Audience for This Book

This book is written for curious users, for software developers, and for hardware developers. Many of the screenshots show images taken from Mac OS X, but that's primarily a reflection of the fact that both the authors primarily use Mac OS X. Don't be misled into thinking this a Macintosh programming book. The concepts and programming examples given in this book are almost exclusively cross-platform. The Zeroconf Multicast DNS daemon and APIs are available on Mac OS X, Windows, Linux, Solaris, FreeBSD, etc. The dns-sd command-line tool is available on all those platforms, as are the dns_sd.h C programming API, the Java™ API, and the other interfaces for languages like Ruby and Python. Just one chapter, Chapter 9, covers APIs that are specific to Mac OS X.

For curious users who want to understand the technology used by iChat, iTunes, iPhoto, network printing, SubEthaEdit, and countless other applications, this book explains the Zeroconf technology.

For software developers making networking applications, this book explains how you can, with very little effort, make your software a lot easier to use. Going beyond that, this newfound ease-of-use means that previously infeasible software products now become viable. Imagine iChat's local Bonjour Window if you had to type in the IP address of each peer you wanted to chat with. It would be pointless. No one would do it, and there would have been no point even having that feature in the first place. Compare that with iChat as it is today, where it automatically discovers all the local peers on the network and displays them in a list. Now it suddenly becomes a lot more interesting, and that feature becomes worth implementing.

For hardware developers currently making IP-based hardware devices, the message is very similar. This book explains how you can, with very little effort, make your devices a lot easier to use. This translates into thinner manuals, lower support costs, and lower return rates. Those effects, in turn, mean that products that previously would not have been economically viable, because of support costs and product returns, can now be profitable. It was not so long ago that a networked printer cost over $1,000. This was not because an Ethernet chip and some IP software cost that much more than a USB chip. No, it was because of the higher support costs and return rates for these products. Zeroconf cuts those support costs and return rates, and, these days, Zeroconf-enabled Ethernet printers are available for about $100. In many cases, what Zeroconf offers is plain and simple: enhanced functionality. When devices on a network can automatically communicate, advertise, and discover services for themselves, things become possible that simply wouldn't happen if humans had to configure everything manually. Sharing idle CPU cycles on the network has long been a popular idea, yet still, as a percentage of all computer users, very few people make the effort to find out how to make that work. If, instead, all the user had to do was just click a checkbox saying "Share my idle CPU cycles," and Zeroconf automatically did the rest, then CPU sharing could become commonplace instead of remaining a rare novelty.

For hardware developers currently making nonnetworked hardware devices, this book explains how you can add the benefits of TCP/IP networking to your products without having to sacrifice ease of use. The marketplace today is full of computer peripherals that connect through serial, USB, FireWire, or similar technologies, but all of these technologies require the device to be tethered to some host computer. Devices that connect via Ethernet or 802.11 wireless interfaces can be accessed by any computer anywhere in the house, but the pain associated with TCP/IP has always been a strong disincentive. By removing that pain, Zeroconf means it's now practical for many of these serial, USB, and FireWire products to migrate to Ethernet or 802.11 wireless interfaces instead.