Implement a websocket servlet in a custom module

Module Development
1

Team, I want to implement a servlet (in a custom module) that uses the websocket protocol. AFAIK, Tomcat has started support for websocket since version 7. Is Tomcat version 7 supported for Ignition? Is any developer guidance (i.e. examples, sample code) available for custom servlets?

2

Hi,

First off, not that it matters much if you’re sticking with servlets, but just so you know… in Ignition 7.7 we switched from tomcat to jetty.

Now, there’s not a real example as far as I know, but the basic procedure to add a custom servlet is pretty easy:

  1. Define your servlet
  2. Add it in your module’s gateway setup function:

@Override public void setup(GatewayContext context) { context.addServlet("MyServlet", MyServlet.class); }
It will be visible from http://localhost:8088/main/System/MyServlet.
(Note: I pulled this from here, but that thread has a lot of unnecessary info)

Regards,

3

Hi Colby,
thank you for the useful information.

Looking at the example: the class MyServlet should extend a class in the Servlet hierarchy, such as HTTPServlet, that is common for handling HTTP requests. However, in my case, I need to handle WebSocket communications. This can be done in Tomcat version 7 (but not in 6) by extending the servlet class named org.apache.catalina.websocket.WebSocketServlet.

I didn’t know about Jetty in Ignition 7.7. In case, do you know the Jetty version?

However, right now I am looking at an earlier Ignition that still uses Tomcat.
So, the residual question is: can Tomcat be upgraded to 7 (so to have WebSocket servlets) within Ignition, without loosing product support?

Regards,

4

Hi,
As a sequel to this question , are there any restrictions of using TCP/IP sockets in Ignition modules (Irrespective of Ignition version 7.6 or 7.7 or which ever web server) ? If yes then what are they?
Best Regards
PRAMANJ

5

No, there are no restrictions on using sockets in modules.

6

Hi Colby,
thanks for the confirmation. Kevin had also confirmed the same in another post of mine. However i have seen the sockets don’t work in a module when accessed by a client on a separate machne in the network. Whereas it works if its on the same host as the server in side an ignition module.

I have tested is several times! can you try once and reconfirm?

BR
PRAMANJ

7

I’ve personally implemented websockets (which uses TCP/IP sockets) in a module in Ignition. I had no problem communicating from remote devices.

  1. Pick a port not in use (I used 9000)
  2. Make sure that the port is not firewalled on the gateway machine
8

Ok let me probe further.
Thanks for your inputs.
BR
PRAMANJ