XMLRPC for Ruby

Author and Copyright

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

Released under the same term of license as Ruby.

Overview

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/projects/xmlrpc4r. There is plenty of detail there to use the client and implement a server.

Features of XMLRPC for Ruby

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 XMLRPC::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

Client using 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

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::iPIMethods})) 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, only that the line

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 XML Parser or XML Writer

The examples above all use the default parser (which is now since 1.8 REXMLStreamParser) and a default XML writer. If you want to use a different XML parser, then you have to call the set_parser method of XMLRPC::Client instances or instances of subclasses of XMLRPC::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::XMLStreamParser.new)
# ...

or:

# ...
server = XMLRPC::Server.new(8080)
server.set_parser(XMLRPC::XMLParser::NQXMLParser.new)
# ...

Note that XMLStreamParser is incredible faster (and uses less memory) than any other parser and scales well for large documents. For example for a 0.5 MB XML document with many tags, XMLStreamParser is ~350 (!) times faster than NQXMLTreeParser and still ~18 times as fast as XMLTreeParser.

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

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