Docker, Perl

Get started with Perl on Docker

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Docker is the modern way for distribute applications. It allows you to create a deployable entity that will run in the same way on almost every *unix platform without the need to install anything more than same basic dependencies required by Docker itself. An ideal choice to run a code sample, a testing environment or your production application. Let’s see how to use it to run a simple Perl script. Continue reading Get started with Perl on Docker →

Perl

Upload huge files with Perl’s LWP::UserAgent

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Everybody who work with Perl knows LWP::UserAgent, the most used library when you need to work with HTTP connections.

The library has some methods that cover the most common usage cases, such as GET and POST request.
If you need something more particular you have to set up a HTTP::Request object and pass it to LWP::UserAgent’s request method. I don’t think I’m saying something unexpected.

I recently got some problems by sending a bug file. It wasn’t really big because I’m talking about a 100 MB file, but it was bit enough to send my small VPS server out of memory. This was because I needed to pass it as raw POST payload for Google Drive API and to do that I was slurping it into memory. A bad idea.

Continue reading Upload huge files with Perl’s LWP::UserAgent →

Code

Extending PDOStatement for errors checking and other tasks

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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;
  }
}