EHLL Integration for Web Terminal

by Green Screens Ltd.

Green Screens Web 5250 Terminal is the only web terminal with integration support for IBM HLL API enabling you to automate tasks with external programs.

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What is EHLL API?

EHLL API is an IBM specification for communicating with desktop terminal clients allowing integration with other external programs. Classic 5250 terminal clients come with hll.dll client library responsible for communication with live 5250 terminal sessions. Functions available inside DLL allows developers to programmatically send cursor navigation commands, key press events, to retrieve screen data etc.

This module enables 3rd party to create various tools as ERP automation testing or screen data extraction into MS Word, MS Excel, Email integration etc.

One of the great examples of such products are developed by our business partner VR-Tech.  Their Linkit Product through our EHLL implementation already supports Green Screens ltd. web terminal advanced integration with Office documents, emailing and many more.

How does it work?

As our terminal is web based, it means the terminal is running inside a secure isolated browser environment without possibility to directly communicate with the underlying OS system. Thus, to enable linkage, we created our own EHLL integration supporting specification API functions.

Web to desktop integration requires browser extension and integration host module. Browser extension is here to enable link between web application and native host program (using browser extension native messaging protocol).

The Host program itself is MS Windows console program which receive messages from a web terminal through browser extension. Host itself is EHLL API provider for client programs enabling them to send requests to active web terminal sessions.

Client programs must use our version of hll.dll with full specification format support. Client hll.dll is responsible to communicate with integration module.

As the module is compatible with standard HLL specification, it is an easy replacement for existing products using HLL from other vendors.

Previous version of our host module was based on web socket service listening on localhost address. With the latest release we switched to the non-network version using browser extension native messaging protocol for increased security and installation simplicity.

Advanced features

Transparent protocol
With the incoming browser extension release 4.2 we will add the new HLL command function 200 (Transparent Data). The Purpose of this function is to forward data to the web terminal. Data can be JSON for an example to enable development of custom communication protocol between desktop application and web terminal.

This is possible as a web terminal unlike a classic desktop terminal client is highly extensible with JavaScript enabling advanced teams to add extra features or to develop advanced integration products.

Asynchronous calls
The Standard HLL API function is request/response blocking protocol. With asynchronous calls API is split to read and write functions allowing full duplex asynchronous communication which opens a lot of new integration possibilities.

Message signaling
We also added Win API PostMessage to browser terminal  sessions for simple signal messaging. For details, see demo app source code at link below.

How to use it?

  1. Install browser extension from link below.
  2. Install host client (download link in extension settings under tab Link)
  3. Connect to our web terminal with session ID set to one of alphabet letters.
  4. Use demo app (JavaFX program) with included HLL.dll's. Download it from link below.
  5. Send commands as specified by IBM EHLL API specification.

Full source of JavaFX example program with 23bit and 64bit hll.dll modules are available at link below.

Download: Browser Extension
Download : GreenScreens-HLL-Client.zip