XML-RPC (XML Remote Procedure Call) is a protocol that encodes calls to functions, methods, or procedures in XML format and sends them via HTTP to a remote server that processes the request and sends back the response, also encoded in XML. It is a way to perform remote procedure calls (RPCs) between different systems on a network, enabling communication and data exchange in a decentralized, distributed environment.

Here’s a breakdown of the core elements and concepts related to XML-RPC:

  1. Simple and Lightweight:
    • XML-RPC is known for its simplicity and lightweight nature, which makes it easy to implement and use.
  2. Platform Agnostic:
    • Being based on standard technologies like XML and HTTP, XML-RPC is platform-independent, enabling communication between different systems regardless of the underlying technologies or platforms they use.
  3. Encoding:
    • XML-RPC uses XML to encode the data, which is a text-based encoding. This encoding is human-readable and straightforward to understand, although not as efficient as binary encodings like Protocol Buffers or MessagePack.
  4. Transport:
    • XML-RPC relies on HTTP as the transport protocol, which is universally supported and works well with existing network infrastructures including firewalls and routers.
  5. Procedure Calls:
    • In XML-RPC, a procedure call is represented as an XML document that includes the name of the procedure and the parameters to be passed to it. The server processes the request, executes the procedure, and returns the result, also formatted as an XML document.
  6. Data Types:
    • XML-RPC supports a limited set of data types, including basic types like strings, integers, booleans, and arrays. Complex or custom data types need to be serialized into one of the supported types before transmission.
  7. Synchronous Communication:
    • XML-RPC is synchronous, meaning that the client sends a request and waits for a response from the server. This is in contrast to asynchronous communication where the client could continue with other tasks without waiting for the response.
  8. Use Cases:
    • XML-RPC is suited for basic remote procedure calls, especially in environments where simplicity and ease of implementation are prioritized over performance and advanced features.
  9. Alternatives:
    • Newer technologies and protocols such as REST, JSON-RPC, gRPC, and SOAP offer different advantages and might be preferred over XML-RPC depending on the use case and requirements.
  10. Decline in Popularity:
    • With the advent of RESTful APIs and other modern communication protocols, XML-RPC has seen a decline in popularity. Nonetheless, it remains in use in legacy systems and specific scenarios where its simplicity is beneficial.