Module field with feeds, module generating data - drupal

Question

I have an issue with triming a field before it is saved. I wanted to use substr(), or regex() with preg_match(). I have built a Drupal 7 module, but it can't work at all. I have tried using the trim plugin in feeds tamper module, but it doesn't seem to work. The data I am using is from a feed from Google Alerts. I have posted this issue here.
This is what I have done so far, and I know my regular expression is wrong; I was trying to get it do anything, just to see if I could get it to work, but I am pretty lost on how to add this type of function to a Drupal module.
function sub_node_save() {
$url = $node->field_web_screenhot['und'][0]['url'];
$url = preg_match('~^(http|ftp)(s)?\:\/\/((([a-z0-9\-]*)(\.))+[a-z0-9]*)($|/.*$)~i',$url );
$node->field_web_screenhot['und'][0]['url'] =$url;
return ;
}
I used the Devel module to get the field.
If there's an easy way to use substr(), I would consider that or something else.
Basically, I just want to take the Google redirect off the URL, so it is just the basic URL to the web site.

Answer 1

Depending on your question and later comments, I'd suggesting using node_presave hook (http://api.drupal.org/api/drupal/modules!node!node.api.php/function/hook_node_presave/7) for this.
It's called before both insert (new) and update ops so you will need extra validations to prevent it from executing on node updates if you want.
<?php
function MYMODULE_node_presave($node) {
// check if nodetype is "mytype"
if ($node->type == 'mytype'){
// PHP's parse_url to get params set to an array.
$parts = parse_url($node->field_web_screenhot['und'][0]['url']);
// Now we explode the params by "&" to get the URL.
$queryParts = explode('&', $parts['query']);
$params = array();
foreach ($queryParts as $param) {
$item = explode('=', $param);
$params[$item[0]] = $item[1];
}
//valid_url validates the URL (duh!), urldecode() makes the URL an actual one with fixing "//" in http, q is from the URL you provided.
if (valid_url(urldecode($parms['q']))){
$node->field_web_screenhot['und'][0]['url'] = urldecode($parms['q']);
}
}
}