Erlang, the language for network programming Issue 2: binary pattern matching

Much is being said about the excellent capabilities of Erlang to write distributed fault-tolerant programs, but little has been said about how easy and fun it is to write servers (those programs at the other end of the line) with it. And by easy I don’t just mean that you can put up a web server in two lines of code and hope it’ll work, I mean it’ll be easy to built robust servers.

One example of this is ejabberd, a free Jabber server.

I’ll start this second part, the one with real networking programming, with a bet. Think about the IPv4 protocol, its header is like this:

0                   1                   2                   30
  1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version|  IHL  |Type of Service|          Total Length         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Identification        |Flags|      Fragment Offset    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Time to Live |    Protocol   |         Header Checksum       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Source Address                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Destination Address                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Options                    |    Padding    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

you can check RFC791, page 11 for more information. At a glance, the first 4 bits are the version, the next 4 bits the IHL (Internet Header Length), then we have a whole byte, 8 bits, of Type of Service. The next two bytes are the total length and I am already tired of it, you get the picture right?

Pick whatever language you want (except Erlang, that’s mine now, but it can be yours latter) and think about how many lines of code would take you to parse that beast, the IP header. Think about how much time it takes you to write those lines, and test them.

Done? come on! really think about it, otherwise the game is boring. Close your eyes, picture the lines of code. If you can’t, go and write some pseudo-code similar to your favorite language to do the parsing. Done? OK.

Here’s my bet: I bet that I can do it, in Erlang, in far less lines than you! I bet you that I can code it so fast that I’d be finished of writing the code to parse the whole header before you finish the code to parse the first line. And while you are testing I’ll go to the beach because I’ll just trust my code to run without problems.
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Erlang, the language for network programming Issue 1: pattern matching

Much is being said about the excellent capabilities of Erlang to write distributed fault-tolerant programs, but little has been said about how easy and fun it is to write servers (those programs at the other end of the line) with it. And by easy I don’t just mean that you can put up a web server in two lines of code and hope it’ll work, I mean it’ll be easy to built robust servers.

One example of this is ejabberd, a free Jabber server.

One of the Erlang features that let us write servers is its binary pattern matching. But to understand binary pattern matching first you have to understand pattern matching.

Let’s start with a classic of functional programming: factorial. This is factorial in Erlang

fac(N) ->
   if N == 0 -> 1;
      true -> N * fac(N - 1)
   end.

Continue reading “Erlang, the language for network programming Issue 1: pattern matching”

Software Release Cycle

Introduction

I am writing this description to remember what to do when I reach the time to release one of my various projects1, that doesn’t happen often enough for me to remember the whole process and it is tedious enough to hate it when I forget a step. So, I decided to describe it.

First I will explain the version numbers I use. At one time I used the Linux version numbers but when I worked in KDE I’ve seen the beauty of their version numbers (if there’s place for beauty in such a thing).

Then I’ll explain how I create and maintain the various branches, tags and tarballs.
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Two-in-one DNS server with BIND9

This tutorial shows you how to configure BIND9 DNS server to serve an internal network and a external network at the same time with different set of information. To accomplish that goal, a new feature of BIND9 called view is used. As a tutorial it’ll walk you through the whole set up, but initial knowledge of BIND and DNS is required, there are plenty of documents that cover that information on the Internet.

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