web-client is an OPC UA client which is also web server.

Usage:

Run the demo-server in one console:

cd opcua/samples/demo-server
cargo run

Then in another console run the web-client

cd opcua/samples/web-client
cargo run -- --url opc.tcp://localhost:4855

Then open a web browser such as Firefox or Chrome and load the url http://localhost:8686. If all goes well you will see a simple control page with buttons to Connect / Disconnect.

Click "Connect" and the page will establish a websocket session with web-client which in turn will connect to the OPC UA server.

The page has a section to subscribe to a comma separated list of variables by node id. It has a section to subscribe to events by a node id. These sections are prefilled with node ids that exist on the demo-server.

The web-client maintains a separate OPC UA client session for each browser page so each has its own OPC UA client session and subscription state. If the "Disconnect" button is clicked, the websocket is dropped and in turn the OPC UA session will be dropped.

Internally, the web-client consists of an actix-web server. There is an OPCUASession actor which is bound to a websocket context. The actor is created by opening ws://servername:8686/ws/ which connects to the OPC UA server when it starts. The client session sends messages to the front end over a websocket as JSON and rendered by the browser.