PHP DomDocument错误-XML声明不在文档的开头

Question

I want to create sitemap with PHP DomDocument class. When I'm trying to get data from database with Kohana model It shows an error with content:

XML declaration not at beginning of document

When I delete these two lines with model access - everything works fine, what's wrong? I need this data to create my urls.

I'm using this function:

public function sitemap()
{
    $doc = new DOMDocument();
    $doc->formatOutput = true;


    $r = $doc->createElementNS("http://www.sitemaps.org/schemas/sitemap/0.9","urlset" );
    $r->setAttributeNS('http://www.w3.org/2001/XMLSchema-instance',
            'xsi:schemaLocation',
            'http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd'
            );

    $doc->appendChild( $r );

    $model = new Data_Model; // THESE TWO LINES CAUSES ERROR
    $arrayofdata = $model->get_all();

for($i=0; $i<10; $i++)
{
    $b = $doc->createElement( "url" );
    $loc = $doc->createElement("loc");
    $loc->appendChild($doc->createTextNode('www.example.com'));
    $b->appendChild( $loc );
        $priority = $doc->createElement( "priority" );
        $priority->appendChild(
                    $doc->createTextNode('1.0')
                    );
        $b->appendChild( $priority );


        $r->appendChild( $b );


        $changefreq = $doc->createElement( "changefreq" );
        $changefreq->appendChild(
                    $doc->createTextNode('Daily')
                    );
        $b->appendChild( $changefreq );

        $lastmod = $doc->createElement( "lastmod" );
        $lastmod->appendChild(
                    $doc->createTextNode(date('Y-m-d'))
                    );
    $b->appendChild( $lastmod );

    $r->appendChild( $b );
}
    $output = $doc->saveXML();
    header("Content-type:text/xml");  
    echo $output;

}

Answer 1

the error

XML declaration not at beginning of document

just means you have got some output (data) before the XML declaration (that is the <?xml version="1.0" ... ?> part). Instead put that output into the document. Here is an example:

<?php
error_reporting(~0);
ini_set('display_errors', 1);

class Data_Model {
    public function __construct() {
        echo "I output something just because I can!\n";
    }

    public function get_all() {
        trigger_error('Yes I can trigger notices baby!', E_USER_NOTICE);
        echo "Output, I love it! Just put it out!\n";
        return array();
    }
}

$doc                     = new DOMDocument();
$doc->formatOutput       = TRUE;
$doc->preserveWhiteSpace = FALSE;

$r = $doc->createElementNS("http://www.sitemaps.org/schemas/sitemap/0.9", "urlset");
$r->setAttributeNS('http://www.w3.org/2001/XMLSchema-instance',
    'xsi:schemaLocation',
    'http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd'
);
$doc->appendChild($r);

// capture leaked output and create a <buffer> element containing the output (if any) with the
// output XML

ob_start();
$model       = new Data_Model; // THESE TWO LINES CAUSES ERROR
$arrayofdata = $model->get_all();
$buffer      = ob_get_clean();

$bufferElement = $doc->createElement('buffer');
$bufferElement->setAttribute('strlen', strlen($buffer));
$bufferElement->appendChild($doc->createCDATASection($buffer));
$bufferElement = $doc->documentElement->appendChild($bufferElement);

# ... 

// output XML
header("Content-Type: text/xml");
$doc->save('php://stdout');

As you can see it is similar to your code. The mock of the Data_Model class just leaks some data - because it can! Yeah! And triggers a notice that's why error reporting is switched on high and display errors is on (don't do that in production, it's here for the examples sake).

What follows is basically your code until it comes to the ob_start() line and then with the ob_get_clean() a new XML element is added to the out.

And then there is the output. If you read closely you find already some little hints how to improve your code. Anyway here is the exemplary output so far:

<?xml version="1.0"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
  <buffer strlen="640"><![CDATA[I output something just because I can!

Notice: Yes I can trigger notices baby! in \home\user\test-parts.php on line 14

Call Stack:
    0.0006     147024   1. {main}() \home\user\test-parts.php:0
    0.0007     165016   2. Data_Model->get_all() \home\user\test-parts.php:36
    0.0007     165128   3. trigger_error() \home\user\test-parts.php:14

Output, I love it! Just put it out!
]]></buffer>
</urlset>

As you can see, all the output is now inside the XML document and not before it. The error is gone.

Try it out your own (or start troubleshooting finding out why your model outputs to Stdout instead of not.

---

Extra Note: When you add an element node to the document and you want to add children to that node in the document later on, you need to re-assign the variable:

$r = $doc->appendChild( $r );
^^^^^

Otherwise $r is still the element not added to the document. So you would need to add it later again which is not what you want. See DOMDocument::appendChild() for the detailed description and example codes that demonstrate so.