/opcua-asyncio

OPC UA library for python > 3.6 asyncio

Primary LanguagePythonGNU Lesser General Public License v3.0LGPL-3.0

OPC UA / IEC 62541 Client and Server for Python >= 3.6 and pypy . http://freeopcua.github.io/, https://github.com/FreeOpcUa/opcua-asyncio

Build Status Scrutinizer Code Quality

PyPI Package

opcua-asyncio

This repository is a fork of python-opcua to rebase it completely on asyncio and drop support for Python < 3.6. Please note that opcua-asyncio is still in development and should be treated as an alpha release. There is also a draft of sync wrapper over async API which may replace python-opcua in the future in asyncua/sync.py

Motivation

The primary goal of this version of python-opcua is to create an asynchronous OPC UA client based on asyncio. Asynchronous programming allows for simpler code (e.g. less need for locks) and potentially performance gains.

Caveats

Since Client and Server share common resources (e.g. Node), the Server has to also use asynchronous methods to access nodes in it's address space although the operation are non-blocking in most cases. This comes with a cost in performance since calling a coroutine is more expensive than a function. This problem should be addressed by a future change in architecture. One possibility would be sans I/O.

Documentation

The API remains mostly unchanged in regards to python-opcua. Main difference is that many methods have been refactored to return coroutines. Please have a look at the examples and/or the code. Below you will find a copy of the documentation from the python-opcua package.

OPC UA binary protocol implementation is quasi complete and has been tested against many different OPC UA stacks. API offers both a low level interface to send and receive all UA defined structures and high level classes allowing to write a server or a client in a few lines. It is easy to mix high level objects and low level UA calls in one application.

Most low level code is autogenerated from xml specification, thus adding missing functionality to client or server is often trivial.

coverage.py reports a test coverage of over 95 % of code, most of non-tested code is autogenerated code that is not used yet.

Installation

With pip (note: the package was ealier called freeopcua)

pip install asyncua

Documentation

Some documentation is available on ReadTheDocs.

A simple GUI client is available: https://github.com/FreeOpcUa/opcua-client-gui

Examples: https://github.com/FreeOpcUa/opcua-asyncio/tree/master/examples

Minimal client example: https://github.com/FreeOpcUa/opcua-asyncio/blob/master/examples/client-minimal.py Minimal server example: https://github.com/FreeOpcUa/opcua-asyncio/blob/master/examples/server-minimal.py

A set of command line tools also available: https://github.com/FreeOpcUa/python-opcua/tree/master/tools

  • uadiscover (find_servers, get_endpoints and find_servers_on_network calls)
  • uals (list children of a node)
  • uahistoryread
  • uaread (read attribute of a node)
  • uawrite (write attribute of a node)
  • uacall (call method of a node)
  • uasubscribe (subscribe to a node and print datachange events)
  • uaclient (connect to server and start python shell)
  • uaserver (starts a demo OPC UA server)
    tools/uaserver --populate --certificate cert.pem --private_key pk.pem

How to generate certificate: https://github.com/FreeOpcUa/opcua-asyncio/tree/master/examples/generate_certificate.sh

Client

What works:

  • connection to server, opening channel, session
  • browsing and reading attributes value
  • getting nodes by path and nodeids
  • creating subscriptions
  • subscribing to items for data change
  • subscribing to events
  • adding nodes
  • method call
  • user and password
  • history read
  • login with certificate
  • communication encryption
  • removing nodes

Tested servers: freeopcua C++, freeopcua Python, prosys, kepware, beckhoff, winCC, B&R, …

Not implemented yet:

  • localized text feature
  • XML protocol
  • UDP
  • maybe automatic reconnection...

Server

What works:

  • creating channel and sessions
  • read/set attributes and browse
  • getting nodes by path and nodeids
  • autogenerate address space from spec
  • adding nodes to address space
  • datachange events
  • events
  • methods
  • basic user implementation (one existing user called admin, which can be disabled, all others are read only)
  • encryption
  • certificate handling
  • removing nodes
  • history support for data change and events
  • more high level solution to create custom structures

Tested clients: freeopcua C++, freeopcua Python, uaexpert, prosys, quickopc

Not yet implemented:

  • UDP
  • session restore
  • alarms
  • XML protocol
  • views
  • localized text features
  • better security model with users and password

Running a server on a Raspberry Pi

Setting up the standard address-space from XML is the most time-consuming step of the startup process which may lead to long startup times on less powerful devices like a Raspberry Pi. By passing a path to a cache-file to the server constructor, a shelve holding the address space will be created during the first startup. All following startups will make use of the cache-file which leads to significantly better startup performance (~3.5 vs 125 seconds on a Raspberry Pi Model B).

Development

Code follows PEP8 apart for line lengths which should be max 120 characters and OPC UA structures that keep camel case from XML definition.

All protocol code is under opcua directory

  • opcua/ua contains all UA structures from specification, most are autogenerated
  • opcua/common contains high level objects and methods used both in server and client
  • opcua/client contains client specific code
  • opcua/server contains server specific code
  • opcua/utils contains some utilities function and classes
  • opcua/tools contains code for command lines tools
  • schemas contains the XML and text files from specification and the python scripts used to autogenerate code
  • tests contains tests
  • docs contains files to auto generate documentation from doc strings
  • examples contains many example files
  • tools contains python scripts that can be used to run command line tools from repository without installing

Running tests:

./run-tests.sh

Coverage

coverage run tests.py
coverage html
firefox htmlcov/index.html