Async OPC-UA Types

Part of async-opcua, a general purpose OPC-UA library in rust.

This library contains a framework for encoding and decoding OPC-UA messages, as well as generated code for all types defined in the standard.

This includes:

1. All of the built-in data types described in OPC Part 6 Chapter 5 that are encodable.
2. All of the standard data types described in OPC Part 3 Chapter 8 (if not covered by 1.).
3. Autogenerated data types and request / responses as described in OPC Part 4.

Notable types include

• Variant, a discriminated union of a number of primitive types.
• ExtensionObject a wrapper around an OPC-UA structure identified by its encoding ID.

Features

• json, enables OPC-UA JSON encoding and decoding.
• xml, enables OPC-UA XML decoding, notably this is not yet full support for OPC-UA XML, only a limited subset intended for use with NodeSet2 XML files.

Usage

Usually this library is used as part of an OPC-UA client or server.

Encoding is done by writing to a type implementing std::io::Write, and decoding by reading from a type implementing std::io::Read:

let context_owned = ContextOwned::default();
let context = context_owned.context();

let my_opcua_value = Variant::from(123);

// Get the byte length before encoding.
// This is not actually required, but can be useful.
let byte_len = my_opcua_value.byte_len(&context);
let mut stream = Cursor::new(vec![0u8; byte_len]);

// Encode to a stream.
let start_pos = stream.position();
value.encode(&mut stream, &context)?;

stream.seek(SeekFrom::Start(0))?;
let decoded = Variant::decode(&mut stream, &context)?;

assert_eq!(my_opcua_value, decoded);

Custom types

In order to make a custom OPC-UA structure, it must implement a number of traits depending on which features are enabled:

• BinaryEncodable and BinaryDecodable, implementing encoding using the OPC-UA Binary protocol.
• JsonEncodable and JsonDecodable, implementing encoding using OPC-UA JSON, if the "json" feature is enabled.
• FromXml, loading the type from a NodeSet2 XML file, if the "xml" feature is enabled.
• Clone, Send, Sync, Debug, PartialEq are all required.
• ExpandedMessageInfo, which provides full encoding IDs.

A type that satisfies these requirements can be stored in an ExtensionObject and sent to OPC-UA. In order to receive the type, it must be added to a TypeLoader.

BinaryEncodable, BinaryDecodable, JsonEncodable, JsonDecodable, and FromXml all have derive macros.

Enums are simpler, the easiest way to make a custom OPC-UA enum (not a union) is to derive the UaEnum trait, which also implements a few other traits needed for numeric OPC-UA enums.