Tag: Programming

From time to time you’re going to need to move some data from one table into another, in particular to generalize or specialize code. I’ve seen amazingly large code blocks written to handle simple cases as this, and here’s a simple trick you’re going to need some day:

INSERT INTO 
    
    (field_1, field_2) 
SELECT
    some_field, some_other_field 
FROM 
    

You can also add conditionals, i.e. to retrieve rows that might have been inserted yesterday, etc:
INSERT INTO 
    
    (field_1, field_2) 
SELECT
    some_field, some_other_field 
FROM 
    
WHERE
    condition = 1

The good thing about this is that all data movement is kept within the database server, so that the data doesn’t have to travel from the server, to the client and then back from the client to the server again. It’s blazingly fast compared to other methods. You can also do transformations with regular SQL functions in your SELECT statement, which should help you do very simple operations at the speed of light.
	

	
	




	
	

		
The Side Effect of Using Return Type To Handle Errors
	


	

		
I came across a curious little side effect of the issue I just posted earlier:
public function action()
{
   $id = filter_input(INPUT_POST, 'id', FILTER_SANITIZE_STRING);
	
   if(is_bool($id))
   {
      die('invalid id');
   }

   if(isset($_POST['accept']))
   {
      $this->acceptId($id);
   }
   else if(isset($_POST['reject']))
   {
      $this->rejectId($id);
   }
}

This is obviously going to do something when a POST has occured, but the method was invoked each and every time. The reason why it works? If there is no variable named ‘id’ POSTed, filter_input returns null. And null is not boolean, so the test passes. But as it’s not a POST request, neither of the two other if-tests are true, so the code silently passes through (id can contain characters here, so the filter isn’t used to just get integers).
If you’re not going to throw an error when the parameter is missing, the test is actually completely useless. This bug had hidden itself within the usage of the type to test for fault instead of actually checking the value, and did not creep out before I rewrote the if-test.
	


	
	




	
	

		
Releasing Keepitclose Alpha
	


	

		
I’ve just created a small project site over at Google Code for Keepitclose. Keepitclose is a HTTP local caching web service written in PHP meant to cache resources retrieved from external and internal web services. It currently supports both an APC backend (using shared memory in the web server itself) and using Memcache (which allows you to have several frontends using one or several backend memcache servers).
Missing features are currently:

Keeping HTTP headers
Adding cache information to HTTP headers
A file based backend
Everything else you can think of

The server do however support:

Time to live (TTL) for a cached resource when stored
TTL Window, i.e.:


A new version should be fetched at regular intervals, such as every sixth hour. New data are available at 00:00, 06:00, 12:00 and 18:00. Use ttlWindowSize=21600 to get six hours window size. Use ttlWindowOffset to add a offset; ttlWindowOffset=900 adds fifteen minutes to the value and retrives new content at 00:15, 06:15, 12:15 and 18:15.



If you want to implement your own backend, implement the Keepitclose_Storage_Interface and add an entry into the config.php file for your module, i.e. ‘file’ => array(‘path’ => ‘/tmp’). 
The current version also supports simple access control using the allowedHosts entry in the config file. This entry contains one row for each allowed host as a regular expression:
    'allowedHosts' => array(
        '^127\\.0\\.0\\.1$',
    ),

.. will only allow requests from localhost. To allow a subnet, you could write ‘^127\\.0\\.0\\.[0-9]+$’.
You can also add several memcache servers, a request will then poll a random server to retrieve the resource. If not found, the content will be retrieved from the web and stored to all memcache servers. This is useful for environments with a very heavy read load.
'storage' => array(
    'memcache' => array(
        array(
            'host' => 'tcp://127.0.0.1',
        ),
    ),
),

To add more memcache servers, simply add another array() of memcache entries:
'memcache' => array(
    array(
        'host' => 'tcp://127.0.0.1',
    ),
    array(
        'host' => 'tcp://127.0.0.2',
    ),
),

You can also set ‘port’ and ‘persistent’ for the memcache connections.
Please leave a comment here or create an issue ticket on the google code page if you need any help or have any suggestions. All patches are welcome.