CodeWord: Apokalyptik

Bash Coding Convention ../

We use dirname() a lot in php to make relative paths work from multiple locations like so. The advantages are many:

require dirname( dirname( __FILE__ ) ) . '/required-file.php';
$data = file_get_contents( dirname(__FILE__).'/data/info.dat');

But in bash we often dont do the same thing, we settle for the old standby “../”. Which is a shame because unless your directory structure is set up exactly right, and you have proper permissions, and you run the command from the right spot, it doesnt work as planned. I think part of the reason is that its not obvious how to reliably get a full path to the script from inside itself. Another reason is that ../ is shorter to type and easier to remember. Finally there’s always one time scripts for which this methodology is overkill. But if you’re planning to write a script which other people will (or might) be using, I think it’s good practice to do it right. Googling for things you’d think to search for on this subject does not yeild very informative results, or incomplete (incorrect) methods… so… here’s how to do the above php in bash:

source $(dirname $(dirname $(readlink -f $0)))/required-file.sh
data=$(cat $(dirname $(readlink -f $0))/data/info.dat)

Hope this helps someone

As a side note, the OSX readlink binary functions differently. You’ll want to use a package manager to install gnu coreutils, and iether use greadlink, or link greadlink to a higher precedence location on your $PATH (I have /opt/local/bin:/opt/local/sbin: at the beginning of my $PATH)

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This deserves some link love

Andy bogged a piece of advice that I have him which I got from Barry… and if you want to know how to get the true absolute path to the real location of the current script is from inside of it (like phps realpath and __FILE__) I suggest you check it out

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Logging post data

Lets say you have a relatively complex php web application, like wordpress. You have it running under apache (which is common.) You have good control of your site via .htaccess (which is common — permalinks and all.) And something happens to your blog (e.g. someone is exploiting some unknown vulnerability to compromise your content), which you want to track down. So you want to log, for instance, HTTP POST data. Your first instinct might be to add some logging code to index.php (mine was) But there are a lot of possible places which might be directly accessed, especially in the admin. So The trick I use (and this is probably the only time I’ve ever condoned this) is to use PHPs auto_prepend_file functionality.

Make a /home/user/postlog/ directory, then a /home/user/postlog/logs/ directory (and chmod a+rw that one.) Next make a simple /home/user/postlog/postlog.php file with the following contents:

<?php
if ( isset($_POST) && is_array($_POST) && count($_POST) > 0 ) {
  $log_dir = dirname( __FILE__ ) . '/logs/';
  $log_name = "posts-" . $_SERVER['REMOTE_ADDR'] . “-” . date(”Y-m-d-H”) . “.log”;
  $log_entry = gmdate(’r') . “\t” . $_SERVER['REQUEST_URI'] . “\r\n” . serialize($_POST) . “\r\n\r\n”;
  $fp=fopen( $log_dir . $log_name, ‘a’ );
  fputs($fp, $log_entry);
  fclose($fp); }
?>

Finally add this line to the top of your .htaccess file:

php_value auto_prepend_file /home/user/postlog/postlog.php

If all went well this should start logging any request to any php file with any post data into the /home/user/postlog/logs/ direcory (with a unique log per ip per day)

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It’s good for the server. It’s good for the soul.

ack (http://petdance.com/ack/), love it (thanks nikolay)

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colorizing php cli scripts

It’s pretty common in most scripting languages which center around the command line (bash, perl, etc) to find information on colorizing your shell script output, mainly because those languages are tied very tightly to command line use. It can be difficult, however, to find information about adding this same nice feature to a php cli script. The reason is simple: most people dont use php for cli applications; most cli programmers use something else. It’s not difficult to adapt the same techniques listed in most bash howtos (generally in the section reserved for colorizing your command prompt) for generating colored terminal output for php.

echo "\033[31mred\033[37m\r\n";

echo "\033[32mgreen\033[37m\r\n";

echo "\033[41;30mblack on red\033[40;37m\r\n";

Simple, functional, useful (even if a bit complicated.) I leave it to you to lookup a bash prompt colorization howto to hunt down your own list of escape color codes (call it homework.)

Cheers

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so-you-wanna-see-an-image

We’ve been asked how we manage serving files from Amazons very cool S3 service at WordPress.com… This is how. (covering a requested image already stored on S3, not the upload -> s3 process)

A request comes into pound for a file. Pound hashes the hostname (via a custom patch which we have not, but may, release) , to determine which of several backend servers the request should hit. Pound forwards the request to that server. This, of course, means that a given blog always serves from the same backend server. The only exception to the afore-mentioned rule is if that server is, for some reason, unavailable in which case it picks another server to serve that hostname from temporarily.

The request then comes into varnishd on the backend servers. The varnishd daemon checks its 300Gb worth of files cache and (for the sake of this example) finds nothing (hey, new images are uploaded all the time!) Varnishd then checks with the web server (running on the same machine, just bound to a different IP/Port#) and that request is handled by a custom script.

So, a http daemon on the same backend server runs the file request. The custom script checks the DB to gather information on the file (specifically which DC’s it is in, size, mod time, and whether its deleted or not) all this info is saved in memcached for 5 minutes. The script increments and checks the “hawtness” (term courtesy of Barry) of the file in memcached (if the file has been accessed over a certain # of times it is then deemed “hawt”, and a special header is sent with the response telling varnishd to put the file into its cache. When that happens the request would be served directly by varnishd in the previous paragraph and never hit the httpd or this script again (or at least not until the cache entry expires.)) At this point, assuming the file should exist (deleted = 0 in the files db) we fetch the file from a backend source.

Which backend source depends on where it is available. The order of preference is as follows: Always fetch from Amazon S3 if the file lives there (no matter what, the following preferences only ever occur if, for some reason, s3 = 0 in the files db), and if that fails fetch from the one files server we still have (which has larger slower disks, and is used for archiving purposes and fault tolerance only)

After fetching the file from the back end… the custom script hands the data and programatically generated headers to the http daemon, which hands the data to varnishd, varnishd hands the data to pound, pound hands the data to the requesting client, and the image appears in the web browser.

And there was much rejoicing (yay.)

For the visual people among us who like visuals and stuff… (I like visuals…) here goes…

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Throughput sensitive fputs/fwrite (in php)

I’d be glad for anyone who cares to look to read and comment on these functions. The idea is to be able to abort and retry, or fail, an operation on a slow link. I’ll work on fgets replacements tomorrow…

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PHP CLI Status Indicator

Most times when people write command line scripts they just let the output flow down the screen as a status indicator, or just figure “it’s done when it’s done” But sometimes it would be nice to have a simple clean status indicator, allowing you to monitor progress and gauge time-to-completion. This is actually very easy to accomplish. Simply use \r instead of \r\n in your output. Obviously the example below is very simplified, and this can be applied in a much more sophisticated fashion. But it works.

$row_count = get_total_rows_for_processing();
$limit=10000;
echo “\r\n[  0%]“;
for ( $i=0; $i < = $row_count; $i = $i + $limit ) {
  $query=”SELECT * FROM table LIMIT {$limit} OFFSET {$i}”;
  // do whatever
  $pct = round((($i+$offset)/$row_count)*100);
  if ( $pct < 10 ) {
    echo “\r[  $pct%]“;
  } else {
    if ( $pct < 100 ) {
      echo “\r[ $pct%]“;
    } else {
      echo “\r[$pct%]“;
    }
  }
}
echo “\r[100%]\r\n”;

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You’re only ever done debugging for now.

I’m the kinda guy who owns up to my mistakes. I also strive to be the kinda guy who learns from them.  So I figured I would pass this on as some good advice from a guy who’s “screwed that pooch”

There was a project on which I was working, and that project sent me e-mail messages with possible problem alerts.  All was going well, and at some point I turned off those alerts.  I don’t remember when.  And I don’t remember why.  Which means I was probably “Cleaning up” the code.  It was, after all, running well (I guess.)  But along comes a bug introduced with new functionality (ironically a from somewhere WAAAAAAY up the process chain from my project).  And WHAM, errors up the wazzoo.  But no e-mails. Oops. Needless to say the cleanup process was long and tedious… especially for something that was avoidable.

I’ve since put the alerting code back into the application, and have my happy little helpers in place fixing the last of the resulting issues.

The lesson to be taken from this is that you’re only ever done debugging for now. Because tomorrow that code, thats working perfectly now, wont be working perfectly anymore.  And that the sources for entropy are, indeed, endless.

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Any… good… php devs out there looking for some side work?

I know a group of guys looking to do some cool stuff who could use a few good contractors. Drop me an e-mail with maybe a sample or something cool you did in php and I’ll pass it on.

apokalyptik apokalyptik com — Subject: “PHP Consulting” (I’ll likely completely overlook your mail if you use some subject not starting with that string)

Cheers

DK

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