go-dnp3

go-dnp3 is a Go library for parsing and encoding DNP3 (Distributed Network Protocol) frames.

Usage

*dnp3.Frame implements the standard gopacket interfaces (Layer, DecodingLayer, SerializableLayer, ApplicationLayer). TCP and UDP port 20000 (DNP3-over-IP) are auto-registered, so gopacket.NewPacket decodes DNP3 automatically.

• Parsing: Use gopacket.NewPacket(data, dnp3.LayerTypeDNP3, gopacket.Default), or dnp3.NewFrameFromBytes(data) for raw frame bytes, or frame.DecodeFromBytes(data, df) to drive gopacket.DecodingLayerParser.
• Encoding: Use gopacket.SerializeLayers(buf, opts, frame). Frame.SerializeTo recomputes DataLink.Length and inserts DNP3 CRCs on the fly.
• Stream parsing: Use dnp3.ParseFrames(data) to consume multiple DNP3 frames out of a single TCP read (handles partial trailing frames).
• Inspection: Use String() for a human-readable, indented packet dump (excludes reserved fields and CRCs).
• Serialization: Full support for json.Marshal() to convert packets into machine-friendly JSON.

Example

// Auto-decode (NewPacket dispatches on LayerTypeDNP3 directly, or on TCP/UDP port 20000 in a pcap):
pkt := gopacket.NewPacket(input, dnp3.LayerTypeDNP3, gopacket.Default)
frame := pkt.Layer(dnp3.LayerTypeDNP3).(*dnp3.Frame)

// Build outbound:
buf := gopacket.NewSerializeBuffer()
gopacket.SerializeLayers(buf, gopacket.SerializeOptions{}, frame)
wire := buf.Bytes()

See example.go for a full end-to-end demo, including in-place point mutation and round-tripping.

Development

Setup

Run make setup to install development tools used by this repository.

Testing

Data for tests is sourced from opendnp3 conformance reports

Run make test to run basic tests.

PCAP Testing

Pass a full PCAP file using the -args option -pcaps=comma.pcap,delimited.pcap,list.pcap.

go test ./dnp3 -v -args -pcaps=my-custom.pcap

Printing Strings

View the string and json outputs of test cases using the -args flag -print-string and -print-json.

go test ./dnp3 -args -print

Linting

golangci-lint is used for lint and format checking. Run make lint to check for errors, and make fix to try to automatically fix linting or formatting errors.

Implementation

Based on Wireshark's parser and publicly available documents (such as this validation guide), as access to the official DNP3 specification is restricted.