XMLRPC Presentation

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XML-RPC Presentation

• Gökhan Önis
• 10276035

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RPC (remote procedure calls)

• A remote procedure call (RPC) is a protocol that
  allows a computer program running on one host to
  cause code to be executed on another host without
  the programmer needing to explicitly code for
  this. When the code in question is written using
  object-oriented principles, RPC is sometimes
  referred to as remote invocation or remote method
  invocation.

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RPC (remote procedure calls)

• RPC is an easy and popular paradigm for
  implementing the client-server model of
  distributed computing. An RPC is initiated by the
  caller (client) sending a request message to a
  remote system (the server) to execute a certain
  procedure using arguments supplied. A result
  message is returned to the caller. There are many
  variations and subtleties in various
  implementations, resulting in a variety of
  different (incompatible) RPC protocols.

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RPC (remote procedure calls)

• In order to allow servers to be accessed by
  differing clients, a number of standardized RPC
  systems have been created. Most of these use an
  interface description language (IDL) to allow
  various platforms to call the RPC. Examples of
  such systems include Sun RPC (sometimes called
  ONC RPC), the Distributed computing environment
  (DCE), Microsoft's DCOM (and ActiveX), which is
  based in part on DCE, and CORBA.
• Recently a number of vendors have started using
  XML as the IDL, and HTTP as the network protocol.
  The advantage of this system, known as web
  services, is simplicity and standardization, the
  IDL is a text file that is widely understood, and
  HTTP is built into almost all modern operating
  systems. An example of such an RPC system is
  SOAP, developed in turn from XML-RPC

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Breif History of XML-RPC

• It was first created by Dave Winer of UserLand
  Software in 1995 with Microsoft. However
  Microsoft considered it too simple, and started
  adding functionality. After several rounds of
  this, the standard was no longer so simple, and
  became what is now SOAP.

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What is XML-RPC?

• XML-RPC is a remote procedure call protocol
  encoded in XML. It is a very simple protocol,
  defining only a handful of data types and
  commands require considerable software support in
  order to be used. It satisfies the needs for
  language independent implementation.

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More Complex Explanation

• What is XML-RPC? 
• Specifications Implementations Services Blogging
  APIs Communities Tutorials/PressIt's a spec and a
  set of implementations that allow software
  running on disparate operating systems, running
  in different environments to make procedure calls
  over the Internet. It's remote procedure
  calling using HTTP as the transport and XML as
  the encoding. XML-RPC is designed to be as simple
  as possible, while allowing complex data
  structures to be transmitted, processed and
  returned.

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Usage Paradigm

• XML-RPC is a Remote Procedure Calling protocol
  that works over the Internet.
• An XML-RPC message is an HTTP-POST request. The
  body of the request is in XML. A procedure
  executes on the server and the value it returns
  is also formatted in XML.
• Procedure parameters can be scalars, numbers,
  strings, dates, etc. and can also be complex
  record and list structures.

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What happens on the server after request arrives?

• Server checks the xmls length.( it must be
  correct)
• If the RPC path speciefied by the client in the
  header server routes it to the part of the server
  which understands xml and then decodes the
  variable names and method names invoke the
  corresponding method in the program and the
  decoded variables as an input.
• If the above part is accomplised than it returns
  the what the program returns in an xml to the
  client.
• If the above part can not be completed in success
  by the server it just returns a fault to the
  client again in xml encoded fault response.

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Examples

• Request example
• Here's an example of an XML-RPC request
• POST /RPC2 HTTP/1.0
• User-Agent Frontier/5.1.2 (WinNT)
• Host betty.userland.com
• Content-Type text/xml
• Content-length 181lt?xml version"1.0"?gt
• ltmethodCallgt
• ltmethodNamegtexamples.getStateNamelt/methodNam
  egt
• ltparamsgt
• ltparamgt ltvaluegtlti4gt41lt/i4gtlt/valuegt lt/paramgt
• lt/paramsgt
• lt/methodCallgt

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Header requirements

• The format of the URL in the first line which is
  POST /RPC2 HTTP/1.0 of the header is not
  specified. For example, it could be empty, a
  single slash, if the server is only handling
  XML-RPC calls. However, if the server is handling
  a mix of incoming HTTP requests, we allow the URI
  to help route the request to the code that
  handles XML-RPC requests. (In the example, the
  URI is /RPC2, telling the server to route the
  request to the "RPC2" responder.)
• A User-Agent and Host must be specified.
• The Content-Type is text/xml.
• The Content-Length must be specified and must be
  correct.

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Fault Example

• lt?xml version"1.0"?gt
• ltmethodResponsegt
• ltfaultgt
• ltvaluegt
• ltstructgt
• ltmembergt
• ltnamegtfaultCodelt/namegt
• ltvaluegtltintgt4lt/intgtlt/valuegt
• lt/membergt
• ltmembergt
• ltnamegtfaultStringlt/namegt ltvaluegt ltstring
  gtToo many parameters.lt/stringgt
• lt/valuegt
• lt/membergt
• lt/structgt lt/valuegt lt/faultgt
• lt/methodResponsegt

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Conclusion

• XML-RPC is a simple method invokation model and
  it is fast for simple needs like short procedures
  as an example learning weather forecasts from the
  server and broadcasting it in your homepage from
  a diffrent platform which the server has. But if
  you need more bandwidth like peer to peer
  networks xml structure is something very
  expensive on networks because for only variable
  it generates almost 15 lines of code. If you are
  saying this is good than than write your own
  binary platform for your applications.

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References

• http//davenet.scripting.com/1998/07/14/xmlRpcForN
  ewbies
• http//xmlrpc.org
• www.wikipedia.org
• Course book