When a QEWD application is started, it triggers the EWD.start() function which establishes a web socket connection to the QEWD backend. This connection registers the client application within QEWD. A session is created, assigned a token, and returned to the client. This allows the client and backend to communicate securely using the session token as a reference.

1. Copyright © 2016 M/Gateway Developments Ltd
EWD 3 Training Course
Part 6
What Happens when a QEWD
Application is Started
Rob Tweed
Director, M/Gateway Developments Ltd
Twitter: @rtweed

2. Copyright © 2016 M/Gateway Developments Ltd
QEWD Application Startup
• Triggered by EWD.start() function in
ewd-client
– Creates the client environment
• Everything protected within a closure
– Establishes a web socket connection to QEWD back-
end
– Registers the client application within QEWD

3. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
Caché,
GT.M or
Redis
EWD.start()
Master
process
Worker
process

4. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
Browser makes web-socket connection
to back-end
Caché,
GT.M or
Redis

5. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
Browser sends
WebSocket message
type: ‘ewd-register’
application: ‘demo1’
Caché,
GT.M or
Redis

6. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
Message queued
and passed
to available worker
type: ‘ewd-register’
application: ‘demo1’
Caché,
GT.M or
Redis

7. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
New QEWD Session
created
application: ‘demo1’
ewd-session
Stored in global named
'CacheTempEWDSession'
Caché,
GT.M or
Redis

8. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
New session token returned, eg:
token: ‘a0a033a9-393a-4e7a-9252-848c24ee5b02’
ewd-session Caché,
GT.M or
Redis

9. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
Token returned to browser
token: ‘a0a033a9-393a-4e7a-9252-848c24ee5b02’
Caché,
GT.M or
Redis

10. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
Token stored within
Closure in browser
Accessible by ewd-client
APIs but not by user
token
Caché,
GT.M or
Redis

11. Copyright © 2016 M/Gateway Developments Ltd
Application registration
Browser QEWD
socket.io
socket.io
token
Registration completed
ewd-registered event fires
Caché,
GT.M or
Redis

12. Copyright © 2016 M/Gateway Developments Ltd
Examine activity in back-end
• Look at Command Prompt or terminal
window in which you're running QEWD:
Should look something like this:
worker 3884 received message: {"type":"ewd-register","application":"demo1","sock
etId":"/#oIQ1LbMUlKew3RefAAAE"}
master process received response from worker 3884: {"type":"ewd-register","finis
hed":true,"message":{"token":"a0a033a9-393a-4e7a-9252-848c24ee5b02"}}
*** handleMessage response {"type":"ewd-register","finished":true,"message":{"to
ken":"a0a033a9-393a-4e7a-9252-848c24ee5b02"}}
sending to socket /#oIQ1LbMUlKew3RefAAAE
Master process has finished processing response from worker process 3884 which i
s back in available pool

13. Copyright © 2016 M/Gateway Developments Ltd
Examine activity in back-end
worker 3884 received message:
{
"type":"ewd-register",
"application":"demo1",
"socketId":"/#oIQ1LbMUlKew3RefAAAE”
}
Let's examine some of those QEWD log messages
(formatted for clarity)
QEWD / ewd-qoper8 worker process was passed the message object
- Message type was 'ewd-register', for an application named 'demo1'
- SocketId is the unique web-socket Id for the client that sent the message

14. Copyright © 2016 M/Gateway Developments Ltd
Examine activity in back-end
master process received response from worker 3884:
{
"type":"ewd-register",
"finished":true,
"message":{
"token":"a0a033a9-393a-4e7a-9252-848c24ee5b02”
}
}
QEWD / ewd-qoper8 worker process finished processing the request
- Returned its response object to the ewd-qoper8 master process
- Message/response type is 'ewd-register'
- Token contains the QEWD session token

15. Copyright © 2016 M/Gateway Developments Ltd
Examine activity in back-end
sending to socket /#oIQ1LbMUlKew3RefAAAE
QEWD returns the response object to the awaiting browser, via
the web-socket connection identified by the socketId

16. Copyright © 2016 M/Gateway Developments Ltd
Examine activity in back-end
Master process has finished processing response
from worker process 3884 which is back in available pool
The ewd-qoper8 worker process has completed its processing, and
the master process has completed handling the response object, so
the worker process is returned to the available pool, ready to handle
another incoming request.

17. Copyright © 2016 M/Gateway Developments Ltd
QEWD is Now Ready for your App
• Registration is complete:
– Browser has a session token
– Back-end has a session indexed by that token
• Now let’s begin building out our
application’s dynamic behaviour
– See Part 7