Archivi categoria: Code

Extending PDOStatement for errors checking and other tasks

PDO is a great OO library for interacting with your database from PHP. It has a very consistent interface and your code will be cleaner than ever. And your PHP script will be more portable because PDO is not related to any database, but is a generic library to work with MySQL, PostgreSQL, SQLite and a lot others.

The only thing I miss in PDO is a better query error management. When I execute a query I have to check every time the PDOStatement->errorCode property to get sure everything is working well. That’s very annoying.

Fortunately there is a way to extend the PDOStatement class to get more comfortable in writing our script. In the official docs there is not a lot about this, but here is an explanation.

The official documentation talks only about a PDO::ATTR_STATEMENT_CLASS attribute for the PDO instance to be set through the setAttribute method. That’s not much, but here is an example:

try {
  $dbh = new PDO(
    "mysql:dbname=my_database;host=localhost;charset=utf8",
    $user,
    $pass
  );
  $dbh->setAttribute(PDO::ATTR_STATEMENT_CLASS, array('MyPDOStatement'));
} catch (PDOException $e) {
  die('Connection failed: ' . $e->getMessage());
}

You can set the attribute after the connection, not a problem. MyPDOStatement is a custom class that extends PDOStatement. A minimal version will look like this:

class MyPDOStatement extends PDOStatement
{
  private function __construct() {}

  function execute($input = array()) {
    parent::execute($input);

    if ($this->errorCode() !== '00000') {
      $err = $this->errorInfo();
      error_log(SQLException($err[2], $err[1]));
      return false;
    }

    return true;
  }
}

The private constructor is mandatory. You can use it to pass some variable to every MyPDOStatement instance, very useful in many situations.

For example we could use an array to track query execution times. So the code will look like this:

$info = array('queries' => 0, 'query_time' => 0);

try {
  $dbh = new PDO(
    "mysql:dbname=my_database;host=localhost;charset=utf8",
    $user,
    $pass
  );
  $dbh->setAttribute(PDO::ATTR_STATEMENT_CLASS, array('MyPDOStatement', array($info)));
} catch (PDOException $e) {
  die('Connection failed: ' . $e->getMessage());
}

class MyPDOStatement extends PDOStatement
{
  private $info;

  private function __construct(&info) {
    $this->info = &$info;
  }

  function execute($input = array()) {
    $t = microtime(true);
    parent::execute($input);
    $t = microtime(true) - $t;

    if ($this->errorCode() !== '00000') {
      $err = $this->errorInfo();
      error_log(SQLException($err[2], $err[1]));
      return false;
    }

    $this->info['queries']++;
    $this->info['query_time'] += $t;

    return true;
  }
}

Display usage hints for your Perl script

Perl is an awesome language. I like it very much more than Python because you can put some imagination inside your code, doing things with your style. I like very much the loose typing because you don’t have to care about the content in your variables: numbers, strings, objects are almost the same. You have to care about what you are doing, not how.

Commenting your code is very important for you and for everybody else that will see it. And if you are writing a standalone script it’s very useful to give hints about the usage without reading the code. Perl has a integrated comment system called Pod that can be used to generated documentation files in a number of format, but how can you display something on the command line by using the common –help parameter?

The answer is the Pod::Usage package. It’s a very powerful package, but I will use it in a minimal way. The official documentation will tell you everything you need to know, but let’s take a taste.

#!/usr/bin/perl
=head1 Example script

This is an example script to taste the Pod::Usage package.

=head1 SYNOPSIS

example.pl [--help] --source=1.2.3.4 --target=5.6.7.8

Options:
--help Displays this help
--source A source
--target A target

=cut

use strict;
use Getopt::Long;
use Pod::Usage;

my ($help, $source, $target);

GetOptions(
'source=s' => $source,
'target=s' => $target,
'help' => $help
);

pod2usage(1) if $help;

[...]

So how does this work? I use the Getopt::Long package to manage command line parameters. I pass two string parameters (source, target) and a flag (help). If flag is set I call the pod2usage function from Pod::Usage with a ‘1’ as parameter. The function will print out everything contained inside the SYNOPSYS paragraph and will exit the script with code 1 (or whatever number you passed).  That’s all!

Send mail with Sendmail from Bash command line

eMails are still the most important communication channel on internet. Most of the web applications you can find on the web require an eMail address to register because they will use it for important communications, to recover you password and so on. It’s still a reliable way to identify the users.

Well, today I was to write a monitor script who checks a server status and send an eMail to the admin if something wrong happens. For some reason I wanted to write it in Bash script and put it directly into the /etc/cron.daily/ folder. The check was pretty easy to write but then I had to send the eMail.

After some searching and trying I finally found out how to send emails directly from Bash with Sendmail and no need to write any file:

echo -e "To: "admin" <admin@example.com>nFrom: "The Server" <server@example.com>rnContent_Type: text/plainnSubject: [Server] Unexpected responsennResponse was wrongn" | sendmail -t

Now a little bit of explanation.

Basically I send all the needed headers and content to Sendmail with a pipe. Sendmail’s -t option forces to search the recipients addresses inside the header. Normally Sendmail expects this kind of addresses as a parameter, but this way everything has the same source, I mean the pipe.

The echo statement sends all the needed data to Sendmail. Remember the -e option to replace the backslashed special characters. This is very important because without it Sendmail will do not understand anything about you want to send.

You can add any kind of headers you need, such as the Cc and the Bcc fields or others, and check that after the last header and before the mail’s content there are two new line characters.

HSL2RGB converter source code (Perl)

Cleaning up my web space I found an old code to convert HSL triplets (Hue Saturation Lightness) to RGB (Red Blue Green). I think the code comes from the Gimp source code and was ported to Perl, but it’s so simple I think you can port easily everywhere.

So, why do you need to convert HSL to RGB? HSL values are more human understandable, so there a good choice for a color picket or something similar. But most graphic application require RGB values which are mostly used by computers.

 

And here is the code:

hsl_to_rgb($h, $s, $l); # Values in 0-255 range

sub hsl_to_rgb {
 my $h = $_[0]/255;
 my $s = $_[1]/255;
 my $l = $_[2]/255;
 my $r, $g, $b;

 if ($h<1/6) {
 $r = 1; $g = 6*$h; $b = 0;
 $g = $g*$s + 1 - $s; $b = $b*$s + 1 - $s;
 $r = $r*$l; $g = $g*$l; $b = $b*$l;
 } elsif ($h<1/3) {
 $r = 1-6*($h - 1/6); $g = 1; $b = 0;
 $r = $r*$s + 1 - $s; $b = $b*$s + 1 - $s;
 $r = $r*$l; $g = $g*$l; $b = $b*$l;
 } elsif ($h<1/2) {
 $r = 0; $g = 1; $b = 6*($h - 1/3);
 $r = $r*$s + 1 - $s; $b = $b*$s + 1 - $s;
 $r = $r*$l; $g = $g*$l; $b = $b*$l;
 } elsif ($h<2/3) {
 $r = 0; $g = 1-6*($h - 1/2); $b = 1;
 $r = $r*$s + 1 - $s; $g = $g*$s + 1 - $s;
 $r = $r*$l; $g = $g*$l; $b = $b*$l;
 } elsif ($h<5/6) {
 $r = 6*($h - 2/3); $g = 0; $b = 1;
 $r = $r*$s + 1 - $s; $g = $g*$s + 1 - $s;
 $r = $r*$l; $g = $g*$l; $b = $b*$l;
 } else {
 $r = 1; $g = 0; $b = 1-6*($h - 5/6);
 $g = $g*$s + 1 - $s; $b = $b*$s + 1 - $s;
 $r = $r*$l; $g = $g*$l; $b = $b*$l;
 }
 $r = int $r * 255;
 $g = int $g * 255;
 $b = int $b * 255;

 return {r => $r, g => $g, b => $b);
}

Enjoy!