XML-RPC

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XML-RPC
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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

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XML-RPC Architecture
HTTP
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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

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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)

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Client-Side XML-RPC

• 2 types of XML-RPCs
• Synchronous
• Asynchronous
• What is the difference?
• What are the advantages and disadvantages of each?

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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_cvalue
• Java (Apache) Library
• Object
• Client must know what type to expect
• Cast generic type to expected type

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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

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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 (its HTTP) of the XML-RPC server
• http//addressport/RPC2
• 3. Execute the RPC
• 4. Handle errors
• 5. Interpret return value

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Build a List of RPC Parameters

• C
• xmlrpc_cparamList params
• params.add(
• xmlrpc_cvalue_string(Hello server.))
• Java
• java.util.Vector params new Vector()
• params.add(new String(Hello server.))

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Initialize the RPC

• C
• xmlrpc_cclientXmlTransport_libwww
• xlmrpcTransport
• xmlrpc_cclient_xml xmlrpcClient(
• xmlrpcTransport)
• xmlrpc_crpcPtr xmlrpc(
• server.sayHello, params)
• xmlrpc_ccarriageParm_libwww0 cParm(
• http//127.0.0.19382/RPC2)

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Initialize the RPC

• Java
• XmlRpcClient client null
• try
• client new XmlRpcClient(
• http//127.0.0.19382/RPC2)
• catch (MalformedURLException e)
• System.err.println(e)

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Execute the RPC

• C
• try
• xmlrpc-gtcall(client, cParm)
• catch (stdexception const e)
• cerr ltlt Connection refused. ltlt endl

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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.)

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Handle errors

• C
• if (xmlrpc-gtisSuccessful() false)
• if (xmlrpc-gtisFinished() true)
• xmlrpc_cfault f xmlrpc-gtgetFault()
• if (f.getCode() 0) // exception
• else // unexpected error
• else // unexpected error cant get fault

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Interpret Return Value

• C
• if (xmlrpc-gtisSuccessful() true)
• xmlrpc_cvalue v xmlrpc-gtgetResult()
• xmlrpc_cvalue_string rpcstr
• (xmlrpc_cvalue_string) v
• stdstring text (stdstring) rpcstr

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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.

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Creating an XML-RPC Server

• 1. Define one or more RPC handlers
• C Subclass xmlrpc_cmethod
• Java Create a new public class
• 2. Initialize the librarys 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

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Define RPC Handlers

• C
• class HelloMethod public xmlrpc_cmethod
• public
• void execute(xmlrpc-cparamList const
  params, xmlrpc_cvalue const retvalP)
• retvalP xmlrpc_cvalue_string(
• Hello client.)

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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.)

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Initialize the Server

• C
• xmlrpc_cregistry reg
• xmlrpc_cserverAbyss server
• Java
• WebServer server null
• try
• server new WebServer(9382)
• catch (Exception e)
• System.err.println(e)

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Add RPC Handlers

• C
• xmlrpc_cmethodPtr const helloMethod(
• new HelloMethod)
• reg.addMethod(server.sayHello,
• helloMethod)
• server xmlrpc_cserverAbyss(reg, 9382,
• xmlrpc.log)

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Add RPC Handlers

• Java
• server.addHandler(
• server,
• new RPCHandler()
• )
• // RPC names will be server. followed by
• // the name of a public method in
• // RPCHandler.

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Start the Server

• C
• // Runs in current thread.
• server.run()
• Java
• // Runs in new thread.
• server.start()

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XML-RPC