candecode

candecode

Convert CAN traffic captured in PCAPNG format into MCAP with rich decoded signal metadata using a DBC file.

Features

• PCAPNG CAN frame ingestion
• DBC-based message and signal decoding (via OpenDBC)
• Protobuf schema for decoded signals
• MCAP output (channel + schema recorded once, per-signal records appended)
• Progress logging with frame and signal counters
• Deterministic, dependency-tracked build via Makefile targets
• Reproducible proto generation with buf

Data Flow

PCAPNG file
  → pcapng reader (raw CAN frames)
    → DBC compiler + decoder
      → decoded signals (metadata & physical values)
        → protobuf (DecodedSignal)
          → MCAP writer (single output .mcap)

Requirements

• Go 1.24+
• Python + uv (for OpenDBC SCons build)
• curl (to fetch buf)
• make
• protoc / buf (buf binary downloaded automatically to ./bin via Makefile)

Installation

git clone --recurse-submodules https://github.com/BIwashi/candecode.git
cd candecode
make setup          # initializes submodules, uv environment, go mod tidy
make build          # builds OpenDBC, generates protobuf, builds binary

If cloned without submodules:

make sync

Build

make build          # all (opendbc + proto + binary)
make build/opendbc
make build/buf
make build/cmd

Artifacts:

• Binary: ./bin/candecode
• Generated protobuf: ./pkg/proto/*.pb.go
• MCAP outputs: ./mcap/*.mcap (created at runtime)

Usage

Convert a PCAPNG capture using a DBC file:

./bin/candecode convert \
  --dbc-file path/to/reference.dbc \
  --pcapng-file capture.pcapng

Output:

• Creates mcap/<capture-basename>.mcap

Required flags:

• --dbc-file path to DBC file
• --pcapng-file path to PCAPNG file containing CAN frames

Example

./bin/candecode convert \
  --dbc-file path/to/reference.dbc \
  --pcapng-file tests/sample_can_capture.pcapng
# Produces mcap/sample_can_capture.mcap

MCAP Content

Each decoded CAN signal is written as a DecodedSignal protobuf record including:

• Frame metadata (CAN ID, extended flag, raw frame bytes)
• Signal definition (bit start/length, endian, scale, offset, min, max, unit)
• Physical value (if derivable) and raw value (bool / int / uint / float / bytes)
• Value descriptions (enumerations) and receiver nodes
• Source DBC path

Schema definition: pkg/proto/dbc.proto (generated Go types in pkg/proto/dbc.pb.go).

Development

Formatting, imports, lint (strict imports + buf):

make lint

Tests:

make test
make test/coverage   # generates coverage.html

Cleaning

make clean          # opendbc build + binaries
make clean/bin
make clean/opendbc

OpenDBC Submodule

third_party/opendbc is a git submodule. Update to latest upstream main:

make sync

The OpenDBC SCons build runs automatically during make build (stamp file at ./bin/.opendbc_stamp).

Project Structure (selected)

cmd/main.go                  # CLI entry point
app/convert/cmd.go           # convert subcommand implementation
pkg/pcapng/reader.go         # PCAPNG frame reader
pkg/dbc/                     # DBC compiler & decoder abstraction
pkg/mcap/writer.go           # MCAP writer for DecodedSignal
pkg/proto/dbc.proto          # Protobuf schema (buf generates *.pb.go)
third_party/opendbc/         # OpenDBC database (submodule)
mcap/                        # Output directory (runtime)
pcapng/                      # Placeholder directory

Roadmap (Potential)

• Additional output channels (raw frame stream)
• Filtering by CAN ID or message name
• Parallel decode pipeline
• Additional export formats (Parquet / JSONL)

License

MIT License (see LICENSE).

Acknowledgements

• OpenDBC (vehicle DBC definitions)
• foxglove MCAP Go library
• buf (Protobuf build tooling)