xmpp muc 群聊协议 4

7. Occupant Use Cases

The main actor in a multi-user chat environment is the occupant, who can be said to be located "in" a multi-user chat room and to participate in the discussions held in that room (for the purposes of this specification, participants and visitors are considered to be "mere" occupants, since they possess no administrative privileges). As will become clear, the protocol elements proposed in this document to fulfill the occupant use cases fall into three categories:

在群聊的环境里，每个人都称得上是一个occupant，所以occupant很重要，我们可以说他是“在”一个聊天室的，可以参与这个房间的讨论。

existing "groupchat 1.0" protocol for minimal functionality
straightforward applications of the "groupchat 1.0" protocol, for example to handle some of the errors related to new room types
additional protocol elements to handle functionality not covered by "groupchat 1.0" (room invites, room passwords, extended presence related to room roles and affiliations); these are qualified by the 'http://jabber.org/protocol/muc#user' namespace

Note: All client-generated examples herein are presented from the perspective of the service, with the result that all stanzas received by a service contain a 'from' attribute corresponding to the sender's full JID as added by a normal Jabber router or session manager. In addition, normal IQ result stanzas sent upon successful completion of a request (as required by RFC 3920 [10]) are not shown.

7.1 Entering a Room 进入一个房间

7.1.1 Groupchat 1.0 Protocol

In order to participate in the discussions held in a multi-user chat room, a Jabber user MUST first become an occupant by entering the room. In the old "groupchat 1.0" protocol, this was done by sending presence to <room@service/nick>, where "room" is the room ID, "service" is the hostname of the chat service, and "nick" is the user's desired nickname within the room:

为了参与一个房间的聊天，一个用户必须首先进入这个房间，成为一个occupant，我们用向roomjid : room@service/nikd 发送presence协议这种方式实现，这里的room是一个roomid，service是服务器的host，nick是用户希望在这个房间里显示的昵称。

一个用户请求进入一个房间

<presence
    from='hag66@shakespeare.lit/pda' jid
    to='darkcave@chat.shakespeare.lit/thirdwitch'/> roomjid

In this example, a user with a full JID of "hag66@shakespeare.lit/pda" has requested to enter the room "darkcave" on the "chat.shakespeare.lit" chat service with a room nickname of "thirdwitch".

在这个例子中，一个带有full jid 的用户 xx 已经请求进入在服务chat.shakespeare.lit 上的 darkcave这个房间，并希望有一个thirdwith这个昵称

If the user does not specify a room nickname, the service MUST return a <jid-malformed/> error:

如果这个用户没有指定昵称，服务器必须要返回error

Example 17. No Nickname Specified

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <error type='modify'>
    <jid-malformed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

7.1.2 Basic MUC Protocol

Compliant multi-user chat services MUST accept the foregoing as a request to enter a room from any Jabber client that knows either the "groupchat 1.0" (GC) protocol or the multi-user chat (MUC) protocol; however, MUC clients SHOULD signal their ability to speak the MUC protocol by including in the initial presence stanza an empty <x/> element qualified by the 'http://jabber.org/protocol/muc' namespace (note the absence of the '#user' fragment):

客户端要让服务器知道他们能够接受群聊服务，方法是加入一个x节，xmlns ='http://jabber.org/protocol/muc'/

Example 18. Jabber User Seeks to Enter a Room (Multi-User Chat)

<presence
    from='hag66@shakespeare.lit/pda' jid
    to='darkcave@chat.shakespeare.lit/thirdwitch'> roomjid
  <x xmlns='http://jabber.org/protocol/muc'/> 
</presence>

Note: If an error occurs in relation to joining a room, the service SHOULD include the MUC child element (i.e., <x xmlns='http://jabber.org/protocol/muc'/>) in the <presence/> stanza of type "error".

Before attempting to enter the room, a MUC-compliant client SHOULD first discover its reserved room nickname (if any) by following the protocol defined in the Discovering Reserved Room Nickname section of this document.

要对昵称进行检查

7.1.3 Presence Broadcast

presence 广播

If the service is able to add the user to the room, it MUST send presence from all the existing occupants' room JIDs to the new occupant's full JID, including extended presence information about roles in an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'role' attribute set to a value of "moderator", "participant", or "visitor", and with the 'affiliation' attribute set to a value of "owner", "admin", "member", or "none" as appropriate:

如果服务器允许这个用户进入房间的话，服务器必须发送 from=roomjids to=加入用户的jid 的presence协议，包含扩展的用来包含role的信息的presence协议的x节，在muc#user这个namespace里面，包含在item这个节内的role属性还有affiliation属性。

Example 19. Service Sends Presence from Existing Occupants to New Occupant

服务器

<presence
    from='darkcave@chat.shakespeare.lit/firstwitch' existing roomjid
    to='hag66@shakespeare.lit/pda'> new jid
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='owner' role='moderator'/>
  </x>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/secondwitch'
    to='hag66@shakespeare.lit/pda'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='admin' role='moderator'/>
  </x>
</presence>

In this example, the user from the previous example has entered the room, by which time two other people had already entered the room: a user with a room nickname of "firstwitch" (who is a room owner) and a user with a room nickname of "secondwitch" (who is a room admin).

在这个例子里面，用户从前一个例子已经进入了这个房间，这个房间里面已经有了两个人了，一个的昵称是firstwitch，是一个owner，另外一个的昵称是secondwitch，是一个房间管理员。

The service MUST also send presence from the new occupant's room JID to the full JIDs of all the occupants (including the new occupant):

服务端也必须发送一个presence协议，from=new roomjid to=existing full jid

Example 20. Service Sends New Occupant's Presence to All Occupants

服务器向所有在房间内部的人发送消息，通知新用户进来了。

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch' new roomjid
    to='crone1@shakespeare.lit/desktop'> existing jid
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
  </x>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='wiccarocks@shakespeare.lit/laptop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
  </x>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
    <status code='110'/>
  </x>
</presence>

In this example, initial room presence is being sent from the new occupant (thirdwitch) to all occupants, including the new occupant. As shown in the last stanza, the presence sent by the room to a user from itself as an occupant SHOULD include a status code of 110 so that the user knows this presence refers to itself as an occupant.

在这个例子里面，开始，presence 已经发送给了所有的occupants，包括这个新用户自己，而且是在最后一个presence 节，一个presence从一个roomjid 发送给一个jid，这两个是相同的用户，应该包含110这个状态码，让客户端知道，这个presence让他自己知道，这个presence是来自作为occupant的他自己的。

The service MAY rewrite the new occupant's roomnick (e.g., if roomnicks are locked down). If the service does not accept the new occupant's requested roomnick but instead assigns a new roomnick, it MUST include a status code of "210" in the presence broadcast that it sends to the new occupant.

服务端或许要记录下这个occupant的昵称，如果服务器不接受这个occupant的昵称，要自己重新给一个昵称的话，一定要包含一个210的状态码。（这个也是发给自己的）

Example 21. Service Sends New Occupant's Presence to New Occupant

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
    <status code='110'/>
    <status code='210'/>
  </x>
</presence>

Note: The order of the presence stanzas sent to the new occupant is important. The service MUST first send the complete list of the existing occupants to the new occupant and only then send the new occupant's own presence to the new occupant. This helps the client know when it has received the complete "room roster".

注意：这个presence协议的发送顺序是需要注意的，很重要，首先服务器必须完成existing 到 new 的通知，然后发送new到new的通知，这样可以帮助客户端知道什么时候他收完了房间列表。

After sending the presence broadcast (and only after doing so), the service may then send discussion history, live messages, presence updates, and other in-room traffic.

在发完presence广播以后，服务端或许会发送聊天记录，

7.1.4 Default Roles

默认的role

The following table summarizes the initial default roles that a service should set based on the user's affiliation (there is no role associated with the "outcast" affiliation, since such users are not allowed to enter the room).

下面的表格说明了，根据用户的affiliation来set用户的role的默认的规则

Table 7: Initial Role Based on Affiliation

Room Type	None	Member	Admin	Owner
Moderated	Visitor	Participant	Moderator	Moderator
Unmoderated	Participant	Participant	Moderator	Moderator
Members-Only	N/A *	Participant	Moderator	Moderator
Open	Participant	Participant	Moderator	Moderator

* Entry is not permitted.

7.1.5 Non-Anonymous Rooms

If the room is non-anonymous, the service MUST send the new occupant's full JID to all occupants using extended presence information in an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with a 'jid' attribute specifying the occupant's full JID:

如果一个房间是一个不匿名的房间，服务器必须发送新进来的用户的fulljid 给所有的existing occupant。在item里面加入一个jid的属性

Example 22. Service Sends Full JID to All Occupants

服务器发送全jid给所有的occupant

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch' new roomjid
    to='crone1@shakespeare.lit/desktop'> existing jid
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='none'
          jid='hag66@shakespeare.lit/pda'
          role='participant'/>
  </x>
</presence>

[ ... ]

If the user is entering a room that is non-anonymous (i.e., which informs all occupants of each occupant's full JID as shown above), the service SHOULD allow the user to enter the room but MUST also warn the user that the room is not anonymous. This SHOULD be done by including a status code of "100" in the initial presence that the room sends to the new occupant:

如果这个用户进入的是一个非匿名的房间，服务器必须要告诉他，他进入的是一个非匿名的房间。可以包含一个100的status code，可以在自己通知自己的时候包含进去

Example 23. Service Sends New Occupant's Presence to New Occupant

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
    <status code='100'/> 非匿名的
    <status code='110'/> 作为结束收roster的标志
    <status code='210'/> 服务器可以改变他的昵称，改变了这个用户的昵称
  </x>
</presence>

However, it MAY be done by sending a message of type "groupchat" to the new occupant containing an <x/> child with a <status/> element that has the 'code' attribute set to a value of "100":

也可以发送一个message消息，在x节里面包含status节，并设置code属性，表明100码

Example 24. Service Warns New Occupant About Lack of Anonymity

<message
    from='darkcave@chat.shakespeare.lit' roomid
    to='hag66@shakespeare.lit/pda' new jid
    type='groupchat'>
  <body>This room is not anonymous.</body>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <status code='100'/>
  </x>
</message>

The inclusion of the status code assists clients in presenting their own notification messages (e.g., information appropriate to the user's locality).

7.1.6 Semi-Anonymous Rooms

If the room is semi-anonymous, the service MUST send presence from the new occupant to all occupants as specified above, but MUST include the new occupant's full JID only in the presence notifications it sends to occupants with a role of "moderator" and not to non-moderator occupants.

如果是半匿名的房间，新进来的用户只发送给moderator，不发送给非moderator的用户

(Note: All subsequent examples include the 'jid' attribute for each <item/> element, even though this information is not sent to non-moderators in semi-anonymous rooms.)

7.1.7 Password-Protected Rooms

If the room requires a password and the user did not supply one (or the password provided is incorrect), the service MUST deny access to the room and inform the user that they are unauthorized; this is done by returning a presence stanza of type "error" specifying a <not-authorized/> error:

如果这个用户没有输入正确的密码，服务器应该通知他。

Example 25. Service Denies Access Because No Password Provided

<presence
    from='darkcave@chat.shakespeare.lit' roomid
    to='hag66@shakespeare.lit/pda' new jid
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='auth'>
    <not-authorized xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

Passwords SHOULD be supplied with the presence stanza sent when entering the room, contained within an <x/> element qualified by the 'http://jabber.org/protocol/muc' namespace and containing a <password/> child. Passwords are to be sent as cleartext; no other authentication methods are supported at this time, and any such authentication or authorization methods shall be defined in a separate specification (see the Security Considerations section of this document).

密码应该发送在protocol/muc这个xmlns下，并且在password节里面用明码发送。

Example 26. User Provides Password On Entering a Room

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/thirdwitch'>
  <x xmlns='http://jabber.org/protocol/muc'>
    <password>cauldronburn</password>
  </x>
</presence>

7.1.8 Members-Only Rooms

If the room is members-only but the user is not on the member list, the service MUST deny access to the room and inform the user that they are not allowed to enter the room; this is done by returning a presence stanza of type "error" specifying a <registration-required/> error condition:

在member-only房间里，如果这个新进入的用户，服务器必须驳回，然后通知用户这个房间不允许其进入。包含一个registration-required的error节

Example 27. Service Denies Access Because User Is Not on Member List

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='auth'>
    <registration-required xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

7.1.9 Banned Users

If the user has been banned from the room (i.e., has an affiliation of "outcast"), the service MUST deny access to the room and inform the user of the fact that he or she is banned; this is done by returning a presence stanza of type "error" specifying a <forbidden/> error condition:

如果一个用户已经被驱逐了，被放入了黑名单，那么，服务不应该让他进入这个房间，返回一个

Example 28. Service Denies Access Because User is Banned

<presence
    from='darkcave@chat.shakespeare.lit' roomid
    to='hag66@shakespeare.lit/pda' newjid
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='auth'>
    <forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

7.1.10 Nickname Conflict

If the room already contains another user with the nickname desired by the user seeking to enter the room (or if the nickname is reserved by another user on the member list), the service MUST deny access to the room and inform the user of the conflict; this is done by returning a presence stanza of type "error" specifying a <conflict/> error condition:

如果这个房间已经存在一个其他的用户，和这个用户的昵称相同的话，或者已经和其他用户的保留的昵称相同，服务器不应该允许他进入房间，应该返回conflict

Example 29. Service Denies Access Because of Nick Conflict

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='cancel'>
    <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

However, if the bare JID <localpart@domain.tld> of the present occupant matches the bare JID of the user seeking to enter the room, then the service SHOULD allow entry to the user, so that the user has two (or more) in-room "sessions" with the same roomnick, one for each resource. If a service allows more than one occupant with the same bare JID and the same room nickname, it SHOULD route in-room messages to all of the user's resources and allow all of the user's resources to send messages to the room; it is up to the implementation to determine how to appropriately handle presence from the user's resources and how to route private messages to all or only one resource (based on presence priority or some other algorithm).

但是，如果这个userid和自己冲突了，如果服务器允许多副本，应该允许其进入，并处理相应的信息。

How nickname conflicts are determined is up to the implementation (e.g., whether the service applies a case folding routine, a stringprep profile such as Resourceprep or Nodeprep, etc.).

7.1.11 Max Users

If the room has reached its maximum number of occupants, the service SHOULD deny access to the room and inform the user of the restriction; this is done by returning a presence stanza of type "error" specifying a <service-unavailable/> error condition:

如果这个房间已经进入了上线用户。服务器应该不允许其进入，返回一个error，包含一个service-unavailable节

Example 30. Service Informs User that Room Occupant Limit Has Been Reached

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='wait'>
    <service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

Alternatively, the room could kick an "idle user" in order to free up space.

If the room has reached its maximum number of occupants and a room admin or owner attempts to join, the room SHOULD allow the admin or owner to join, up to some reasonable number of additional occupants, which number MAY be configurable.

7.1.12 Locked Room

If a user attempts to enter a room while it is "locked" (i.e., before the room creator provides an initial configuration and therefore before the room officially exists), the service MUST refuse entry and return an <item-not-found/> error to the user:

在一个房间没有被完全创建之前，也就是一个被锁住的房间，这个房间的主人没有设置完这个房间的配置，服务器不应该让其进入，返回一个item-not-found错误节

Example 31. Service Denies Access Because Room Does Not Exist

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='cancel'>
    <item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

7.1.13 Nonexistent Room

If the room does not already exist when the user seeks to enter it, the service SHOULD create it; however, this is not required, since an implementation or deployment MAY choose to restrict the privilege of creating rooms. For details, see the Creating a Room section of this document.

7.1.14 Room Logging

If the user is entering a room in which the discussions are logged to a public archive (often accessible via HTTP), the service SHOULD allow the user to enter the room but MUST also warn the user that the discussions are logged. This SHOULD be done by including a status code of "170" in the initial presence that the room sends to the new occupant:

如果这个房间的聊天记录是被记录的，应该发170提醒用户

Example 32. Service Sends New Occupant's Presence to New Occupant

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
    <status code='100'/>
    <status code='110'/>
    <status code='170'/>
    <status code='210'/>
  </x>
</presence>

7.1.15 Discussion History

After sending initial presence as shown above, a room MAY send discussion history to the new occupant. (The room MUST NOT send any discussion history before it finishes sending room presence as specified in the Presence Broadcast section of this document.) Whether such history is sent, and how many messages comprise the history, shall be determined by the chat service implementation or specific deployment.

在发送完毕presence后，服务器可以选择发送聊天记录给这个新用户。一定要在发送完了所有的presence之后。但是聊天记录是否发送，发送多少由服务器决定

Example 33. Delivery of Discussion History

<message
    from='darkcave@chat.shakespeare.lit/firstwitch'
    to='hecate@shakespeare.lit/broom'
    type='groupchat'>
  <body>Thrice the brinded cat hath mew'd.</body>
  <delay xmlns='urn:xmpp:delay'
     from='crone1@shakespeare.lit/desktop'
     stamp='2002-10-13T23:58:37Z'/>
</message>

<message
    from='darkcave@chat.shakespeare.lit/secondwitch'
    to='hecate@shakespeare.lit/broom'
    type='groupchat'>
  <body>Thrice and once the hedge-pig whined.</body>
  <delay xmlns='urn:xmpp:delay'
     from='wiccarocks@shakespeare.lit/laptop'
     stamp='2002-10-13T23:58:43Z'/>
</message>

<message
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hecate@shakespeare.lit/broom'
    type='groupchat'>
  <body>Harpier cries 'Tis time, 'tis time.</body>
  <delay xmlns='urn:xmpp:delay'
     from='hag66@shakespeare.lit/pda'
     stamp='2002-10-13T23:58:49Z'/>
</message>

Discussion history messages MUST be stamped with Delayed Delivery [11] information qualified by the 'urn:xmpp:delay' namespace to indicate that they are sent with delayed delivery and to specify the times at which they were originally sent. (Note: The 'urn:xmpp:delay' namespace defined in XEP-0203 supersedes the older 'jabber:x:delay' namespace defined in Legacy Delayed Delivery [12]; until the status of XEP-0091 is changed to Obsolete, implementations SHOULD include both datetime formats.) The 'from' attribute SHOULD be the full JID of the original sender in non-anonymous rooms, but MUST NOT be in semi-anonymous rooms (where the 'from' attribute SHOULD be set to the JID of the room itself). The service SHOULD send all discussion history messages before delivering any "live" messages sent after the user enters the room.

7.1.16 Managing Discussion History

A user MAY want to manage the amount of discussion history provided on entering a room (perhaps because the user is on a low-bandwidth connection or is using a small-footprint client). This MUST be accomplished by including a <history/> child in the initial presence stanza sent when joining the room. There are four allowable attributes for this element:

Table 8: History Management Attributes

Attribute	Datatype	Meaning
maxchars	int	Limit the total number of characters in the history to "X" (where the character count is the characters of the complete XML stanzas, not only their XML character data).
maxstanzas	int	Limit the total number of messages in the history to "X".
seconds	int	Send only the messages received in the last "X" seconds.
since	dateTime	Send only the messages received since the datetime specified (which MUST conform to the DateTime profile specified in XMPP Date and Time Profiles [13]).

The service MUST send the smallest amount of traffic that meets any combination of the above criteria, taking into account service-level and room-level defaults. The service MUST send complete message stanzas only (i.e., it MUST not literally truncate the history at a certain number of characters, but MUST send the largest number of complete stanzas that results in a number of characters less than or equal to the 'maxchars' value specified). If the client wishes to receive no history, it MUST set the 'maxchars' attribute to a value of "0" (zero).

The following examples illustrate the use of this protocol.

Example 34. User Requests Limit on Number of Messages in History

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/thirdwitch'>
  <x xmlns='http://jabber.org/protocol/muc'>
    <history maxstanzas='20'/>
  </x>
</presence>

Example 35. User Requests History in Last 3 Minutes

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/thirdwitch'>
  <x xmlns='http://jabber.org/protocol/muc'>
    <history seconds='180'/>
  </x>
</presence>

Example 36. User Requests All History Since the Beginning of the Unix Era

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/thirdwitch'>
  <x xmlns='http://jabber.org/protocol/muc'>
    <history since='1970-01-01T00:00:00Z'/>
  </x>
</presence>

Obviously the service SHOULD NOT return all messages sent in the room since the beginning of the Unix era, and SHOULD appropriately limit the amount of history sent to the user based on service or room defaults.

Example 37. User Requests No History

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/thirdwitch'>
  <x xmlns='http://jabber.org/protocol/muc'>
    <history maxchars='0'/>
  </x>
</presence>

7.2 Exiting a Room

In order to exit a multi-user chat room, an occupant sends a presence stanza of type "unavailable" to the <room@service/nick> it is currently using in the room.

Example 38. Occupant Exits a Room

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/thirdwitch'
    type='unavailable'/>

The service MUST then send presence stanzas of type "unavailable" from the departing occupant's room JID to the full JIDs of the departing occupant and of the remaining occupants:

Example 39. Service Sends Presence Related to Departure of Occupant

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'
    type='unavailable'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='none'/>
    <status code='110'/>
  </x>
</presence>
<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='crone1@shakespeare.lit/desktop'
    type='unavailable'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='none'/>
  </x>
</presence>
<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='wiccarocks@shakespeare.lit/laptop'
    type='unavailable'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='none'/>
  </x>
</presence>

Presence stanzas of type "unavailable" reflected by the room MUST contain extended presence information about roles and affiliations; the 'role' attribute SHOULD be set to a value of "none" to denote that the individual is no longer an occupant.

The occupant MAY include normal <status/> information in the unavailable presence stanzas; this enables the occupant to provide a custom exit message if desired:

Example 40. Custom Exit Message

<presence
    from='wiccarocks@shakespeare.lit/laptop'
    to='darkcave@chat.shakespeare.lit/oldhag'
    type='unavailable'>
  <status>gone where the goblins go</status>
</presence>

Normal presence stanza generation rules apply as defined in XMPP IM [14], so that if the user sends a general unavailable presence stanza, the user's server will broadcast that stanza to the <room@service/nick> to which the user's client has sent directed presence.

It is possible that a user may not be able to gracefully exit the room by sending unavailable presence directly to the room. If the user goes offline without sending unavailable presence, the user's server is responsible for sending unavailable presence on behalf of the user (in accordance with RFC 3921). If the user's server goes offline or connectivity is lost between the user's server and the MUC service to which the user is connected (e.g., in federated communications), the MUC service is responsible for monitoring error stanzas it receives in order to determine if the user has gone offline. If the MUC service determines that the user has gone offline, it must treat the user as if the user had itself sent unavailable presence.

Note: If the room is not persistent and this occupant is the last to exit, the service is responsible for destroying the room.

7.3 Changing Nickname

A common feature of multi-user chat rooms is the ability for an occupant to change his or her nickname within the room. In MUC this is done by sending updated presence information to the room, specifically by sending presence to a new room JID in the same room (changing only the resource identifier in the room JID).

Example 41. Occupant Changes Nickname

<presence
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit/oldhag'/>

The service then sends two presence stanzas to the full JID of each occupant (including the occupant who is changing his or her room nickname), one of type "unavailable" for the old nickname and one indicating availability for the new nickname.

The unavailable presence MUST contain the following as extended presence information in an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace:

The new nickname (in this case, nick='oldhag')
A status code of 303

This enables the recipients to correlate the old roomnick with the new roomnick.

Example 42. Service Updates Nick

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='crone1@shakespeare.lit/desktop'
    type='unavailable'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          nick='oldhag'
          role='participant'/>
    <status code='303'/>
  </x>
</presence>
<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='wiccarocks@shakespeare.lit/laptop'
    type='unavailable'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          nick='oldhag'
          role='participant'/>
    <status code='303'/>
  </x>
</presence>
<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'
    type='unavailable'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          nick='oldhag'
          role='participant'/>
    <status code='303'/>
    <status code='110'/>
  </x>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/oldhag'
    to='crone1@shakespeare.lit/desktop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          role='participant'/>
  </x>
</presence>
<presence
    from='darkcave@chat.shakespeare.lit/oldhag'
    to='wiccarocks@shakespeare.lit/laptop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          role='participant'/>
  </x>
</presence>
<presence
    from='darkcave@chat.shakespeare.lit/oldhag'
    to='hag66@shakespeare.lit/pda'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          role='participant'/>
    <status code='110'/>
  </x>
</presence>

If the user attempts to change his or her room nickname to a room nickname that is already in use by another user (or that is reserved by another user affiliated with the room, e.g., a member or owner), the service MUST deny the nickname change request and inform the user of the conflict; this is done by returning a presence stanza of type "error" specifying a <conflict/> error condition:

Example 43. Service Denies Nickname Change Because of Nick Conflict

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='cancel'>
    <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

However, if the bare JID <localpart@domain.tld> of the present occupant matches the bare JID of the user seeking to change his or her nickname, then the service MAY allow the nickname change. See the Nickname Conflict section of this document for details.

If the user attempts to change his or her room nickname but room nicknames are "locked down", the service MUST deny the nickname change request and return a presence stanza of type "error" specifying a <not-acceptable/> error condition:

Example 44. Service Denies Nickname Change Because Roomnicks Are Locked Down

<presence
    from='darkcave@chat.shakespeare.lit'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <x xmlns='http://jabber.org/protocol/muc'/>
  <error type='cancel'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</presence>

The user SHOULD then discover its reserved nickname as specified in the Discovering Reserved Room Nickname section of this document.

7.4 Changing Availability Status

In multi-user chat systems such as IRC, one common use for changing one's room nickname is to indicate a change in one's availability (e.g., changing one's room nickname to "thirdwitch|away"). In Jabber, availability is of course noted by a change in presence (specifically the <show/> and <status/> elements), which can provide important context within a chatroom. An occupant changes availability status within the room by sending the updated presence to its <room@service/nick>.

Example 45. Occupant Changes Availability Status

<presence
    from='wiccarocks@shakespeare.lit/laptop'
    to='darkcave@chat.shakespeare.lit/oldhag'>
  <show>xa</show>
  <status>gone where the goblins go</status>
</presence>

The service then sends a presence stanza from the occupant changing his or her presence to the full JID of each occupant, including extended presence information about the occupant's role and full JID to those with privileges to view such information:

Example 46. Service Passes Along Changed Presence to All Occupants

<presence
    from='darkcave@chat.shakespeare.lit/secondwitch'
    to='crone1@shakespeare.lit/desktop'>
  <show>xa</show>
  <status>gone where the goblins go</status>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='admin'
          jid='wiccarocks@shakespeare.lit/laptop'
          role='moderator'/>
  </x>
</presence>

[ ... ]

7.5 Inviting Another User to a Room

7.5.1 Direct Invitation

A method for sending a direct invitation (not mediated by the room itself) is defined in Direct MUC Invitations [15]. Sending the invitation directly can help to work around communications blocking on the part of the invitee (which might refuse communication with entities not in its roster).

7.5.2 Mediated Invitation

It can be useful to invite another user to a room in which one is an occupant. To do this, a MUC client MUST send XML of the following form to the <room@service> itself (the reason is OPTIONAL and the message MUST be explicitly or implicitly of type "normal"):

Example 47. Occupant Sends an Invitation by Way of Room

<message
    from='crone1@shakespeare.lit/desktop'
    to='darkcave@chat.shakespeare.lit'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <invite to='hecate@shakespeare.lit'>
      <reason>
        Hey Hecate, this is the place for all good witches!
      </reason>
    </invite>
  </x>
</message>

The <room@service> itself MUST then add a 'from' address to the <invite/> element whose value is the bare JID, full JID, or room JID of the invitor and send the invitation to the invitee specified in the 'to' address (the service MAY include a message body explaining the invitation or containing the reason, for the sake of older clients; in addition, the room SHOULD add the password if the room is password-protected):

Example 48. Room Sends Invitation to Invitee on Behalf of Invitor

<message
    from='darkcave@chat.shakespeare.lit'
    to='hecate@shakespeare.lit'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <invite from='crone1@shakespeare.lit/desktop'>
      <reason>
        Hey Hecate, this is the place for all good witches!
      </reason>
    </invite>
    <password>cauldronburn</password>
  </x>
</message>

If the room is members-only, the service MAY also add the invitee to the member list. (Note: Invitation privileges in members-only rooms SHOULD be restricted to room admins; if a member without privileges to edit the member list attempts to invite another user, the service SHOULD return a <forbidden/> error to the occupant; for details, see theModifying the Member List section of this document.)

If the invitor supplies a non-existent JID, the room SHOULD return an <item-not-found/> error to the invitor.

The invitee MAY choose to formally decline (as opposed to ignore) the invitation; and this is something that the sender may want to be informed about. In order to decline the invitation, the invitee MUST send a message of the following form to the <room@service> itself:

Example 49. Invitee Declines Invitation

<message
    from='hecate@shakespeare.lit/broom'
    to='darkcave@chat.shakespeare.lit'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <decline to='crone1@shakespeare.lit'>
      <reason>
        Sorry, I'm too busy right now.
      </reason>
    </decline>
  </x>
</message>

Example 50. Room Informs Invitor that Invitation Was Declined

<message
    from='darkcave@chat.shakespeare.lit'
    to='crone1@shakespeare.lit/desktop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <decline from='hecate@shakespeare.lit'>
      <reason>
        Sorry, I'm too busy right now.
      </reason>
    </decline>
  </x>
</message>

It may be wondered why the invitee does not send the decline message directly to the invitor. The main reason is that certain implementations MAY choose to base invitations on room JIDs rather than bare JIDs (so that, for example, an occupant could invite someone from one room to another without knowing that person's bare JID). Thus the service MUST handle both the invites and declines.

7.6 Converting a One-to-One Chat Into a Multi-User Conference

Sometimes it is desirable to convert a one-to-one chat into a multi-user conference. The process flow is shown in the following examples.

First, two users begin a one-to-one chat.

Example 51. A One-to-One Chat

<message
    from='crone1@shakespeare.lit/desktop'
    to='wiccarocks@shakespeare.lit/laptop'
    type='chat'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>Thrice the brinded cat hath mew'd.</body>
</message>

<message
    from='wiccarocks@shakespeare.lit/laptop'
    to='crone1@shakespeare.lit/desktop'
    type='chat'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>Thrice and once the hedge-pig whined.</body>
</message>

Now the first person decides to include a third person in the discussion, so she (or, more precisely, her client) does the following:

Creates a new multi-user chatroom
Optionally sends history of the one-to-one chat to the room
Sends an invitation to the second person and the third person, including a <continue/> element (optionally including a 'thread' attribute).

Note: The new room SHOULD be non-anonymous, MAY be an instant room as specified in the Creating an Instant Room section of this document, and MAY have a unique room name received from the service as specified in the Requesting a Unique Room Name section of this document.

Note: If the one-to-one chat messages included a <thread/> element, the person who creates the room SHOULD include the ThreadID with the history messages, specify the ThreadID in the invitations as the value of the <continue/> element's 'thread' attribute, and include the ThreadID in any new messages sent to the room. Use of ThreadIDs is RECOMMENDED because it helps to provide continuity between the one-to-one chat and the multi-user chat.

Example 52. Continuing the Discussion I: User Creates Room

<presence
    from='crone1@shakespeare.lit/desktop'
    to='darkcave@chat.shakespeare.lit/firstwitch'>
  <x xmlns='http://jabber.org/protocol/muc'/>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/firstwitch'
    to='crone1@shakespeare.lit/desktop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='owner' role='moderator'/>
    <status code='110'/>
  </x>
</presence>

Example 53. Continuing the Discussion II: Owner Sends History to Room

<message
    from='crone1@shakespeare.lit/desktop'
    to='darkcave@chat.shakespeare.lit'
    type='groupchat'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>Thrice the brinded cat hath mew'd.</body>
  <delay xmlns='urn:xmpp:delay'
     from='crone1@shakespeare.lit/desktop'
     stamp='2004-09-29T01:54:37Z'/>
</message>

<message
    from='crone1@shakespeare.lit/desktop'
    to='darkcave@chat.shakespeare.lit'
    type='groupchat'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>Thrice and once the hedge-pig whined.</body>
  <delay xmlns='urn:xmpp:delay'
     from='wiccarocks@shakespeare.lit/laptop'
     stamp='2004-09-29T01:55:21Z'/>
</message>

Note: Use of the Delayed Delivery protocol enables the room creator to specify the datetime of each message from the one-to-one chat history (via the 'stamp' attribute), as well as the JID of the original sender of each message (via the 'from' attribute). The room creator SHOULD send the complete one-to-one chat history before inviting additional users to the room, and SHOULD also send as history any messages appearing in the one-to-one chat interface after joining the room and before the second person joins the room; if the one-to-one history is especially large, the sending client may want to send the history over a few seconds rather than all at once (to avoid triggering rate limits). The service SHOULD NOT add its own delay elements (as described in the Discussion History section of this document) to prior chat history messages received from the room owner.

Example 54. Continuing the Discussion III: Owner Sends Invitations, Including Continue Flag

<message
    from='crone1@shakespeare.lit/desktop'
    to='darkcave@chat.shakespeare.lit'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <invite to='wiccarocks@shakespeare.lit/laptop'>
      <reason>This coven needs both wiccarocks and hag66.</reason>
      <continue thread='e0ffe42b28561960c6b12b944a092794b9683a38'/>
    </invite>
    <invite to='hag66@shakespeare.lit'>
      <reason>This coven needs both wiccarocks and hag66.</reason>
      <continue thread='e0ffe42b28561960c6b12b944a092794b9683a38'/>
    </invite>
  </x>
</message>

Note: Since the invitor's client knows the full JID of the person with whom the invitor was having a one-to-one chat, it SHOULD include the full JID (rather than the bare JID) in the invitation.

The invitations are delivered to the invitees:

Example 55. Invitations Delivered

<message
    from='darkcave@chat.shakespeare.lit'>
    to='wiccarocks@shakespeare.lit/laptop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <invite from='crone1@shakespeare.lit'>
      <reason>This coven needs both wiccarocks and hag66.</reason>
      <continue thread='e0ffe42b28561960c6b12b944a092794b9683a38'/>
    </invite>
  </x>
</message>

<message
    from='darkcave@chat.shakespeare.lit'>
    to='hag66@shakespeare.lit'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <invite from='crone1@shakespeare.lit'>
      <reason>This coven needs both wiccarocks and hag66.</reason>
      <continue thread='e0ffe42b28561960c6b12b944a092794b9683a38'/>
    </invite>
  </x>
</message>

When the client being used by <wiccarocks@shakespeare.lit/laptop> receives the invitation, it SHOULD auto-join the room or prompt the user whether to join (subject to user preferences) and then seamlessly convert the existing one-to-one chat window into a multi-user conferencing window:

Example 56. Invitee Accepts Invitation, Joins Room, and Receives Presence and History

<presence
    from='wiccarocks@shakespeare.lit/laptop'
    to='darkcave@chat.shakespeare.lit/secondwitch'>
  <x xmlns='http://jabber.org/protocol/muc'/>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/firstwitch'
    to='wiccarocks@shakespeare.lit/laptop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='owner' role='moderator'/>
  </x>
</presence>

<presence
    from='darkcave@chat.shakespeare.lit/secondwitch'
    to='wiccarocks@shakespeare.lit/laptop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member' role='participant'/>
  </x>
</presence>

<message
    from='darkcave@chat.shakespeare.lit'
    to='wiccarocks@shakespeare.lit/laptop'
    type='groupchat'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>Thrice the brinded cat hath mew'd.</body>
  <delay xmlns='urn:xmpp:delay'
     from='crone1@shakespeare.lit/desktop'
     stamp='2004-09-29T01:54:37Z'/>
</message>

<message
    from='darkcave@chat.shakespeare.lit'
    to='wiccarocks@shakespeare.lit/laptop'
    type='groupchat'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>Thrice and once the hedge-pig whined.</body>
  <delay xmlns='urn:xmpp:delay'
     from='wiccarocks@shakespeare.lit/laptop'
     stamp='2004-09-29T01:55:21Z'/>
</message>

Note: The fact that the messages come from the <room@service> itself rather than <room@service/nick> is a clue to the receiving client that these messages are prior chat history, since any message from a room occupant will have a 'from' address equal to the sender's room JID.

7.7 Occupant Modification of the Room Subject

If allowed in accordance with room configuration, a mere occupant MAY be allowed to change the subject in a room. For details, see the Modifying the Room Subject section of this document.

7.8 Sending a Private Message

Since each occupant has a unique room JID, an occupant MAY send a "private message" to a selected occupant via the service by sending a message to the occupant's room JID. The message type SHOULD be "chat" and MUST NOT be "groupchat", but MAY be left unspecified (i.e., a normal message). This privilege SHOULD be allowed to any occupant (even a visitor in a moderated room).

Example 57. Occupant Sends Private Message

<message
    from='wiccarocks@shakespeare.lit/laptop'
    to='darkcave@chat.shakespeare.lit/firstwitch'
    type='chat'>
  <body>I'll give thee a wind.</body>
</message>

The service is responsible for changing the 'from' address to the sender's room JID and delivering the message to the intended recipient's full JID.

Example 58. Recipient Receives the Private Message

<message
    from='darkcave@chat.shakespeare.lit/secondwitch'
    to='crone1@shakespeare.lit/desktop'
    type='chat'>
  <body>I'll give thee a wind.</body>
</message>

If the sender attempts to send a private message of type "groupchat" to a particular occupant, the service MUST refuse to deliver the message (since the recipient's client would expect in-room messages to be of type "groupchat") and return a <bad-request/> error to the sender:

Example 59. Occupant Attempts to Send a Message of Type "Groupchat" to a Particular Occupant

<message
    from='wiccarocks@shakespeare.lit/laptop'
    to='darkcave@chat.shakespeare.lit/firstwitch'
    type='groupchat'>
  <body>I'll give thee a wind.</body>
</message>

<message
    from='darkcave@chat.shakespeare.lit'
    to='wiccarocks@shakespeare.lit/laptop'
    type='error'>
  <body>I'll give thee a wind.</body>
  <error type='modify'>
    <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</message>

If the sender attempts to send a private message to a room JID that does not exist, the service MUST return an <item-not-found/> error to the sender.

If the sender is not an occupant of the room in which the intended recipient is visiting, the service MUST return a <not-acceptable/> error to the sender.

7.9 Sending a Message to All Occupants

An occupant sends a message to all other occupants in the room by sending a message of type "groupchat" to the <room@service> itself (a service MAY ignore or reject messages that do not have a type of "groupchat"). In a moderated room, this privilege is restricted to occupants with a role of participant or higher.

Example 60. Occupant Sends a Message to All Occupants

<message
    from='hag66@shakespeare.lit/pda'
    to='darkcave@chat.shakespeare.lit'
    type='groupchat'>
  <body>Harpier cries: 'tis time, 'tis time.</body>
</message>

If the sender has voice in the room (this is the default except in moderated rooms), the service MUST change the 'from' attribute to the sender's room JID and reflect the message out to the full JID of each occupant.

Example 61. Service Reflects Message to All Occupants

<message
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='crone1@shakespeare.lit/desktop'
    type='groupchat'>
  <body>Harpier cries: 'tis time, 'tis time.</body>
</message>
<message
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='wiccarocks@shakespeare.lit/laptop'
    type='groupchat'>
  <body>Harpier cries: 'tis time, 'tis time.</body>
</message>
<message
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='hag66@shakespeare.lit/pda'
    type='groupchat'>
  <body>Harpier cries: 'tis time, 'tis time.</body>
</message>

If the sender is a visitor (i.e., does not have voice in a moderated room), the service MAY return a <forbidden/> error to the sender and MUST NOT reflect the message to all occupants. If the sender is not an occupant of the room, the service SHOULD return a <not-acceptable/> error to the sender and SHOULD NOT reflect the message to all occupants; the only exception to this rule is that an implementation MAY allow users with certain privileges (e.g., a room owner, room admin, or service-level admin) to send messages to the room even if those users are not occupants.

7.10 Registering with a Room

An implementation MAY allow an unaffiliated user (in a moderated room, normally a participant) to register with a room and thus become a member of the room (conversely, an implementation MAY restrict this privilege and allow only room admins to add new members). In particular, it is not possible to join a members-only room without being on the member list, so an entity may need to request membership in order to join such a room.

If allowed, this functionality SHOULD be implemented by enabling a user to send a request for registration requirements to the room qualified by the 'jabber:iq:register' namespace as described in In-Band Registration [16]:

Example 62. User Requests Registration Requirements

<iq from='hag66@shakespeare.lit/pda'
    id='reg1'
    to='darkcave@chat.shakespeare.lit'
    type='get'>
  <query xmlns='jabber:iq:register'/>
</iq>

If the user requesting registration requirements is not allowed to register with the room (e.g., because that privilege has been restricted), the room MUST return a <not-allowed/> error to the user. If the user is already registered, the room MUST reply with an IQ stanza of type "result" that contains an empty <register/> element as described in XEP-0077. If the room does not exist, the service MUST return an <item-not-found/> error.

Otherwise, the room MUST then return a Data Form to the user (as described in Data Forms [17]). The information required to register MAY vary by implementation or deployment and is not fully specified in this document (e.g., the fields registered by this document for the 'http://jabber.org/protocol/muc#register' FORM_TYPE may be supplemented in the future via the mechanisms described in the Field Standardization section of this document). The following can be taken as a fairly typical example:

Example 63. Service Returns Registration Form

<iq from='darkcave@chat.shakespeare.lit'
    id='reg1'
    to='hag66@shakespeare.lit/pda'
    type='result'>
  <query xmlns='jabber:iq:register'>
    <instructions>
      To register on the web, visit http://shakespeare.lit/
    </instructions>
    <x xmlns='jabber:x:data' type='form'>
      <title>Dark Cave Registration</title>
      <instructions>
        Please provide the following information
        to register with this room.
      </instructions>
      <field
          type='hidden'
          var='FORM_TYPE'>
        <value>http://jabber.org/protocol/muc#register</value>
      </field>
      <field
          label='Given Name'
          type='text-single'
          var='muc#register_first'>
        <required/>
      </field>
      <field
          label='Family Name'
          type='text-single'
          var='muc#register_last'>
        <required/>
      </field>
      <field
          label='Desired Nickname'
          type='text-single'
          var='muc#register_roomnick'>
        <required/>
      </field>
      <field
          label='Your URL'
          type='text-single'
          var='muc#register_url'/>
      <field
          label='Email Address'
          type='text-single'
          var='muc#register_email'/>
      <field
          label='FAQ Entry'
          type='text-multi'
          var='muc#register_faqentry'/>
    </x>
  </query>
</iq>

The user SHOULD then submit the form:

Example 64. User Submits Registration Form

<iq from='hag66@shakespeare.lit/pda'
    id='reg2'
    to='darkcave@chat.shakespeare.lit'
    type='set'>
  <query xmlns='jabber:iq:register'>
    <x xmlns='jabber:x:data' type='submit'>
      <field var='FORM_TYPE'>
        <value>http://jabber.org/protocol/muc#register</value>
      </field>
      <field var='muc#register_first'>
        <value>Brunhilde</value>
      </field>
      <field var='muc#register_last'>
        <value>Entwhistle-Throckmorton</value>
      </field>
      <field var='muc#register_roomnick'>
        <value>thirdwitch</value>
      </field>
      <field var='muc#register_url'>
        <value>http://witchesonline/~hag66/</value>
      </field>
      <field var='muc#register_email'>
        <value>hag66@witchesonline</value>
      </field>
      <field var='muc#register_faqentry'>
        <value>Just another witch.</value>
      </field>
    </x>
  </query>
</iq>

If the desired room nickname is already reserved for that room, the room MUST return a <conflict/> error to the user:

Example 65. Room Returns Conflict Error to User

<iq from='darkcave@chat.shakespeare.lit'
    id='reg2'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <error type='cancel'>
    <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>

If the room or service does not support registration, it MUST return a <service-unavailable/> error to the user:

Example 66. Room Returns Service Unavailable Error to User

<iq from='darkcave@chat.shakespeare.lit'
    id='reg2'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <error type='cancel'>
    <service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>

If the user did not include a valid data form, the room MUST return a <bad-request/> error to the user:

Example 67. Room Returns Service Bad Request Error to User

<iq from='darkcave@chat.shakespeare.lit'
    id='reg2'
    to='hag66@shakespeare.lit/pda'
    type='error'>
  <error type='modify'>
    <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
  </error>
</iq>

Otherwise, the room MUST inform the user that the registration request was successfully received:

Example 68. Room Informs User that Registration Request Has Been Processed

<iq from='darkcave@chat.shakespeare.lit'
    id='reg2'
    to='hag66@shakespeare.lit/pda'
    type='result'/>

After the user submits the form, the service MAY request that the submission be approved by a room admin/owner (see the Approving Registration Requests section of this document) or MAY immediately add the user to the member list by changing the user's affiliation from "none" to "member". If the service changes the user's affiliation and the user is in the room, it MUST send updated presence from this individual to all occupants, indicating the change in affiliation by including an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace and containing an <item/> child with the 'affiliation' attribute set to a value of "member".

Example 69. Service Sends Notice of Membership to All Occupants

<presence
    from='darkcave@chat.shakespeare.lit/thirdwitch'
    to='crone1@shakespeare.lit/desktop'>
  <x xmlns='http://jabber.org/protocol/muc#user'>
    <item affiliation='member'
          jid='hag66@shakespeare.lit/pda'
          role='participant'/>
  </x>
</presence>

[ ... ]

If a user has registered with a room, the room MAY choose to restrict the user to use of the registered nickname only in that room. If it does so, it SHOULD return a <not-acceptable/> error to the user if the user attempts to join the room with a roomnick other than the user's registered roomnick (this enables a room to "lock down" roomnicks for consistent identification of occupants).

7.11 Getting Member List

If allowed in accordance with room configuration, an occupant MAY be allowed to retrieve the list of room members. For details, see the Modifying the Member List section of this document.

7.12 Discovering Reserved Room Nickname

A user MAY have a reserved room nickname, for example through explicit room registration, database integration, or nickname "lockdown". A user SHOULD discover his or her reserved nickname before attempting to enter the room. This is done by sending a Service Discovery information request to the room JID while specifying a well-known Service Discovery node of "x-roomuser-item".

Example 70. User Requests Reserved Nickname

<iq from='hag66@shakespeare.lit/pda'
    id='getnick1'
    to='darkcave@chat.shakespeare.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='x-roomuser-item'/>
</iq>

It is OPTIONAL for a multi-user chat service to support the foregoing service discovery node. If the room or service does not support the foregoing service discovery node, it MUST return a <feature-not-implemented/> error to the user. If it does and the user has a registered nickname, it MUST return the nickname to the user as the value of the 'name' attribute of a Service Discovery <identity/> element (for which the category/type SHOULD be "conference/text"):

Example 71. Room Returns Nickname

<iq from='darkcave@chat.shakespeare.lit'
    id='getnick1'
    to='hag66@shakespeare.lit/pda'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='x-roomuser-item'>
    <identity
        category='conference'
        name='thirdwitch'
        type='text'/>
  </query>
</iq>

If the user does not have a registered nickname, the room MUST return a service discovery <query/> element that is empty (in accordance with XEP-0030).

Even if a user has registered one room nickname, the service SHOULD allow the user to specify a different nickname on entering the room (e.g., in order to join from different client resources), although the service MAY choose to "lock down" nicknames and therefore deny entry to the user, including a <not-acceptable/> error. The service MUST NOT return an error to the user if his or her client sends the foregoing request after having already joined the room, but instead SHOULD reply as described above.

If another user attempts to join the room with a nickname reserved by the first user, the service MUST deny entry to the second user and return a <conflict/> error as previously described.

7.13 Requesting Voice

It is not possible for a visitor to speak (i.e., send a message to all occupants) in a moderated room. To request voice, a visitor SHOULD send a <message/> stanza containing a data form to the room itself, where data form contains only a 'muc#role' field with a value of "participant".

Example 72. Occupant Requests Voice

<message from='hag66@shakespeare.lit/pda'
         to='darkcave@chat.shakespeare.lit'>
  <x xmlns='jabber:x:data' type='submit'>
    <field var='FORM_TYPE'>
      <value>http://jabber.org/protocol/muc#request</value>
    </field>
    <field var='muc#role'
           type='text-single'
           label='Requested role'>
      <value>participant</value>
    </field>
  </x>
</message>

The service then SHOULD forward the request to the room moderator(s) as described in the Approving Voice Requests section of this document.