Since 2020, DUECA has a module for WebSocket connections, dueca::websock::WebSocketsServer. This module may be used for channel data communication between DUECA and web applications, or other applications, for example by using the Python WebSockets libraries. Communication is through JSON encoded messages, with information exchange in the very first message on the structure and type of the data.

An additional use of this module is to generate live plots from your DUECA channel data. To this end, a web application is available that can be served by the same WebSocket module. The web application enables you to have a view of your data from a connected web browser, configure plots that use your data, and show these plots in your browser. Since normally you would want to have the same set of plots for a certain experiment or simulation, you can also store the data connection and plot configuration in a file, for later re-loading.

The application is still a bit rough around the edges, any suggestions for improvement will be welcomed.

Setting up the data communication

To receive channel information over a WebSocket connection, you need to enable the websocket module (–websock to the DCOMPONENTS variable in the main Makefile), and configure which channels need to be exported. The example given here is with python:

mymods.append(
   dueca.Module(
       "web-sockets-server", "", admin_priority).param(
           ('info', ("mydata", "MyData://PHLAB")),
           ('write-and-read', ("plotconfig",
                               "ConfigFileRequest://dueca",
                               "ConfigFileData://dueca")),
           ('http-port', 8000),
           ('document-root', '/usr/share/dplotter/dist')))

The 'info' configurations define endpoints that contain your available channels. The 'write-and-read' endpoint is for storing and retrieving configuration files. A module in the "dueca" entity handles these file actions, add that to the DUECA_mods variable:

DUECA_mods.append(dueca.Module("config-storage", "", admin_priority))

With this, you can start up a browser, and connect to a running DUECA process, on port 8000. That will open a page with four tabs;

Info. For indicating which endpoints/channels you want to read

Data. Each configured channel may have one or multiple entries, indicate which entries you want to read, and optionally inspect the data.

Plots. Create plots here.

Config. Save or load configuration files.

The plots have controls to run, pause, pause&clear, or be edited. Only one plot can be edited at a time. When a plot is edited, lines can be added to the plot on the data page, just add a line with the line button, and then drag variables from the data view to the x or y field. If you drag the channel's tick, this will be converted to time with DUECA's current time granule.

There is also an option to control the lines in the plot through a run-control channel; this channel has a variable that is 0 for pause, 1 for run, 2 for clearing; drag the runcontrol variable to the reset field; this allows for programmatic control of the plots, for example starting a new line when a new run is made. The eraser can be used to clear lines.

A standard module, "PlotRunControl/plot-run-control", can be configured to start plots in Advance, and stop and clear them again in HoldCurrent mode.