Regex Flickr Parser

By Patrick Talmadge On December 20, 2011 · Leave a Comment

Today’s Regex is used to parse a string for Flickr links and extract the Photo_ID. Once we have the Photo_ID we’re able to create a standard embed code from nearly any Flickr URL.

Supported Links:

The following Regex supports these Flickr links and embed code snippets.

Normal URL : http://www.flickr.com/photos/gambort/6501997531/
Short URL :  http://flic.kr/p/aUyrkH
Embed :      >a href="http://www.flickr.com/photos/gambort/6501997531/"
             title="Skyrim black dragon by gambort, on Flickr"><img
	     src="http://farm8.staticflickr.com/7004/6501997531_80aa9da91a.jpg"
             width="500" height="334" alt="Skyrim black dragon"></a>

****Short Code id needs to be decoded and replaced with the full photo ID****

Again, I’ve broken it up the Regex and commented each line.

$regexstr = '~
# Match Flickr link and embed code
(?:<a [^>]*href=")?		# If a tag match up to first quote of src
(?:				# Group Flickr url
	https?:\/\/		# Either http or https
	(?:[\w]+\.)*		# Optional subdomains
	(?:               		# Group host alternatives.
		flic\.kr     	# Either flic.kr
	        	| flickr\.com	# or flickr.com 
	)			# End Host Group
	(?:\/photos)?		# Optional video sub directory
	\/[^\/]+\/		# Slash and stuff before Id
	([0-9a-zA-Z]+)	# $1: PHOTO_ID is numeric
	[^\s]*			# Not a space
)				# End group
"?				# Match end quote if part of src
(?:.*></a>)?			# Match the end of the a tag
~ix';

Usage Example:

This example is more involved than the previous posts because we need to make an API call to get the image URL after we get the Flickr Photo_ID. I’ve also included a Base58 decode function incase the url is the short flic.kr style link.

function ParseForFlickr($string){
	$regexstr = <<REGEX FROM ABOVE>>;
 
	require_once('phpFlickr.php');
	$f = new phpFlickr("<<Flickr API Key>>");
 
	preg_match_all($regexstr, $string, $matches, PREG_SET_ORDER);
 
	//Loop results		
	foreach ($matches as $val) {	
		//If short code decode it     
		if (strpos($val[0], "flic.kr") !== false) {
			$val[1] = $this->flickrDecode($val[1]);
		} 
 
		//make flickr api call with photo id
		$pinfo = $f->photos_getSizes($val[1]);
		//Array 3 is the medium 500 size
		$imgstr = ' <p><img class="upostimg" src="'.$pinfo[3]['source'].'" /></p> ';
		$string = str_replace($val[0],$imgstr,$string);
	}
	return $string;
}
 
function flickrDecode($num){
	$alphabet = "123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";
 
	$decoded = 0;
	$multi = 1;
	while (strlen($num) > 0) {
		$digit = $num[strlen($num)-1];
		$decoded += $multi * strpos($alphabet, $digit);
		$multi = $multi * strlen($alphabet);
		$num = substr($num, 0, -1);
	}
 
	return $decoded;
}