OPC

15 min

The OPC UA module manages the OPC UA server on Litmus Edge: service configuration, security policies, and the node hierarchy.

Imports

from litmussdk import opc

All functions are accessible directly from the opc namespace.

Service Management

Start / Stop

opc.start_stop_opc(start=True)
opc.start_stop_opc(start=False)

Service Configuration

# Get current config
config = opc.get_service_config()
# {host, port, nodesUnderRoot, ...}

# Update config
opc.change_service_config(
    host="0.0.0.0",
    port=4840,
    nodes_under_root=True,
)

Security and Authentication

# Get current settings
settings = opc.get_security_and_auth_settings()

# Update policies
opc.change_security_and_auth_settings(
    enabled_security_modes=["None", "Sign", "SignAndEncrypt"],
    enabled_security_policies=["Basic256Sha256", "Aes128_Sha256_RsaOaep"],
    enabled_auth_modes=["Anonymous", "Password"],
)

Valid enabled_security_modes: "None", "Sign", "SignAndEncrypt"

Valid enabled_security_policies: "Basic256Sha256", "Basic256", "Basic128Rsa15", "Aes128_Sha256_RsaOaep", "Aes256_Sha256_RsaPss"

Valid enabled_auth_modes: "Anonymous", "Certificate", "Password"

Certificates and Metrics

certs = opc.get_server_certificates()  # dict
metrics = opc.get_server_metrics()     # dict

Hierarchy

The OPC hierarchy is a tree of Folder, Device, and Tag nodes.

Viewing the Hierarchy

# Root node
root = opc.get_root_node()

# Specific nodes by path
nodes = opc.get_node_by_paths(["edgedevice/MyFolder", "edgedevice/MyFolder/MyDevice"])

# Export entire hierarchy as JSON
hierarchy = opc.export_as_json()

Adding Nodes

# Folder
folder_id = opc.add_node_folder(
    name="MyFolder",
    parent_id="edgedevice",
    worker_node_id_mode="hierarchical",  # or "fixed"
)

# Device (under a folder)
device_id = opc.add_node_device(
    name="MyDevice",
    parent_id=folder_id,
)

# Tag (under a device)
tag = opc.add_node_tag(
    name="Pressure",
    parent_id=device_id,
    data_type="uint32",
    topic_name="plant/pump/01/pressure",
)

worker_node_id_mode:

"hierarchical" (default): node ID is auto-generated from the tree position

"fixed": provide an explicit worker_node_id

Updating a Node

All fields must be specified:

opc.update_node_by_id(
    node_id=folder_id,
    parent_id="edgedevice",
    name="RenamedFolder",
    node_type="FOLDER",
    worker_node_id="edgedevice.RenamedFolder",
    worker_node_id_mode="fixed",
)

For TAG nodes, also pass data_type and topic_name.

Removing a Node

opc.remove_single_node(node_id)

Reset Hierarchy

opc.reset_manual_hierarchy()    # removes manually created nodes
opc.reset_imported_hierarchy()  # removes auto-imported nodes
opc.reset_all_hierarchy()       # removes everything

Import from DeviceHub

Auto-import all DeviceHub tags as OPC nodes:

opc.import_all_dh_tags()

Import / Export JSON

import json

# Export
hierarchy = opc.export_as_json()
with open("opc_hierarchy.json", "w") as f:
    json.dump(hierarchy, f)

# Import (replaces current hierarchy)
with open("opc_hierarchy.json") as f:
    opc.import_json(json.load(f))

OPC