Using the server push (applet) method

There are two functions performed by the server push (applet) implementation method, also known as the asynchronous update applet:

• Pushing asynchronous host updates to the browser:
  • This enables the user to see host updates automatically without the user clicking the Refresh button
• Notification of browser close to HATS server:
  • This allows the HATS server to clean up resources associated with the browser session and reduces the load on the server

When using the asynchronous update applet, in addition to the connection used to send transformed terminal screens from the HATS server to the user's browser, a separate socket connection is established between the applet running on the client and the HATS server. This separate socket connection is used to pass small messages, between the client and server, relating to asynchronous screen refreshes from the host and notification to the HATS server that the browser has been closed. Typically, the amount of traffic over this separate socket connection is very small. The sequence of events which occurs to set up this separate socket connection is as follows:

1. The user enters the HATS application URL in the browser (using a link or typing in the address bar).
2. The HATS server receives the request and sends a response to the browser, which includes the asynchronous update applet Java™ code.
3. Once the applet is downloaded to the client, it attempts to communicate directly back to the HATS server by opening a separate socket connection. The local port used on the client for making this socket connection is chosen at random from the available unused ports on the client, and is not configurable. The remote HATS server IP name and port information that the applet attempts to connect to are supplied by the server when the applet is downloaded to the client. If a value of 0 is specified for the server's port number in the HATS application configuration on the server, then one random, unused port number above 1024 is chosen on the HATS server and supplied to the applet as a parameter. The port number that has been chosen by the server can be seen by viewing the page source of the HATS transformation in the browser. Search the page source for the value specified for PARAM NAME="port". For more information about the applet parameter settings, see Server push (applet) settings.

In order to run the applet, a Java-enabled browser is needed. See "System Requirements for Host Access Transformation Services" at https://www.ibm.com/support/pages/node/320035 for the current list of supported browsers.