gopcua

The repository includes several examples to demonstrate common OPC/UA tasks. You can run these directly using go run after installing the library.

Get current date and time

To retrieve the current date and time from a server (using the node ID ns=0;i=2258):

go run examples/datetime/datetime.go -endpoint opc.tcp://localhost:4840

Read the server version

To read the server version (using the node ID ns=0;i=2261):

go run examples/read/read.go -endpoint opc.tcp://localhost:4840 -node 'ns=0;i=2261'

Use security and authentication modes

To connect using specific security policies and certificates:

go run examples/crypto/*.go -endpoint opc.tcp://localhost:4840 -cert path/to/cert.pem -key path/to/key.pem -sec-policy Basic256 -sec-mode SignAndEncrypt

# get current date and time 'ns=0;i=2258'
go run examples/datetime/datetime.go -endpoint opc.tcp://localhost:4840

# read the server version
go run examples/read/read.go -endpoint opc.tcp://localhost:4840 -node 'ns=0;i=2261'

# get the current date time using different security and authentication modes
go run examples/crypto/*.go -endpoint opc.tcp://localhost:4840 -cert path/to/cert.pem -key path/to/key.pem -sec-policy Basic256 -sec-mode SignAndEncrypt

The library uses a functional options pattern. You pass Option functions to ApplyConfig. Each Option is a function that modifies the internal Config struct, which contains:

• dialer: Configuration for the underlying network connection (uacp.Dialer).
• sechan: Configuration for the Secure Channel (uasc.Config).
• session: Configuration for the OPC UA Session (uasc.SessionConfig).

Common categories of options include:

• Identity/Session: ApplicationName, ApplicationURI, ProductURI, Locales, SessionTimeout.
• Secure Channel: SecurityMode, SecurityPolicy, Lifetime, AutoReconnect, ReconnectInterval, RequestTimeout.
• Security/Certificates: PrivateKey, PrivateKeyFile, Certificate, CertificateFile, RemoteCertificate.
• Authentication: AuthAnonymous, AuthUsername, AuthCertificate, AuthIssuedToken, AuthPrivateKey.
• Connection/Dialer: DialTimeout, MaxMessageSize, MaxChunkCount, ReceiveBufferSize, SendBufferSize.

The Client is the primary high-level interface for interacting with an OPC UA server. It manages the secure channel and session lifecycle.

1. Create a Client: Use NewClient(endpoint, ...opts) to initialize a client. If no options are provided, it uses default configurations. If no authentication is configured, it defaults to anonymous authentication.
2. Connect: Call Connect(ctx) to establish a secure channel and create/activate a session. This method also starts background monitoring for connection maintenance and automatic reconnection.
3. Close: Call Close(ctx) to gracefully shut down the session, secure channel, and underlying connection.

import "github.com/gopcua/opcua/opcua"

client, err := opcua.NewClient("opc.tcp://localhost:4840")
if err != nil {
    log.Fatal(err)
}

// Establish connection and session
if err := client.Connect(ctx); err != nil {
    log.Fatal(err)
}

// Ensure cleanup
defer client.Close(ctx)

Use the following package-level functions to discover available OPC UA servers and their endpoints without manually managing a client lifecycle:

• FindServers(ctx, endpoint, ...opts): Returns a list of *ua.ApplicationDescription for servers known to a discovery server.
• FindServersOnNetwork(ctx, endpoint, ...opts): Returns a list of *ua.ServerOnNetwork. This is typically only implemented by discovery servers.
• GetEndpoints(ctx, endpoint, ...opts): Returns the available *ua.EndpointDescription for a specific server.

To select the best endpoint from a list, use SelectEndpoint(endpoints, policy, mode). It sorts endpoints by security level and returns the one that best matches the provided security policy URI and ua.MessageSecurityMode.

import "github.com/gopcua/opcua/opcua"

// Example: Getting endpoints
endpoints, err := opcua.GetEndpoints(ctx, "opc.tcp://localhost:4840")
if err != nil {
    log.Fatal(err)
}

// Example: Selecting an endpoint
endpoint, err := opcua.SelectEndpoint(endpoints, "http://opcfoundation.org/UA/SecurityPolicy#Basic256Sha256", ua.MessageSecurityModeSignAndEncrypt)
if err != nil {
    log.Fatal(err)
}