OPC UA

OPC Unified Architecture (OPC UA) is the interoperability standard of industrial automation. A server exposes an address space: a graph of nodes (objects, variables, methods) identified by NodeIds. Clients browse that graph, read and write values, call methods, and subscribe to data changes and events, over secure channels with X.509 certificates.

Where you meet it

• PLCs and controllers from most major vendors
• SCADA, MES and historian servers
• Industrial gateways that translate fieldbus protocols into a single OPC UA model

Quickstart

From the command line

Download opcuactl from GitHub Releases, then:

# List endpoints and their security configurations
opcuactl discover endpoints -e opc.tcp://localhost:4840

# Browse the address space
opcuactl browse children -e opc.tcp://localhost:4840

# Read a value (anonymous / None, fine for lab servers)
opcuactl get value -e opc.tcp://localhost:4840 -n i=2258

# Monitor live value changes
opcuactl monitor value -e opc.tcp://localhost:4840 -n i=2258

For production servers, connect securely with endpoint auto-selection:

opcuactl get value -e opc.tcp://plc.example:4840 -n i=2258 \
  --auth username --username operator --password "$OPCUACTL_PASSWORD" \
  --security-policy auto --security-mode auto \
  --cert ./pki/client.pem --key ./pki/client.key \
  --trusted-cert ./pki/server-ca.pem

From Go

go get github.com/otfabric/go-opcua

Read the server’s current time:

package main

import (
  "context"
  "fmt"
  "log"

  "github.com/otfabric/go-opcua"
  "github.com/otfabric/go-opcua/ua"
)

func main() {
  ctx := context.Background()

  c, err := opcua.NewClient("opc.tcp://localhost:4840")
  if err != nil {
    log.Fatal(err)
  }
  if err := c.Connect(ctx); err != nil {
    log.Fatal(err)
  }
  defer c.Close(ctx)

  v, err := c.Node(ua.MustParseNodeID("i=2258")).Value(ctx)
  if err != nil {
    log.Fatal(err)
  }
  fmt.Println("Server time:", v.Value())
}

What go-opcua supports

Interoperability

opcua-interop runs go-opcua in all applicable client and server directions against open62541 (C) and Eclipse Milo (Java).