test I ran was 100 nodes which was much fun to watch.

---

One thing that I find seriously lacking, is the ability to identify a peer
by IP address.  I've seen the recent patch for ZMQ_SRCFD, which will be
handy in C and presumably in other languages as patches are made to the
bindings.  I'm wondering, though, if the ROUTER and STREAM sockets couldn't
be configured (perhaps by default) to providing some useful information in
the identity string such as the descriptor, address family, address, port,
and perhaps topic.

One other thing that I'm wondering, if there couldn't be a low-level
broadcast/flood mechanism built into the ROUTER/STREAM socket.  Sure, it's
easy enough to iterate through all peers, but if I want to send the same
message to several hundred peers, doing so at the lowest level in the 0MQ
API should make the operation much less expensive.  Of course, not all peers
will want to receive floods, so we would probably need a flag for that.
Perhaps the first byte of the identity string could be used for flagging.

0x00 - Random 32bit ID  (current)
0x01 - Peer generated ID (minor change)
0x02 - Socket Info ID (added functionality)
0x04 - Can receive floods (capability flag)
...
0xFF - Broadcast a flood (sending only)

All in all, I'm not even close to being up to speed in C/C++ to do this
myself, mostly I'm just thinking about ways to extend functionality without
incurring too much cost and hoping to catch someone's attention.  We would
probably need much discussion to flesh these ideas out if it is to go
anywhere at all.

-Troy





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