Defining a Remote Method Call in XML

Perl Tutorials - Herong's Tutorial Examples

Dr. Herong Yang, Version 5.10

Perl Tutorials - Herong's Tutorial Examples

∟XML-RPC - Remote Procedure Call with XML and HTTP

∟Defining a Remote Method Call in XML

This section describes how a remote method call can be defined in XML format. The root element name is 'methodCall'.

The first item of the XML-RPC specification is about how to define a remote method call in XML.

XML-RPC defines a method call as an XML element called "methodCall". I have tried to find a copy of the official XML Schema Definition (XSD) of "methodCall". But I had no success. So I wrote one myself. It is definitely not 100% accurate. But it does show you how the "methodCall" XML structure should be.

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<!-- xmlRpcMethodCall.xsd
     Copyright (c) 2005 by Dr. Herong Yang, http://www.herongyang.com/
-->
 <xsd:element name="methodCall" type="methodCallType"/>
 <xsd:complexType name="methodCallType">
  <xsd:sequence>
   <xsd:element name="methodName" type="xsd:string" 
      minOccurs="1" maxOccurs="1"/>
   <xsd:element name="params" type="paramsType" 
      minOccurs="0"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="paramsType">
  <xsd:sequence>
   <xsd:element name="param" type="paramType" 
      minOccurs="1"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="paramType">
  <xsd:sequence>
   <xsd:element name="value" type="valueType" 
      minOccurs="1" maxOccurs="1"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="valueType">
  <xsd:choice>
   <xsd:element name="int" type="xsd:int" />
   <xsd:element name="boolean" type="xsd:boolean" />
   <xsd:element name="string" type="xsd:string" />
   <xsd:element name="double" type="xsd:double" />
   <xsd:element name="dateTime.iso8601" type="xsd:string" />
   <xsd:element name="base64" type="xsd:xsd:base64Binary" />
   <xsd:element name="struct" type="structType" />
   <xsd:element name="array" type="arrayType" />
  </xsd:choice>
 </xsd:complexType>
 <xsd:complexType name="structType">
  <xsd:sequence>
   <xsd:element name="member" type="memberType"
      minOccurs="1"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="memberType">
  <xsd:sequence>
   <xsd:element name="name" type="xsd:string"
      minOccurs="1" maxOccurs="1"/>
   <xsd:element name="value" type="valueType"
      minOccurs="1" maxOccurs="1"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="arrayType">
  <xsd:sequence>
   <xsd:element name="data" type="dataType"
      minOccurs="1" maxOccurs="1"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="dataType">
  <xsd:sequence>
   <xsd:element name="value" type="valueType"
      minOccurs="0"/>
  </xsd:sequence>
 </xsd:complexType>
</xsd:schema>

From this XML schema, we can see that:

A "methodCall" element will have a required "methodName" element and an optional "params" element.
A "methodName" element specifies the name of the method.
A "params" element specifies a list of "param" elements as parameters for the method.
A "param" element will have a "value" element.
A "value" element will have a value type element, which contains the actual value of the parameter.
There are 7 value type elements: "int", "boolean", "string", "double", "dateTime.iso8601", "base64", "struct" and "array". The first 6 are simple elements and the last 2 are complex elements.
A "struct" element will have a list of "member" elements. A "member" element will have a "name" element and a "value" element.
An "array" element will have a "data" elements, which will have a list of "value" elements.

The following is an example of "methodCall":

<methodCall>
 <methodName>somePackage.someSort</methodName>
 <params>
  <param><value><int>3</int></value></param>
  <param><value><string>Descending</string></value></param>
  <param><value><struct>
   <member><name>Yang</name><value><int>9647</int></value></member>
   <member><name>Bush</name><value><int>3014</int></value></member>
   <member><name>Gate</name><value><int>6618</int></value></member>
  </struct></value></param>
 </params>
</methodCall>

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