In addition to the reply from @Evgeny Shvarov  :

INT is highly important to identify error locations.
eg. <DIVIDE>label+5^routinename refers to the location in routinename.INT  

Out of curiosity, I have built a  more exotic solution that is easier to understand. (At least for me)
I don't like so much this protocol upgrade stuff and encrypting and simulation of a browser.

My personal workaround:

• start browser over ZF(-1, "start chrome http://.................my csp......")
• the page gets my request passed with the URL. very simple just as a Hash
• the page does all the WS stuff via JavaScript
• the reply is returned using Hyperevent #call(....) 

It works fine and is rather "classic CSP" style.

OK.

I tried it and found:  sock.Open(  does not accept "/ws/v2/?&token=<token>"  only the server name

Now you have the connection BUT no server to take care of it as you see:

Investigating the browser it became clear what's going on:
- you begin with HTTP to start your WebSocketServer
- an then initiate the WS connection.

This is the output from TcpTrace: 

>>>>>  GET /csp/samples/websocketdemo.csp HTTP/1.1 >> .......

>>>>>  GET /csp/samples/Web.SocketTest.cls HTTP/1.1  >> ... >> Upgrade: websocket

That's my point:
      With the actual approach starting the requres WS Server is missing. 

To me, this looks like your port doesn't like WS as initial connection protocol but expect the switch from HTTPS -> WSS or the port is just wrong.

several suggestions for the investigation to get it moving:

#1) verify your server from a normal web page (e.g. based websocketdem.csp in Samples) especially the port !!!!

#2) If you have control over your server then skip SSL and get running over HTTP -> WS first. You can add this once it works.

#3) If you have no server just use Caché / SAMPLES /  Web.SocketTest.cls 
I found it very useful to have control over both ends and now I own several variants for testing.

Staying tuned 

at first sight, I miss in this  piece  of code

ClassMethod GetPage() As %String) [ ZenMethod ]
{ quit %session.Data("currPage") }

and

var pageNo = zenPage.GetPage() ;

as pointed out by Alexander Koblov  already:

you can create a $LB() od $LB(undefined) and it's all the same

set a=$LB() zzdump a
0000: 01

or 

write $d(undefined)

0

set a=$lb(undefined) zzdump a

0000: 01

Your coincidence of NULL, null, Null, nuLL,  .... is just an optical eye-catcher without syntactical relevance in COS

See details in NoSQL Methods for Global Nodes

Especially  Get the Next Global Subscript: next() lets you iterate over first subscript  ^Customer(id)   1, 2, 3, ...

next using Retrieve a Global Node: get() you access ^Customer(id, "Address", 1) and check if it is "London"

from docs mydata.retrieve 

In your call, you get the full global. but you have to do the detail work yourself.

There is no such thing as SELECT ...... FROM GLOBAL WHERE .......

This is NoSQL.

But you may hide your functionality in a ClassMethod inCaché and use invoke_classmethod()

Hi John,

Would this include a certain level of independence between editing and Caché, Ensemble, IRIS version?
Especially a kind of "forward" compatibility as long as you don't go for new features?

Did you check it with Chrome or just the default browser ?

for similar reasons I have set my default browser to Chrome

I'm glad I could help the community with my answers and
I especially like to express my BIG THANK to my readers voting for me.
This clear and positive feedback is a strong motivation for me for the future years.   

Hi Wolf,

I ran into a similar problem a few weeks ago: IRIS on Linux - no studio

My solution: Custom install on my local WIN10 desktop. Only the Studio (and ODBC drivers).
Nice side effect: the new IRIS-Studio also talks seamlessly to my local Caché. 

My assumption: As it works for an isolated Linux it should work for Docker as well (if no firewall blocks you )