Binary strings (set with xmlrpc_set_type) go into a <base64>...</base64> block like you'd expect. But after every 80th character, this function inserts the XML entity "&#10;", which is a Unicode newline, as if to cause a line-wrap, which is admittedly silly.

Silly though it may be, it causes real problems for some XML-RPC servers, such as http://jakarta.apache.org/xmlrpc/ (nee Helma). Stripping out those entities with something like

$req = preg_replace('/&#10;/', '', xmlrpc_encode_request("my.method", $args));

works around the problem.

It should be noted that encoding does not seem to encode anything, just specify what goes into the XML header.

We had problems with double-encoded UTF strings being saved to database when using this function, sending it of to a apache xml-rpc servlet and storing it in mysql database. It was solved by setting 'escaping' to just 'markup' and 'encoding' to 'UTF-8' (don't forget to set 'utf-8' in xmlrpc_decode too).

It seems that UTF-8 encoded strings gets escaped with their bytes as entities instead of their characters as entites.

The example above is incorrect - the header needs to be an array, see post by "chris dot vigelius at gmx dot net": http://au.php.net/manual/en/function.stream-context-create.php#74431
His post also shows how to do browser authentication, as below:
<?php
   $request = xmlrpc_encode_request("methodName", array("methodParam"));
   $auth = base64_encode($username.":".$password);
   $header = (version_compare(phpversion(), '5.2.8'))
     ? array("Content-Type: text/xml","Authorization: Basic $auth")
     : "Content-Type: text/xml\r\nAuthorization: Basic $auth" ; //[1]
   $context = stream_context_create(array('http' => array(
      'method' => "POST",
      'header' => $header,
      'content' => $request
   )));
   $webservice="http://www.example.com/rpc";
   $file = file_get_contents($webservice, false, $context);
   $response = xmlrpc_decode($file);
   if (xmlrpc_is_fault($response)) {
      return "xmlrpc: $response[faultString] ($response[faultCode])";
   } else {
      return $response;
   }
?>

1 - EDITOR NOTE: THIS IS A FIX FROM "SandersWang dt php at gmail dot com"

This function should be used by an XML-RPC client to create an XML payload for an XML-RPC request;

<?php
$params = "system.methodSignature";
$method = "system.methodHelp";
$request = xmlrpc_encode_request($method,$params);
echo ( $request );
?>

Produces;

<?xml version='1.0' encoding="iso-8859-1" ?>
<methodCall>
<methodName>system.methodHelp</methodName>
<params>
 <param>
  <value>
   <string>system.methodSignature</string>
  </value>
 </param>
</params>
</methodCall>

The second argument recognises the type of variable and generates the correct XML-RPC structure. See xmlrpc_encode() for more details.

ever tried transmitting an array like the following with xmlrpc?
$var1=array(7=>14,9=>18);

The output array looks quite different! It will look like that:
$var2=array(14,18);

The only solution i found is to prepend a space to the index:
$var3=array(' 7'=>14,' 9'=>18);

Using that method you'll get the right result. ($var1)

Simple OO client with function Overload : 

the php metho test_helloworld is translated to xmlrpc method test.helloworld.

class RpcClient {
    
    private $_methods;
    private $_context;
    private $_url;
    
    function __construct ($url, $user, $passwd) {
        $auth = base64_encode(sprintf('%s:%s', $user,$passwd));
        $this->_context = stream_context_create(array(
            'http' => array(
                'method' => 'POST',
                'header' => "Content-Type: text/xml\r\n".
                            "Authorization: Basic $auth" ,
                
            )
        ));
        $this->_url = $url;
        
        $this->registerMethod ("Test_HelloWorld");
        
    }
    
    
    function __call($methodName, $params) {
        if (array_key_exists($methodName,$this->_methods)) {
            // on appelle la fonction RPC
            $m = str_replace('_', '.', $methodName);
            $r = xmlrpc_encode_request($m, $params,array('verbosity'=>'newlines_only'));
            $c = $this->_context;
            stream_context_set_option($c,'http','content',$r);
            $f = file_get_contents($this->_url,false,$c);
            $resp = xmlrpc_decode($f);
            return $resp;
        } else {
            // on appelle la fonction de l'objet
            call_user_method_array($methodName, $this,$params);
        }
    }
    
    private function registerMethod ($method) {
        $this->_methods[$method] = true;
    }
    
}

Note that as far as I can tell, the 
 characters generated by PHP in the base64 fields don't appear to violate the XML-RPC standard at all.  XML-RPC messages *are* in XML format, and as such, the XML entities should be getting decoded before being passed to a base64 decoder.  So, the previously-mentioned Jakarta-based XML-RPC server appears to violate the XML spec.  i.e. There's nothing here that needs to be "fixed" in PHP.

For examples / documentation of the array output_options, see http://xmlrpc-epi.sourceforge.net/main.php?t=php_api#output_options

In short, output_options lets you send compact xmlrpc (without all the "pretty whitespace" xmlrpc_encode adds normally), apply an own escaping table prior to sending, set the encoding, and a couple of other things (the page even says something about soap 1.1 ... I don't know details).

Take care that this function will generate invalid xmlrpc content when invoked with certain parameters (said content will be happily parsed by the lib itself, but not by other implementations).

xmlrpc_encode_request(null, null)
will generate a response without a value

xmlrpc_encode_request('myfunc', array('faultCode' => 666, 'faultString' => 'hello world')
will generated a request containing a <fault> member instead of <params>