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PHP - Valid DNS name

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  1. function isValidDomain($value) {
  2. 	if($value) {
  3. 		//Max 255 chars
  4. 		if(strlen($value) > 255) {
  5. 			return false;
  6. 		}
  7. 		//Remove trailing .
  8. 		if(substr($value,-1,1) == '.') {
  9. 			$value = substr($value,0,-1);
  10. 		}
  11. 		$labels = explode('.',$value);
  12. 		//More than 2 labels
  13. 		if(count($labels) >= 2) {
  14. 			foreach($labels as $label) {
  15. 				//Cannot start or end with a -
  16. 				if(substr($label,0,1) == '-' || substr($label,-1,1) == '-') {
  17. 					return false;
  18. 				}
  19. 				//Allowed characters a-z, 0-9, -
  20. 				if(!preg_match('/^[a-z\d-]{1,63}$/i',$label)) {
  21. 					return false;
  22. 				}
  23. 			}
  24. 		} else {
  25. 			return false;
  26. 		}
  27. 		return true;
  28. 	}
  29. 	return false;
  30. }

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