C# Client to Consume Google App Engine RESTful Webservice (rpc XML)

Question

I think I hit a problem when using C# client to consume Google App Engine Webservice. The Google App Engine code I use is here. This is how the python script on server would look like:

from google.appengine.ext import webapp                                        
from google.appengine.ext.webapp.util import run_wsgi_app                      
import logging                                                                 

from StringIO import StringIO                                                  
import traceback
import xmlrpclib
from xmlrpcserver import XmlRpcServer

class Application:
    def __init__(self):
        pass                    

    def getName(self,meta):                                                    
        return 'example'

class XMLRpcHandler(webapp.RequestHandler):                                    
    rpcserver = None

    def __init__(self):         
        self.rpcserver = XmlRpcServer()                                        
        app = Application()                                                    
        self.rpcserver.register_class('app',app)                               

    def post(self):
        request = StringIO(self.request.body)
        request.seek(0)                                                        
        response = StringIO()                                                  
        try:
            self.rpcserver.execute(request, response, None)                    
        except Exception, e:                                                   
            logging.error('Error executing: '+str(e))                          
            for line in traceback.format_exc().split('\n'):                    
                logging.error(line)
        finally:
            response.seek(0)  

        rstr = response.read()                                                 
        self.response.headers['Content-type'] = 'text/xml'                     
        self.response.headers['Content-length'] = "%d"%len(rstr)               
        self.response.out.write(rstr)

application = webapp.WSGIApplication(                                          
                                     [('/xmlrpc/', XMLRpcHandler)],
                                     debug=True)                               
def main():
  run_wsgi_app(application)                                                    

if __name__ == "__main__":
    main()

The client side ( in Python) is this:

import xmlrpclib
s = xmlrpclib.Server('http://localhost:8080/xmlrpc/')
print s.app.getName()

I have no problem in using Python client to retrieve values from Google App Engine, but I do have difficulties in using a C# client to retrieve the values. The error I got was 404 method not found when I am trying to GetResponse from the web request.

This is my code

        var request = (HttpWebRequest)WebRequest.Create("http://localhost:8080/xmlrpc/app");

        request.Method = "GET";
        request.ContentLength = 0;
        request.ContentType = "text/xml";
        using (HttpWebResponse response = request.GetResponse() as HttpWebResponse) //404 method not found error here.
        {

        }  

Edit: For end points, I've tried:

1. http://localhost:8080/xmlrpc
2. http://localhost:8080/xmlrpc/
3. http://localhost:8080/xmlrpc/app
4. http://localhost:8080/xmlrpc/app/

But none works

I think it must be that the url is wrong, but I don't know how to get it right. Any idea?

Answer 1

The regular expression in your App Engine app for the endpoint is exactly '/xmlrpc/', which is what you use in the Python test, but in your C# client you're using '/xmlrpc/app', which isn't mapped to anything.

Answer 2

I guess what happens is that your request sent using HttpWebRequest is missing actual content; which should be your rpc method information in xml format. Please check if code below would work for you; it should send request to http://localhost:8080/xmlrpc/ and dump resulting xml into console.

// send request
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://localhost:8080/xmlrpc/");
request.Method = "POST";
request.ContentType = "text/xml; encoding=utf-8";

string content = "<?xml version='1.0'?><methodCall><methodName>app.getName</methodName><params></params></methodCall>"; 
byte[] contentBytes = System.Text.UTF8Encoding.UTF8.GetBytes(content);                      
request.ContentLength = contentBytes.Length;
using (Stream stream = request.GetRequestStream())
{
    stream.Write(contentBytes, 0, contentBytes.Length); 
}

// get response
WebResponse response = request.GetResponse();
XmlDocument xmlDoc = new XmlDocument();
using (Stream responseStream = response.GetResponseStream())
{
    xmlDoc.Load(responseStream);
    Console.WriteLine(xmlDoc.OuterXml);
}       

hope this helps, regards

Answer 3

In addition to the excellent answer posted here, one can also use xml-rpc.net to do the job.

Here's the code on the server side, assuming that getName now takes a string parameter:

def getName(self,meta, keyInput):                                                    
    return keyInput

And this would be the C# Client code, by making use of xml-rpc.net:

[XmlRpcUrl("http://localhost:8080/xmlrpc")]
public interface IMath : IXmlRpcProxy
{
    [XmlRpcMethod("app.getName")]
    string GetName(string number);

}

public string GetName(string keyInput)
{
        var  mathProxy = XmlRpcProxyGen.Create<IMath>();
        mathProxy.Url = "http://localhost:8080/xmlrpc/";
        return mathProxy.GetName(keyInput);

}

Hope this helps everyone who's struggling to make rpc call to GAE from C# client.