CL-ZEROCONF

Introduction

CL-ZEROCONF is a Lisp interface to Apple's open source implementation of the Zeroconf service discovery protocol, called Bonjour. Apple does a good job of describing why Zeroconf is useful:

Bonjour lets you create an instant network of computers and smart devices just by getting them connected to each other. The computers and devices take over from there, automatically broadcasting and discovering what services each is offering for the use of others. The network could be as simple as two AirPort Extreme-equipped PowerBook users sitting in a hotel meeting room miles from the nearest !AirPort Extreme Base Station with some large files they need to share. Before Bonjour, frustration. With Bonjour, your computer will discover others, making file sharing completely simple.

Examples

Here's an example of advertising a service with CL-ZEROCONF:

(dns-sd:publish (make-instance 'dns-sd:service
                               :name "My CLiki"
                               :type "_http._tcp"
                               :port 80)
                nil)

(dns-sd:process-dns-sd-events 3.0)

Here's an example of browsing for services on the local network:

(defclass my-observer ()
  ())

(defmethod dns-sd:browse-add-service ((self my-observer) service &key more-coming-p)
  (declare (ignore more-coming-p))
  (format T "~&Found service ~S." service))

;; Look for iTunes servers.
(let ((browser (dns-sd:browse "_daap._tcp" nil (make-instance 'my-observer))))
  (dotimes (i 10)
    (dns-sd:process-dns-sd-events 3.0))
  (dns-sd:cancel browser))

(For an explanation of the meanings of the _http._tcp and _daap._tcp strings, see DNS SRV (RFC 2782) Service Types.)

For some other short examples of how to use the library, see examples.lisp. A small example application can be found in test-browse.lisp, which generates an Araneida-based web page that displays services on the local network:

Richard Newman used CL-ZEROCONF to create a simple web interface to iTunes.

Apple's DNSServiceDiscovery API docs may be helpful in understanding how to use CL-ZEROCONF, as might their Bonjour Network Services pages.

Availability and Implementation Support

You can download CL-ZEROCONF manually: http://lemonodor.com/code/cl-zeroconf_0.2.tar.gz

Or you can use ASDF-INSTALL: (asdf-install:install '#:cl-zeroconf)

CL-ZEROCONF has been tested under OS X 10.4.3 with OpenMCL 1.0, ACL 7.0, and !LispWorks Personal 4.3.0. Under Linux, it has been tested with ACL 7.0 (but see the notes below for ACL). SBCL's support for foreign callbacks is incomplete, and it therefore will not work with CL-ZEROCONF.

See ReleaseNotes for more information.

Notes

Even though it's named CL-ZEROCONF, this library only deals with one part of Zeroconf: service discovery. Link-local addressing (allocation of IP addresses without a DHCP server) is outside its scope, and probably doesn't make much sense for a Lisp library.

CL-ZEROCONF is really just a UFFI-based wrapper around Apple's multicast DNS Responder, which is a daemon that handles most of the work in doing service discovery for you. mDNSResponder is built in to OS X, and is offered as open source for other operating systems.

It took me a while to come to mDNSResponder. I tried Howl, but it was buggy, the API was incomplete and the event handling model was different in OS X than in the other OSes it supports. I tried the Cocoa NSNetService API and the Core Foundation CFNetServices API, but they weren't portable. I considered writing a complete Lisp implementation of multicast DNS that didn't rely on any external libraries other than for basic networking, but that has some disadvantages too. mDNSResponder is free and quite portable, and saved me a lot of work.

In order to use CL-ZEROCONF on Linux, you will need to download and install mDNSResponder. It can be downloaded from Apple] as a tarball, or via CVS. Make sure to read the instructions on using Apple's Darwin CVS repository--you will need to get a (free) Apple ID first. The mDNSResponder code base is under active development, so I recommend getting the code from CVS. If you run into any trouble, the tagged version I used was mDNSResponder-86. Once you've compiled the code, install it and start the mdnsd daemon.

Coincidentally, both SBCL and ACL seem to have had an identical bug in their handling of foreign short on PowerPC. Franz recently fixed the bug in patch update/paa005.001, which you can automatically download and install (along with many other patches) by doing (sys:update-allegro). The bug exhibits itself in CL-ZEROCONF by causing all service port numbers to be reported as 0.

Once you've patched up your compilers and compiled new daemons, you can install CL-ZEROCONF with ASDF-INSTALL (of course).

I hope you find this useful.