Notifications

Callstack:
    at User:dev/Specs_(Implemented)/Notifications

MindTouch.Deki.Script.Runtime.DekiScriptUndefinedNameException: reference to undefined name 'graphviz' Exception of type 'MindTouch.Deki.Script.Runtime.DekiScriptUndefinedNameException' was thrown.
  at MindTouch.Deki.Script.Compiler.DekiScriptExpressionEvaluation.Visit (MindTouch.Deki.Script.Expr.DekiScriptVar expr, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Expr.DekiScriptVar.VisitWith[DekiScriptExpressionEvaluationState,Range] (IDekiScriptExpressionVisitor`2 visitor, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Compiler.DekiScriptExpressionEvaluation.Evaluate (MindTouch.Deki.Script.Expr.DekiScriptAccess expr, DekiScriptExpressionEvaluationState state, Boolean evaluateProperties) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Compiler.DekiScriptExpressionEvaluation.Visit (MindTouch.Deki.Script.Expr.DekiScriptAccess expr, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Expr.DekiScriptAccess.VisitWith[DekiScriptExpressionEvaluationState,Range] (IDekiScriptExpressionVisitor`2 visitor, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Compiler.DekiScriptExpressionEvaluation.Visit (MindTouch.Deki.Script.Expr.DekiScriptCall expr, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Expr.DekiScriptCall.VisitWith[DekiScriptExpressionEvaluationState,Range] (IDekiScriptExpressionVisitor`2 visitor, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Compiler.DekiScriptExpressionEvaluation.Visit (MindTouch.Deki.Script.Expr.DekiScriptSequence expr, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Expr.DekiScriptSequence.VisitWith[DekiScriptExpressionEvaluationState,Range] (IDekiScriptExpressionVisitor`2 visitor, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Script.Compiler.DekiScriptExpressionEvaluation.Visit (MindTouch.Deki.Script.Expr.DekiScriptReturnScope expr, DekiScriptExpressionEvaluationState state) [0x00000] in <filename unknown>:0 

Services

• Broadcast: forward single alert to all subscribing services.  Uses either HTTP or XMPP depending on configuration.
• Indexer: cares about page/file alerts.  Triggers page/file to re re-indexed.
• WatchlistObserver: check modified page/file alert against user watchlist and notify user if need be
• CommentObserver: check comments for username and turn them into user notifications
• UserNotifier: deliver notification to user

Potentially useful technologies

• Jabber .NET
• agsXMPP
• ejabberd XMPP server
• RabbitMQ

Use cases

• Get changes for a page or optionally its descendants emailed
  • Page change as a result of dekiscript output change?
  • Get a periodic digest of changes
  • Based on search results??
  • Filters
    • New pages created
    • Comment posts
    • File attached
    • Page moved
    • Page updated
    • A descendant of a page 
• Notify another user or GROUP of users to look at a page or some URI?

Alerts

• page/file: added, removed, modified, moved, restored, wiped
  • Optional flag: include descendants
• user: added, removed, renamed, logged in, logged out
  • Are groups relevant here?
  • initial login
• comments: added, changed, removed
• permission: changed
• service: added, removed, restarted
• user-message: send
• errors:
  • on page render if page was edited more than XXX minutes ago
  • on api call failure

XML Notification Envelope

• user who triggered it
• alert type
• affected resource
• alert meta-data

User Interface

• A screen that shows your notification settings and allows setting up new alerts. This would need to be driven by a Deki API that exposes CRUD for these alerts.

API Interface

• POST: users/{userid}/alerts
  • //TODO: XML for an alert
• PUT: users/{userid}/alerts/{alertid}
• GET: users/{userid}/alerts
• GET: users/{userid}/alerts/{alertid}

DB Model for subscription settings

• Needs to store: 
  • Who is subscribed
  • to what events
  • delivered by what mechanism
  • with what settings
  • how often

Delivery mechanisms

• HTTP post to a URI
• XMPP message to an account/channel
• SMTP message
  • Can the email address be configured or is it always the users address? Is lack of email confirmation a concern?
• IRC message
• Local executable
• Twitter/Yammer/etc
• ???

Recent changes/transactions DB tables

• Transaction table can log every alert type (as listed above)
• Recent changes API expanded
  • Allow filtering by event(s)
  • Allow filtering by date ranges
• Why?
  • Will allow users to get an rss feed of their subscriptions
  • Will allow simpler digest creation for users (simply query the rc api)
  • Provides persistence of alerts allowing observer services to uniquely identify each alert by id and retry delivery failures
  • Allows for improvements in the frontend recent changes screen
  • Allow natural associations between notifications to system events
• Why not?
  •  

Related forum posts

• http://forums.developer.mindtouch.co...ead.php?t=1989
• http://forums.developer.mindtouch.co...ead.php?t=3332

Design q's:

• How to efficiently determine for a given alert who is subscribed if the subscription has options/filters?
  • Example: I want to get notified about comment posts for page foo and all of its descendants.
• Throttling of pushing out events to observers and messages to delivery services. Each event/message is being handled on its own thread in a simple event driven push model. These services may get overwhelmed. A queuing/long polling model that simulates pub/sub by giving each subscriber a channel could be worth considering.