XML-RPC [1] is a method of encoding RPC requests and responses in XML. The original specification defines HTTP (see RFC 2068 [2]) as the only valid transport for XML-RPC payloads.
Various initiatives exist already to transport XML-RPC payloads over Jabber. These initiatives were independent of each other and used slightly differing methods (e.g. carrying the payload in a <message/> element as opposed to an <iq/> stanza), resulting in potential interoperability problems.
A working session during JabberCon 2001 resulted in formalisation of a single method. This document describes that method, which is labelled as Jabber-RPC to differentiate it from XML-RPC itself.
The <iq/> stanza is used to transport XML-RPC payloads. XML-RPC requests are transported using an <iq/> stanza of type "set", and XML-RPC responses are transported using an <iq/> stanza of type "result". An <iq/> stanza MUST NOT contain more than one request or response.
The <iq/> stanza contains a single <query/> sub-element in the jabber:iq:rpc namespace. The direct child of the <query/> element will be either a single <methodCall/> element (in the case of a request) or a single <methodResponse/> element (in the case of a response). This child element will contain the XML-RPC payload. Note that the XML declaration that normally appears at the head of an XML-RPC request or response when transported as the payload of an HTTP POST request MUST BE omitted when it is transported via a Jabber <iq/> stanza.
The encoding of the Jabber XML stream is UTF-8. It is assumed that the encoding of the XML-RPC payload is also UTF-8.
Application-level errors will be indicated within the XML-RPC payload (as is the case with the traditional HTTP-based XML-RPC mechanism). Transport level errors will be indicated in the normal way for <iq/> stanzas -- namely, by an <iq/> stanza of type "error" and the addition of an <error/> tag as a direct child of the <iq/> stanza. There are no specific XML-RPC-related, transport-level errors.
In September of 2011, it was discovered that the XML schema quoted in Section 8 contains an error, showing a child element of <Base64/> (uppercase "B") instead of <base64/> (lowercase "b"). A review of the XML-RPC specification and of numerous XML-RPC and Jabber-RPC implementations showed that the element name is properly "base64" and that the quoted schema was in error by having an element name of "Base64". Therefore this specification and its associated schema were modified to use the correct element name: "base64". It is possible that some existing Jabber-RPC implementations might send a child element of <Base64/>.
<iq type='set'
from='requester@company-b.com/jrpc-client'
to='responder@company-a.com/jrpc-server'
id='rpc1'>
<query xmlns='jabber:iq:rpc'>
<methodCall>
<methodName>examples.getStateName</methodName>
<params>
<param>
<value><i4>6</i4></value>
</param>
</params>
</methodCall>
</query>
</iq>
<iq type='result'
from='responder@company-a.com/jrpc-server'
to='requester@company-b.com/jrpc-client'
id='rpc1'>
<query xmlns='jabber:iq:rpc'>
<methodResponse>
<params>
<param>
<value><string>Colorado</string></value>
</param>
</params>
</methodResponse>
</query>
</iq>
If the requesting entity does not have sufficient permissions to perform remote procedure calls, the responding entity MUST return a <forbidden/> error:
<iq type='error'
from='responder@company-a.com/jrpc-server'
to='requester@company-b.com/jrpc-client'
id='rpc1'>
<query xmlns='jabber:iq:rpc'>
<methodCall>
<methodName>examples.getStateName</methodName>
<params>
<param>
<value><i4>6</i4></value>
</param>
</params>
</methodCall>
</query>
<error code='403' type='auth'>
<forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If an entity supports the Jabber-RPC protocol, it SHOULD advertise that fact in response to Service Discovery (XEP-0030) [3] information ("diso#info") requests by returning an identity of "automation/rpc" and a feature of "jabber:iq:rpc":
<iq type='get'
from='requester@company-b.com/jrpc-client'
to='responder@company-a.com/jrpc-server'
id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<iq type='result'
to='requester@company-b.com/jrpc-client'
from='responder@company-a.com/jrpc-server'
id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<identity category='automation' type='rpc'/>
<feature var='jabber:iq:rpc'/>
</query>
</iq>
An entity that supports Jabber-RPC SHOULD establish a permitted list of entities that are allowed to perform remote procedure calls and MUST return a <forbidden/> error if entities with insufficient permissions attempt such calls.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [4].
The XMPP Registrar [5] includes 'jabber:iq:rpc' in its registry of protocol namespaces.
The XMPP Registrar includes a Service Discovery type of "rpc" within the "automation" category in its registry of service discovery identities.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:iq:rpc'
xmlns='jabber:iq:rpc'
elementFormDefault='qualified'>
<xs:annotation>
<xs:documentation>
The protocol documented by this schema is defined in
XEP-0009: http://www.xmpp.org/extensions/xep-0009.html
There is no official XML schema for XML-RPC. The main body
of this schema has been borrowed from an unofficial schema
representation contained in the book "Processing XML With
Java" by Elliotte Rusty Harold, as located at:
http://www.ibiblio.org/xml/books/xmljava/chapters/ch02s05.html
</xs:documentation>
</xs:annotation>
<xs:element name='query'>
<xs:complexType>
<xs:choice minOccurs='0' maxOccurs='1'>
<xs:element ref='methodCall'/>
<xs:element ref='methodResponse'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name="methodCall">
<xs:complexType>
<xs:all>
<xs:element name="methodName">
<xs:simpleType>
<xs:restriction base="ASCIIString">
<xs:pattern value="([A-Za-z0-9]|/|\.|:|_)*" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="params" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:sequence>
<xs:element name="param" type="ParamType"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:all>
</xs:complexType>
</xs:element>
<xs:element name="methodResponse">
<xs:complexType>
<xs:choice>
<xs:element name="params">
<xs:complexType>
<xs:sequence>
<xs:element name="param" type="ParamType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="fault">
<!-- What can appear inside a fault is very restricted -->
<xs:complexType>
<xs:sequence>
<xs:element name="value">
<xs:complexType>
<xs:sequence>
<xs:element name="struct">
<xs:complexType>
<xs:sequence>
<xs:element name="member"
type="MemberType">
</xs:element>
<xs:element name="member"
type="MemberType">
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:complexType name="ParamType">
<xs:sequence>
<xs:element name="value" type="ValueType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="ValueType" mixed="true">
<xs:choice>
<xs:element name="i4" type="xs:int"/>
<xs:element name="int" type="xs:int"/>
<xs:element name="string" type="ASCIIString"/>
<xs:element name="double" type="xs:decimal"/>
<xs:element name="base64" type="xs:base64Binary">
<xs:annotation>
<xs:documentation>
Corrected from "Base64" to "base64" in version 2.2 of XEP-0009.
</xs:documentation>
</xs:annotation>
</xs:element>
<xs:element name="boolean" type="NumericBoolean"/>
<xs:element name="dateTime.iso8601" type="xs:dateTime"/>
<xs:element name="array" type="ArrayType"/>
<xs:element name="struct" type="StructType"/>
</xs:choice>
</xs:complexType>
<xs:complexType name="StructType">
<xs:sequence>
<xs:element name="member" type="MemberType"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="MemberType">
<xs:sequence>
<xs:element name="name" type="xs:string" />
<xs:element name="value" type="ValueType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="ArrayType">
<xs:sequence>
<xs:element name="data">
<xs:complexType>
<xs:sequence>
<xs:element name="value" type="ValueType"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="ASCIIString">
<xs:restriction base="xs:string">
<xs:pattern value="([ -~]|\n|\r|\t)*" />
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="NumericBoolean">
<xs:restriction base="xs:boolean">
<xs:pattern value="0|1" />
</xs:restriction>
</xs:simpleType>
</xs:schema>
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The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XML-RPC <http://www.xmlrpc.com/spec>.
2. RFC 2068: Hypertext Transport Protocol -- HTTP/1.1 <http://tools.ietf.org/html/rfc2068>.
3. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
4. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
5. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Cross-document editorial adjustments for inclusive language.
END