Skip to content

tag_introspection.md

Latest commit

 

History

History
61 lines (45 loc) · 1.99 KB

tag_introspection.md

File metadata and controls

61 lines (45 loc) · 1.99 KB

Tag introspection

Use tag introspection to discover a tag’s type, size, dimensions, and scope before reading or writing. This is useful for:

  • Validating tag names and types at startup
  • Building generic tools that work with any tag
  • Handling arrays and UDTs when you don’t have a fixed schema

API

let attrs = client.get_tag_attributes("MyTag").await?;

TagAttributes includes:

Field Description
name Tag name as returned by the PLC
data_type CIP type code (e.g. 0xC4 for DINT)
data_type_name Human-readable type (e.g. "DINT")
dimensions Array dimensions; empty for scalars
permissions ReadOnly, ReadWrite, or WriteOnly
scope Controller or Program(name)
size Size in bytes
template_instance_id Set for UDTs (for template discovery)

Example: discover then read

use rust_ethernet_ip::{EipClient, PlcValue};

let attrs = client.get_tag_attributes("ProductionCount").await?;
println!("Type: {}, size: {} bytes", attrs.data_type_name, attrs.size);

let value = client.read_tag("ProductionCount").await?;
match value {
    PlcValue::Dint(n) => println!("Count: {}", n),
    _ => println!("Unexpected type"),
}

Example: check if tag is an array

let attrs = client.get_tag_attributes("LineData").await?;
if attrs.dimensions.is_empty() {
    println!("Scalar tag");
} else {
    println!("Array dimensions: {:?}", attrs.dimensions);
}

Caching

Attributes are cached per tag for the lifetime of the EipClient. The first call for a given tag name performs a CIP Get Attribute List request; subsequent calls for the same tag return the cached result.

Related