XML-RPC
In this section you will learn about XML-RPC APIs, what they are, their benefits and drawbacks with some real world examples.

What is XML-RPC?
XML-RPC is a remote procedure call (RPC) protocol which encodes its calls as XML. It's a protocol for executing procedures on remote servers, making it a precursor to SOAP and REST. XML-RPC allows you to send a request to a remote server, execute a given procedure, and return the results, all encapsulated in XML format.
Principles of XML-RPC
Transport Agnostic: Similar to JSON-RPC, XML-RPC doesn't mandate a specific transport mechanism. It can be utilized over HTTP, SMTP, TCP, or any other reliable transport layer, making it versatile for different networking scenarios.
Example: You can send an XML-RPC message via HTTP like so:
In this example, a POST
request is made to the /RPC2
endpoint on www.example.com
with a XML-RPC message requesting the state name for the number 41.
Simple Protocol: XML-RPC is designed to be as simple as possible, while allowing for complex structures to be transmitted, processed, and returned.
Structured Data Communication: XML-RPC utilizes XML encoding to enable structured data communication, ensuring a standardized data exchange format.
Benefits of XML-RPC
XML-RPC stands out due to its simple and structured communication model. It's particularly useful in environments where different platforms need to communicate with each other.
Simplicity: XML-RPC's protocol design is straightforward, making it easy to implement and use. It's well-suited for cross-platform communication as XML is a widely accepted standard for data encoding.
Example: An XML-RPC request to get the state name for a given state number looks like:
The methodName
field specifies the operation, and the params
field specifies the input values.
Cross-platform Communication: The use of XML as a data encoding format ensures that XML-RPC can be used for communication between different platforms and programming environments.
Transport Flexibility: Being transport agnostic, XML-RPC can be utilized over different transport mechanisms, providing flexibility in network configurations.
How does XML-RPC Work?
XML-RPC follows a simple request-response model:
Client Sends a Request
Clients send a request to the server encoded in XML with a specified method and parameters.
In this request
, the methodName
field indicates the operation to perform, getStateName
in this case, and the params
field provides the arguments for the method, here 41
.
Server Processes the Request
The server processes the request, performs the specified method with the provided parameters, and prepares a response. It decodes the XML message, extracts the method name and parameters, performs the operation, and then prepares an XML-encoded response.
Server Sends a Response to the Client
The server sends a response back to the client with the result of the request.
In this response
, the methodResponse
element contains a params
element with the result of the getStateName
operation.
Components of an XML-RPC Request
Each XML-RPC request consists of several key components:
methodCall
: This element encloses the entire method call.
methodName
: ThemethodName
element specifies the name of the method to be invoked on the server.
params
: Theparams
element encloses the method parameters.
XML-RPC Error Handling
XML-RPC has a structured error handling mechanism through the fault
element in the response:
Error Object:
Components of an XML-RPC Response
When a server sends back a response, it provides the result of the method invocation or an error object if something went wrong:
methodResponse
: This element encloses the entire method response.params
orfault
: Theparams
element contains the result of the method invocation, or thefault
element contains an error object if something went wrong.
or
Real-world example of XML-RPC
To further understand XML-RPC, let's consider a real-world scenario of a "To-Do List" application similar to the previous modules. In this scenario, XML-RPC is used to manage tasks between the client and server.
API Endpoints in Action
For our hypothetical To-Do List application, the XML-RPC defines several methods, each corresponding to a specific action:
getTasks
: Viewing All Tasks
This method provides a comprehensive list of all tasks stored in the application's database.
Request:
Response:
Conclusion
XML-RPC serves as a simple, yet powerful protocol for executing remote procedure calls, especially in a cross-platform environment. Its usage of XML for encoding requests and responses ensures structured communication, making it a reliable choice for developing web services that require remote procedure calls. Through the understanding of XML-RPC, developers can leverage its simplicity and structured communication model to build robust and interoperable web services.