Module: XMLRPC

Author and Copyright

Copyright © 2001-2004 by Michael Neumann (mneumann@ntecs.de)

Released under the same term of license as Ruby.

XMLRPC is a lightweight protocol that enables remote procedure calls over HTTP. It is defined at www.xmlrpc.com.

XMLRPC allows you to create simple distributed computing solutions that span computer languages. Its distinctive feature is its simplicity compared to other approaches like SOAP and CORBA.

The Ruby standard library package ‘xmlrpc’ enables you to create a server that implements remote procedures and a client that calls them. Very little code is required to achieve either of these.

Example

Try the following code. It calls a standard demonstration remote procedure.

require 'xmlrpc/client'
require 'pp'

server = XMLRPC::Client.new2("http://xmlrpc-c.sourceforge.net/api/sample.php")
result = server.call("sample.sumAndDifference", 5, 3)
pp result

Documentation

See www.ntecs.de/ruby/xmlrpc4r/. There is plenty of detail there to use the client and implement a server.

Features of XMLRPC for Ruby

• Extensions

  • Introspection

  • multiCall

  • optionally nil values and integers larger than 32 Bit

• Server

  • Standalone XML-RPC server

  • CGI-based (works with FastCGI)

  • Apache mod_ruby server

  • WEBrick servlet

• Client

  • synchronous/asynchronous calls

  • Basic HTTP-401 Authentication

  • HTTPS protocol (SSL)

• Parsers

  • REXML (XMLParser::REXMLStreamParser)

    • Not compiled (pure ruby)

    • See ruby standard library

  • libxml (LibXMLStreamParser)

    • Compiled

    • See rubygems.org/gems/libxml-ruby/

• General

  • possible to choose between XMLParser module (Expat wrapper) and REXML (pure Ruby) parsers

  • Marshalling Ruby objects to Hashes and reconstruct them later from a Hash

  • SandStorm component architecture XMLRPC::Client interface

Howto

Client

require "xmlrpc/client"

# Make an object to represent the XML-RPC server.
server = XMLRPC::Client.new( "xmlrpc-c.sourceforge.net", "/api/sample.php")

# Call the remote server and get our result
result = server.call("sample.sumAndDifference", 5, 3)

sum = result["sum"]
difference = result["difference"]

puts "Sum: #{sum}, Difference: #{difference}"

Client with XML-RPC fault-structure handling

There are two possible ways, of handling a fault-structure:

by catching a FaultException exception

require "xmlrpc/client"

# Make an object to represent the XML-RPC server.
server = XMLRPC::Client.new( "xmlrpc-c.sourceforge.net", "/api/sample.php")

begin
  # Call the remote server and get our result
  result = server.call("sample.sumAndDifference", 5, 3)

  sum = result["sum"]
  difference = result["difference"]

  puts "Sum: #{sum}, Difference: #{difference}"

rescue XMLRPC::FaultException => e
  puts "Error: "
  puts e.faultCode
  puts e.faultString
end

by calling “call2” which returns a boolean

require "xmlrpc/client"

# Make an object to represent the XML-RPC server.
server = XMLRPC::Client.new( "xmlrpc-c.sourceforge.net", "/api/sample.php")

# Call the remote server and get our result
ok, result = server.call2("sample.sumAndDifference", 5, 3)

if ok
  sum = result["sum"]
  difference = result["difference"]

  puts "Sum: #{sum}, Difference: #{difference}"
else
  puts "Error: "
  puts result.faultCode
  puts result.faultString
end

Using ::XMLRPC::Client::Proxy

You can create a Proxy object onto which you can call methods. This way it looks nicer. Both forms, call and call2 are supported through proxy and proxy2. You can additionally give arguments to the Proxy, which will be given to each XML-RPC call using that Proxy.

require "xmlrpc/client"

# Make an object to represent the XML-RPC server.
server = XMLRPC::Client.new( "xmlrpc-c.sourceforge.net", "/api/sample.php")

# Create a Proxy object
sample = server.proxy("sample")

# Call the remote server and get our result
result = sample.sumAndDifference(5,3)

sum = result["sum"]
difference = result["difference"]

puts "Sum: #{sum}, Difference: #{difference}"

CGI-based server using CGIServer

There are also two ways to define handler, the first is like C/PHP, the second like Java, of course both ways can be mixed:

C/PHP-like (handler functions)

require "xmlrpc/server"

s = XMLRPC::CGIServer.new

s.add_handler("sample.sumAndDifference") do |a,b|
  { "sum" => a + b, "difference" => a - b }
end

s.serve

Java-like (handler classes)

require "xmlrpc/server"

s = XMLRPC::CGIServer.new

class MyHandler
  def sumAndDifference(a, b)
    { "sum" => a + b, "difference" => a - b }
  end
end

# NOTE: Security Hole (read below)!!!
s.add_handler("sample", MyHandler.new)
s.serve

To return a fault-structure you have to raise an FaultException e.g.:

raise XMLRPC::FaultException.new(3, "division by Zero")

Security Note

From Brian Candler:

Above code sample has an extremely nasty security hole, in that you can now call
any method of 'MyHandler' remotely, including methods inherited from Object
and Kernel! For example, in the client code, you can use

  puts server.call("sample.send","`","ls")

(backtick being the method name for running system processes). Needless to
say, 'ls' can be replaced with something else.

The version which binds proc objects (or the version presented below in the next section)
doesn't have this problem, but people may be tempted to use the second version because it's
so nice and 'Rubyesque'. I think it needs a big red disclaimer.

From Michael:

A solution is to undef insecure methods or to use ::XMLRPC::Service::PublicInstanceMethodsInterface as shown below:

class MyHandler
  def sumAndDifference(a, b)
    { "sum" => a + b, "difference" => a - b }
  end
end

# ... server initialization ...

s.add_handler(XMLRPC::iPIMethods("sample"), MyHandler.new)

# ...

This adds only public instance methods explicitly declared in class MyHandler (and not those inherited from any other class).

With interface declarations

Code sample from the book Ruby Developer’s Guide:

require "xmlrpc/server"

class Num
  INTERFACE = XMLRPC::interface("num") {
    meth 'int add(int, int)', 'Add two numbers', 'add'
    meth 'int div(int, int)', 'Divide two numbers'
  }

  def add(a, b) a + b end
  def div(a, b) a / b end
end

s = XMLRPC::CGIServer.new
s.add_handler(Num::INTERFACE, Num.new)
s.serve

Standalone Server

Same as CGI-based server, the only difference being

server = XMLRPC::CGIServer.new

must be changed to

server = XMLRPC::Server.new(8080)

if you want a server listening on port 8080. The rest is the same.

Choosing a different XMLParser or XMLWriter

The examples above all use the default parser (which is now since 1.8 ::XMLRPC::XMLParser::REXMLStreamParser) and a default XMLWriter. If you want to use a different XMLParser, then you have to call the ParserWriterChooseMixin#set_parser method of Client instances or instances of subclasses of BasicServer or by editing xmlrpc/config.rb.

Client Example:

# ...
server = XMLRPC::Client.new( "xmlrpc-c.sourceforge.net", "/api/sample.php")
server.set_parser(XMLRPC::XMLParser::XMLParser.new)
# ...

Server Example:

# ...
s = XMLRPC::CGIServer.new
s.set_parser(XMLRPC::XMLParser::XMLParser.new)
# ...

You can change the XML-writer by calling method ParserWriterChooseMixin#set_writer.