An implementation Dimple-II membership protocol for epidemic protocols with support for automatic discovery. Dimple2 is an library designed to be used from within a haskell program. However, the Dimple2 peers interact with one another through a REST api and that REST api has been extended to support all Dimple2 interactions.

The membership protocol is full discussed in the dimple-ii.pdf document in the doc directory and can also be readily found with an internet search for 'Dimple-II membership protocol'. The exception to this is the discovery protocol which will be described here.

When the Dimple2 system is started it sends out a multicast broadcast containing the URL in Netstrings format. Peers that hear that broadcast should optionally POST their URL to the interested peer API. Regardless of the number of nodes that hear this broadcast no more then about 10 - 100 nodes should respond. This implementation uses a probabilist algorythim based on the estimated number of nodes in the system to ensure that property.

0. Check to see if there are any peers in the localview
1. If peers exist wait N seconds and try again
2. If no peers exist, Broadcast Peer URL in Netstrings format
3. Collect responses from interested parties for N seconds
4. If interested parties have responded, start join operation
5. If interested parties have not responded start broadcast process again

To manually force discovery you may put a url end point to the local view. This will have a high probability of forcing a shuffle to occur.

All json descriptions are in the format of js-schema. They should be readable on their own, but more information can be found at the js-schema site.

var URL = String;

var Peer = schema ({url : URL,             // The url of the peer
                    age : Number.min(0)}); // the number of failed
                                           // sync attemps

 var Interested = URL;                     // url of the node interested
                                           // in communicating

/dimple2/interested
  GET - Get the list of interested nodes
  POST - Post a new nod to the list of interested nodes

This api exists to allow for automated discovery. Peers interested in participating are expected to POST a value represented by the Interested scheme to /dimple2/interested.

 Array.of(Interested)

This api returns a list of urls that are currently in the interested list of this target Peer. NOTE The vast majority of the time the interested list is empty! It is only populated in the short period of time between when a Peer begins the discovery process and starts interacting with the discovered peers. That being the case this operation is probably only useful during development.

/dimple2/localview
  GET - get the list of Peers in the local view

This allows a caller to get the current list of urls in this peers local view. This is not used as part of the shuffle algorithym, but simple exists for informational and monitoring purposes. This returns the following

Array.of(Peer)

This may take 1 parameter oldest=true. This will return an array of a single peer that is the current oldest member of the local view.

/dimple2/localview/{url}
  PUT - Put the url indentified by {url}, initiating a shuffle response

This starts a shuffle process. The body of the PUT request should be a Peer object. See the Dimple-II, Algorithym 4,5, and 6 for details.

/dimple2/joinlocalview
  GET - get the generated local view

Provides a generated local view as described in Dimple-II, Algorythim 7.

/dimple2/nodeestimate
  GET - provides the current estimate of the number of nodes in
        the system. See Dimple-II Algorythim 8.