This JEP defines a protocol that enables entities to request, and servers to perform, advanced processing of XMPP <message/> stanzas, including reliable data transport, time-sensitive delivery, and transient messages.
NOTICE: The protocol defined herein is a Draft Standard of the Jabber Software Foundation. Implementations are encouraged and the protocol is appropriate for deployment in production systems, but some changes to the protocol are possible before it becomes a Final Standard.
Status: Draft
Type: Standards Track
Number: 0079
Version: 1.0
Last Updated: 2004-10-11
JIG: Standards JIG
Approving Body: Jabber Council
Dependencies: XMPP Core, JEP-0030, JEP-0082
Supersedes: JEP-0023
Superseded By: None
Short Name: amp
Schema for amp: <http://jabber.org/protocol/amp/amp.xsd>
Schema for amp#errors: <http://jabber.org/protocol/amp/errors.xsd>
Registry:
<http://www.jabber.org/registrar/amp.html>
Email: linuxwolf@outer-planes.net
JID: linuxwolf@outer-planes.net
Email: stpeter@jabber.org
JID: stpeter@jabber.org
This Jabber Enhancement Proposal is copyright 1999 - 2005 by the Jabber Software Foundation (JSF) and is in full conformance with the JSF's Intellectual Property Rights Policy <http://www.jabber.org/jsf/ipr-policy.shtml>. This material may be distributed only subject to the terms and conditions set forth in the Creative Commons Attribution License (<http://creativecommons.org/licenses/by/2.5/>).
The preferred venue for discussion of this document is the Standards-JIG discussion list: <http://mail.jabber.org/mailman/listinfo/standards-jig>.
The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the Jabber Software Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this JEP has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The keywords "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 RFC 2119.
This JEP defines a protocol that enables an end-point entity to specify additional delivery semantics for an XMPP <message/> stanza. This protocol is typically used by clients to inform the receiving server how to deliver a particular stanza, such as providing an expiration time or a resource-matching strategy.
The built-in delivery semantics for <message/> stanzas (defined in XMPP Core [1] and, for instant messaging applications, also in XMPP IM [2]) are adequate for most current applications. However, there are various cases where more stringent delivery semantics are necessary. The most common cases discussed in this JEP are:
This protocol is mostly handled by the server or servers processing the <message/>. The protocol consists of a list of rules, with conditions and actions for each rule. Upon receipt of an appropriately marked message, the server interprets the rules in the order they are received, looking for met conditions. When a condition is met, the action for that rule is executed, and message processing stops.
Each rule is flagged for the scope it applies to, whether it be the overall route, or for each hop in the route. Additionally, while this JEP defines a default set of conditions and actions, the protocol is extensible enough to allow for more to be defined in the future.
The namespace for the protocol is "http://jabber.org/protocol/amp".
In order for this protocol to function properly, the containing <message/> stanza MUST possess an 'id' attribute, and the value of the 'id' attribute MUST NOT be an empty string. The server MUST specify this 'id' attribute value with any response back to the sender. This is necessary so that servers and clients can properly relate the initial request with any subsequent error or notification.
This flow describes the interaction between the sender and a server. As illustrated below, this interaction is actually rather simple:
Sending entities that wish to use AMP SHOULD discover support for this protocol (using Service Discovery [3]) along the intended path. Typically, this would involve sending disco#info queries to the sending entity's own server and the server of the intended recipient. The results of these queries MAY be cached for up to 24 hours, unless otherwise expired.
If a server supports Advanced Message Processing, it MUST report that by including a service discovery feature of "http://jabber.org/protocol/amp" in the service discovery information result that it returns to the requesting entity.
Example 1. Initial Service Discovery information request
<iq from='northumberland@shakespeare.lit/westminster'
to='shakespeare.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
Example 2. Service Discovery information response
<iq from='shakespeare.lit'
to='northumberland@shakespeare.lit/westminster'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<identity name='Shakespeare IM' category='im' type='server'/>
...
<feature var='http://jabber.org/protocol/amp'/>
...
</query>
</iq>
A server SHOULD also maintain a service discovery node named "http://jabber.org/protocol/amp", at which it advertises the individual actions and conditions it supports. If an entity needs to determine whether the server supports individual actions and conditions, it SHOULD send a service discovery information request to that node; the server then MUST either return the list of supported actions and conditions or return an error such as <feature-not-implemented/>. (Note: If the server does not provide information for this disco node, the requesting entity MUST assume that all actions and conditons are supported for each reported action set or condition set.)
Each supported action shall be reported as a feature using the following format:
http://jabber.org/protocol/amp?action={action}Each supported condition shall be reported as a feature using the following format:
http://jabber.org/protocol/amp?condition={condition}The following examples show the request-response flow for information about individual actions and conditions (note the inclusion of the 'node' attribute).
Example 3. Request for information about individual actions and conditions
<iq from='northumberland@shakespeare.lit/westminster'
to='shakespeare.lit'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='http://jabber.org/protocol/amp'/>
</iq>
Example 4. Response for individual actions and conditions
<iq from='shakespeare.lit'
to='northumberland@shakespeare.lit/westminster'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'
node='http://jabber.org/protocol/amp'>
<identity name='Shakespeare IM AMP Support' category='im' type='server'/>
...
<feature var='http://jabber.org/protocol/amp'/>
<feature var='http://jabber.org/protocol/amp?action=drop'/>
<feature var='http://jabber.org/protocol/amp?action=error'/>
<feature var='http://jabber.org/protocol/amp?action=notify'/>
<feature var='http://jabber.org/protocol/amp?condition=deliver'/>
<feature var='http://jabber.org/protocol/amp?condition=expire-at'/>
<feature var='http://jabber.org/protocol/amp?condition=match-resource'/>
...
</query>
</iq>
Once support is determined, the sender can attach the desired delivery semantics to the message:
Example 5. A message with semantics
<message
from='northumberland@shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
</message>
The semantics are defined as a set of <rule/> elements within the <amp/> root element. Each <rule/> declares the condition to trigger on and the action to execute if triggered.
By default, the ruleset applies only to the "edge servers": those servers to which the sending and receiving entities are connected. (Note: For the purposes of Advanced Message Processing, "server" is defined as in XMPP Core and does not include any internal components, such as connection managers, that may provide functionality within a server implementation or installation.)
The ruleset MAY be applied to all server-to-server "hops" along the route from the sending and receiving entities by adding the "per-hop' attribute to the <amp/> element. The value of this attribute is either "true" (apply rules to all hops) or "false" (follow default behavior, i.e., apply rules at the edge servers only).
Example 6. A message with semantics
<message
from='northumberland@shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'
per-hop='true'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
</message>
For examples of validation failure, refer to the Error Handling section of this document.
Note: Even if "per-hop" processing is requested, each server in the route MUST ignore rules that cannot apply to it; the Defined Conditions outline if they can be applied per-hop.
Server operation is where the bulk of the work is performed. Upon receiving a message with an AMP extension, the server performs the following flow:
Validation can take many forms, but at the very least the server MUST verify that it understands each of the rule conditions and actions, and that the condition contents are appropriate. The server MAY also refused to accept certain combinations of conditions and actions, for example if they present a risk of overriding security. If the semantics are not valid, supported, or acceptable, the server MUST reply with an error specifying the rule(s) that are at issue. The server SHOULD validate all the semantics before returning an error. For syntax and examples of error handling related to validation failure, refer to the Error Handling section of this document.
This step is essentially what a server normally does, except that it does not actually perform the action. This determines what would happen to the message if there were no semantics attached (such as dispatch to another server or store offline). At this point, the server SHOULD also calculate any timing or calendar requirements (if applicable).
At this step, the server processes the attached semantics. The server MUST process the rules serially, and in the order they are presented within the <amp/> element. As soon as a rule's condition is met, processing ends with that action overriding the default action determined earlier (unless the action permits continued processing).
Once all rules have been processed or otherwise accounted for, the server executes the action determined at this point.
A server SHOULD NOT dispatch a <message/> stanza with AMP semantics to another server unless it knows that the next server supports AMP (this SHOULD be discovered via Service Discovery and MAY be cached to avoid delivery delays). If the next server does not support AMP, the current server replies to the original sender with a <service-unavailable/> error condition. Otherwise this flow starts again for the server to which the message has been dispatched.
The preceding sections of this JEP define the general behavior regarding AMP. This section outlines how <rule/> action and condition sets are defined. It also provides defined action and condition sets; these action and condition sets SHOULD be supported by any implementation of Advanced Message Processing, but support for any given action or condition set it not required. (Note: The action and condition sets defined herein may be supplemented in the future via registration of additional action and condition sets with the Jabber Registrar.)
The definition of a <rule/> condition MUST provide the following information:
The definition of a <rule/> action MUST provide the following information:
The condition defines how or when a particular rule is triggered. The value of the condition attribute determines what the contents of the <rule/> mean.
The following conditions are defined by this JEP and SHOULD be supported by any implementation.
In the following sections, the terms "content" and "contents" refers to the XML character data contained by the <rule/> element.
The "deliver" condition is used to ensure delivery (or non-delivery) in one of five ways:
The possible contents for this condition are defined in the following table:
Table 1: "deliver" values
| Value | Description |
|---|---|
| "direct" | The message can be delivered immediately to the intended resource. |
| "forward" | The message cannot be delivered immediately to the intended resource and shall be forwarded to another XMPP address. |
| "gateway" | The message cannot be delivered immediately to the intended resource and shall be sent through a gateway to an address on a non-XMPP system. |
| "none" | The message cannot be delivered immediately to the intended resource and is to be dropped (e.g., because offline storage is not enabled). |
| "stored" | The message cannot be delivered immediately to the intended resource and shall be stored offline for later delivery via XMPP. |
This condition is met based on what the processor is able to do with the message at the moment of receipt. To correctly process this condition, a processor first determines if the message can be delivered immediately to the intended resource or further dispatched to another hop. If so and the contents are "direct", the condition is met. If not and the contents are "stored", the condition is also met if offline storage is enabled. In all other cases the condition is not met.
This condition MAY be applied to each "hop" in the server route.
The "expire-at" condition is used to ensure delivery before an absolute point in time. Naturally, this does not guarantee [4] that the message will not be delivered after that time from the sender's perspective, since this JEP does not assume that all machine clocks (e.g., for all servers along the delivery route) are synchronized. However, in order to help ensure that this condition is met correctly, servers that implement this JEP (or the machines that host such servers) SHOULD use the Network Time Protocol (RFC 1305 [5]) to keep in sync with established time authorities. Note also that expire-at functionality becomes less reliable the closer the expire-at time is to the present (e.g., the sender will receive less reliable delivery of a message speciifying an expire-at time two seconds in the future than of a message specifying an expire-at time two hours or two days in the future).
The content of the 'value' attribute specifies some point after the exact moment the message is sent; the content MUST be a DateTime as specified in Jabber Date and Time Profiles [6], and the timezone MUST be UTC.
The condition is met if the message cannot be delivered to the recipient before the specified datetime. To determine the datetime to compare to, the processor first determines if and when a message can be dispatched (e.g. not stored offline). The processor then records this datetime, and compares it with the specified datetime. If the current datetime is on or after that specified, the condition is met.
This condition MAY be applied to each "hop" in the server route.
The "match-resource" condition is used to restrict delivery based on the resource identifier of the recipient JID.
The possible contents for this condition are:
Table 2: "match-resource" values
| Value | Description | Example |
|---|---|---|
| "exact" | Destination resource exactly matches the specified resource. | "home/laptop" only matches "home/laptop" and not "home/desktop" or "work/desktop" |
| "any" | Destination resource matches any value, effectively ignoring the specified resource. | "home/laptop" matches "home", "home/desktop" or "work/desktop" |
| "other" | Destination resource matches any value except for the specified resource. | "home/laptop" matches "work/desktop", "home" or "home/desktop", but not "home/laptop" |
The condition is met if the resource for the actual destination JID matches the specified destination JID using the above rules. For instance, if a message is intended for "romeo@montague.net/work" with the "match-resource" condition of "other", the condition is met if the message can be immediately delivered only to "romeo@montague.net/home".
For purposes of this condition, a JID with no resource has the following behavior:
This condition MUST NOT be applied to each "hop" in the server route, only at the edge servers. If an <amp/> element includes this condition and also indicates that it should be processed per hop, this <rule/> shall be ignored.
Note: By design, this protocol does not include support for partial JID matching (which would stipulate, for example, that the resource identifiers "home/laptop" and "homeboy" both match "home").
The action defines what occurs when a particular rule is triggered. The value of the action attribute determines the behavior if the rule's condition is met.
The following actions are defined by this JEP.
The "drop" action silently discards the message from any further delivery attempts and ensures that it is not placed into offline storage. The drop MUST NOT result in other responses.
The "error" action triggers a reply <message/> stanza of type "error" to the sending entity. The <message/> stanza's <error/> child MUST contain a <failed-rules xmlns='http://jabber.org/protocol/amp#errors'/> error condition, which itself contains the rules that triggered this action.
Example 7. "error" response
<message from='hamlet.lit' to='bernardo@hamlet.lit/elsinore' type='error' id='chatty2'> <body>Who's there?</body> <amp xmlns='http://jabber.org/protocol/amp' status='error' from='francisco@hamlet.lit' to='bernardo@hamlet.lit/elsinore'> <rule condition='deliver' value='stored' action='error'/> </amp> <error type='modify' code='500'> <undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/> <failed-rules xmlns='http://jabber.org/protocol/amp#errors'> <rule condition='deliver' value='stored' action='error'/> </failed-rules> </error> </message>
Note that the error SHOULD be of type "modify", and the general error condition SHOULD be <undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>.
The "notify" action triggers a reply <message/> stanza to the sending entity. This <message/> stanza MUST contain the element <amp status='notify'/>, which itself contains the <rule/> that triggered this action. Unlike the other actions, this action does not override the default behavior for a server. Instead, the server then executes its default behavior after sending the notify.
Example 8. "error" response
<message from='hamlet.lit' to='bernardo@hamlet.lit/elsinore' id='chatty2'> <body>Who's there?</body> <amp xmlns='http://jabber.org/protocol/amp' status='notify' from='francisco@hamlet.lit' to='bernardo@hamlet.lit/elsinore'> <rule condition='deliver' value='stored' action='notify'/> </amp> </message>
The "alert" action triggers a reply <message/> stanza to the sending entity. This <message/> stanza MUST contain the element <amp type='alert'/>, which itself contains the <rule/> that triggered this action. In all other respects, this action behaves as "drop".
Example 9. "error" response
<message from='hamlet.lit' to='bernardo@hamlet.lit/elsinore' id='chatty2'> <body>Who's there?</body> <amp xmlns='http://jabber.org/protocol/amp' status='alert' from='francisco@hamlet.lit' to='bernardo@hamlet.lit/elsinore'> <rule condition='deliver' value='stored' action='alert'/> </amp> </message>
This condition has the largest potential for abuse, as it can appear to bypass presence. [8] A naive server could simply check to see the outcome for a particular message, regardless of whether the sender and receiver are subscribed to each other. This behavior SHOULD NOT be implemented, although it may be desirable in some environments (such as fully-trusted networks).
There are several directions server implementors can follow in this regard:
All delivery semantics are encapsulated in the <amp/> element. This element contains one or more <rule/> elements specifying the specific rules to process. It can optionally possess attributes about the current status, the original sender and recipient, and route applicability.
The 'status' attribute specifies the reason for this <amp/> element. When specifying semantics to be applied (client to server), this attribute MUST NOT be present. When replying to a sending entity regarding a met condition, this attribute MUST be present and SHOULD be the value of the 'action' attribute for the triggered rule. (Note: Individual action definitions MAY provide their own requirements.)
The 'from' attribute specifies the original sender of the containing <message/> stanza. This attribute MUST be specified for any <message/> stanza sent from a supporting server, regardless of the recipient. It SHOULD NOT be specified otherwise. The value of the 'from' attribute MUST be the full JID (node@domain/resource) of the sender for the original <message/> stanza.
The 'to' attribute specifies the original (intended) recipient of the containing <message/> stanza. This attribute MUST be specified for any <message/> stanza sent from a supporting server, regardless of the recipient. It SHOULD NOT be specified otherwise. The value of the 'to' attribute MUST be the full JID (node@domain/resource) of the intended recipient for the original <message/> stanza.
The 'per-hop' attribute flags the contained ruleset for processing at each server in the route between the original sender and original intended recipient. This attribute MAY be present, and MUST be either "true" or "false". If not present, the default is "false".
Each semantic rule is specified with a <rule/> element. This element possesses attributes for the condition, value, and action.
The 'action' attribute defines the result for this rule. This attribute MUST be present, and MUST be either a value defined in the Defined Actions section, or one registered with the Jabber Registrar.
The 'condition' attribute defines the overall condition this rule applies to. This attribute MUST be present, and MUST be either a value defined in the Defined Conditions section, or one registered with the Jabber Registrar.
The 'value' attribute defines how the condition is matched. This attribute MUST be present, and MUST NOT be an empty string (""). The interpretation of this attribute's value is determined by the 'condition' attribute.
The <message/> stanza is nearly ideal for data transport, but to ensure reliability it is often desirable that such messages not be delivered to any resource but that specified. To facilitate this, the sending entity includes a <rule action='drop' condition='match-resource' value='exact'/> (if failure notification is unnecessary) or <rule action='error' condition='match-resource' value='exact'/> (if failure notification is required). The following example illustrates this using In-Band Bytestreams [9]:
Example 10. Sending a message for reliable data transport
<message to='francisco@hamlet.lit/pda'
from='bernardo@hamlet.lit/elsinore'
id='ibb1'>
<data xmlns='http://jabber.org/protocol/ibb' sid='mySID' seq='0'>
qANQR1DBwU4DX7jmYZnncmUQB/9KuKBddzQH+tZ1ZywKK0yHKnq57kWq+RFtQdCJ
WpdWpR0uQsuJe7+vh3NWn59/gTc5MDlX8dS9p0ovStmNcyLhxVgmqS8ZKhsblVeu
IpQ0JgavABqibJolc3BKrVtVV1igKiX/N7Pi8RtY1K18toaMDhdEfhBRzO/XB0+P
AQhYlRjNacGcslkhXqNjK5Va4tuOAPy2n1Q8UUrHbUd0g+xJ9Bm0G0LZXyvCWyKH
kuNEHFQiLuCY6Iv0myq6iX6tjuHehZlFSh80b5BVV9tNLwNR5Eqz1klxMhoghJOA
</data>
<amp xmlns='http://jabber.org/protocol/amp' per-hop='true'>
<rule condition='expire-at' value='2004-09-10T08:33:14Z' action='error'/>
<rule condition='match-resource' value='exact' action='error'/>
</amp>
</message>
In the above case, the sender would receive an error reply if the message could not be delivered specifically to "francisco@hamlet.lit/pda" within 500 seconds.
Example 11. Failed reliable data transport message
<message from='hamlet.lit'
to='bernardo@hamlet.lit/elsinore'
id='ibb1'>
<data xmlns='http://jabber.org/protocol/ibb' sid='mySID' seq='0'>
qANQR1DBwU4DX7jmYZnncmUQB/9KuKBddzQH+tZ1ZywKK0yHKnq57kWq+RFtQdCJ
WpdWpR0uQsuJe7+vh3NWn59/gTc5MDlX8dS9p0ovStmNcyLhxVgmqS8ZKhsblVeu
IpQ0JgavABqibJolc3BKrVtVV1igKiX/N7Pi8RtY1K18toaMDhdEfhBRzO/XB0+P
AQhYlRjNacGcslkhXqNjK5Va4tuOAPy2n1Q8UUrHbUd0g+xJ9Bm0G0LZXyvCWyKH
kuNEHFQiLuCY6Iv0myq6iX6tjuHehZlFSh80b5BVV9tNLwNR5Eqz1klxMhoghJOA
</data>
<amp xmlns='http://jabber.org/protocol/amp'
from='bernardo@hamlet.lit/elsinore'
to='francisco@hamlet.lit/pda'>
<rule condition='match-resource' value='exact' action='error'/>
</amp>
<error type='modify' code='500'>
<undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<failed-rules xmlns='http://jabber.org/protocol/amp#errors'>
<rule condition='match-resource' value='exact' action='error'/>
</failed-rules>
</error>
</message>
Time-sensitive messages are a frequent occurrence in some environments (e.g., front-office personnel routinely notify others of "events" such as guests, unexpected refreshments, and ad-hoc gatherings). To send a time-sensitive message, the sending entity includes a <rule condition='expire-at' action='drop'/> with the time when the event is to occur:
Example 12. Sending a time-sensitive message
<message to='linuxwolf@outer-planes.net'
from='receptionist@outer-planes.net'
id='alert849'>
<subject>Guest Alert!</subject>
<body>
There will be clients in the conference room today around 1 PM!
As always, be courteous and quiet nearby...
</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2003-06-23T23:00:00Z'/>
</amp>
</message>
In the above case, the server for "linuxwolf@outer-planes.net" would not deliver the message once 23:00 UTC (3:00 PM Pacific Daylight Time) has passed.
Transient messages are messages that should never be stored offline. To send a transient message, the sending entity includes a <rule condition='deliver' action='drop' value='stored'/>:
Example 13. Sending a transient message
<message to='francisco@hamlet.lit'
from='bernardo@hamlet.lit/elsinore'
type='chat'
id='chatty1'>
<body>Who's there?</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='deliver' value='stored' action='drop'/>
</amp>
</message>
Alternatively, the sending entity includes a <rule condition='deliver' action='alert' value='stored'/> to be alerted instead of having the message silently dropped:
Example 14. Sending a transient message (requesting alert)
<message to='francisco@hamlet.lit'
from='bernardo@hamlet.lit/elsinore'
type='chat'
id='chatty2'>
<body>Who's there?</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='deliver' value='stored' action='alert'/>
</amp>
</message>
Example 15. Sender alerted regarding transient message
<message from='hamlet.lit'
to='bernardo@hamlet.lit/elsinore'
id='chatty2'>
<amp xmlns='http://jabber.org/protocol/amp'
action='alert'
from='bernardo@hamlet.lit/elsinore'
to='francisco@hamlet.lit'>
<rule condition='deliver' value='stored' action='alert'/>
</amp>
</message>
To simplify the discussion of error conditions, this document uses the following mappings between namespace URIs and namespace prefixes (note: this mapping is provided only for the purpose of simplifying the discussion and is not intended for use within the protocol itself).
Table 3: Namespace Mappings
| Prefix | URI |
|---|---|
| xmpp | urn:ietf:params:xml:ns:xmpp-stanzas |
| msg | http://jabber.org/protocol/amp |
| err | http://jabber.org/protocol/amp#errors |
The following table shows the possible error conditions in relation to general AMP rules and conditions as well as the Defined Actions.
Table 4: Error conditions
| General Condition | Error Type | Specific Condition | Description |
|---|---|---|---|
| <xmpp:bad-request/> | modify | <msg:unsupported-actions/> | One or more rule's specified actions are not supported. The element <msg:unsupported-actions/> contains the <rule/> elements that specify the unsupported actions. |
| <xmpp:bad-request/> | modify | <msg:unsupported-conditions/> | One or more rule's specified conditions are not supported. The element <msg:unsupported-conditions/> contains the <rule/> elements that specify the unsupported conditions. |
| <xmpp:not-acceptable/> | modify | <msg:invalid-rules/> | One or more rules are not acceptable by this server, usually because the condition/action combination is restricted. The element <msg:invalid-rules/> contains the <rule/> elements that are not acceptable. |
| <xmpp:service-unavailable/> | cancel | NONE | This protocol is not supported. This error is returned to the sending entity if a server along the route to the recipient does not implement this protocol. |
| <xmpp:undefined-condition/> | modify | <err:failed-rules/> | One or more <rule/> elements triggered the "error" action. This condition contains the triggered <rule/> elements. |
This section shows examples of the error conditions described in the previous section (for information regarding mapping of XMPP error conditions to Jabber error codes, refer to Error Condition Mappings [10]).
Example 16. A message with semantics
<message
from='northumberland@shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
</message>
Example 17. Server does not support action
<message
from='shakespeare.lit'
id='richard2-4.1.247'
to='northumberland@shakespeare.lit'
type='error'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
<error type='modify' code='400'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<unsupported-actions xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</unsupported-actions>
</error>
</message>
Example 18. A message with semantics
<message
from='shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
</message>
Example 19. Server does not support condition
<message
from='shakespeare.lit'
id='richard2-4.1.247'
to='northumberland@shakespeare.lit'
type='error'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
<error type='modify' code='400'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<unsupported-conditions xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</unsupported-conditions>
</error>
</message>
Example 20. A message with semantics
<message
from='northumberland@shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
</message>
Example 21. The rule is not acceptable to the server
<message
from='shakespeare.lit'
id='richard2-4.1.247'
to='northumberland@shakespeare.lit'
type='error'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
<error type='modify' code='405'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<invalid-rules xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</invalid-rules>
</error>
</message>
Example 22. A message with semantics
<message
from='northumberland@shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
</message>
Example 23. AMP service is unavailable
<message
from='royalty.england.lit'
id='richard2-4.1.247'
to='northumberland@shakespeare.lit'
type='error'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule condition='expire-at'
action='drop'
value='2004-01-01T00:00:00Z'/>
</amp>
<error type='cancel' code='503'>
<service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</message>
Example 24. A message with semantics
<message from='hamlet.lit'
to='bernardo@hamlet.lit/elsinore'
id='chatty2'>
<body>Who's there?</body>
<amp xmlns='http://jabber.org/protocol/amp'
status='error'
from='francisco@hamlet.lit'
to='bernardo@hamlet.lit/elsinore'>
<rule condition='deliver' value='stored' action='error'/>
</amp>
</message>
Example 25. Failed rules
<message from='hamlet.lit'
to='bernardo@hamlet.lit/elsinore'
type='error'
id='chatty2'>
<body>Who's there?</body>
<amp xmlns='http://jabber.org/protocol/amp'
status='error'
from='francisco@hamlet.lit'
to='bernardo@hamlet.lit/elsinore'>
<rule condition='deliver' value='stored' action='error'/>
</amp>
<error type='modify' code='500'>
<undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<failed-rules xmlns='http://jabber.org/protocol/amp#errors'>
<rule condition='deliver' value='stored' action='error'/>
</failed-rules>
</error>
</message>
If the recipient's server implements "offline storage", it will need to keep track of which offline messages are subject to expiration and not deliver those which have expired. Exactly how to do so is a matter of implementation. One possible implementation is for the server to maintain a separate database of expirable messages and periodically scan it; upon discovering an expired message, it could flag the messages as eligible for discarding and inform the sender, but not discard the message until the intended recipient next becomes available.
The security considerations are dependent upon the specific conditions and actions in use. The considerations for the defined conditions and actions are outlined with their definitions in the Conditions and Actions section of this document.
No interaction with the Internet Assigned Numbers Authority (IANA) [11] is necessary as a result of this JEP.
The Jabber Registrar [12] includes 'http://jabber.org/protocol/amp' and 'http://jabber.org/protocol/amp#errors' in its registry of protocol namespaces.
The Jabber Registrar includes 'http://jabber.org/protocol/amp' in its registry of well-known Service Discovery nodes.
The Jabber Registrar maintains a registry of AMP <rule/> conditions (see <http://www.jabber.org/registrar/amp-conditions.html>).
In order to submit new values to this registry, the registrant must define an XML fragment of the following form and either include it in the relevant Jabber Enhancement Proposal or send it to the email address <registrar@jabber.org>:
<condition>
<name>the value of the 'condition' attribute</name>
<ns>the namespace to be used as a service discovery feature</ns>
<per-hop>does the "per-hop" flag apply? [true|false]</per-hop>
<value>
The syntax (e.g., datatype or allowable values) of the
'value' attribute.
</value>
<processing>values that result in message processing</processing>
<doc>the document (e.g., JEP) in which this condition is specified</doc>
</condition>
The registrant may register more than one condition at a time, each contained in a separate <condition/> element.
Note: The namespace for the condition set shall be included in the Service Discovery features registry.
<condition>
<name>deliver</name>
<ns>http://jabber.org/protocol/amp?condition=deliver</ns>
<per-hop>true</per-hop>
<value>[direct|forward|gateway|none|stored]</value>
<processing>
The condition is met if (1) the value is "direct" and the message
can be immediately delivered or further dispatched, or (2) the
value is "stored" and offline storage is enabled.
</processing>
<doc>JEP-0079</doc>
</condition>
<condition>
<name>expire-at</name>
<ns>http://jabber.org/protocol/amp?condition=expire-at</ns>
<per-hop>true</per-hop>
<value>DateTime per JEP-0082</value>
<processing>
The condition is met if the message cannot be delivered before
the specified DateTime.
</processing>
<doc>JEP-0079</doc>
</condition>
<condition>
<name>match-resource</name>
<ns>http://jabber.org/protocol/amp?condition=match-resource</ns>
<per-hop>false</per-hop>
<value>[any|exact|other]</value>
<processing>
The condition is met if (1) the value is "any" and the intended
recipient has at least one available resource (as defined in the
XMPP IM specification); (2) the value "exact" and the intended
recipient has an available resource that exactly matches the JID
specified in the 'to' address; (3) the value is "other" and the
intended recipient has an available resource whose full JID is
other than that specified in the 'to' address.
</processing>
<doc>JEP-0079</doc>
</condition>
The Jabber Registrar maintains a registry of AMP <rule/> actions (see <http://www.jabber.org/registrar/amp-actions.html>).
In order to submit new values to this registry, the registrant must define an XML fragment of the following form and either include it in the relevant Jabber Enhancement Proposal or send it to the email address <registrar@jabber.org>:
<action>
<name>the value of the 'action' attribute</name>
<ns>the namespace to be used as a service discovery feature</ns>
<behavior>the expected behavior if the rule is triggered</behavior>
<doc>the document (e.g., JEP) in which this action is specified</doc>
</action>
The registrant may register more than one action at a time, each contained in a separate <action/> element.
Note: The namespace for the action set shall be included in the Service Discovery features registry.
<action>
<name>alert</name>
<ns>http://jabber.org/protocol/amp?action=drop</ns>
<behavior>
The message is silently discarded but an alert is returned to the
sender.
</behavior>
<doc>JEP-0079</doc>
</action>
<action>
<name>drop</name>
<ns>http://jabber.org/protocol/amp?action=drop</ns>
<behavior>
The message is silently discarded.
</behavior>
<doc>JEP-0079</doc>
</action>
<action>
<name>error</name>
<ns>http://jabber.org/protocol/amp?action=error</ns>
<behavior>
The message is not processed and an error is returned to the sender,
specifying which rule resulted in failed processing.
</behavior>
<doc>JEP-0079</doc>
</action>
<action>
<name>notify</name>
<ns>http://jabber.org/protocol/amp?action=notify</ns>
<behavior>
The message is processed and a notification message is returned to
the sender, specifying which rule was processed.
</behavior>
<doc>JEP-0079</doc>
</action>
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://jabber.org/protocol/amp'
xmlns='http://jabber.org/protocol/amp'
elementFormDefault='qualified'>
<xs:annotation>
<xs:documentation>
The protocol documented by this schema is defined in
JEP-0079: http://www.jabber.org/jeps/jep-0079.html
</xs:documentation>
</xs:annotation>
<xs:element name='amp'>
<xs:complexType>
<xs:sequence>
<xs:element ref='rule' minOccurs='1' maxOccurs='unbounded'/>
</xs:sequence>
<xs:attribute name='from' usage='optional' type='xs:string'/>
<xs:attribute name='per-hop' use='optional' type='xs:bool' default='false'/>
<xs:attribute name='status' usage='optional' type='xs:NCName'/>
<xs:attribute name='to' usage='optional' type='xs:string'/>
</xs:complexType>
</xs:element>
<xs:element name='invalid-rules'>
<xs:complexType>
<xs:sequence>
<xs:element ref='rule' minOccurs='1' maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='unsupported-actions'>
<xs:complexType>
<xs:sequence>
<xs:element ref='rule' minOccurs='1' maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='unsupported-conditions'>
<xs:complexType>
<xs:sequence>
<xs:element ref='rule' minOccurs='1' maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='rule'>
<xs:complexType>
<xs:attribute name='action' use='required' type='xs:NCName'/>
<xs:attribute name='condition' use='required' type='xs:NCName'/>
<xs:attribute name='value' use='required' type='xs:string'/>
</xs:complexType>
</xs:element>
</xs:schema>
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://jabber.org/protocol/amp#errors'
xmlns='http://jabber.org/protocol/amp#errors'
elementFormDefault='qualified'>
<xs:annotation>
<xs:documentation>
The protocol documented by this schema is defined in
JEP-0079: http://www.jabber.org/jeps/jep-0079.html
</xs:documentation>
</xs:annotation>
<xs:element name='failed-rules'>
<xs:complexType>
<xs:sequence>
<xs:element ref='rule' minOccurs='1' maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='rule'>
<xs:complexType>
<xs:attribute name='action' use='required' type='xs:NCName'/>
<xs:attribute name='condition' use='required' type='xs:NCName'/>
<xs:attribute name='value' use='required' type='xs:string'/>
</xs:complexType>
</xs:element>
</xs:schema>
Thanks to Marshall Rose and Craig Kaes for their comments.
1. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://www.ietf.org/rfc/rfc3920.txt>.
2. RFC 3921: Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence <http://www.ietf.org/rfc/rfc3921.txt>.
3. JEP-0030: Service Discovery <http://www.jabber.org/jeps/jep-0030.html>.
4. Guarantee is a strong word. This JEP defines methods for making message delivery more reliable within certain bounds, but does not pretend that such methods provide any form of guaranteed delivery.
5. RFC 1305: Network Time Protocol (Version 3) <http://www.ietf.org/rfc/rfc1305.txt>.
6. JEP-0082: Jabber Date and Time Profiles <http://www.jabber.org/jeps/jep-0082.html>.
7. JEP-0045: Multi-User Chat <http://www.jabber.org/jeps/jep-0045.html>.
8. Consider the following scenario: the user <romeo@montague.net> is not an authorized subscriber to the presence of the user <nurse@capulet.com>, but sends a <message/> stanza with a "deliver" rule of "direct" to that address; if the Nurse is not online, Romeo could discover that fact if the capulet.com server informs him that the message could not be delivered immediately.
9. JEP-0047: In-Band Bytestreams <http://www.jabber.org/jeps/jep-0047.html>.
10. JEP-0086: Error Condition Mappings <http://www.jabber.org/jeps/jep-0086.html>.
11. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
12. The Jabber Registrar maintains a list of reserved Jabber protocol namespaces as well as registries of parameters used in the context of protocols approved by the Jabber Software Foundation. For further information, see <http://www.jabber.org/registrar/>.
END