XML-RPC. XML-RPC Architecture Client-server architecture Client executes RPCs on the server Server has 3 components: –The main thread –The XML-RPC server.

XML-RPC

XML-RPC Architecture

• Client-server architecture

• Client executes RPCs on the server

• Server has 3 components:– The main thread– The XML-RPC server (takes place of stubs)– One or more RPC handlers

• Server processes each RPC by calling the corresponding RPC handler

XML-RPC Architecture

Client Server

XML-RPCServer

RPCHandler

HTTP

XML-RPC Types

• 4-byte signed integer• Boolean• String• Double• Date/Time (not fully ISO 8601 compatible!)– No time zone information

• Binary (base-64)• Arrays of any of these types• Structures containing these types– Map of element names to types/values

XML-RPC Libraries

• C++: xmlrpc-c– http://xmlrpc-c.sourceforge.net– Only installed on ccc1 right now

• Java: Apache XML-RPC– http://ws.apache.org/xmlrpc– Required: Apache commons-codec library

• http://jakarta.apache.org/commons/codec

– Use on any machine except ccc1 (no Java 1.5)

Client-Side XML-RPC

• 2 types of XML-RPCs– Synchronous– Asynchronous

• What is the difference?

• What are the advantages and disadvantages of each?

Synchronous XML-RPCs

• Client executes RPC on server– Client blocks until the RPC returns

• Server returns a generic object/type– C++ (xmlrpc-c) Library• xmlrpc_c::value

– Java (Apache) Library• Object

• Client must know what type to expect– Cast generic type to expected type

Asynchronous XML-RPCs

• Client must define a call-back object–Method to handle RPC success–Method to handle RPC failure/error

• Client makes asynchronous RPC– Simply spawns a new thread for the RPC– Returns immediately

• When the RPC has finished, one of the call-back methods will be executed– Cast return value to expected type

Executing an XML-RPC

• 1. Build a list of RPC parameters– Analogous to function/method parameters

• 2. Initialize the RPC– Name of the RPC– URL (it’s HTTP) of the XML-RPC server• http://address:port/RPC2

• 3. Execute the RPC• 4. Handle errors• 5. Interpret return value

Build a List of RPC Parameters

• C++xmlrpc_c::paramList params;params.add(

xmlrpc_c::value_string(“Hello server.”));

• Javajava.util.Vector params = new Vector();params.add(new String(“Hello server.”));

Initialize the RPC

• C++xmlrpc_c::clientXmlTransport_libwww

xlmrpcTransport;xmlrpc_c::client_xml xmlrpcClient(

&xmlrpcTransport);xmlrpc_c::rpcPtr xmlrpc(

“server.sayHello”, params);xmlrpc_c::carriageParm_libwww0 cParm(

“http://127.0.0.1:9382/RPC2”);

Initialize the RPC

• JavaXmlRpcClient client = null;try {

client = new XmlRpcClient(“http://127.0.0.1:9382/RPC2”);

} catch (MalformedURLException e) {System.err.println(e);

}

Execute the RPC

• C++

try {

xmlrpc->call(&client, &cParm);

} catch (std::exception const e) {

cerr << “Connection refused.” << endl;

}

Execute the RPC

• Javatry {

Object returnValue = client.execute(“server.sayHello”, params);

} catch (XmlRpcException e) {System.err.println(e); // some RPC problem

} catch (IOException e) {System.err.println(“Connection refused.”);

}

Handle errors

• C++if (xmlrpc->isSuccessful() == false) {

if (xmlrpc->isFinished() == true) {xmlrpc_c::fault f = xmlrpc->getFault();if (f.getCode() == 0) {…} // exceptionelse {…} // unexpected error

}else {…} // unexpected error – can’t get fault

}

Interpret Return Value

• C++

if (xmlrpc->isSuccessful() == true) {

xmlrpc_c::value v = xmlrpc->getResult();

xmlrpc_c::value_string rpcstr =

(xmlrpc_c::value_string) v;

std::string text = (std::string) rpcstr;

}

Interpret Return Value

• Java// The return value of the RPC was stored// in returnValue, which is of type Object.try {

String text = (String) returnValue;} catch (ClassCastException e) {

// returnValue was not a String.// It could have been an Exception.

}

Creating an XML-RPC Server

• 1. Define one or more RPC handlers– C++: Subclass xmlrpc_c::method– Java: Create a new public class

• 2. Initialize the library’s server object– Provide port number on which to listen

• 3. Add RPC handlers to the server– Library-specific call

• 4. Start the server– Optionally create new thread for server

Define RPC Handlers

• C++class HelloMethod : public xmlrpc_c::method {

public:void execute(xmlrpc-c::paramList

const& params, xmlrpc_c::value* const retvalP) {

*retvalP = xmlrpc_c::value_string(“Hello client.”);

}};

Define RPC Handlers

• Javapublic class RPCHandler {

// All public methods in this class are // RPC handlerspublic String sayHello(String param) {

return new String(“Hello client.”);}

}

Initialize the Server

• C++xmlrpc_c::registry reg;xmlrpc_c::serverAbyss server;• JavaWebServer server = null;try {

server = new WebServer(9382);} catch (Exception e) {

System.err.println(e);}

Add RPC Handlers

• C++

xmlrpc_c::methodPtr const helloMethod(

new HelloMethod);

reg.addMethod(“server.sayHello”,

helloMethod);

server = xmlrpc_c::serverAbyss(reg, 9382,

“xmlrpc.log”);

Add RPC Handlers

• Javaserver.addHandler(

“server”, new RPCHandler()

);// RPC names will be “server.” followed by // the name of a public method in // RPCHandler.

Start the Server

• C++

// Runs in current thread.

server.run();

• Java

// Runs in new thread.

server.start();

XML-RPC