XML-RPC

XML-RPC is a remote procedure call (RPC) which uses XML to encode its calls and HTTP as a transport mechanism. "XML-RPC" also refers generically to the use of XML for remote procedure call, independently of the specific protocol. This article is about the protocol named "XML-RPC".

The XML-RPC protocol was created in 1998 by Dave Winer of UserLand Software and Microsoft, with Microsoft seeing the protocol as an essential part of scaling up its efforts in business-to-business e-commerce. As new functionality was introduced, the standard evolved into what is now .

UserLand supported XML-RPC from version 5.1 of its Frontier web content management system, released in June 1998.

XML-RPC's idea of a human-readable-and-writable, script-parsable standard for HTTP-based requests and responses has also been implemented in competing specifications such as Allaire's Web Distributed Data Exchange (WDDX) and webMethod's Web Interface Definition Language (WIDL). Prior art wrapping COM, CORBA, and Java RMI objects in XML syntax and transporting them via HTTP also existed in DataChannel's WebBroker technology.

The generic use of XML for remote procedure call (RPC) was patented by Phillip Merrick, Stewart Allen, and Joseph Lapp in April 2006, claiming benefit to a provisional application filed in March 1998. The patent is assigned to webMethods, located in Fairfax, VA.

XML-RPC works by sending an HTTP request to a server implementing the protocol. The client in that case is typically software wanting to call a single method of a remote system. Multiple input parameters can be passed to the remote method, one return value is returned. The parameter types allow nesting of parameters into maps and lists, thus larger structures can be transported. Therefore, XML-RPC can be used to transport objects or structures both as input and as output parameters.

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