Php 剥离SOAP信封以将响应保存到XML文件

我有一个SOAP响应，希望将其保存到XML文件中。将响应写入文件时，SOAP信封也随之写入，这使得XML文件由于以下错误而变得无用：

XML declaration allowed only at the start of the document in ...

在本例中，XML被声明两次：

<?xml version="1.0" encoding="ISO-8859-1"?>
    <SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
        <SOAP-ENV:Body><ns1:NDFDgenResponse xmlns:ns1="http://graphical.weather.gov/xml/DWMLgen/wsdl/ndfdXML.wsdl">
           <dwmlOut xsi:type="xsd:string">
           <?xml version="1.0"?>
           ...

问题在于htmlspecialchars_解码。信封文档包含其他XML文档作为文本节点。如果对XML文档中的实体进行解码，就会破坏它。切勿在XML文档上使用htmlspecialchars\u解码

将信封XML加载到DOM中并从中读取所需的值

$xml = <<<'XML'
<?xml version="1.0" encoding="ISO-8859-1"?>
<SOAP-ENV:Envelope 
  SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" 
  xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
  <SOAP-ENV:Body>
    <ns1:NDFDgenResponse 
      xmlns:ns1="http://graphical.weather.gov/xml/DWMLgen/wsdl/ndfdXML.wsdl">
      <dwmlOut xsi:type="xsd:string">
        &lt;?xml version="1.0"?>
        &lt;weather>XML&lt;/weather>
      </dwmlOut>
     </ns1:NDFDgenResponse>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>
XML;

$dom = new DOMDocument();
$dom->loadXml($xml);
$xpath = new DOMXPath($dom);
$xpath->registerNamespace('soap', 'http://schemas.xmlsoap.org/soap/envelope/');
$xpath->registerNamespace('ndfd', 'http://graphical.weather.gov/xml/DWMLgen/wsdl/ndfdXML.wsdl');

$innerXml = $xpath->evaluate(
  'string(/soap:Envelope/soap:Body/ndfd:NDFDgenResponse/dwmlOut)'
);
echo $innerXml;

输出：

<?xml version="1.0"?>
<weather>XML</weather>

<?xml version="1.0"?>
<weather>XML</weather>