General/XMLRPC: Useful error messages

[kraftbj]

When our debugging tools fails at authenticated_xmlrpc_request_for_jetpack_passes_connection_test that often suggests the failure happened when verifying the signature. When the issue isn't obvious, it would be helpful if xmlrpc would respond with something more notable than [faultCode] => -32601 [faultString] => server error. requested method jetpack.testConnection does not exist.

[PatelUtkarsh]

Hey @kraftbj you want something like this

// Is the message a fault?
        if ( $this->message->messageType == 'fault' ) {
            switch ( $this->message->faultCode ) {
                case -32601:
                    $this->message->faultString = 'Server error occurred while verifying signature.';
                    break;
            }
            $this->error = new IXR_Error( $this->message->faultCode, $this->message->faultString );
            return false;
        }

Or something on server side itself ?

[kraftbj]

@PatelUtkarsh I'm so sorry I didn't see your comment until now. Something along those lines. There are a few cases where, when we see the error in support, we know 99% what it probably is. i'm thinking we should communicate the common causes back.

[kraftbj]

With regard to negative error code #4410, those are XML-RPC error codes that we mimic from WordPress itself ( https://github.com/WordPress/WordPress/blob/master/wp-includes/class-IXR.php#L777 ), which I think we overall get from http://xmlrpc-epi.sourceforge.net/specs/rfc.fault_codes.php