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Page last modified 09:21, 25 Jul 2007 by SteveB
Permalink: http://tinyurl.com/5s8nge
MindTouch Developer Center > Dream > Services > Events

Events

Table of contents
  1. 1. Overview
  2. 2. Data Types
    1. 2.1. Config
    2. 2.2. Message
    3. 2.3. MessageList
    4. 2.4. Subscription
  3. 3. Features
      1. 3.1.1. GET:events/
        1. 3.1.1.1. Query Parameters
        2. 3.1.1.2. Response
        3. 3.1.1.3. Version History
      2. 3.1.2. GET:/
        1. 3.1.2.1. Query Parameters
        2. 3.1.2.2. Response
        3. 3.1.2.3. Version History
      3. 3.1.3. POST:events/
        1. 3.1.3.1. Query Parameters
        2. 3.1.3.2. Request Body
        3. 3.1.3.3. Response
        4. 3.1.3.4. Version History
      4. 3.1.4. POST:/
        1. 3.1.4.1. Query Parameters
        2. 3.1.4.2. Request Body
        3. 3.1.4.3. Response
        4. 3.1.4.4. Version History
      5. 3.1.5. POST:subscribe/
        1. 3.1.5.1. Query Parameters
        2. 3.1.5.2. Request Body
        3. 3.1.5.3. Response
        4. 3.1.5.4. Version History
      6. 3.1.6. POST:unsubscribe/
        1. 3.1.6.1. Request Body
        2. 3.1.6.2. Response
        3. 3.1.6.3. Version History
  4. 4. Future Extensions

Assembly: mindtouch.dream
Class: MindTouch.Dream.EventsService
SID: http://services.mindtouch.com/dream/...2007/03/events

Overview

The Events service provides simple publication/subscription API for messages. An application publishes a message by doing a POST:events/ request on the service.  The service will queue the message, give it a unique eventid, and notify any active listeners about its arrival.

Listeners can be notified via two different means: either they subscribe to the event service with a POST:subscribe/ request, or they poll with a GET:events/ request.  The latter can be set to wait until a message arrives, avoiding repetitive polling operations when no messages are present.

Verb:Suffix Description
GET:events Get list of all messages
GET: Get list of all messages
POST:events Add a message
POST: Add a message
POST:subscribe Add a subscriber
POST:unsubscribe Remove a subscriber

Data Types

Config

<config>
	<!-- default duration in seconds to keep a message for -->
	<default-ttl>30</default-ttl>

	<!-- default duration in seconds to keep a GET:events/ operation alive when no messages are present -->
	<default-wait>10</default-wait>
</config>

Message

A message can be any valid XML document.  Every message is tagged with a sequential eventid and eventdate (Beryil and later).  If the following document is posted to the Events service.

<ticker>
	<symbol>GE</symbol>
	<price>32.82</price>
</ticker>

It will be sent to listeners as:

<ticker eventid="42" eventdate="2006-05-22T01:16:03.0716064Z">
	<symbol>GE</symbol>
	<price>32.82</price>
</ticker>

MessageList

<list maxeventid="42" eventdate="2006-05-22T01:16:03.0716064Z">
	<ticker eventid="42">
		<symbol>GE</symbol>
		<price>32.82</price>
	</ticker>
</list>

Subscription

<subscription>
	<uri>http://localhost/myService/myListener</node>
</subscription>

Features

GET:events/

Get a list of all events.
Query Parameters
Name Type Default
Description
after int 0 Only send events that occurred after this eventid
wait int? variable Duration in seconds to block the request until until a message arrives.  Default behavior does not block.  Value can be omitted, defaulting to service specific duration.
Response
Status Response Body Description
200 MessageList A list of messages matching the request.
Version History
Aqua: feature added

GET:/

Get a list of all events.
Query Parameters
Name Type Default
Description
after int 0 Only send events that occurred after this eventid
wait int? variable Duration in seconds to block the request until until a message arrives.  Default behavior does not block.  Value can be omitted, defaulting to service specific duration.
Response
Status Response Body Description
200 MessageList A list of messages matching the request.
Version History
Beryl: feature added

POST:events/

Add a message to the list of messages.  If any listeners are waiting or if subscribers are present, notify them about the new message.

Query Parameters
Name Type Defaut
Description
ttl double variable Time-to-live in seconds for the posted message.  If not specified, service default will be used.
Request Body

The request body must contain a valid XML document.

Response
Status Response Body Description
200 --- No result returned.
Version History

Beryl: ttl is now a double representing seconds (in Aqua, it was an integer representing days)

Aqua: feature added

POST:/

Add a message to the list of messages.  If any listeners are waiting or if subscribers are present, notify them about the new message.

Query Parameters
Name Type Defaut
Description
ttl double variable Time-to-live in seconds for the posted message.  If not specified, service default will be used.
Request Body

The request body must contain a valid XML document.

Response
Status Response Body Description
200 --- No result returned.
Version History

Aqua: feature added

POST:subscribe/

Adds a subscriber to the Events service.  By default, a new subscriber only receives messages that are sent after the subscription has been established.  However, by providing the after query parameter, this behavior can be changed to return all message in the Event service that occurred after the specified eventid, but before the subscription was established.

Query Parameters
Name Type Defaut
Description
after int MaxInt Only send events that occurred after this eventid.
Request Body

A Subscription XML document specifying the uri of the subscriber.

Response
Status Response Body Description
200 --- No result returned.
400 XHTML The reason why the request failed.
Version History
Aqua: feature added

POST:unsubscribe/

Removes a subscriber from the Events service.  This operation succeeds regardless if the specified subscription has established a subscription or not.

Request Body

A Subscription XML document specifying the uri of the subscriber.

Response
Status Response Body Description
200 --- No result returned.
Version History

Aqua: feature added

Future Extensions

  • Allow Subsription to contain an xpath expression so that only matching messages are sent to the subscriber.
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