Multi-User Chat (XEP-0045) [1] defines a protocol for groupchat over XMPP. That specification includes a method for inviting a contact to a room, where the invitation is mediated by the room itself: the user sends the invitation to the room, which in turn sends it to the contact. Unfortunately, a mediated invitation might not be delivered to the contact, for example if the contact blocks communication with entities not in its roster as specified in Privacy Lists (XEP-0016) [2]. As privacy lists have become more common, MUC invitations have been increasingly blocked at the server side, resulting in an undesirable user experience. Therefore, this specification defines a method for sending an invitation directly from the user to the contact, which re-uses the original 'jabber:x:conference' namespace in use before Multi-User Chat (XEP-0045) [1] was written (with the addition of 'reason', 'continue', and 'thread' attributes for feature parity with mediated invitations).
A user invites a contact to a room by sending a <message/> stanza containing only an <x/> element qualified by the 'jabber:x:conference' namespace.
<message
from='crone1@shakespeare.lit/desktop'
to='hecate@shakespeare.lit'>
<x xmlns='jabber:x:conference'
jid='darkcave@macbeth.shakespeare.lit'
password='cauldronburn'
reason='Hey Hecate, this is the place for all good witches!'/>
</message>
The 'jid' attribute, which is REQUIRED, specifies the address of the groupchat room to be joined.
The 'password' attribute, which is OPTIONAL, specifies a password needed for entry into a password-protected room and maps to the <password/> element in a mediated invitation.
The 'reason' attribute, which is OPTIONAL, specifies a human-readable purpose for the invitation and maps to the <reason/> element in a mediated invitation.
The 'continue' and 'thread' attributes, which are OPTIONAL, specify that the groupchat room continues a one-to-one chat having the designated thread; these map to the <continue/> element (with 'thread' attribute) in a mediated invitation. Note that the 'continue' attribute has a datatype of boolean. [3]
<message
from='crone1@shakespeare.lit/desktop'
to='hecate@shakespeare.lit'>
<x xmlns='jabber:x:conference'
continue='true'
jid='darkcave@macbeth.shakespeare.lit'
password='cauldronburn'
reason='Hey Hecate, this is the place for all good witches!'
thread='e0ffe42b28561960c6b12b944a092794b9683a38'/>
</message>
Upon receiving a direct invitation, the contact's client SHOULD present the invitation to the contact so that the contact can accept it or decline it. If the contact accepts the invitation, the contact's client shall join the room as described in Multi-User Chat (XEP-0045) [1]. If the contact declines the invitation, it shall silently discard the invitation.
If an entity supports the protocol specified herein, it MUST advertise that fact by returning a feature of "jabber:x:conference" in response to Service Discovery (XEP-0030) [4] information requests (see Protocol Namespaces regarding issuance of one or more permanent namespaces).
<iq from='crone1@shakespeare.lit/desktop'
id='disco1'
to='hecate@shakespeare.lit/broom'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<iq from='hecate@shakespeare.lit/broom'
id='disco1'
to='crone1@shakespeare.lit/desktop'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<feature var='jabber:x:conference'/>
</query>
</iq>
In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities (XEP-0115) [5]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.
Before inviting a contact to a members-only room, a user SHOULD check to see if the contact is already a member and, if not, add the contact to the member list (or ask a room administrator to do so).
If a client receives multiple invitations to the same room (e.g., a mediated invitation as defined in Multi-User Chat (XEP-0045) [1] and a direct invitation as defined here), the client SHOULD present only one of the invitations to a human user. If a client receives an invitation to a room in which the user is already an occupant, the client SHOULD silently discard the invitation.
The following attacks are possible, in roughly the order of probability. See also Best Practices to Discourage Denial of Service Attacks (XEP-0205) [6] and RFC 3552 [7].
The sender of an invitation could overload the 'reason' attribute with malicious or offensive text. The recipient can mitigate this attack by blocking the sender using technologies such as Privacy Lists (XEP-0016) [2] and Blocking Command (XEP-0191) [8].
A passive attacker could flood the recipient with a large number of chatroom invitations. This attack, too, can be mitigated with Privacy Lists or Simple Communications Blocking.
A passive attacker could use a mimicked JID to fool the recipient into thinking that the sender is a known or trusted contact. This attack requires knowledge of the recipient's known or trusted contacts, and can be mitigated by following the recommendations in Best Practices to Prevent JID Mimicking (XEP-0165) [9].
In the absence of end-to-end encryption, a passive attacker could eavesdrop on the chatroom invitations that a user sends or receives. This is especially threatening if the invitation includes a 'password' attribute for a password-protected room.
In the absence of end-to-end encryption or signing, an active attacker could modify the invitation in transit so that the recipient is directed to a different room than intended by the sender.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [10].
The XMPP Registrar [11] includes 'jabber:x:conference' in its registry of protocol namespaces at <https://xmpp.org/registrar/namespaces.html>, as described in Section 4 of XMPP Registrar Function (XEP-0053) [12].
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:x:conference'
xmlns='jabber:x:conference'
elementFormDefault='qualified'>
<xs:annotation>
<xs:documentation>
The protocol documented by this schema is defined in
XEP-0249: http://www.xmpp.org/extensions/xep-0249.html
</xs:documentation>
</xs:annotation>
<xs:element name='x'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='empty'>
<xs:attribute
name='continue'
type='xs:boolean'
use='optional'/>
<xs:attribute
name='jid'
type='xs:string'
use='required'/>
<xs:attribute
name='password'
type='xs:string'
use='optional'/>
<xs:attribute
name='reason'
type='xs:string'
use='optional'/>
<xs:attribute
name='thread'
type='xs:string'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Thanks to Joe Hildebrand for his feedback.
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <https://xmpp.org/community/> for a complete list.
Errata can be sent to <editor@xmpp.org>.
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. XEP-0045: Multi-User Chat <https://xmpp.org/extensions/xep-0045.html>.
2. XEP-0016: Privacy Lists <https://xmpp.org/extensions/xep-0016.html>.
3. In accordance with Section 3.2.2.1 of XML Schema Part 2: Datatypes, the allowable lexical representations for the xs:boolean datatype are the strings "0" and "false" for the concept 'false' and the strings "1" and "true" for the concept 'true'; implementations MUST support both styles of lexical representation.
4. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
5. XEP-0115: Entity Capabilities <https://xmpp.org/extensions/xep-0115.html>.
6. XEP-0205: Best Practices to Discourage Denial of Service Attacks <https://xmpp.org/extensions/xep-0205.html>.
7. RFC 3552: Guidelines for Writing RFC Text on Security Considerations <http://tools.ietf.org/html/rfc3552>.
8. XEP-0191: Blocking Command <https://xmpp.org/extensions/xep-0191.html>.
9. XEP-0165: Best Practices to Prevent JID Mimicking <https://xmpp.org/extensions/xep-0165.html>.
10. 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/>.
11. 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/>.
12. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
Added continue and thread attributes for feature parity with mediated invitations when converting a one-to-one chat to a groupchat.
Added password attribute for feature parity with mediated invitations.
Per a vote of the XMPP Council, advanced specification from Experimental to Draft.
Defined several possible security attacks along with solutions.
Added optional reason attribute for feature parity with XEP-0045.
Initial published version.
Modified to use old jabber:x:conference namespace.
Added note about handling multiple invitations.
Added implementation note about members-only rooms.
Changed venue element to conference element.
First draft.
@report{saint-andre2008x-conference,
title = {Direct MUC Invitations},
author = {Saint-Andre, Peter},
type = {XEP},
number = {0249},
version = {1.2},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-0249.html},
date = {2008-08-12/2011-09-22},
}END