RFC 6120 [1] specifies that XMPP servers and clients can send whitespace characters between first-level elements of an XML stream as a way to maintain the state of the stream. These "whitespace keepalives" are widely used on the XMPP network. However, currently it is not possible to negotiate the frequency of sending keepalives, or even whether to send keepalives at all (the server simply sends them according to its own schedule). Because certain kinds of devices might not want to use keepalives, or might wish to receive keepalives more frequently or less frequently than the server's default, this specification defines a method for negotiating how to send whitespace keepalives between an XMPP server and an XMPP client (this method could also be used between two servers, although that usage is expected to be rare).
The protocol defined in this document enables a client negotiate the time interval between whitespace keepalives, within a range determined by the server. Normally, the client starts the negotiation since not all kinds of the client support the feature.
The protocol defines a keepalive element and the normal negotaition process is quite simple, demonstrated as following:
Then server and client send whitespace keepalive to each other at the agreed time interval.
During the stream negotiation process, the server can advertise this feature. The feature is negotiated after the resource binding. (See Recommended Order of Stream Feature Negotiation (XEP-0170) [2] regarding the recommended order of stream feature negotiation.)
C: <stream:stream
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
C: <stream:stream
from='example.com'
id='KskA2O2BEn5mL7mABTq9X3DTPHO44vAMaIg1nG9O1vo'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
<keepalive xmlns='urn:xmpp:keepalive:0'>
<interval min='60' max='300'/>
</keepalive>
</stream:features>
Client negotiates the keepalive feature by providing an interval value based on server limits and its own condition. The interval SHOULD be a positive interger, and zero is invalid.
<iq from='client@example.com/foo' id='p03ns61g' to='example.com' type='set'>
<keepalive xmlns='urn:xmpp:keepalive:0'>
<interval>60</interval>
</keepalive>
</iq>
The server checks the keepalive interval value and returns a success:
<iq from='example.com' id='p03ns61g' to='client@example.com/foo' type='result'/>
If a problem occurs, the server returns an error (in this example, the client sent a value outside the range of the server's preferences):
<iq from='example.com' id='p03ns61g' to='client@example.com/foo' type='error'>
<error type='cancel'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Then both the server and the client send whitespace keepalives at the interval of the negotiated value. The server SHOULD check to see if has received keepalives and MAY drop the connection if it has not received a keepalive for a period of time significantly longer than the negotiated value (the client MAY also implement this behavior).
Several things need to be noted:
During negotiation, the server MUST check the keepalive interval value and reject any invalid values.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [4].
The XMPP Registrar [5] is requested to issue an initial namespace 'urn:xmpp:keepalive:0'
The XMPP Registrar [5] is requested to issue an initial stream feature namespace 'urn:xmpp:keepalive:0'.
<?xml version='1.0' encoding='utf-8'?>
<xsd:schema xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:xmpp:keepalive:0'
xmlns='urn:xmpp:keepalive:0'
elementFormDefault='unqualified'>
<xsd:element name='keepalive'>
<xsd:complexType>
<xsd:attribute name='min' type='positiveShort' use='optional'/>
<xsd:attribute name='max' type='positiveShort' use='optional'/>
<xsd:assert test='@min le @max'/>
<xsd:element name='interval' type='positiveShort' minOccurs='0' maxOccurs='1'/>
</xsd:complexType>
</xsd:element>
<xsd:simpleType name='positiveShort'>
<xsd:restriction base='xsd:unsignedShort'>
<xsd:minExclusive value='0'/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>
Thanks to Matt Miller and Peter Saint-Andre for their 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 <http://xmpp.org/about/discuss.shtml> 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. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.
2. XEP-0170: Recommended Order of Stream Feature Negotiation <https://xmpp.org/extensions/xep-0170.html>.
3. XEP-0198: Stream Management <https://xmpp.org/extensions/xep-0198.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/
END