Beej's Guide to Network Programming | Hacker News Reader

Beej's Guide to Network Programming

beej.us

72 pointsstreblo22 comments

Beej was there for me when I was a poor boy living in a 3rd world country with no Richard Stevens on any shelf. Along with Beej, I also thoroughly devoured NeHe's tutorials, the DOS assembly programming manual "Help PC", Ralph Brown's Interrupt list, Jack Crenshaw's "Let's Build a Compiler", and many many of the early Free programming texts in the web along with the "free" ones that were floating around in the various underground "scenes" ;-)

Just to add. If anybody remembers a phile by the name "masm32.doc" which was an assembly programming tutorial for 32bit Windows. It came out right around the time Windows 95 was released, and us assembly hackers didn't have a 32bit assembler. This document showed you how you could encode 32bit instructions as inline byte definitions (db in masm/tasm.)

I had this document, the Trumpet Winsock manual, and a b-grade text on BSD sockets programming. I was foolish enough to have written socket code in assembly for a platform I have never programed for before, with an assembler that didn't support the opcodes I was typing in. This is all hard to imagine, FUCK, but I was 17, and I had a heart.

(considered a fool cuz I dropped outta high school, stereo type of another blackhat misunderstood, and it's still all good.)

Wow. I remember this thing. I'm pretty sure I was a senior in High School when it came out (1994?). Reading through it today is trippy.

Of course --- don't do anything he says anymore; all due respect (because I used to love this thing), but pick up libevent instead. Writing your own select() loop was malpractice in 1999.

Or, if you're not attached to needing the speed that C provides, use something like Erlang, Tcl, or Python's twisted that has a nice event-based system built in.

The irony is, if you use Twisted Python or EventMachine Ruby and pit it against Beej-style socket code, you're likely to wind up faster in Ruby or Python.

In all sincerity, I'd like to understand how and why you would use libevent instead of the approach outlined by Beej,

Is there any link or other reference you could recommend for further study? The documentation on libevent's home page is big on "how", but not on "why".

Beej's guide is really about writing synchronous network code. You connect a socket. Your program waits for the connect to complete. You write something to the socket. What, the write might only complete 10 of your 20 bytes? Wrap the write in a loop that keeps feeding more bytes to the system call! Ok, the request is completely sent? Great! Now write a loop that sits there waiting for all the data that we need to come back on the socket. Back and forth, back and forth, in lock-step.

Efficient network code just isn't written like this. It's scheduled, the same way processes are in the kernel. Even in threaded code, nothing sits there waiting on a socket.

Beej touches on this a little with his description of select(). But select isn't a utility function in socket programming. It's the kernel. And getting that loop completely right isn't trivial (timers alone can offer you 4-5 mainstream data structures to choose from). Moreover, select isn't the end-all kernel interface to scheduling I/O; if you're writing a server, it's probably much faster to use a more modern interface.

Libevent both hides the complexity of the event loop from you, and also abstracts it so you can drop in kqueue or epoll or whatever without being tied to a single old system call interface.

None of this is a knock against Beej's guide. I loved this thing, 15 years ago. =)

Thanks for the crash course.

Don't do "anything he says" because of the inclusion of the section on select()? Now, that's a little harsh, isn't it? After all, there's much more to the guide than that. I'll readily admit that select() is absolutely dated and inefficient, but it is also POSIX-compliant, and the guide is about (specifically) beginning network programming in (specifically) C, not event management or Python or tcl.

Plus, I just updated it to IPv6, man! Cut me some slack! :) I could take the select() thing out, but then I'd instantly get questions about it in the mail. But honestly, I'll take any serious feedback, including "give it up"--it is a time sink, and if it's not worth it, it's not worth it. Contact info's in the Guide.

All that being said, adding information about the inefficiencies of select() (and poll()) and a pointer to something better (e.g. libevent) would totally be a good addition. Additionally, a quick section about "why use C for network programming when every scripting language makes it easier" might be good (at least "because the rest of my project is written in C" comes to mind.) What do you think?

Are the other (preferably cross-platform) competitors to libevent that might be useful? I wouldn't talk about them in detail, because it's out of scope, but I definitely don't mind dropping pointers.

This was a lifesaver during my networking class at UC Berkeley. I think I spent more time referencing this than the textbook, although not much substitutes for just writing code and seeing what happens.

At Brown, it WAS our textbook.

Same thing at UCLA for the networking class I took there. It was a refreshing change of pace.

Wonderful document. My favorite quote, which apparently has been cut out of this newer version:

Now, you may think you're wising up to this. You might think, "What do I do if I have to change byte order on a char?" Then you might think, "Uh, never mind."

This is invaluable, it got me through a lot of systems programming courses. The examples are invaluable. This is the perfect resource for anyone who wants to get down and dirty with unix sockets.

Where would I go nowadays for similar, but more up-to-date, materials?

I love how most of the comments are reflections, or stories about how useful this is. I agree wholeheartedly, and when I saw the link was hoping it was now a full blown book or something.

This was how I learned to program with sockets 15 years ago, too. I'm surprised that none of the people who criticize it in the comments here have linked to what they consider a suitable replacement.

tpacek: writing networking code in C instead of Perl was malpractice in 1999, too. Except when it wasn't. You could make a reasonable argument that most things you would have done with sockets in 1994 should be done with a web server today...

Substitute Perl for Python, Ruby, Tcl, or any other language and I'll almost agree with you. ;)

Maybe I was just ignorant, but to me, Python and Ruby didn't seem like plausible alternatives to Perl in 1999. I don't know why; lack of libraries? Lack of documentation? Tcl, yes, but I'm glad I didn't spend too much time doing that.

Nice introduction to socket programming.