Extensible Messaging and Presence Protocol (XMPP): Address Format&yetpeter@andyet.comhttps://andyet.com/Extensible Messaging and Presence ProtocolXMPPJabberMessagingInstant MessagingPresenceInternationalizationi18nPRECISThis document defines the address format for the Extensible Messaging
and Presence Protocol (XMPP), including support for code points outside
the ASCII range. This document obsoletes RFC 6122.The Extensible Messaging and Presence Protocol (XMPP) is an application profile of the Extensible Markup
Language for streaming XML data in close to real time
between any two or more network-aware entities. The address format for
XMPP entities was originally developed in the Jabber open-source community
in 1999, first described by in 2002, and then
defined canonically by in 2004 and in 2011.As specified in RFCs 3920 and 6122, the XMPP address format used the
"stringprep" technology for preparation and comparison of non-ASCII
characters . Following the movement of
internationalized domain names away from stringprep, this document defines
the XMPP address format in a way that no longer depends on stringprep (see
the Preparation, Enforcement, and Comparison of Internationalized Strings
(PRECIS) problem statement ). Instead, this
document builds upon the internationalization framework defined by the
IETF's PRECIS working group .Although every attempt has been made to ensure that the characters
allowed in Jabber Identifiers (JIDs) under stringprep are still allowed
and handled in the same way under PRECIS, there is no guarantee of strict
backward compatibility because of changes in Unicode and the fact that
PRECIS handling is based on Unicode properties, not a hardcoded table of
characters. Because it is possible that previously valid JIDs might no
longer be valid (or previously invalid JIDs might now be valid), operators
of XMPP services are advised to perform careful testing before migrating
accounts and other data (see Section 6 of
for guidance).This document obsoletes RFC 6122.Many important terms used in this document are defined in , , ,
, and .The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in .An XMPP entity is anything that can communicate using XMPP. For
historical reasons, the network address of an XMPP entity is called a
JID. A valid JID is a string of Unicode code points
, encoded using UTF-8 ,
and structured as an ordered sequence of localpart, domainpart, and
resourcepart, where the first two parts are demarcated by the
'@' character used as a separator and the last two parts are similarly
demarcated by the '/' character (e.g.,
<juliet@example.com/balcony>).The syntax for a JID is defined as follows, using the Augmented
Backus-Naur Form (ABNF) as specified in .All JIDs are based on the foregoing structure. However, note that
the formal syntax provided above does not capture all of the rules and
restrictions that apply to JIDs, which are described below.Each allowable portion of a JID (localpart, domainpart, and
resourcepart) is 1 to 1023 octets in length, resulting in a maximum
total size (including the '@' and '/' separators) of 3071 octets.Implementation Note: The length limits on JIDs
and parts of JIDs are based on octets (bytes), not characters. UTF-8
encoding can result in more than one octet per character.Implementation Note: When dividing a JID into
its component parts, an implementation needs to match the separator
characters '@' and '/' before applying any transformation algorithms,
which might decompose certain Unicode code points to the separator
characters.Implementation Note: Reuse of the IP-literal
rule from implies that IPv6 addresses are
enclosed within square brackets (i.e., beginning with '[' and ending
with ']'), which was not the case with the definition of the XMPP
address format in but which was changed in
. Also note that the IP-literal rule was
updated between and to
optionally add a zone identifier to any literal address.This document defines the native format for JIDs; see for information about the representation of a JID as
a Uniform Resource Identifier (URI) or
Internationalized Resource Identifier (IRI) and
the extraction of a JID from an XMPP URI or IRI.The domainpart of a JID is the portion that remains once the
following parsing steps are taken:Remove any portion from the first '/' character to the end of the
string (if there is a '/' character present).Remove any portion from the beginning of the string to the first
'@' character (if there is an '@' character present).This parsing order is important, as illustrated by example 15 in
.The domainpart is the primary identifier and is the only REQUIRED
element of a JID (a mere domainpart is a valid JID). Typically, a
domainpart identifies the "home" server to which clients connect for XML
routing and data management functionality. However, it is not necessary
for an XMPP domainpart to identify an entity that provides core XMPP
server functionality (e.g., a domainpart can identify an entity such as
a multi-user chat service , a publish-subscribe
service , or a user directory).The domainpart for every XMPP service MUST be a fully qualified
domain name (FQDN), an IPv4 address, an IPv6 address, or an unqualified
hostname (i.e., a text label that is resolvable on a local network).Informational Note: The term "fully qualified
domain name" is not well defined. In , it is
also called an absolute domain name, and the two terms are associated in
. The earliest use of the term can be found in
. References to those older specifications
ought not to be construed as limiting the characters of a
fully qualified domain name to the ASCII range; for example, mentions that a fully qualified domain name can
contain one or more U-labels.Interoperability Note: Domainparts that are IP
addresses might not be accepted by other services for the purpose of
server-to-server communication, and domainparts that are unqualified
hostnames cannot be used on public networks because they are resolvable
only on a local network.If the domainpart includes a final character considered to be a label
separator (dot) by , this character MUST be
stripped from the domainpart before the JID of which it is a part is
used for the purpose of routing an XML stanza, comparing against another
JID, or constructing an XMPP URI or IRI . In
particular, such a character MUST be stripped before any other
canonicalization steps are taken.In general, the content of a domainpart is an Internationalized
Domain Name (IDN) as described in the specifications for
Internationalized Domain Names in Applications (commonly called
"IDNA2008"), and a domainpart is an "IDNA-aware domain name slot" as
defined in .After any and all normalization, conversion, and mapping of code
points as well as encoding of the string as UTF-8, a domainpart MUST NOT
be zero octets in length and MUST NOT be more than 1023 octets in
length. (Naturally, the length limits of
apply, and nothing in this document is to be interpreted as overriding
those more fundamental limits.)Detailed rules and considerations for preparation, enforcement, and
comparison are provided in the following sections.An entity that prepares a string for inclusion in an XMPP
domainpart slot MUST ensure that the string consists only of Unicode
code points that are allowed in NR-LDH labels or U-labels as defined
in . This implies that the string MUST NOT
include A-labels as defined in ; each A-label
MUST be converted to a U-label during preparation of a string for
inclusion in a domainpart slot. In addition, the string MUST be
encoded as UTF-8 .An entity that performs enforcement in XMPP domainpart slots MUST
prepare a string as described in
and MUST also apply
the normalization, case-mapping, and width-mapping rules defined
in .Informational Note: The order in which
the rules are applied for IDNA2008 (see
and ) is different from the order for
localparts and resourceparts as described under
Sections
and .
An entity that performs comparison of two strings before or after
their inclusion in XMPP domainpart slots MUST prepare each string
as specified in and then
enforce the normalization, case&nbhy;mapping, and width-mapping rules
specified in .
The two strings are to be considered equivalent if they are an exact
octet-for-octet match (sometimes called "bit-string identity").The localpart of a JID is an optional identifier placed before the
domainpart and separated from the latter by the '@' character.
Typically, a localpart uniquely identifies the entity requesting and
using network access provided by a server (i.e., a local account),
although it can also represent other kinds of entities (e.g., a
chatroom associated with a multi-user chat service ). The entity represented by an XMPP localpart is
addressed within the context of a specific domain (i.e.,
<localpart@domainpart>).The localpart of a JID MUST NOT be zero octets in length and MUST NOT
be more than 1023 octets in length. This rule is to be enforced after
any normalization and mapping of code points as well as encoding of the
string as UTF-8.The localpart of a JID is an instance of the UsernameCaseMapped
profile of the PRECIS IdentifierClass, which is specified in . The rules and considerations provided in that
specification MUST be applied to XMPP localparts.Implementation Note: XMPP uses the Simple
Authentication and Security Layer (SASL) for
authentication. At the time of this writing, some SASL mechanisms use
SASLprep for the handling of usernames and
passwords; in the future, these SASL mechanisms will likely transition to
the use of PRECIS-based handling rules as specified in . For a detailed discussion about the implications
of that transition (including the potential need to modify or remove
certain characters in the underlying account database), see both
Section 6 and Appendix A of .In XMPP, the following characters are explicitly disallowed in XMPP
localparts, even though they are allowed by the IdentifierClass base
class and the UsernameCaseMapped profile:
" U+0022 (QUOTATION MARK)& U+0026 (AMPERSAND)' U+0027 (APOSTROPHE)/ U+002F (SOLIDUS): U+003A (COLON)< U+003C (LESS-THAN SIGN)> U+003E (GREATER-THAN SIGN)@ U+0040 (COMMERCIAL AT)Implementation Note: An XMPP-specific method
for escaping the foregoing characters (along with U+0020, i.e., ASCII
space) has been defined in the JID Escaping specification .The resourcepart of a JID is an optional identifier placed after the
domainpart and separated from the latter by the '/' character. A
resourcepart can modify either a <localpart@domainpart> address or
a mere <domainpart> address. Typically, a resourcepart uniquely
identifies a specific connection (e.g., a device or location) or object
(e.g., an occupant in a multi-user chatroom )
belonging to the entity associated with an XMPP localpart at a domain
(i.e., <localpart@domainpart/resourcepart>).XMPP entities SHOULD consider resourceparts to be opaque strings and
SHOULD NOT impute meaning to any given resourcepart. In particular:Use of the '/' character as a separator between the domainpart
and the resourcepart does not imply that XMPP addresses are
hierarchical in the way that, say, HTTP URIs are hierarchical (see
for general discussion); thus, for example,
an XMPP address of the form <localpart@domainpart/foo/bar>
does not identify a resource "bar" that exists below a resource
"foo" in a hierarchy of resources associated with the entity
"localpart@domainpart".The '@' character is allowed in the resourcepart and is often
used in the "handle" shown in XMPP chatrooms . For example, the JID
<room@chat.example.com/user@host> describes an entity who is
an occupant of the room <room@chat.example.com> with a handle
of <user@host>. However, chatroom services do not necessarily
check such an asserted handle against the occupant's real JID.The resourcepart of a JID MUST NOT be zero octets in length and MUST
NOT be more than 1023 octets in length. This rule is to be enforced
after any normalization and mapping of code points as well as encoding
of the string as UTF-8.The resourcepart of a JID is an instance of the OpaqueString profile
of the PRECIS FreeformClass, which is specified in
. The rules and considerations provided in
that specification MUST be applied to XMPP resourceparts.In some contexts, it might be appropriate to apply more restrictive
rules to the preparation, enforcement, and comparison of XMPP
resourceparts. For example, in XMPP Multi-User Chat it might be appropriate to apply the rules
specified in . However, the
application of more restrictive rules is out of scope for
resourceparts in general and is properly defined in specifications for
the relevant XMPP extensions.The following examples illustrate a small number of JIDs that are
consistent with the format defined above (note that the characters
"<" and ">" are used to delineate the
actual JIDs and are not part of the JIDs themselves). | A "bare JID" |
+----------------------------------+-------------------------------+
| 2 | | A "full JID" |
+----------------------------------+-------------------------------+
| 3 | | Single space in resourcepart |
+----------------------------------+-------------------------------+
| 4 | | "At" sign in resourcepart |
+----------------------------------+-------------------------------+
| 5 | | Single space in localpart, as |
| | | optionally escaped using the |
| | | XMPP JID Escaping extension |
+----------------------------------+-------------------------------+
| 6 | | Another bare JID |
+----------------------------------+-------------------------------+
| 7 | | The third character is LATIN |
| | | SMALL LETTER SHARP S (U+00DF) |
+----------------------------------+-------------------------------+
| 8 | <π@example.com> | A localpart of GREEK SMALL |
| | | LETTER PI (U+03C0) |
+----------------------------------+-------------------------------+
| 9 | <Σ@example.com/foo> | A localpart of GREEK CAPITAL |
| | | LETTER SIGMA (U+03A3) |
+----------------------------------+-------------------------------+
| 10| <σ@example.com/foo> | A localpart of GREEK SMALL |
| | | LETTER SIGMA (U+03C3) |
+----------------------------------+-------------------------------+
| 11| <ς@example.com/foo> | A localpart of GREEK SMALL |
| | | LETTER FINAL SIGMA (U+03C2) |
+----------------------------------+-------------------------------+
| 12| ; | A resourcepart of the Unicode |
| | | character BLACK CHESS KING |
| | | (U+265A) |
+----------------------------------+-------------------------------+
| 13| | A domainpart |
+----------------------------------+-------------------------------+
| 14| | A domainpart and resourcepart |
+----------------------------------+-------------------------------+
| 15| | A domainpart followed by a |
| | | resourcepart that contains an |
| | | "at" sign |
+----------------------------------+-------------------------------+
]]>Table 1: A Sample of Legal JIDsSeveral points are worth noting. Regarding examples 6 and 7:
although in German the character esszett (LATIN SMALL LETTER SHARP S
(U+00DF)) can mostly be used interchangeably with the two characters
"ss", the localparts in these examples are different, and (if desired) a
server would need to enforce a registration policy that disallows one of
them if the other is registered. Regarding examples 9, 10, and 11:
case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to lowercase (i.e.,
to GREEK SMALL LETTER SIGMA (U+03C3)) during comparison would result in
matching the JIDs in examples 9 and 10; however, because the PRECIS
mapping rules do not account for the special status of GREEK SMALL
LETTER FINAL SIGMA (U+03C2), the JIDs in examples 9 and 11 or examples
10 and 11 would not be matched. Regarding example 12: symbol characters
such as BLACK CHESS KING (U+265A) are allowed by the PRECIS
FreeformClass and thus can be used in resourceparts. Regarding examples
14 and 15: JIDs consisting of a domainpart and resourcepart are rarely
seen in the wild but are allowed according to the XMPP address format.
Example 15 illustrates the need for careful extraction of the domainpart
as described in .The following examples illustrate strings that are not JIDs because
they violate the format defined above. | Quotation marks (U+0022) in |
| | | localpart |
+----------------------------------+-------------------------------+
| 17| | Space (U+0020) in localpart |
+----------------------------------+-------------------------------+
| 18| | Leading space in resourcepart |
+----------------------------------+-------------------------------+
| 19| <@example.com/> | Zero-length localpart and |
| | | resourcepart |
+----------------------------------+-------------------------------+
| 20| | The sixth character is ROMAN |
| | | NUMERAL FOUR (U+2163) |
+----------------------------------+-------------------------------+
| 21| <♚@example.com> | A localpart of BLACK CHESS |
| | | KING (U+265A) |
+----------------------------------+-------------------------------+
| 22| | A localpart without a |
| | | domainpart |
+----------------------------------+-------------------------------+
| 23| | A resourcepart without a |
| | | domainpart |
+----------------------------------+-------------------------------+
]]>Table 2: A Sample of Strings That Violate the JID RulesHere again, several points are worth noting. Regarding example 17:
even though ASCII space (U+0020) is disallowed in the PRECIS
IdentifierClass, it can be escaped to "\20" in XMPP localparts by using
the JID Escaping rules defined in , as
illustrated by example 5 in Table 1. Regarding example 20: the Unicode
character ROMAN NUMERAL FOUR (U+2163) has a compatibility equivalent of
the string formed of LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL
LETTER V (U+0056), but characters with compatibility equivalents are not
allowed in the PRECIS IdentifierClass. Regarding example 21: symbol
characters such as BLACK CHESS KING (U+265A) are not allowed in the
PRECIS IdentifierClass; however, both of the non-ASCII characters in
examples 20 and 21 are allowed in the PRECIS FreeformClass and
therefore in the XMPP resourcepart (as illustrated for U+265A by example
12 in Table 1). Regarding examples 22 and 23: the domainpart is
required in a JID.Enforcement entails applying all of the rules specified in this
document. Enforcement of the XMPP address format rules is the
responsibility of XMPP servers. Although XMPP clients SHOULD prepare
complete JIDs and parts of JIDs in accordance with this document before
including them in protocol slots within XML streams, XMPP servers MUST
enforce the rules wherever possible and reject stanzas and other XML
elements that violate the rules (for stanzas, by returning a
<jid-malformed/> error to the sender as described in Section 8.3.3.8
of ).Entities that enforce the rules specified in this document are
encouraged to be liberal in what they accept by following this
procedure:Where possible, map characters (e.g., through width mapping,
additional mapping, special mapping, case mapping, or normalization)
and accept the mapped string.If mapping is not possible (e.g., because a character is disallowed
in the FreeformClass), reject the string and return a
<jid-malformed/> error.Enforcement applies to complete JIDs and to parts of JIDs. To
facilitate implementation, this document defines the concepts of "JID
slot", "localpart slot", and "resourcepart slot" (similar to the concept
of a "domain name slot" for IDNA2008 as defined in Section 2.3.2.6 of ):An XML element or attribute explicitly
designated in XMPP or in XMPP extensions for carrying a complete
JID.An XML element or attribute explicitly
designated in XMPP or in XMPP extensions for carrying the localpart of
a JID.An XML element or attribute
explicitly designated in XMPP or in XMPP extensions for carrying the
resourcepart of a JID.A server is responsible for enforcing the address format rules when
receiving protocol elements from clients where the server is expected to
handle such elements directly or to use them for purposes of routing a
stanza to another domain or delivering a stanza to a local entity; two
examples from are the 'to' attribute on XML
stanzas (which is a JID slot used by XMPP servers for routing of outbound
stanzas) and the <resource/> child of the <bind/> element
(which is a resourcepart slot used by XMPP servers for binding of a
resource to an account for routing of stanzas between the server and a
particular client). An example from is the 'jid'
attribute of the roster <item/> element.A server is not responsible for enforcing the rules when the protocol
elements are intended for communication among other entities, typically
within the payload of a stanza that the server is merely routing to
another domain or delivering to a local entity. Two examples are the
'initiator' attribute in the Jingle extension
(which is a JID slot used for client-to-client coordination of multimedia
sessions) and the 'nick' attribute in the Multi-User Chat extension (which is a resourcepart slot used for administrative
purposes in the context of XMPP chatrooms). In such cases, the entities
involved SHOULD enforce the rules themselves and not depend on the server
to do so, and client implementers need to understand that not enforcing
the rules can lead to a degraded user experience or to security
vulnerabilities. However, when an add-on service (e.g., a multi-user chat
service) handles a stanza directly, it ought to enforce the rules as well,
as defined in the relevant specification for that type of service.This document does not provide an exhaustive list of JID slots,
localpart slots, or resourcepart slots. However, implementers of core
XMPP servers are advised to consider as JID slots at least the following
elements and attributes when they are handled directly or used for
purposes of routing to another domain or delivering to a local entity:The 'from' and 'to' stream attributes and the 'from' and 'to'
stanza attributes .The 'jid' attribute of the roster <item/> element for contact
list management .The 'value' attribute of the <item/> element for Privacy
Lists when the
value of the 'type' attribute is "jid".The 'jid' attribute of the <item/> element for Service
Discovery defined in .The <value/> element for Data Forms when the 'type' attribute is "jid-single" or
"jid-multi".The 'jid' attribute of the <conference/> element for Bookmark
Storage .The <JABBERID/> of the <vCard/> element for vCard 3.0
and the <uri/> child of the
<impp/> element for vCard 4.0 when the
XML character data identifies an XMPP URI .The 'from' attribute of the <delay/> element for Delayed
Delivery .The 'jid' attribute of the <item/> element for the Blocking
Command .The 'from' and 'to' attributes of the <result/> and
<verify/> elements for Server Dialback
.The 'from' and 'to' attributes of the <iq/>,
<message/>, and <presence/> elements for the Jabber
Component Protocol .Developers of XMPP clients and specialized XMPP add-on services are
advised to check the appropriate specifications for JID slots, localpart
slots, and resourcepart slots in XMPP protocol extensions such as Service
Discovery , Multi-User Chat , Publish-Subscribe , SOCKS5
Bytestreams , In-Band Registration , Roster Item Exchange , and
Jingle .XMPP applications MUST support IDNA2008 for domainparts as described
under , the UsernameCaseMapped
profile for localparts as described under , and the OpaqueString profile for
resourceparts as described under .
This enables XMPP addresses to include a wide variety of characters
outside the ASCII range. Rules for enforcement of the XMPP address format
are provided in and specifications for various
XMPP extensions.Interoperability Note: For backward
compatibility, many existing XMPP implementations and deployments support
IDNA2003 for domainparts, and the stringprep
profiles Nodeprep and Resourceprep for localparts and resourceparts.The stringprep specification did not provide
for entries in the "Stringprep Profiles" registry to have any state
except "Current" or "Not Current". Because this document obsoletes
RFC 6122, which registered the Nodeprep and Resourceprep profiles of
stringprep, IANA has marked those profiles as "Not Current"
and cited this document as an additional reference.The security considerations described in
apply to the IdentifierClass and FreeformClass base string classes used
in this document for XMPP localparts and resourceparts, respectively.
The security considerations described in apply
to internationalized domain names, which are used here for XMPP
domainparts.The security considerations described in apply
to the use of Unicode characters in XMPP addresses.There are two forms of address spoofing: forging and mimicking.In the context of XMPP technologies, address forging occurs when an
entity is able to generate an XML stanza whose 'from' address does not
correspond to the account credentials with which the entity
authenticated onto the network (or an authorization identity provided
during negotiation of SASL authentication as
described in ). For example, address forging
occurs if an entity that authenticated as "juliet@im.example.com" is
able to send XML stanzas from "nurse@im.example.com" or
"romeo@example.net".Address forging is difficult in XMPP systems, given the requirement
for sending servers to stamp 'from' addresses and for receiving
servers to verify sending domains via server-to-server authentication
(see ). However, address forging is possible
if:A poorly implemented server ignores the requirement for
stamping the 'from' address. This would enable any entity that
authenticated with the server to send stanzas from any
localpart@domainpart as long as the domainpart matches the sending
domain of the server.An actively malicious server generates stanzas on behalf of any
registered account at the domain or domains hosted at that
server.Therefore, an entity outside the security perimeter of a particular
server cannot reliably distinguish between JIDs of the form
<localpart@domainpart> at that server and thus can authenticate
only the domainpart of such JIDs with any level of assurance. This
specification does not define methods for discovering or counteracting
the kind of poorly implemented or rogue servers just described.
However, the end-to-end authentication or signing of XMPP stanzas
could help to mitigate this risk, because it would require the rogue
server to generate false credentials for signing or encryption of each
stanza, in addition to modifying 'from' addresses.Address mimicking occurs when an entity provides legitimate
authentication credentials for, and sends XML stanzas from, an account
whose JID appears to a human user to be the same as another JID.
Because many characters are visually similar, it is relatively easy to
mimic JIDs in XMPP systems. As one simple example, the localpart
"ju1iet" (using the Arabic numeral one as the third character) might
appear the same as the localpart "juliet" (using lowercase "L" as the
third character).As explained in , ,
, and , there is no
straightforward solution to the problem of visually similar
characters. Furthermore, IDNA and PRECIS technologies do not attempt
to define such a solution. As a result, XMPP domainparts, localparts,
and resourceparts could contain such characters, leading to security
vulnerabilities such as the following:A domainpart is always employed as one part of an entity's
address in XMPP. One common usage is as the address of a server
or server-side service, such as a multi-user chat service . The security of such services could be
compromised based on different interpretations of the
internationalized domainpart; for example, a user might authorize
a malicious entity at a fake server to view the user's presence
information, or a user could join chatrooms at a fake multi-user
chat service.A localpart can be employed as one part of an entity's address
in XMPP. One common usage is as the username of an instant
messaging user; another is as the name of a multi-user chatroom;
and many other kinds of entities could use localparts as part of
their addresses. The security of such services could be
compromised based on different interpretations of the
internationalized localpart; for example, a user entering a single
internationalized localpart could access another user's account
information, or a user could gain access to a hidden or otherwise
restricted chatroom or service.A resourcepart can be employed as one part of an entity's
address in XMPP. One common usage is as the name for an instant
messaging user's connected resource; another is as the nickname of
a user in a multi-user chatroom; and many other kinds of entities
could use resourceparts as part of their addresses. The security
of such services could be compromised based on different
interpretations of the internationalized resourcepart; for
example, two or more confusable resources could be bound at the
same time to the same account (resulting in inconsistent
authorization decisions in an XMPP application that uses full
JIDs), or a user could send a private message to someone other
than the intended recipient in a multi-user chatroom.XMPP services and clients are strongly encouraged to define and
implement consistent policies regarding the registration, storage, and
presentation of visually similar characters in XMPP systems. In
particular, service providers and software implementers are strongly
encouraged to apply the policies recommended in .This section describes a protocol feature set that summarizes the
conformance requirements of this specification (similar feature sets are
provided for XMPP in and ). The summary is purely informational, and the
conformance keywords of as used here are intended
only to briefly describe the referenced normative text from the body of
this specification. This feature set is appropriate for use in software
certification, interoperability testing, and implementation reports. For
each feature, this section provides the following information:A human-readable nameAn informational descriptionA reference to the particular section of this document that
normatively defines the featureWhether the feature applies to the client role, the server role, or
both (where "N/A" signifies that the feature is not applicable to the
specified role)Whether the feature MUST or SHOULD be implemented, where the
capitalized terms are to be understood as described in The feature set specified here provides a basis for interoperability
testing and follows the spirit of a proposal made by Larry Masinter within
the IETF's NEWTRK working group in 2005 .address-domain-lengthEnsure that the domainpart of an XMPP
address is at least one octet in length and at most 1023 octets in
length, and that it conforms to the underlying length limits of the
DNS.Server MUST, client SHOULD.address-domain-prepEnsure that the domainpart of an XMPP
address conforms to IDNA2008, that it contains only NR-LDH labels and
U-labels (not A-labels), and that all uppercase and titlecase code
points are mapped to their lowercase equivalents.Server MUST, client SHOULD.address-localpart-lengthEnsure that the localpart of an XMPP
address is at least one octet in length and at most 1023 octets in
length.Server MUST, client SHOULD.address-localpart-prepEnsure that the localpart of an XMPP
address conforms to the UsernameCaseMapped profile of the PRECIS
IdentifierClass.Server MUST, client SHOULD.address-resource-lengthEnsure that the resourcepart of an XMPP
address is at least one octet in length and at most 1023 octets in
length.Server MUST, client SHOULD.address-resource-prepEnsure that the resourcepart of an XMPP
address conforms to the OpaqueString profile of the PRECIS
FreeformClass.Server MUST, client SHOULD.The Unicode StandardThe Unicode ConsortiumUnicode Security ConsiderationsUnicode Technical Report #36Preparation, Enforcement, and Comparison of Internationalized Strings
Representing NicknamesFormalizing IETF Interoperability ReportingUnicode Security MechanismsUnicode Technical Standard #39Data Formsreatmon@jabber.orgjhildebr@cisco.comjer@jabber.orgtemas@jabber.orgstpeter@jabber.orgPrivacy Listsstpeter@jabber.orgDefinition of Jabber Identifiers (JIDs)craigk@jabber.comService Discoveryjhildebr@cisco.comreatmon@jabber.orgstpeter@jabber.orgMulti-User Chatstpeter@jabber.orgBookmarksrcb@ceruleanstudios.comstpeter@jabber.orgvcard-tempstpeter@jabber.orgPublish-Subscribestpeter@jabber.orgralphm@ik.nuSOCKS5 Bytestreamsdizzyd@jabber.orglinuxwolf@outer-planes.netstpeter@jabber.orgjustin@affinix.comIn-Band Registrationstpeter@jabber.orgJID Escapingjhildebr@cisco.comstpeter@jabber.orgJabber Component Protocolstpeter@jabber.orgRoster Item Exchangestpeter@jabber.orgJinglescottlu@google.comjbeda@google.comstpeter@jabber.orgrobert.mcqueen@collabora.co.ukseanegan@google.comjhildebr@cisco.comBlocking Commandstpeter@jabber.orgDelayed Deliverystpeter@jabber.orgServer Dialbackjer@jabber.orgstpeter@jabber.orgvCard4 Over XMPPstpeter@jabber.orgsamizzi@cisco.comExtensible Markup Language (XML) 1.0 (Fifth Edition)Based on consensus derived from working group discussion,
implementation and deployment experience, and formal interoperability
testing, the following substantive modifications were made from
RFC 6122.Changed domainpart preparation to use IDNA2008 (instead of
IDNA2003).Changed localpart preparation to use the UsernameCaseMapped
profile of the PRECIS IdentifierClass (instead of the Nodeprep
profile of stringprep).Changed resourcepart preparation to use the OpaqueString profile
of the PRECIS FreeformClass (instead of the Resourceprep profile of
stringprep).Specified that internationalized labels within domainparts must
be U-labels (instead of "should be" U-labels).Specified that fullwidth and halfwidth characters must be mapped
to their decomposition mappings (previously handled through the use
of Normalization Form KC).Specified the use of Unicode Normalization Form C (instead of
Unicode Normalization Form KC as specified in the Nodeprep and
Resourceprep profiles of stringprep).Specified that servers must enforce the address-formatting
rules.Thanks to Ben Campbell, Dave Cridland, Miguel Garcia, Joe Hildebrand,
Jonathan Lennox, Matt Miller, Florian Schmaus, Sam Whited, and Florian
Zeitz for their input during working group discussion.Dan Romascanu completed a helpful review on behalf of the General
Area Review Team.During IESG review, Alissa Cooper, Brian Haberman, and Barry Leiba
provided comments that led to improvements in the document.Thanks also to Matt Miller in his role as document shepherd, Joe
Hildebrand in his role as working group chair, and Ben Campbell in his
role as sponsoring Area Director.The author wishes to acknowledge Cisco Systems, Inc., for employing
him during his work on earlier draft versions of this document.