The Cathedral and the Bazaar - Eric S. Raymond (pride and prejudice read .txt) 📗

had been careful to keep the code 8-bit clean (that is, to not press the 8th bit, unused in the ASCII character set, into service to carry information within the program). Not because I anticipated the demand for this feature, but rather in obedience to another rule:

15. When writing gateway software of any kind, take pains to disturb the data stream as little as possible-and never throw away information unless the recipient forces you to!

Had I not obeyed this rule, 8-bit MIME support would have been difficult and buggy. As it was, all I had to do is read the MIME standard (RFC 1652) and add a trivial bit of header-generation logic.

Some European users bugged me into adding an option to limit the number of messages retrieved per session (so they can control costs from their expensive phone networks). I resisted this for a long time, and I’m still not entirely happy about it. But if you’re writing for the world, you have to listen to your customers-this doesn’t change just because they’re not paying you in money.

A Few More Lessons from Fetchmail

Before we go back to general software-engineering issues, there are a couple more specific lessons from the fetchmail experience to ponder. Nontechnical readers can safely skip this section.

The rc (control) file syntax includes optional `noise’ keywords that are entirely ignored by the parser. The English-like syntax they allow is considerably more readable than the traditional terse keyword-value pairs you get when you strip them all out.

These started out as a late-night experiment when I noticed how much the rc file declarations were beginning to resemble an imperative minilanguage. (This is also why I changed the original popclient “server” keyword to “poll”).

It seemed to me that trying to make that imperative minilanguage more like English might make it easier to use. Now, although I’m a convinced partisan of the “make it a language” school of design as exemplified by Emacs and HTML and many database engines, I am not normally a big fan of “English-like” syntaxes.

Traditionally programmers have tended to favor control syntaxes that are very precise and compact and have no redundancy at all. This is a cultural legacy from when computing resources were expensive, so parsing stages had to be as cheap and simple as possible. English, with about 50% redundancy, looked like a very inappropriate model then.

This is not my reason for normally avoiding English-like syntaxes; I mention it here only to demolish it. With cheap cycles and core, terseness should not be an end in itself. Nowadays it’s more important for a language to be convenient for humans than to be cheap for the computer.

There remain, however, good reasons to be wary. One is the complexity cost of the parsing stage-you don’t want to raise that to the point where it’s a significant source of bugs and user confusion in itself. Another is that trying to make a language syntax English-like often demands that the “English” it speaks be bent seriously out of shape, so much so that the superficial resemblance to natural language is as confusing as a traditional syntax would have been. (You see this bad effect in a lot of so-called “fourth generation” and commercial database-query languages.)

The fetchmail control syntax seems to avoid these problems because the language domain is extremely restricted. It’s nowhere near a general-purpose language; the things it says simply are not very complicated, so there’s little potential for confusion in moving mentally between a tiny subset of English and the actual control language. I think there may be a broader lesson here:

16. When your language is nowhere near Turing-complete, syntactic sugar can be your friend.

Another lesson is about security by obscurity. Some fetchmail users asked me to change the software to store passwords encrypted in the rc file, so snoopers wouldn’t be able to casually see them.

I didn’t do it, because this doesn’t actually add protection. Anyone who’s acquired permissions to read your rc file will be able to run fetchmail as you anyway-and if it’s your password they’re after, they’d be able to rip the necessary decoder out of the fetchmail code itself to get it.

All .fetchmailrc password encryption would have done is give a false sense of security to people who don’t think very hard. The general rule here is:

17. A security system is only as secure as its secret. Beware of pseudo-secrets.

Necessary Preconditions for the Bazaar Style

Early reviewers and test audiences for this essay consistently raised questions about the preconditions for successful bazaar-style development, including both the qualifications of the project leader and the state of code at the time one goes public and starts to try to build a co-developer community.

It’s fairly clear that one cannot code from the ground up in bazaar style [IN]. One can test, debug and improve in bazaar style, but it would be very hard to originate a project in bazaar mode. Linus didn’t try it. I didn’t either. Your nascent developer community needs to have something runnable and testable to play with.

When you start community-building, what you need to be able to present is a plausible promise. Your program doesn’t have to work particularly well. It can be crude, buggy, incomplete, and poorly documented. What it must not fail to do is (a) run, and (b) convince potential co-developers that it can be evolved into something really neat in the foreseeable future.

Linux and fetchmail both went public with strong, attractive basic designs. Many people thinking about the bazaar model as I have presented it have correctly considered this critical, then jumped from that to the conclusion that a high degree of design intuition and cleverness in the project leader is indispensable.

But Linus got his design from Unix. I got mine initially from the ancestral popclient (though it would later change a great deal, much more proportionately speaking than has Linux). So does the leader/coordinator for a bazaar-style effort really have to have exceptional design talent, or can he get by through leveraging the design talent of others?

I think it is not critical that the coordinator be able to originate designs of exceptional brilliance, but it is absolutely critical that the coordinator be able to recognize good design ideas from others.

Both the Linux and fetchmail projects show evidence of this. Linus, while not (as previously discussed) a spectacularly original designer, has displayed a powerful knack for recognizing good design and integrating it into the Linux kernel. And I have already described how the single most powerful design idea in fetchmail (SMTP forwarding) came from somebody else.

Early audiences of this essay complimented me by suggesting that I am prone to undervalue design originality in bazaar projects because I have a lot of it myself, and therefore take it for granted. There may be some truth to this; design (as opposed to coding or debugging) is certainly my strongest skill.

But the problem with being clever and original in software design is that it gets to be a habit-you start reflexively making things cute and complicated when you should be keeping them robust and simple. I have had projects crash on me because I made this mistake, but I managed to avoid this with fetchmail.

So I believe the fetchmail project succeeded partly because I restrained my tendency to be clever; this argues (at least) against design originality being essential for successful bazaar projects. And consider Linux. Suppose Linus Torvalds had been trying to pull off fundamental innovations in operating system design during the development; does it seem at all likely that the resulting kernel would be as stable and successful as what we have?

A certain base level of design and coding skill is required, of course, but I expect almost anybody seriously thinking of launching a bazaar effort will already be above that minimum. The open-source community’s internal market in reputation exerts subtle pressure on people not to launch development efforts they’re not competent to follow through on. So far this seems to have worked pretty well.

There is another kind of skill not normally associated with software development which I think is as important as design cleverness to bazaar projects-and it may be more important. A bazaar project coordinator or leader must have good people and communications skills.

This should be obvious. In order to build a development community, you need to attract people, interest them in what you’re doing, and keep them happy about the amount of work they’re doing. Technical sizzle will go a long way towards accomplishing this, but it’s far from the whole story. The personality you project matters, too.

It is not a coincidence that Linus is a nice guy who makes people like him and want to help him. It’s not a coincidence that I’m an energetic extrovert who enjoys working a crowd and has some of the delivery and instincts of a stand-up comic. To make the bazaar model work, it helps enormously if you have at least a little skill at charming people.

The Social Context of Open-Source Software

It is truly written: the best hacks start out as personal solutions to the author’s everyday problems, and spread because the problem turns out to be typical for a large class of users. This takes us back to the matter of rule 1, restated in a perhaps more useful way:

18. To solve an interesting problem, start by finding a problem that is interesting to you.

So it was with Carl Harris and the ancestral popclient, and so with me and fetchmail. But this has been understood for a long time. The interesting point, the point that the histories of Linux and fetchmail seem to demand we focus on, is the next stage-the evolution of software in the presence of a large and active community of users and co-developers.

In The Mythical Man-Month, Fred Brooks observed that programmer time is not fungible; adding developers to a late software project makes it later. As we’ve seen previously, he argued that the complexity and communication costs of a project rise with the square of the number of developers, while work done only rises linearly. Brooks’s Law has been widely regarded as a truism. But we’ve examined in this essay an number of ways in which the process of open-source development falsifies the assumptionms behind it-and, empirically, if Brooks’s Law were the whole picture Linux would be impossible.

Gerald Weinberg’s classic The Psychology of Computer Programming supplied what, in hindsight, we can see as a vital correction to Brooks. In his discussion of “egoless programming”, Weinberg observed that in shops where developers are not territorial about their code, and encourage other people to look for bugs and potential improvements in it, improvement happens dramatically faster than elsewhere. (Recently, Kent Beck’s `extreme programming’ technique of deploying coders in pairs looking over one anothers’ shoulders might be seen as an attempt to force this effect.)

Weinberg’s choice of terminology has perhaps prevented his analysis from gaining the acceptance it deserved-one has to smile at the thought of describing Internet hackers as “egoless”. But I think his argument looks more compelling today than ever.

The bazaar method, by harnessing the full power of the “egoless programming” effect, strongly mitigates the effect of Brooks’s Law. The principle behind Brooks’s Law is not repealed, but given a large developer population and cheap communications its effects can be swamped by competing nonlinearities that are not otherwise visible. This resembles the relationship between Newtonian and Einsteinian physics-the older system is still valid at low energies, but if you push mass and velocity high enough you get surprises like nuclear explosions or Linux.

The history of Unix should have prepared us for what we’re learning from Linux (and what I’ve verified experimentally on a smaller scale by deliberately copying Linus’s methods [EGCS]). That is, while coding remains an essentially solitary activity, the really great hacks come