Demo Server

Implementation of the optional live host-metrics demo used by s7 demo. Install python-snap7[demo] before running it. This module is intended for examples and integration testing, not production monitoring.

Live demo server that exposes real host metrics as S7 PLC tags.

Starts an emulated S7 server and continuously writes real CPU / memory / disk / network readings into well-known DB1 offsets, plus a writable DB2 block that clients (e.g. the ha-s7 Home Assistant integration) can write to. An optional rich live display shows the current values and logs any writes with a timestamp.

This is a demo, not a production tool. Install with:

pip install "python-snap7[demo]"
s7 demo --port 10102

The demo extras pull in everything the demo needs: psutil for metrics, rich for the live dashboard, and click for the CLI entry point.

DB layout

DB1 (read-only — updated by the host):

DB1.DBD0:REAL    cpu_percent          0..100
DB1.DBD4:REAL    memory_percent       0..100
DB1.DBD8:REAL    disk_read_mbps       megabytes/second
DB1.DBD12:REAL   disk_write_mbps      megabytes/second
DB1.DBD16:REAL   net_rx_mbps          megabytes/second
DB1.DBD20:REAL   net_tx_mbps          megabytes/second
DB1.DBD24:REAL   cpu_temp_c           0 if sensor not available
DB1.DBD28:REAL   fan_rpm              0 if sensor not available
DB1.DBD32:DINT   uptime_seconds
DB1.DBX36.0:BOOL overheating          cpu_temp > 75
DB1.DBX36.1:BOOL high_load            cpu_percent > 80
DB1.DBX36.2:BOOL disk_busy            disk_read+write > 50 MB/s

DB2 (writable — observe writes from a client):

DB2.DBX0.0:BOOL  lamp_on
DB2.DBX0.1:BOOL  alarm_enable
DB2.DBW2:INT     brightness           0..255
DB2.DBW4:INT     setpoint_c
DB2:10:STRING[32] message

class snap7.demo.ControlWatcher(buffer: bytearray, on_change: Callable[[str, str], None])

Diffs the controls DB buffer on each tick and reports human-readable changes.

The server emulator doesn’t expose a write callback, so we just snapshot the buffer and compare — simpler than monkey-patching internals and it’s good enough for a demo (sub-second resolution).

class snap7.demo.MetricCollector

Polls psutil for metrics, computing rate deltas against the previous reading.

sample() → Metrics

Take a metrics snapshot. Rates are computed over the interval since the last sample.

class snap7.demo.Metrics(cpu_percent: float = 0.0, memory_percent: float = 0.0, disk_read_mbps: float = 0.0, disk_write_mbps: float = 0.0, net_rx_mbps: float = 0.0, net_tx_mbps: float = 0.0, cpu_temp_c: float = 0.0, fan_rpm: float = 0.0, uptime_seconds: int = 0)

Snapshot of host metrics.

snap7.demo.run_demo(port: int = 10102, refresh_seconds: float = 2.0, live: bool = True) → None

Run the demo server until interrupted.

Parameters:

• port – TCP port the server listens on.

• refresh_seconds – Interval between metric samples and DB2 diffs.

• live – Use the rich live display. Falls back to plain logging if rich is not installed.