feat: sample Raspberry Pi primary interface traffic rates

app/network_rates.py

@@ -0,0 +1,29 @@
+"""Sample interface counters without summing physical and virtual interfaces."""
+import re
+from pathlib import Path
+
+
+class NetworkRates:
+    def __init__(self, root='/sys/class/net'):
+        self.root = Path(root)
+        self.previous = None
+
+    def sample(self, interface, now):
+        try:
+            if not re.fullmatch(r'[\w.:-]{1,64}', interface):
+                raise ValueError('invalid interface')
+            directory = self.root / interface / 'statistics'
+            rx = int((directory / 'rx_bytes').read_text())
+            tx = int((directory / 'tx_bytes').read_text())
+            if rx < 0 or tx < 0:
+                raise ValueError('negative counter')
+        except (OSError, ValueError, TypeError):
+            self.previous = None
+            return None, None
+        previous = self.previous
+        self.previous = interface, now, rx, tx
+        if previous is None or previous[0] != interface or now <= previous[1]:
+            return None, None
+        elapsed = now - previous[1]
+        return (None if rx < previous[2] else (rx - previous[2]) / elapsed,
+                None if tx < previous[3] else (tx - previous[3]) / elapsed)