feat(metrics): add rate + blockstats/netstat/fsinfo parsing helpers

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/services/metrics_history.py

@@ -0,0 +1,47 @@
+"""Pure helpers + read query for instance metric history."""
+from __future__ import annotations
+
+import re
+
+_RD_OPS = re.compile(r"rd_operations=(\d+)")
+_WR_OPS = re.compile(r"wr_operations=(\d+)")
+
+
+def compute_rate(prev, cur, dt):
+    """Per-second rate from cumulative counters. None if unknowable; 0 on reset."""
+    if prev is None or cur is None or not dt or dt <= 0:
+        return None
+    delta = float(cur) - float(prev)
+    if delta < 0:
+        return 0.0
+    return delta / dt
+
+
+def parse_blockstats(text: str):
+    """Sum rd_operations / wr_operations across all block devices in HMP output."""
+    rd = sum(int(m) for m in _RD_OPS.findall(text or ""))
+    wr = sum(int(m) for m in _WR_OPS.findall(text or ""))
+    return rd, wr
+
+
+def parse_netstat(rows, vmid: int):
+    """Map dev -> (in_bytes, out_bytes) for the given vmid from /nodes/{node}/netstat."""
+    out: dict[str, tuple[int, int]] = {}
+    for r in rows or []:
+        try:
+            if int(r.get("vmid")) != int(vmid):
+                continue
+        except (TypeError, ValueError):
+            continue
+        dev = r.get("dev")
+        if not dev:
+            continue
+        out[dev] = (int(float(r.get("in", 0) or 0)), int(float(r.get("out", 0) or 0)))
+    return out
+
+
+def aggregate_fsinfo(disks):
+    """Sum used/total bytes across guest filesystems."""
+    used = sum(int(d.get("used", 0) or 0) for d in disks or [])
+    total = sum(int(d.get("total", 0) or 0) for d in disks or [])
+    return used, total