XML-RPC

XML-RPC
Name	XML-RPC
Type	Remote procedure call protocol
Introduced	1998
Developer	Dave Winer, Microsoft
Based on	XML, HTTP

XML-RPC XML-RPC is a protocol that uses XML to encode remote procedure calls and HTTP as a transport for invoking procedures on remote systems. It was created to enable interoperability between disparate systems using simple XML serialization, and it influenced later protocols and specifications in web services and distributed computing. The protocol connects applications across platforms and languages via well-formed XML and ubiquitous HTTP endpoints.

Overview

XML-RPC defines a lightweight mechanism for invoking procedures on remote machines using XML encoding and HTTP transport. It leverages Extensible Markup Language and Hypertext Transfer Protocol to provide a cross-platform bridge among implementations in environments such as Microsoft Windows, Linux, macOS, Sun Microsystems-based systems, and embedded devices. The design emphasizes simplicity compared with more feature-rich standards produced by bodies like the World Wide Web Consortium and the Organization for the Advancement of Structured Information Standards. Its influence is seen in later specifications from organizations such as the Apache Software Foundation, OASIS, and vendors like IBM and Oracle Corporation that incorporated XML-based interoperation in their stacks.

History and Development

XML-RPC originated in the late 1990s amid a surge of XML-based technologies championed by figures such as Dave Winer and companies including Microsoft. Early development occurred alongside contemporaneous efforts like SOAP from Don Box and workgroups within W3C and IETF communities. Adoption grew through implementations from projects hosted by the Apache Software Foundation and independent efforts in languages promoted by organizations such as the Free Software Foundation and vendors like Sun Microsystems (later Oracle Corporation). Debates about simplicity versus extensibility involved stakeholders such as IBM, Microsoft Research, and standards bodies including OASIS, which shaped subsequent web services and RPC approaches.

Protocol and Message Format

XML-RPC messages are composed using elements defined by Extensible Markup Language schemas and transmitted as HTTP POST requests, often to URLs hosted on servers running stacks from Apache HTTP Server or IIS (Internet Information Services). A request encodes a method name and parameters within XML elements, while the response returns structured data or faults following a rigid value typing scheme influenced by data types used in languages promoted by Sun Microsystems (for example, Java platforms), Microsoft (for example, .NET platforms), and scripting environments from projects like Mozilla Foundation and Python Software Foundation. The protocol relies on existing HTTP status semantics defined by organizations like Internet Engineering Task Force while interoperating with authentication schemes from OAuth and transport mechanisms used by Amazon Web Services and Google-style APIs in practice. Tooling and validators from entities such as W3C and developer communities around GitHub aid in verifying compliance.

Implementations and Libraries

Implementations span many ecosystems, including libraries for languages and platforms backed by communities and companies like Sun Microsystems (Java), Microsoft (.NET), the Python Software Foundation (Python), the Ruby on Rails community (Ruby), and projects hosted on GitHub and SourceForge. Notable servers and toolkits have been integrated into stacks from the Apache Software Foundation and commercial middleware from IBM and Oracle Corporation. Client libraries have been created for environments used by organizations such as Mozilla Foundation and cloud providers like Amazon Web Services and Google. Open-source projects from the Free Software Foundation and academic groups at institutions such as Massachusetts Institute of Technology and Stanford University produced reference implementations and testing harnesses that helped verify interoperability across diverse platforms.

Security and Limitations

XML-RPC inherits security considerations from its use of Hypertext Transfer Protocol and textual XML payloads. Vulnerabilities associated with XML parsing, including entity expansion and injection, were analyzed by researchers at institutions like SANS Institute, CERT Coordination Center, and universities such as Carnegie Mellon University. Transport-layer confidentiality and integrity are typically provided by Transport Layer Security as promoted by bodies like IETF, while authentication and authorization mechanisms are often integrated from ecosystems led by OAuth or enterprise solutions from Microsoft and IBM. Architectural limitations include lack of built-in type extensibility, constrained fault handling compared with specifications from W3C and OASIS, and scaling challenges in high-throughput environments managed by cloud providers like Amazon Web Services and Google Cloud Platform.

Comparison with Other Remote Procedure Calls

Compared with SOAP—a competing XML-based protocol developed with input from Microsoft and IBM—XML-RPC emphasizes minimalism over the extensive extensibility frameworks championed by standards organizations like W3C and OASIS. Alternative binary and efficient RPC mechanisms promoted by organizations and projects such as gRPC from Google and Apache Thrift from the Apache Software Foundation focus on schema-driven, high-performance serialization for systems used by Facebook and Netflix. Legacy RPC systems like Sun RPC and CORBA-driven stacks from Object Management Group address different interoperability and performance trade-offs, while RESTful architectures influential in platforms from Amazon Web Services and Google favor resource-oriented interactions over procedure invocation. Each approach reflects choices made by companies and institutions including Microsoft, IBM, Oracle Corporation, and open-source communities around GitHub and SourceForge.

Category:Application layer protocols