Overview(简介)

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.

工作机制：

Request example（请求示例）

POST /RPC2 HTTP/1.0
User-Agent: Frontier/5.1.2 (WinNT)
Host: betty.userland.com
Content-Type: text/xml
Content-length: 181

<?xml version="1.0"?>
<methodCall>
   <methodName>examples.getStateName</methodName>
   <params>
      <param>
         <value><i4>41</i4></value>
      </param>
   </params>
</methodCall>

Header requirements（请求中需设置header的必要信息）

The format of the URI in the first line 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.)

1. A User-Agent and Host must be specified.
2. The Content-Type is text/xml.
3. The Content-Length must be specified and must be correct.

Payload format（请求的数据格式）

The payload is in XML, a single <methodCall> structure.

The <methodCall> must contain a <methodName> sub-item, a string, containing the name of the method to be called. The string may only contain identifier characters, upper and lower-case A-Z, the numeric characters, 0-9, underscore, dot, colon and slash. It's entirely up to the server to decide how to interpret the characters in a methodName.

For example, the methodName could be the name of a file containing a script that executes on an incoming request. It could be the name of a cell in a database table. Or it could be a path to a file contained within a hierarchy of folders and files.

If the procedure call has parameters, the <methodCall> must contain a <params> sub-item. The <params> sub-item can contain any number of <param>s, each of which has a <value>.

Scalar <value>s （基本数据类型）

<value>s can be scalars, type is indicated by nesting the value inside one of the tags listed in this table:

If no type is indicated, the type is string.

<struct>s （结构体类型）

A value can also be of type <struct>.

A <struct> contains <member>s and each <member> contains a <name> and a <value>.

Here's an example of a two-element <struct>:

<struct>
   <member>
      <name>lowerBound</name>
      <value><i4>18</i4></value>
   </member>
   <member>
      <name>upperBound</name>
      <value><i4>139</i4></value>
   </member>
</struct>

<struct>s can be recursive, any <value> may contain a <struct> or any other type, including an <array>, described below.

<array>s （数组类型）

A value can also be of type <array>.

An <array> contains a single <data> element, which can contain any number of <value>s.

Here's an example of a four-element array:

<array>
   <data>
      <value><i4>12</i4></value>
      <value><string>Egypt</string></value>
      <value><boolean>0</boolean></value>
      <value><i4>-31</i4></value>
   </data>
 </array>

<array> elements do not have names.

You can mix types as the example above illustrates.

<arrays>s can be recursive, any value may contain an <array> or any other type, including a <struct>, described above.

Response example （回复示例）

HTTP/1.1 200 OK
Connection: close
Content-Length: 158
Content-Type: text/xml
Date: Fri, 17 Jul 1998 19:55:08 GMT
Server: UserLand Frontier/5.1.2-WinNT

<?xml version="1.0"?>
<methodResponse>
   <params>
      <param>
         <value><string>South Dakota</string></value>
      </param>
   </params>
 </methodResponse>

Response format （回复的数据格式）

Unless there's a lower-level error, always return 200 OK.

The Content-Type is text/xml. Content-Length must be present and correct.

The body of the response is a single XML structure, a <methodResponse>, which can contain a single <params> which contains a single <param> which contains a single <value>.

The <methodResponse> could also contain a <fault> which contains a <value> which is a <struct> containing two elements, one named <faultCode>, an <int> and one named <faultString>, a <string>.

A <methodResponse> can not contain both a <fault> and a <params>.

Fault example （请求出错时的回复示例）

HTTP/1.1 200 OK
Connection: close
Content-Length: 426
Content-Type: text/xml
Date: Fri, 17 Jul 1998 19:55:02 GMT
Server: UserLand Frontier/5.1.2-WinNT

<?xml version="1.0"?>
<methodResponse>
   <fault>
      <value>
         <struct>
            <member>
               <name>faultCode</name>
               <value><int>4</int></value>
            </member>
            <member>
               <name>faultString</name>
               <value><string>Too many parameters.</string></value>
            </member>
         </struct>
       </value>
   </fault>
</methodResponse>

官方spec: http://www.xmlrpc.com/spec