Hướng dẫn dùng xsd validator trong PHP

It’s 2017 and you still prefer using XML(Extensible Markup Language) to JSON(JavaScript Object Notation) for data-interchange? Well, that is not the point about this article. Everything you want to say about the trade-offs of either of them has been dealt with here. But there are still a lot of systems using XML today and I can assure you that it would still be the case X years from now.
Validating XML against XSD might be the first step to take especially when building a feed Reader/Ingester. For Starters, any file like the sample below is a well-formed XML file.

  2002-05-30T09:30:10.5
   
      Gambardella, Matthew
      
      Computer
      44.95
      2000-10-01
      An in-depth look at creating applications 
      with XML.
   
   
      Ralls, Kim
      
      Fantasy
      5.95
      2000-12-16
      A former architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.
   

and below is a sample XSD (XML Schema Definition) file:

Writing a XSD for your XML is actually easy to do, you make use of tools like freeformatter or do a crash course on w3Schools.
Now, we are ready to validate our XML file against the XSD using either DOMDocument or XMLReader. First, make sure that these extensions are enabled on PHP installation.

Validating With DOMDocument

handler = new \DOMDocument('1.0', 'utf-8');
    }
    /**
     * @param \libXMLError object $error
     *
     * @return string
     */
    private function libxmlDisplayError($error)
    {
        $errorString = "Error $error->code in $error->file (Line:{$error->line}):";
        $errorString .= trim($error->message);
        return $errorString;
    }
    /**
     * @return array
     */
    private function libxmlDisplayErrors()
    {
        $errors = libxml_get_errors();
        $result    = [];
        foreach ($errors as $error) {
            $result[] = $this->libxmlDisplayError($error);
        }
        libxml_clear_errors();
        return $result;
    }
    /**
     * Validate Incoming Feeds against Listing Schema
     *
     * @param resource $feeds
     *
     * @return bool
     *
     * @throws \Exception
     */
    public function validateFeeds($feeds)
    {
        if (!class_exists('DOMDocument')) {
            throw new \DOMException("'DOMDocument' class not found!");
            return false;
        }
        if (!file_exists($this->feedSchema)) {
            throw new \Exception('Schema is Missing, Please add schema to feedSchema property');
            return false;
        }
        libxml_use_internal_errors(true);
        if (!($fp = fopen($feeds, "r"))) {
           die("could not open XML input");
        }
        
        $contents = fread($fp, filesize($feeds));
        fclose($fp);
       
        $this->handler->loadXML($contents, LIBXML_NOBLANKS);
        if (!$this->handler->schemaValidate($this->feedSchema)) {
           $this->errorDetails = $this->libxmlDisplayErrors();
           $this->feedErrors   = 1;
        } else {
          //The file is valid
           return true;
        }
    }
    /**
     * Display Error if Resource is not validated
     *
     * @return array
     */
    public function displayErrors()
    {
        return $this->errorDetails;
    }
}

This DomValidator can be easily used like so:

validateFeeds('sample.xml');
if ($validated) {
  echo "Feed successfully validated";
} else {
  print_r($validator->displayErrors());
}

The above piece of code is actually easy to understand, the most important method here is the validateFeeds() method.

Validating With XMLReader

The upside of using XMLReader over DomDocument is scalability. XMLReader can handle very large files better than DomDocument. Our class will be very similar to that of DomDocument. Also note that your libxml version is above 2.6.

handler = new \XMLReader();
    }
    /**
     * @param \libXMLError object $error
     *
     * @return string
     */
    private function libxmlDisplayError($error)
    {
        $errorString = "Error $error->code in $error->file (Line:{$error->line}):";
        $errorString .= trim($error->message);
        return $errorString;
    }
    /**
     * @return array
     */
    private function libxmlDisplayErrors()
    {
        $errors = libxml_get_errors();
        $result    = [];
        foreach ($errors as $error) {
            $result[] = $this->libxmlDisplayError($error);
        }
        libxml_clear_errors();
        return $result;
    }
    /**
     * Validate Incoming Feeds against Listing Schema
     *
     * @param resource $feeds
     *
     * @return bool
     *
     * @throws \Exception
     */
    public function validateFeeds($feeds)
    {
        if (!class_exists('XMLReader')) {
            throw new \DOMException("'XMLReader' class not found!");
            return false;
        }
        
        if (!file_exists($this->feedSchema)) {
            throw new \Exception('Schema is Missing, Please add schema to feedSchema property');
            return false;
        }
        
        $this->handler->open($feeds);
        $this->handler->setSchema($this->feedSchema);
        libxml_use_internal_errors(true);
        while($this->handler->read()) {
            if (!$this->handler->isValid()) {
                $this->errorDetails = $this->libxmlDisplayErrors();
                $this->feedErrors   = 1;
            } else {
                return true;
            }
        };
    }
    /**
     * Display Error if Resource is not validated
     *
     * @return array
     */
    public function displayErrors()
    {
        return $this->errorDetails;
    }
}

We use this class too similar to how we used the DomValidator class.

validateFeeds('sample.xml');
if ($validated) {
  echo "Feed successfully validated";
} else {
  print_r($validator->displayErrors());
}

So that’s it. I hope to follow this up with ingesting feeds very soon. You can reach me on for feedback, I will appreciate it.

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A passionate learner and elucidative teacher.

I am a Full-Stack PHP Engineer who has worked extensively using PHP and modern PHP Frameworks. I also develop Front-end Applications using JS and JQuery.

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