enip

enip

EtherNet/IP in pure Go: a client (scanner) and an adapter (server) for Logix controller tags, tag browsing, structures, CIP object attributes and class 1 implicit I/O.

The module reads and writes Logix controller tags by name and reads and sets CIP object attributes on any CIP device, over a class 3 connection (Forward Open or Large Forward Open) or unconnected, directly or through a backplane route. It discovers devices with ListIdentity over UDP. Since v0.2.0 it browses a controller's tags and structure definitions (ListTags, ReadTemplate), runs class 1 I/O as a scanner (OpenIO), and the server package is the adapter role: a Logix-like target with tags, structures, browsing, member access and class 1 assemblies. It has no cgo and no dependency beyond the standard library and lanbcast. It was written for SigmaM2M, a oneM2M platform, where it serves the EtherNet/IP integration; it does not depend on it.

Features

Choosing an EtherNet/IP library

Compared from each project's source at the version named, in October 2026. "Tested" means run against this module in the interop tests below. Check the projects themselves before relying on a row.

Pick this module for a Go program without cgo that reads, writes and browses Logix tags and structures, CIP attributes and class 1 I/O, or that must act as an EtherNet/IP adapter a Logix-style client can browse. Pick gologix if its I/O server has been checked against your scanner (this module's I/O is not yet checked against another implementation); pick libplctag when cgo is fine and you need PCCC or many PLC families; pick pycomm3 in Python.

Install

go get github.com/cB-Sigma/enip@latest

Requires Go 1.22 or later.

Quick start

import "github.com/cB-Sigma/enip"

route, _ := enip.Route("1,0") // backplane port 1, slot 0
c := &enip.Client{Addr: "192.0.2.20:44818", Route: route, Timeout: 2 * time.Second, Connected: true}
defer c.Close()
ty, data, err := c.ReadTag(ctx, "Program:Main.Flow", 1)
v, _ := enip.Decode(ty, data, 1, nil)
err = c.WriteTag(ctx, "Setpoint", enip.Type{Code: enip.TypeREAL}, 1, b)
id, err := c.ListIdentity(ctx)

Browsing and the adapter (v0.2.0):

tags, _ := c.ListTags(ctx, "")              // controller scope; ListTags(ctx, "Main") for a program
tmpl, _ := c.ReadTemplate(ctx, tags[0].Template)
_, data, _ := c.ReadTag(ctx, tags[0].Name, 1)
v, _ := tmpl.DecodeStruct(data, nil)       // map of member name to value

s := server.New()
s.DefineStruct(server.StructDef{Name: "Motor", Handle: 0x2002, Size: 8, Fields: fields})
s.SetTag("Pump", enip.Type{Code: enip.TypeStruct, Handle: 0x2002}, 1, raw)
s.Start(":44818")

TestListTagsAndTemplates and TestImplicitIO (server/) run these. The runnable examples in this module are ExampleEncodeString and ExampleRoute; enip-sim has a client example against the simulated controller.

Documentation

API reference: https://pkg.go.dev/github.com/cB-Sigma/enip

Testing

go vet ./...
go test -race ./...

Tests carry // Covers: SIG-... comments: requirement IDs of the SigmaM2M project's compliance report, with no meaning outside it. The tests that drive the simulated controller are in enip-sim, so this module does not depend on its simulator.

interop/ is a nested module with its own go.mod. It runs cpppo 5.2.5 (GPL, installed from PyPI in a container, used only as a test peer) as a simulated Logix controller and runs this module's client against it. The tests are skipped unless SIGMA_ENIP_INTEROP=1 is set and Docker is running:

cd interop && SIGMA_ENIP_INTEROP=1 go test -race -v ./...

Interop tested against

Run on 2026-10-11 on macOS with Docker Desktop; every item below passed. cpppo 5.2.5's EtherNet/IP server, this module's client, unconnected without a route, over Forward Open (500 octets), over Large Forward Open (4000 octets), and through route 1/2 both unconnected and connected:

Found on the way and fixed in this module (v0.1.0): cpppo puts our own O→T connection ID in the address item of its connected replies, where the T→O ID is expected, and the client refused every reply. The client now accepts either of its own two IDs and still refuses any other connection (TestConnectedReplyWithEchoedOTID).

Behaviour of the reference peer met on the way (not ours): cpppo treats any unrouted unconnected service 0x52 as Unconnected Send, so a fragmented read sent straight to it, unrouted and unconnected, cannot be tested; it wants a pad octet after an odd-length CIP STRING in a write.

pycomm3 1.2.16's LogixDriver against this module's adapter role (2026-10-12, python:3.12.10-slim in Docker; interop/pycomm3_test.go, our script in interop/pycomm3), opened with its own tag upload (init_tags, init_program_tags); every item passed:

Found on the way (in this module's own test, not in pycomm3): the test's UDT had a member overlapping the next; CheckStruct now reports such layouts (TestCheckStruct).

Not tested against an independent implementation:

• This module's ListTags and ReadTemplate against another adapter (cpppo has no Symbol or Template object; a real controller is hardware).
• Class 1 I/O: scanner and adapter are tested against each other only. gologix's I/O server binds UDP 2222 itself, which a scanner on the same host cannot share; a run in separate containers is next.
• Whether a route inside the Forward Open path is checked (cpppo checks routes on Unconnected Send only).
• Real controllers (ControlLogix, CompactLogix) and other CIP devices.
• In process: the simulated controller of enip-sim (same author, so not independent). pycomm3 1.2.16 is run against that simulator in enip-sim's interop tests.

Not yet

Related repositories

• enip-sim: a simulated Logix controller, as a Go package and a command.
• lanbcast: the LAN broadcast helper used by Discover.

Status

v0.x: the API may change before v1.

Contributing

See CONTRIBUTING.md.

Security

See SECURITY.md to report a vulnerability privately.

Licence

Apache-2.0 (see LICENSE and NOTICE). Copyright 2026 Abhinav Gautam. EtherNet/IP and CIP are trademarks of ODVA; Logix, ControlLogix and CompactLogix are trademarks of Rockwell Automation. This project is not affiliated with or endorsed by either.