Test if string is URL encoded in PHP


Question

How can I test if a string is URL encoded?

Which of the following approaches is better?

  • Search the string for characters which would be encoded, which aren't, and if any exist then its not encoded, or
  • Use something like this which I've made:

function is_urlEncoded($string){
 $test_string = $string;
 while(urldecode($test_string) != $test_string){
  $test_string = urldecode($test_string);
 }
 return (urlencode($test_string) == $string)?True:False; 
}

$t = "Hello World > how are you?";
if(is_urlEncoded($sreq)){
 print "Was Encoded.\n";
}else{
 print "Not Encoded.\n";
 print "Should be ".urlencode($sreq)."\n";
}

The above code works, but not in instances where the string has been doubly encoded, as in these examples:

  • $t = "Hello%2BWorld%2B%253E%2Bhow%2Bare%2Byou%253F";
  • $t = "Hello+World%2B%253E%2Bhow%2Bare%2Byou%253F";
1
20
9/10/2015 11:30:01 PM

Accepted Answer

You'll never know for sure if a string is URL-encoded or if it was supposed to have the sequence %2B in it. Instead, it probably depends on where the string came from, i.e. if it was hand-crafted or from some application.

Is it better to search the string for characters which would be encoded, which aren't, and if any exist then its not encoded.

I think this is a better approach, since it would take care of things that have been done programmatically (assuming the application would not have left a non-encoded character behind).

One thing that will be confusing here... Technically, the % "should be" encoded if it will be present in the final value, since it is a special character. You might have to combine your approaches to look for should-be-encoded characters as well as validating that the string decodes successfully if none are found.

10
8/23/2014 1:20:30 PM

i have one trick :

you can do this to prevent doubly encode. Every time first decode then again encode;

$string = urldecode($string);

Then do again

$string = urlencode($string);

Performing this way we can avoid double encode :)


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