Crate opcua_client[][src]

Expand description

The OPC UA Client module contains the functionality necessary for a client to connect to an OPC UA server, authenticate itself, send messages, receive responses, get values, browse the address space and provide callbacks for things to be propagated to the client.

A client has to specify the endpoint description they wish to connect to, security policy and other configurable options, e.g. paths to PKI keys. All of this is encapsulated in a Client object.

One of these may be made programatically using a ClientBuilder or from a preexisting ClientConfig which can be loaded fully or partially from disk. Use the way that suits you.

Once the Client is created it can connect to a server by creating a Session. Multiple sessions can be created from the same client. Functions on the Session correspond to OPC UA services so it can be used to:

  • Discover endpoints
  • Activate a session
  • Create / modify / delete subscriptions
  • Create / modify / delete monitored items
  • Read and write values
  • Browse the address space
  • Add or remove nodes

Functionality is synchronous and housekeeping such as renewing the active session and sending publish requests is handled automatically.

Data change and event notifications are via asynchronous callbacks.


Here is a complete example of a client that connects to the samples/simple-server, subscribes to some values and prints out changes to those values. This example corresponds to the one described in the in docs/ tutorial.

use std::sync::{Arc, RwLock};
use opcua_client::prelude::*;

fn main() {
    let mut client = ClientBuilder::new()
        .application_name("My First Client")

    // Create an endpoint. The EndpointDescription can be made from a tuple consisting of
    // the endpoint url, security policy, message security mode and user token policy.
    let endpoint: EndpointDescription = ("opc.tcp://localhost:4855/", "None", MessageSecurityMode::None, UserTokenPolicy::anonymous()).into();

    // Create the session
    let session = client.connect_to_endpoint(endpoint, IdentityToken::Anonymous).unwrap();

    // Create a subscription and monitored items
    if subscribe_to_values(session.clone()).is_ok() {
        let _ = Session::run(session);
    } else {
        println!("Error creating subscription");

fn subscribe_to_values(session: Arc<RwLock<Session>>) -> Result<(), StatusCode> {
    let mut session = session.write().unwrap();
    // Create a subscription polling every 2s with a callback
    let subscription_id = session.create_subscription(2000.0, 10, 30, 0, 0, true, DataChangeCallback::new(|changed_monitored_items| {
        println!("Data change from server:");
        changed_monitored_items.iter().for_each(|item| print_value(item));
    // Create some monitored items
    let items_to_create: Vec<MonitoredItemCreateRequest> = ["v1", "v2", "v3", "v4"].iter()
        .map(|v| NodeId::new(2, *v).into()).collect();
    let _ = session.create_monitored_items(subscription_id, TimestampsToReturn::Both, &items_to_create)?;

fn print_value(item: &MonitoredItem) {
   let node_id = &item.item_to_monitor().node_id;
   let data_value = item.value();
   if let Some(ref value) = data_value.value {
       println!("Item \"{}\", Value = {:?}", node_id, value);
   } else {
       println!("Item \"{}\", Value not found, error: {}", node_id, data_value.status.as_ref().unwrap());