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 ClientServer XML-RPC Server RPC Handler 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 – –Only installed on ccc1 right now Java: Apache XML-RPC – –Required: Apache commons-codec library –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 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.”)); Java java.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( “

Initialize the RPC Java XmlRpcClient client = null; try { client = new XmlRpcClient( “ } 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 Java try { 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) {…} // exception else {…} // 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 Java public class RPCHandler { // All public methods in this class are // RPC handlers public String sayHello(String param) { return new String(“Hello client.”); }

Initialize the Server C++ xmlrpc_c::registry reg; xmlrpc_c::serverAbyss server; Java WebServer 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 Java server.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