Subscription Event Protocol

Draft Specification

This specification is currently a draft under development.

The CloudOS Subscription Event Protocol provides an event based model for managing subscriptions between Personal Clouds. The current implementation of the protocol will create a symmetric relationship between both Personal Clouds. Cloud subscriptions are done in such a way that both the originating and target clouds end up with a unique event channel to the other that is specific to the purpose for the subscription.

Rulesets do not manage subscriptions directly, but rather rely on the CloudOS service to do it for them. Consequently, to use the Subscription Event Protocol the CloudOS service ruleset must be installed in the Personal Cloud for both the originator and target. The CloudOS service listens for certain events, manages subscriptions, and provides functions for getting information about subscriptions.

Events

The system:subscribe event is used to create a channel between two Personal Clouds.

cloudos:subscribe(channelName, namespace, relationship, targetChannel)

The attributes have the following semantics:

The channelName attribute is a label associated with the subscription that should convey meaning to developer. The channelName is only used as a component in the creation of the event channel identifier. If no channelName is specified the value of "orphan" will be used.
The namespace attribute is provided as a means for the developer to group subscriptions within a single, or group, or applications. The namespace is used to filter the list of subscriptions returned by the subscriptionList() function. If no namespace is specified the value of "shared" will be used.
The relationship attribute allows the developer to characterize the relationship between the originator and target clouds. The relationship attribute should be specified as a pair of values separated by a dash (e.g. parent-child, peer-peer, master-slave). The first value of the relationship attribute will be stored with the originating Personal Cloud subscription, the second value will be stored with the target Personal Cloud subscription. The relationship attribute values are used to filter the list of subscriptions returned by the subscriptionList() function. If no relationship is specified the value of "peer-peer" will be used.
The targetChannel attribute is the event channel identifier (ECI) for the target cloud to which the subscription is to be made. Usually, this is the well-known ECI (doorbell) for the target cloud. The well-known ECI provides a means for bootstrapping subscriptions between clouds.

The ruleset wishing to create the subscription signals the CloudOS to do so by raising the system:subscribe event. This is most often done in a rule postlude as shown in the following example:

fired {
  raise cloudos event subscribe
    with channelName   = "Coworkers Bob+Ted"
    and  namespace     = "MyFriends"
    and  relationship  = "friend-friend"
    and  targetChannel = "3f15b820-fa7f-012f-4c6e-00163ebccdcd"
    and  _api = "sky";
}

The CloudOS service raises the cloudos:subscriptionRequestAdded to the target cloud:

cloudos:subscriptionRequestAdded(targetChannel, backChannel, namespace, relationship, channelName)

The backChannel attribute contains an ECI for the originating cloud that the CloudOS service has created and will pass to the target cloud.

The following rule would be selected upon seeing the cloudos:subscriptionRequestAdded event with appropriate values for the event attributes:

rule process_subscriptionRequestAdded {
  select when cloudos subscriptionRequestAdded
    namespace re/MyFriends/"
    channelName re/Coworkers Bob+Ted/
    relationship re/friend-friend/
  ...
}

The CloudOS services in the target cloud raises the cloudos:subscriptionRequestPending to signal the receipt of a pending subscription request:

cloudos:subscriptionRequestPending(eventChannel, namespace, relationship, channelName)

Subscription Approval or Rejection

With the subscription request pending approval, the target cloud can either approve or reject the request.

Approval

To approve the subscription request a ruleset in the the target cloud raises the cloudos:subscriptionRequestApproved event to signal the CloudOS service that the subscription is approved:

cloudos:subscriptionRequestApproved(eventChannel)

For example, the following postlude would raise the cloudos:subscriptionRequestApproved event:

fired {
  raise cloudos event subscriptionRequestApproved
    with eventChannel = "3f15b820-af7f-012f-4c6e-00163ebcaaaa"
    and  _api = "sky";
}

Once the subscription request is approved, the CloudOS service in both the orginating and target clouds will raise the cloudos:CloudOS_subscriptionAdded event so that a ruleset can take additional actions once the subscription has been created

cloudos:CloudOS_subscriptionAdded(eventChannel, backChannel, namespace, relationship, channelName)

The following shows a rule that is selected when the cloudos:CloudOS_subscriptionAdded event is raised:

rule process_subscriptionRequestAdded {
  select when cloudos subscriptionRequestAdded
    namespace re/MyFriends/
    channelName re/Coworkers Bob+Ted/
    relationship re/friend-friend/
  ...
}

Rejection

To reject the subscription request the following event should be raised:

domain: cloudos
type: subscriptionRequestRejected
attributes: eventChannel

fired {
  raise cloudos event subscriptionRequestRejected
    with eventChannel = "3f15b820-af7f-012f-4c6e-00163ebcaaaa"
    and  _api = "sky";
}

When the subscription request is rejected the following event will be raised with the Personal Cloud:

domain: cloudos
type: subscriptionRejected
attributes: eventChannel, namespace, relationship, channelName

rule receive_subscriptionRejected
  select when cloudos subscriptionRejected
    namespace re/MyFriends/
    channelName re/Coworkers Bob+Ted/
    relationship re/friend-friend/

And the following event will be raised in the Personal Cloud which made the subscription request:

domain: cloudos
type: subscriptionRejected
attributes: backChannel, namespace, relationship, channelName

rule receive_subscriptionRejected
  select when cloudos subscriptionRejected
    namespace re/MyFriends/
    channelName re/Coworkers Bob+Ted/
    relationship re/friend-friend/

Unsubscribe

The system:unsubscribe event is used to remove the Personal Channels between two Personal Clouds.

domain: cloudos
type: unsubscribe
attribute: backChannel

fired {
  raise cloudos event unsubscribe
    with eventChannel = "3f15b820-af7f-012f-4c6e-00163ebcfddfd"
    and  _api = "sky";
}

The backChannel attribute uniquely identifies the Personal Channel within the Personal Cloud, and provided to the target Personal Cloud for raising events into the current Personal Cloud. The backChannel is one of the attributes provided by the subscriptionList() function.

During the processing of removing the Personal Channels bewteen the two Personal Clouds callback events are raised within each respective Personal Cloud. These events are raised to enable the developer to take additional actions when the Personal Channels are actually being removed.

domain: cloudos
type: CloudOS_subscriptionRemoved
attributes: eventChannel, backChannel, namespace, relationship, channelName

rule receive_CloudOS_subscriptionRemoved
  select when cloudos CloudOS_subscriptionRemoved
    namespace re/MyFriends/
    channelName re/Coworkers Bob+Ted/
    relationship re/friend-friend/

Functions

subscriptionList(namespace, relationship)

The subscriptionList() function will return a map of the subscriptions within the specified namespace and relationship. In order to use the function you must include the CloudOS module as a pragma in the meta section of your ruleset:

use module a169x625 alias CloudOS