13

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Motivation

Thus [Smalltalk's] semantics are a bit like having thousands and thousands of computers all hooked together by a very fast network.
                                                                                                                    Alan Kay, The Early History Of Smalltalk

Simple yet powerful metaphor,
can we scale it beyond the image level?

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Goals

■ OO-style messaging for Lively Web
    □ Lively worlds (and other participants in Lively Web) should be able to communicate
    □ Pure message-based communication
    □ Network abstraction but not complete transparency, i.e. separated JS address spaces
    □ Dynamic: Participants join and leave, change state and behavior
    □ doesNotUnderstand    

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Goals (continued)

■ Base layer for other collaboration mechanisms
   □ Multi-user awareness (session tracking)
   □ Synchronization services
   □ Audio/video connections

■ Reliable
   □ Automatically recover from network failures

■ Efficient connection for service consumption
   □ Data streaming
   □ Peer-to-peer connections, no server bottleneck

■ Leightweight
   □ Make it easy to connect and extend the network and its services

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Lively2Lively

■ Session tracking
   □ Participants can register to become discoverable message receivers
   □ Optional (not every participant needs registration)

■ Messaging framework
   □ Establishes a network of Lively worlds and other participants and services
   □ Message format (protocol)
   □ Should eventually support different transportation layers (WebSockets, WebRTC, HTTP)
   □ Not restricted to Lively/JavaScript(!)
   □ Participants need to support a transportation layer and know message format (slide 13)

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Lively2Lively Client Interface

1
// if not disabled a session gets established on world load
session = lively.net.SessionTracker.getSession();
// all the sessions in LivelyWeb that we know of
session.getUserInfo(inspect);
// loopback: send a message to myself
session.sendTo(session.sessionId, 'askFor', {bar: 23}, inspect);
// what services are provided by this session?
session.sendTo(session.sessionId, 'reportServices', null, inspect);
// what services are provided by my tracker?
session.sendTo(session.trackerId, 'reportServices', {}, inspect);
// how to implement a new message
// 1) messageNotUnderstood
session.sendTo(session.sessionId, 'foobar', {}, show);
// 2) Implement service
lively.net.SessionTracker.registerActions({
    foobar: function(msg, session) {
        session.answer(msg, 'Howdy!');
    }
})
// 3) message responds successfully
session.sendTo(session.sessionId, 'foobar', {}, show);
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Interface for non-Lively environments

reset

source code

1
# This starts an external nodejs process that sends a message to this Lively
# session. This is an example of how a system outside of LivelyWeb can connect
# to it.
# Note that any kind of environment/language can be used, not just JS. The
# requirements for communication are: 1) websocket support, 2) knowledge
# of the lively-json websocket format (see slide 13).
node nodejs2lively.example.js "client-session:35950F90-79E6-43B4-9FC5-FDE564B88B31"
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Architectural Overview

■ Infrastructure/Network
■ Session tracking
■ Rules for message dispatch and routing
■ Message protocol
■ Services (message -> method)

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Infrastructure/Network

■ Currently only websockets
■ WebRTC support soon
■ For reliability maybe HTTP fallback necessary (socket.io)
■ The network layer is hidden by default
   □ Users only need to specify receiver, selector, arguments of message

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Infrastructure/Network (Message Forwarding)

■ Transparent routing via HTTP/WebSockets

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Infrastructure/Network (Peer-to-Peer)

■ Real peer-to-peer connections via WebRTC (coming soon)

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Session Tracking

■ Participants can register with unique id
   □ Become discoverable and can receive messages
■ Participants can implement tracker behavior

Who is online?

1
unknown                                                                                                                                   
http://lively-web.org/users/robertkrahn/2013-08-17_Lively2Lively.html 1:33 PM 8/19/13  client-session:EDA4666E-1454-48DB-A344-4E7FBF4D534A
http://lively-web.org/users/Dan/binomial-wedge.html                   3:54 PM 8/9/13   client-session:7029528B-3DF8-4C50-A92E-CD779F894361
http://lively-web.org/users/Dan/QBF2B.html                            4:49 PM 8/9/13   client-session:8D873406-2A70-477E-B874-0C14382CFA42
http://lively-web.org/users/Dan/FabBrowser.html                       12:25 PM 8/14/13 client-session:C76EDBA4-9730-4A05-97EB-94B94A178663
http://lively-web.org/blank.html                                      3:22 PM 8/16/13  client-session:05FDEEB0-0E7E-46A1-8BC9-C9DE3BF0809E
http://lively-web.org/blank.html                                      2:11 PM 8/19/13  client-session:3A1676EA-8CF8-4FD4-A632-CCC6A912DDDB
http://www.lively-web.org/users/Dan/Fab1.html                         4:50 PM 8/9/13   client-session:09A160A9-5DEF-43B8-BDF5-8BA7090682B5
http://lively-web.org/users/Dan/Fab1.html                             3:06 PM 8/9/13   client-session:F0E4FCBF-2399-449E-BE2B-8013ED91E8A6
robertkrahn                                                                                                                               
http://lively-web.org/users/robertkrahn/2013-08-17_Lively2Lively.html 10:36 PM 8/19/13 client-session:2769F35D-0309-42AB-B24A-E46942D66C2A
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Message Routing

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Message Protocol (lively-json)

1
message = {
    // REQUIRED selector for service lookup. By convention action gets
    // postfixed with "Result" for response messages
    action: STRING,
    // REQUIRED target of the message
    target: UUID,
    // OPTIONAL arguments
    data: OBJECT,
    // OPTIONAL identifier of the message
    messageId: UUID,
    // OPTIONAL sender of the message
    sender: UUID,
    // OPTIONAL identifier of a message that this message answers
    inResponseTo: UUID,
    // OPTIONAL if message is an answer. Can be interpreted by the receiver as
    // a streaming response. Lively participants (tracker and clients) will
    // trigger data bindings and fire callbacks for a message for every streaming
    // response
    expectMoreResponses: BOOL,
    // EXPERIMENTAL UUIDs of trackers/sessions handlers that forwarded this
    // message
    route: ARRAY
}
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the essential part

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Services

1
// this is server code:
util._extend(require("./LivelyServices").services, {
    serverSayHello: function(sessionServer, connection, msg) {
        connection.send({
            action: msg.action + 'Result',
            inResponseTo: msg.messageId,
            data: 'Hello!'});
    }
});
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■ New server service:

1
// this is client code
var sess = lively.net.SessionTracker.getSession();
sess.sendTo(sess.trackerId, 'serverSayHello', {}, show);
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■ New Lively world service:

1
lively.net.SessionTracker.registerActions({
    foobar: function(msg, session) {
        session.answer(msg, 'Howdy!');
    }
})
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Next steps

■ Explore usage for collaborative applications
   □ Worlds as: service providers, workers, PartsBins, ...objects
   □ "Teach" other worlds/objects new behaviors --> modularization!
   □ Decentralized behaviors and state? PartsBin in the "cloud"

■ Is it possible to integrate JS and network address space?
   □ Receiver search and match ($morph? broadcasting? object matching?)

■ Underlaying mechanism for a synchronization framework?