PHP: How to get base URL from HTML page - php

Question

I'm struggling with figuring out how to do this. I have an absolute URL to an HTML page, and I need to get the base URL for this. So the URLs could be for example:
http://www.example.com/
https://www.example.com/foo/
http://www.example.com/foo/bar.html
https://alice#www.example.com/foo
And so on. So, first problem is to find the base URL from those and other URLs. The second problem is that some HTML pages contain a base tag, which could be for example http://example.com/ or simply / (although I think some browser only support the one starting with protocol://?).
Either way, how can I do this in PHP corrrectly? I have the URL and I have the HTML loaded up in a DOMDocument so should be able to grab the base tag fairly easily if it exists. How do browsers solve this for example?
Clarification on why I need this
I'm trying to create something which takes a URL to a web page and returns the absolute URL to all the images this web page links to. Since some/many/all of these images might have relative URLs, I need to find the base URL to use when I make them absolute. This might be the base URL of the web page, or it might be a base URL specified in the HTML itself.
I have managed to fetch the HTML and find the URLs. I think I've also found a working method of making the URLs absolute when I have the base URL to use. But finding the base URL is what I'm missing, and what I'm asking about here.

Answer 1

See parse_url().
$result=parse_url('http://www.google.com');
print_r($result);
Pick out of there whichever element you are looking for. You probably want $result['path'].

Answer 2

Fun with snippets!
if (!function_exists('base_url')) {
function base_url($atRoot=FALSE, $atCore=FALSE, $parse=FALSE){
if (isset($_SERVER['HTTP_HOST'])) {
$http = isset($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) !== 'off' ? 'https' : 'http';
$hostname = $_SERVER['HTTP_HOST'];
$dir = str_replace(basename($_SERVER['SCRIPT_NAME']), '', $_SERVER['SCRIPT_NAME']);
$core = preg_split('#/#', str_replace($_SERVER['DOCUMENT_ROOT'], '', realpath(dirname(__FILE__))), NULL, PREG_SPLIT_NO_EMPTY);
$core = $core[0];
$tmplt = $atRoot ? ($atCore ? "%s://%s/%s/" : "%s://%s/") : ($atCore ? "%s://%s/%s/" : "%s://%s%s");
$end = $atRoot ? ($atCore ? $core : $hostname) : ($atCore ? $core : $dir);
$base_url = sprintf( $tmplt, $http, $hostname, $end );
}
else $base_url = 'http://localhost/';
if ($parse) {
$base_url = parse_url($base_url);
if (isset($base_url['path'])) if ($base_url['path'] == '/') $base_url['path'] = '';
}
return $base_url;
}
}
Use as simple as:
// url like: http://stackoverflow.com/questions/2820723/how-to-get-base-url-with-php
echo base_url(); // will produce something like: http://stackoverflow.com/questions/2820723/
echo base_url(TRUE); // will produce something like: http://stackoverflow.com/
echo base_url(TRUE, TRUE); || echo base_url(NULL, TRUE); // will produce something like: http://stackoverflow.com/questions/
// and finally
echo base_url(NULL, NULL, TRUE);
// will produce something like:
// array(3) {
// ["scheme"]=>
// string(4) "http"
// ["host"]=>
// string(12) "stackoverflow.com"
// ["path"]=>
// string(35) "/questions/2820723/"
// }