rust-ethernet-ip-udt

Logix UDT parsing and serialization helpers for the rust-ethernet-ip ecosystem.

Operates on the UdtData envelope (raw { symbol_id, data } bytes returned by the PLC) and a UdtDefinition (member layout) to:

• Parse UdtData bytes into a HashMap<String, PlcValue> keyed by member name
• Serialize a HashMap<String, PlcValue> back into UdtData bytes for write-back
• Read or write a single named member with correct byte-offset and DWORD-bit handling
• Walk nested arrays inside UDTs (e.g. Array_DINT[5] inside a UDT element)

Built on rust-ethernet-ip-types for the shared PlcValue / UdtData model.

Who should use this crate

Most consumers want the top-level rust-ethernet-ip crate, which uses these helpers internally and exposes EipClient::read_udt_chunked / read_udt_member / write_udt_member directly.

Depend on rust-ethernet-ip-udt directly only if you are building an out-of-band UDT-mapping layer (schema export, code generation against L5X exports, byte-level UDT auditing) without the network client.

Allen-Bradley firmware notes

UDT member-write behavior depends on the target member type and exact Logix wire encoding. Scalar UDT-array-element members are confirmed writeable on 5069-L330ERM fw38 when the full member path is preserved. STRING members inside UDTs and UDT-array elements reject with CIP 0x2107 under the current member encoding, so the top-level rust-ethernet-ip crate keeps a read-modify-write path for those cases.

License

MIT. Part of the rust-ethernet-ip workspace.