为什么SimpleXMLElement无法找到XML文件的内容？

Question

I need to parse an xml document that I receive from a third party using php. I am not able to ask the maintainers of the document to fix its structure. When I parse the document using simplexml_load_file the XML documen is empty.

Here is a stripped down example of what I am seeing.

my-file.xml:

<?xml version="1.0" encoding="utf-8"?>
<DataSet>
  <diffgr:diffgram xmlns:diffgr="urn:schemas-microsoft-com:xml-diffgram-v1">
    aaa
  </diffgr:diffgram>
</DataSet>

And I process it like this (from the command line):

php > $xml = simplexml_load_file('my-file.xml');
php > print_r($xml);
SimpleXMLElement Object
(
)

I was expecting that the xml structure is displayed through print_r.

Indeed, when I remove the namespace declaration, things seem to work (despite some expected XML parse warnings):

my-file-nonamespace.xml:

<?xml version="1.0" encoding="utf-8"?>
<DataSet>
  <diffgr:diffgram>
    aaa
  </diffgr:diffgram>
</DataSet>

Processing it the same way on the command line (with warnings removed):

php > $xml = simplexml_load_file('my-file-nonamespace.xml');

// a bunch of xml parse warnings
php > print_r($xml);
SimpleXMLElement Object
(
    [diffgr:diffgram] =>
    aaa

)

So, the problem has to do with an invalid namespace declaration. I can probably use a regular expression on the file to remove the namespace declaration before parsing, but that is not a direction I want to go.

What is the best way to properly parse the first document in PHP?

Answer 1

The issue is not that the data isn't loaded, but the fact that the child elements are in a different namespace.

$xml = simplexml_load_file('my-file.xml');
var_dump($xml->children("diffgr", true));

This selects the children from a specific namespace from the current element.

Note that you should use the URI as the prefix may change, but this is just to show that the data is there.

Edit: If the XML has issues, then the first stage is to ignore the errors and then check what is loaded ...

libxml_use_internal_errors(true);
$xml = simplexml_load_file('my-file.xml');
echo $xml->asXML();

This will give you an idea of what state the result is and even if it loads. A quick example is...

libxml_use_internal_errors(true);
$xml = simplexml_load_file('my-file.xml');
echo $xml->asXML();
var_dump($xml->children());

With..

<?xml version="1.0" encoding="utf-8"?>
<DataSet>
  <diffgr:diffgram>
    aaa
  </diffgr:diffgram>
</DataSet>

Notice how the namespace is there, but the namespace isn't declared. The output is...

<?xml version="1.0" encoding="utf-8"?>
<DataSet>
  <diffgr:diffgram>
    aaa
  </diffgr:diffgram>
</DataSet>
/home/nigel/workspace2/Test/t1.php:22:
class SimpleXMLElement#2 (1) {
  public $diffgr:diffgram =>
  string(11) "
    aaa
  "
}

This outputs the children without having to use the namespace.