mqtty 0.1.9

Bridges MQTT topics to a pseudo-terminal device

mqtty

mqtty bridges MQTT topics to either your local terminal or a pseudoterminal (PTY), and now also ships log capture and replay helpers for the same serial stream format.

This is useful for debugging, automation, or tunneling serial communication through a networked MQTT broker.

Commands

mqtty mqtt://<host>/<topic> [--pts-only]
mqtty --list mqtt://<host>/<topic-base>

mqtty runs in bidirectional terminal mode by default:

• bytes from stdin are published to .../device_serial_input
• bytes from .../device_serial_output are written to stdout
• if stdin is a TTY, it is placed into raw mode while mqtty is running
• type Ctrl-A Ctrl-X to exit, matching picocom's default exit sequence
• type Ctrl-A Ctrl-A to send a literal Ctrl-A

Use --pts-only if you only want a PTY device:

• --pts-only, -p: Print the path to the PTS device and keep it open without attaching local stdin/stdout. Useful for tools or scripts that want to use the virtual serial port.

Use --list to discover serial ports below a base topic:

• --list, -l: Subscribe below <topic-base> for retained .../_mqtty/available discovery messages, print matching serial URLs, and exit.
• --list-timeout: Seconds to wait for retained discovery messages. Defaults to 1.0.

mqtty-log records .../device_serial_output into replay files:

mqtty-log device mqtt://<host>/<serial-server>/<device> capture.jsonl.zst
mqtty-log prefix mqtt://<host>/<topic-prefix> logs/

• device records one full device URL into a single compressed replay file and adds .zst if omitted
• prefix subscribes to <topic-prefix>/#, keeps topics ending in device_serial_output, and rotates per-device logs under <outdir>/<topic-path-below-prefix>/YYYY-MM-DD_replay.jsonl.zst
• each replay record stores an absolute Unix epoch timestamp in milliseconds (ts) before relative delay (t) and payload (d)

mqtty-log-replay replays either plain or compressed replay logs:

mqtty-log-replay path/to/replay.jsonl.zst [--raw] [--follow] [--info]

Raw .jsonl logs are still accepted for replay and inspection.

mqtty-serial-bridge discovers local serial devices and bridges them to MQTT:

mqtty-serial-bridge [--config /etc/mqtty-serial-bridge.toml]

It subscribes to:

• <topic_base>/<port>/device_serial_input

And publishes:

• <topic_base>/<port>/device_serial_output
• retained <topic_base>/<port>/_mqtty/available

The retained availability payload is JSON:

{"port":"<port>","alias":"<alias>"}

The MQTT broker stores retained discovery messages, so clients only need to connect to the broker. The bridge does not use a database. Removed ports may remain listed until retained messages are cleared from the broker.

Port aliases are resolved in this order:

1. [serial_aliases] entries in the bridge config
2. <serial-base-path>/<port>.alias text files
3. the resolved local device path, such as /dev/ttyACM0

Default config path:

1. /etc/mqtty-serial-bridge.toml

The <topic> segment of the URI is used as the base path for MQTT messages across both live commands:

• .../device_serial_input receives bytes from local input and sends them to the device
• .../device_serial_output carries device output back to your terminal or PTY

Example

mqtty mqtt://broker.local/mydevice

This connects your terminal directly to mydevice/device_serial_input and mydevice/device_serial_output.

To expose a PTY instead:

mqtty mqtt://broker.local/mydevice --pts-only

This prints the local PTY path and keeps it bridged to the same MQTT topics until interrupted.

To capture a replay log while a device is running:

mqtty-log device mqtt://broker.local/mydevice mydevice.jsonl.zst

To capture every device under one serial-server or a broader base prefix:

mqtty-log prefix mqtt://broker.local/testbench/mark-pantry logs/
mqtty-log prefix mqtt://broker.local/testbench logs/

To inspect or replay that log later:

mqtty-log-replay mydevice.jsonl.zst --info
mqtty-log-replay mydevice.jsonl.zst

To run the serial bridge:

mqtty-serial-bridge

To list retained serial bridge ports under a base topic:

mqtty --list mqtt://broker.local/testbench/serial
mqtty --list mqtt://broker.local/testbench/

Example output:

mqtt://broker.local/testbench/serial/platform-ci_hdrc.1-usb-0:1.2:1.0 (/dev/ttyACM0)
mqtt://broker.local/testbench/mark-desktop/platform-ci_hdrc.1-usb-0:1.2:1.0 (/dev/ttyACM0)

Testing

Run the test suite with:

pytest

Integration tests in tests/test_integration_mqtt_apps.py spin up a temporary local mosquitto broker and use Linux PTYs (pty.openpty) as fake serial devices.

Integration tests require mosquitto and fail if it is not available on PATH.

Repeatable Docker run (includes mosquitto in the container):

./scripts/run-tests-docker.sh

Show each executed test (verbose):

./scripts/run-tests-docker.sh --verbose

License

MIT