Now, some of my readers, are probably asking themselves: what is it all about? why is this bug important? Ok. Let’s find out!

How does browser usually find which server to ask, when you enter URL? Well, at first, it parses out protocol and domain name from URL. For example, if URL is http://www.example.com/page.html then protocol is http and domain name is www.example.com. After that, browser sends request for “A” type record to DNS server and server replies with IP address (or several IP addresses). After that, browser tries to open connection with these addresses one by one, until it finds one which really works. Hopefully, first one will work, but sometimes each one will fail; In this case, browser will show us an error.

“A” records have the following format:

    hostname    IN  A   ip-address  time-to-live

For basic cases, this scheme seems to work just fine, but it has some inherent flaws, when you start to think about scalability.

1. It is impossible to map different services on the same domain-name to different servers. For example: I can’t have FTP and HTTP servers responding on example.com and, at the same time, located on different physical machines. My only option would be some kind of router, which would forward requests on different ports to different IP’s.
2. It is impossible to map service to specific port of server. Browsers just looks for TCP-connection on port 80 while using HTTP, for example.
3. It is impossible to implement sophisticated load-balancing rules in DNS. Having several A-records in DNS just gives possibility to have equal-load of several machines, nothing fancy.

It is an interesting fact, that all this problems are solved long time ago for one specific protocol called SMTP (yes, the one which delivers emails all around the globe). SMTP uses special kind of DNS-records called “MX” which allow to specify which machine(s) are waiting for SMTP-connections targeted to domain name and allow to specify priority of these machines, so, at first, clients will try to access machines with high priority and in case of problems will fallback to low-priority ones. So, MX records make email-infrastructure seriously more robust and scalable then anything else. Why such special treatment?

“MX” records have the following format:

    domainname  IN  MX  priority    hostname  time-to-live

Here, RFC 2782 comes on scene. Idea of this standard is to achieve similiar flexibility for any protocol used on internet.

“SRV” records allow to specify that specific application protocol, used over specific transport protocol of this domainname is handled by several servers on specific ports with various priority. That is as flexible as it can be. Let me throw some examples:

    _http._tcp.example.com. 86400 IN SRV 0 5 81 www1.example.com.
    _http._tcp.example.com. 86400 IN SRV 0 5 80 www2.example.com.
    _http._tcp.example.com. 86400 IN SRV 1 9 81 www-backup.example.com.
    _http._tcp.example.com. 86400 IN SRV 1 1 8000 www-weak-backup.example.com.

These four records tell browser, that:

• HTTP-over-TCP connections for “example.com” domain are handled by 4 servers: www1.example.com on port 81, www2.example.com on port 80, www-backup.example.com on port 81 and www-weak-backup.example.com on port 8000.
• www1.example.com and www2.example.com have priority “0″ (highest), so should be first to try. Both have weight “5″, which means, that they have 50% chance to be selected by client (equal load)
• In case both of these are not reachable, browser should check lower-priority servers www-backup.example.com and www-weak-backup.example.com, but www-backup.example com should be preferred in 9 out of 10 cases (it has weight=9, while another one has weight=1).

Sounds pretty cool, but, unfortunately, this technology is still not implemented in any of the browsers. Mozilla(Firefox) has this bug for 10 years, WebKit has this bug for 3+ years and Chromium has this bug since today.

There is no need for special support on webserver-side — that’s a good side of this technology too. Just add relevant records to DNS-server and all compliant clients will see it.

At the moment, SRV-records are widely used by XMPP/Jabber, SIP, LDAP software and Kerberos. I believe, any protocol in use can benefit.

Here’s the description from Twitter Data site:

Twitter Data is a simple, open, semi-structured format for embedding machine-readable, yet human-friendly, data in Twitter messages. This data can then be transmitted, received, and interpreted in real time by powerful new kinds of applications built on the Twitter platform. Here is an example Twitter Data message:

I love the #twitterdata proposal! $vote +1

The part with the dollar sign, $vote +1, is a piece of data embedded using the Twitter Data format.

To use php-twitterdata library, download it into the sub-direcory in your project’s directory (or any other place you like) and init the autoloader:

PHP API provided by php-twitterdata has 2 layers. On lower level, there are 3 classes: TwitterData_Message, TwitterData_Frame and TwitterData_Tuple which correspond to parts of data-enabled twitter-message. Message can consist of several Frames, Frame can consist of several Tuples and a “subject”. Objects of each of these classes can be created programmatically and combined in hierarchy. Each of them has “magic” __toString() method, so, to export them as a valid twitter-message, you just need to put objects in string context. Something like this:

and the result will be:

Hello, world! $foo bar


If you need to parse Twitter Data messages you should use TwitterData_Parser class. It is a SAX-style parser, with DOM-style export. If all you need is a hierarchy of objects, use it like this:

Otherwise, you can specify another handler-class as a second parameter of constructor. Such class has to implement TwitterData_Parser_CallbackInterface.

Does it all sound too complex? No problem!

php-twitterdata library also includes high-level interface, which consists of 2 simple functions: TwitterData::array_to_TwitterData() and TwitterData::TwitterData_to_array(). First one converts associative array into the string, which can be inserted into twitter-message, and second one takes message-string received from twitter and returns associative array parsed out of tuples from the first frame of message (If you need to get all possible data from message, you will still need to use low-level API).

Example of high-level API:

Library has unit-tests, which cover all examples provided on Twitter Data site both on Introduction page and on Examples page and is licensed under MIT-style license.

PHP-FPM is “deciphered” as “PHP FastCGI Process Manager” and is a patch for php to greatly improve FastCGI SAPI usage in production. It adds a bunch of additional features to php’s fastcgi such as: easy php-process daemonization (with ability to specify uid/gid/chroot/log-file), safe php-processes restart (without losing requests), custom error-handling and accelerated file-upload support (requires additional support from web-server).

There’s not much documentation in english, currently, but, again, there is a good chance that it will be added really soon.

May the force be with you!

• WebKit students
• PHP students
• MySQL students

[official announcement]

Top reasons:
1. FastCGI process can be run using the actual uid of user who creates the files (no need to allow group-readability of files)
2. Apache2 can be run in multithreaded-mode (aka “worker mpm“)
3. It is much easier to switch to any other server (fastcgi is an industry standard and works with any web-server software I know of)
4. It is much easier to scale — fastcgi-application can be moved to another physical server and http-server will still be able to talk with it

FastCGI is about flexibility and it deserves a lot of good words not only in IIS context

]]> http://blog.milkfarmsoft.com/2007/11/all-those-iis-talks/feed/ 5 http://blog.milkfarmsoft.com/2007/11/move-to-the-new-server/ http://blog.milkfarmsoft.com/2007/11/move-to-the-new-server/#comments Wed, 14 Nov 2007 16:47:58 +0000 indeyets http://blog.milkfarmsoft.com/?p=75 Ok, the transition is over and DNS is propagated. Both web-site and blog are on a new server now.

I guess I can put a badge “Powered by OpenSolaris” somewhere around

. . . → Read More: move to the new server]]> Ok, the transition is over and DNS is propagated. Both web-site and blog are on a new server now.

I guess I can put a badge “Powered by OpenSolaris” somewhere around

]]> http://blog.milkfarmsoft.com/2007/11/move-to-the-new-server/feed/ 1 http://blog.milkfarmsoft.com/2007/09/fink-new-pdb/ http://blog.milkfarmsoft.com/2007/09/fink-new-pdb/#comments Fri, 28 Sep 2007 08:29:13 +0000 indeyets http://blog.milkfarmsoft.com/?p=69 Fink project has launched the new Package Database (aka PDB) interface. Looks neat . . . → Read More: Fink, new PDB]]> Fink project has launched the new Package Database (aka PDB) interface. Looks neat