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{canscope}

CAN bus sniffer and SAE J1939 protocol analyzer. Reads CAN frames from an external process (e.g. candump), decodes them using a J1939 Digital Annex (xlsx), and presents results in an interactive terminal UI or as JSON output.

Features

TUI mode -- full-screen interactive terminal interface (FTXUI). Multiple display modes per CAN ID: deployed, brief, verbose, manual, little-endian
Headless mode -- JSON output to stdout or file, for scripting and automation
Recording -- decoded J1939 SPN values saved to SQLite database with gzip compression and batch flushing
J1939 decoding -- PGN/SPN lookup, bit-level value extraction from payload
CAN playback -- replay recorded CAN frames
Custom SPN configuration -- per-parameter settings, parameter export
Real-time -- 30 fps UI refresh

Build

Requirements:

clang++ with C++23 support
CMake >= 3.13
System libraries: boost (signals2, spirit, phoenix), sqlite3, systemd, zlib

The rest of the dependencies are fetched automatically via CMake FetchContent:

FTXUI -- terminal UI framework
tiny-process-library -- subprocess management
sqlite_modern_cpp -- modern C++ SQLite wrapper
xlnt -- xlsx reading
fmt -- text formatting
nlohmann/json -- JSON library
spdlog -- logging
clipp -- CLI argument parsing

cmake -B build -S . && cmake --build build -j$(nproc)

Binary: build/canscope

Docker

docker build -t canscope .

# TUI mode -- requires terminal and CAN interface access
docker run -it --network=host canscope -e "candump can0" -j1939 /app/thirdparty/j1939da_2018.xlsx

# Headless mode
docker run --network=host canscope -hl -e "candump can0" -j1939 /app/thirdparty/j1939da_2018.xlsx

# Read from stdin
candump can0 | docker run -i canscope -j1939 /app/thirdparty/j1939da_2018.xlsx -hl

Usage

# TUI mode (default)
./build/canscope -e "candump can0" -j1939 thirdparty/j1939da_2018.xlsx

# Headless -- JSON to stdout
./build/canscope -hl -e "candump can0" -j1939 thirdparty/j1939da_2018.xlsx

# Headless -- JSON to file
./build/canscope -hl -e "candump can0" -j1939 thirdparty/j1939da_2018.xlsx -of output.json

# Read from stdin (pipe)
candump can0 | ./build/canscope -j1939 thirdparty/j1939da_2018.xlsx

# Headless with stdin
candump can0 | ./build/canscope -hl -j1939 thirdparty/j1939da_2018.xlsx

# Docker -- TUI with CAN interface access
docker run -it --network=host canscope -e "candump can0" -j1939 /app/thirdparty/j1939da_2018.xlsx

# Docker -- headless
docker run --network=host canscope -hl -e "candump can0" -j1939 /app/thirdparty/j1939da_2018.xlsx

# Docker -- read from stdin
candump can0 | docker run -i canscope -hl -j1939 /app/thirdparty/j1939da_2018.xlsx

# Record to SQLite database
./build/canscope -rec -db recording.db -e "candump can0" -j1939 thirdparty/j1939da_2018.xlsx

# Record + TUI
./build/canscope -rec -db recording.db -tui -e "candump can0" -j1939 thirdparty/j1939da_2018.xlsx

Note: J1939 decoding has only been tested with the Digital Annex 2018 edition. Other editions may work but are not guaranteed.

CLI flags

Flag	Long form	Description
`-j1939`	`--j1939-document`	(required) J1939 Digital Annex xlsx file
`-e`	`--execute-command`	Command to read CAN frames from (e.g. `"candump can0"`)
`-hl`	`--headless`	Headless mode (no TUI)
`-of`	`--output-file`	Output file path (headless mode)
`-rec`	`--record`	Record decoded values to SQLite
`-db`	`--database`	SQLite database path (required with `-rec`)
`-tui`		Show TUI alongside recording
`-h`	`--help`	Show help

Architecture

candump / other CAN source
        |  stdout
        v
  aggregator_task ──> shared JSON (mutex-protected)
        |
   diff_task (33ms)
        |
   "new_entry" signal
      /    \
    TUI   headless/recorder

Patterns

Components communicate through a type-safe signal map (signals_map_t)
nlohmann::json as universal data interchange between all layers
Factory functions via extern declarations instead of header includes
std::jthread / std::stop_token for async task management
SIGINT gracefully stops all background tasks

Roadmap

Cross-platform support -- Windows and macOS in addition to Linux
Docker deployment -- pre-built image for quick setup without manual compilation
CANopen protocol support -- CANopen decoding alongside J1939

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