$doc = domxml_open_mem($HTTP_RAW_POST_DATA);
if (!$doc) {
  soap_fault("BAD_DATA","The content supplied was invalid");
}

$env = $doc->document_element();
$body = $env->first_child();
$nodes = $body->child_nodes();
$c = sizeof($nodes);
for($i=0;$i<$c;$i++)
{
  if ($nodes[$i]->tagname == "method") $method = $nodes[$i]->get_content();
  if ($nodes[$i]->tagname == "argv") $argv = $nodes[$i]->child_nodes();
}

echo "AnyData Here";
results in:
c
AnyData Here

That 'c' represents 12, the number of bytes written.
It will do this for every usage of echo, here is a more complicated response result (can't show code cause my company won't allow that, will try to provide another sample later)

Sample Code/Output:
-- begin code --
header("Content-Type: text/xml; charset=\"UTF-8\")");
header("Cache-control: private");
echo "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\" ?>";
echo "<SOAP-ENV:Envelope xmlns:SOAP-ENV=\"http://schemas.xmlsoap.org/soap/envelope/\">";
echo "<SOAP-ENV:Body>";
echo "<status>success</status>";
echo "</SOAP-ENV:Body></SOAP-ENV:Envelope>";
exit();
-- end code --
-- begin output --
d0
<?xml version="1.0" encoding="UTF-8" standalone="no" ?><SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"><SOAP-ENV:Body><status>success</status></SOAP-ENV:Body></SOAP-ENV:Envelope>
0

-- end output --