Go OPC DA Client

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This is an OPC DA client written in Go language, allowing you to communicate with OPC DA servers and retrieve data. OPC DA is a commonly used industrial automation communication protocol that enables data exchange between devices and control systems.

Features

• Get all OPC DA servers
• Connect to OPC DA server
• Browse tags on OPC DA server
• Synchronously read tag values
• Asynchronously read tag values
• Synchronously write tag values
• Asynchronously write tag values
• Subscribe to real-time data changes of tags

Prerequisites

Before using this client, make sure you meet the following prerequisites:

• Windows operating system with amd64/i386 architecture
• Go version 1.20 or higher

Go 1.20 is the last version that supports Microsoft Windows 7 / 8 / Server 2008 / Server 2012. To ensure compatibility, this client will continue to support Go 1.20.

Testing is done with both Go 1.20 and the latest version of Go, covering both 32-bit and 64-bit testing.

Installation

Use the following command to install this client:

go get github.com/huskar-t/opcda

Types

This client provides support for the following types:

OPC Type	Go Type	Description
VT_BOOL	bool	Boolean value
VT_I1	int8	8-bit signed integer
VT_I2	int16	16-bit signed integer
VT_I4	int32	32-bit signed integer
VT_I8	int64	64-bit signed integer
VT_UI1	uint8	8-bit unsigned integer
VT_UI2	uint16	16-bit unsigned integer
VT_UI4	uint32	32-bit unsigned integer
VT_UI8	uint64	64-bit unsigned integer
VT_R4	float32	32-bit floating point number
VT_R8	float64	64-bit floating point number
VT_BSTR	string	String
VT_DATE	time.Time	Date time
VT_ARRAY|VT_BOOL	[]bool	Boolean array
VT_ARRAY|VT_I1	[]int8	8-bit signed integer array
VT_ARRAY|VT_I2	[]int16	16-bit signed integer array
VT_ARRAY|VT_I4	[]int32	32-bit signed integer array
VT_ARRAY|VT_I8	[]int64	64-bit signed integer array
VT_ARRAY|VT_UI1	[]uint8	8-bit unsigned integer array
VT_ARRAY|VT_UI2	[]uint16	16-bit unsigned integer array
VT_ARRAY|VT_UI4	[]uint32	32-bit unsigned integer array
VT_ARRAY|VT_UI8	[]uint64	64-bit unsigned integer array
VT_ARRAY|VT_R4	[]float32	32-bit floating point number array
VT_ARRAY|VT_R8	[]float64	64-bit floating point number array
VT_ARRAY|VT_BSTR	[]string	String array
VT_ARRAY|VT_DATE	[]time.Time	Date time array

Other types are not currently supported.

Usage Examples

• Get all OPC DA servers
• Browse tags
• Subscribe to tags
• Synchronously read tags
• Asynchronously read tags
• Synchronously write tags
• Asynchronously write tags

API Documentation

All APIs can be found in the API documentation.

Why Choose This Client

1. There is currently no mature OPC DA client in the Go language ecosystem, and this client was developed to fill this gap.
2. This client is written purely in Go language and supports both 32-bit and 64-bit architectures.
3. This client also provides relatively complete functionality, including reading, writing, and subscribing to real-time data changes of tags.

Why Not konimarti/opc

1. konimarti/opc uses the OPC DA Automation Wrapper interface, which cannot be modified for bug fixes. For example, using the Graybox DA Automation Wrapper cannot compile for 64-bit operation (HIGHENTROPYVA is enabled by default, leading to out-of-bounds memory address conversion within the Wrapper).
2. There are memory leaks when reading string types.
3. Insufficient functionality, such as inability to subscribe to real-time data changes of tags.
4. go-ole has not been updated #252, making it unable to obtain millisecond timestamps.

Frequently Questions

1. Cross-platform support

   This client only supports the Windows operating system.

2. Multi-platform compilation

   This client cannot be compiled on non-Windows platforms because it relies on Windows platform COM interfaces. If the program needs to support multiple platforms, interfaces can be encapsulated, and non-Windows platform interfaces can be set to empty implementations.

3. Memory leaks

   This client uses COM interfaces, and memory release has been handled internally, with fatigue testing done for all supported types. However, if memory leak issues are found during use, you can submit an issue and provide reproduction steps.