Tag Archives: PHP

Use fopen() to Check File Availability?

Zend Framework and Zend_Http_Client

PHP's fopen() can be used to check remote file existence
PHP's fopen() can be used to check remote file existence

I’ve posted about Zend_Http_Client. Simply there you can ‘make’ your own http client and you can request a remote file. Just to check what’s going on with this file.

// new HTTP request to a file
$httpClient = new Zend_Http_Client('http://www.example.com/myfile.mp4');
 
// get the HEAD of the response and match agains the
// Content-Length. That's because using the Content-Type is slower
$response = $httpClient->request(Zend_Http_Client::HEAD);
 
// if the Content-Length is 0 the file doesn't exists
if (0 === (int)$response->getHeader('Content-Length')) {
	echo 'the file doesn\'t exits';
}

However is there any other way to answer the same question?

fopen()

Yes and no? Perhaps yes, but you should be careful. I’m still not sure it can be used in any case. However here’s the snippet.

if (FALSE === @fopen('http://www.example.com/myfile.mp4', 'r')) {
	echo 'the file doesn\'t exists';
}

fopen() will return FALSE whenever the file doesn’t exists.

In both cases I request a remote file – an MPEG-4 file. Note that fopen()’s first parameter can be a HTTP resource.

jQuery.unbind()

Binding Problems

jQuery JavaScript Library
jQuery JavaScript Library

Typically in jQuery when you bind an HTML element with some event this event is fired every time the user (client) triggers it. Thus when you’ve a click event attached on a button you can click it as many times as you want. In some rare cases this can be tricky. Let’s imagine the following scenario.

  1. The user clicks on a “vote” button.
  2. Some AJAX calls are performed.
  3. After a successful AJAX call you setup a cookie to deny further votes from this machine.

This seems to be pretty well known scenario, but as the click event is attached to the button there is enough time to click several times on the “vote” button and to vote several times. In this case before the cookie is set the user can vote more than once. Continue reading jQuery.unbind()

How to Collect the Images and Meta Tags from a Webpage with PHP

Meta Tags and the Facebook Example

You’ve definitely seen the “share a link” screen in Facebook. When you paste a link into the box (fig. 1) and press the “Attach” button you’ll get the prompted cite parsed with a title, description and possibly thumb (fig. 2). This functionality is well known in Facebook, but it appears to be well known also in various social services. In fact Linkedin, Reddit, Dzone‘s bookmarklet use it.

Facebook Attach a Link Prompt Screen
fig. 1 - Facebook Attach a Link Prompt Screen

Fist thing to notice is that this information, prompted by Facebook, is the same as the meta tag information. However there is a slight difference.

Facebook Attached Link Screen
fig. 2 - Facebook Attached Link Screen

Facebook prefers for the thumb the image set into the <meta property=”og:image” … />. In the case above this tag appears to be:

<meta property="og:image" content="http://b.vimeocdn.com/ts/572/975/57297584_200.jpg" />

And the image pointed in the SRC attribute is exactly the same as the one prompted by Facebook (fig. 3).

Vimeo Thumb
fig. 3 - Vimeo Thumb

First thing to note is that the real thumb is bigger than the thumb shown in Facebook, so Facebook resizes it and the second thing to note is that there are more meta tags of the og:… format. Continue reading How to Collect the Images and Meta Tags from a Webpage with PHP

From SVG to Geo Coordinates – A Complete Guide

Why This Task Is Not Trivial?

First of all what do we have? There is a vector shape, which may represent a map, which we’d like to convert into a GEO map. In other words there is a SVG file containing the source shape, that you’d like to convert in geoJSON or whatever collection of geo points. This is not trivial, of course, first of all because there’s no an algorithm or automation that can do this, and because everybody knows that the resulting map will be only approached, but will never be so accurate as the vector shape. This is because in a vector shape you may contain Bézier Curves, which I’ll show a little bit later in this post, that are difficult to represent in geo coordinates.

So the first task will be to find an approaching algorithm. However there are two things that are optimistic:

  1. You can’t effectively represent Bézier curves in geo coordinates, but even if you could do it there’s no practical need, because the collection of geo coordinates will be huge and this will slow down you’re application. Remember that geoJSON is yet again possibly used by your browser and the amount of geo points will be proportionally slowing down the app.
  2. As you may know Google’s visualization map is representing the World’s countries again with quite approached maps. Take a look at the following image – the country borders are quite sharpened:

Google Visualization Map

So far we know that we need an approaching algorithm that will convert vector lines and possibly curves in geo coordinates, but before we proceed we’ve to understand the SVG format. Continue reading From SVG to Geo Coordinates – A Complete Guide