title: WSO2 ESB print all TRANSPORT_HEADERS
body: <p>I can print individual transport headers in the WSO2 ESB with the following code inside a sequence: </p>
  
  <pre><code>&lt;log level="custom"&gt;
      &lt;property name="oneHeader" expression="$trp:FILE_NAME"/&gt;
  &lt;/log&gt;
  </code></pre>
  
  <p>But I need to print all available transport properties. There is a axis2 property called "[TRANSPORT_HEADERS][1]", but when printing this property it is always empty. </p>
  
  <pre><code>&lt;log level="custom"&gt;
      &lt;property name="allHeaders" expression="get-property('axis2','TRANSPORT_HEADERS')"/&gt;
  &lt;/log&gt;
  </code></pre>
  
  <p>Because I don't know all header names, I need to know <strong>how to print all transport headers?</strong></p>