add one minute chart + refactor rpc

- add one minute charts
- update disk io to use bytes
- update hub and agent connection interfaces / handlers to be more
flexible
- change agent cache to use cache time instead of session id
- refactor collection of metrics which require deltas to track
separately per cache time

agent/cpu.go

@@ -0,0 +1,66 @@
+package agent
+
+import (
+	"math"
+	"runtime"
+
+	"github.com/shirou/gopsutil/v4/cpu"
+)
+
+var lastCpuTimes = make(map[uint16]cpu.TimesStat)
+
+// init initializes the CPU monitoring by storing the initial CPU times
+// for the default 60-second cache interval.
+func init() {
+	if times, err := cpu.Times(false); err == nil {
+		lastCpuTimes[60000] = times[0]
+	}
+}
+
+// getCpuPercent calculates the CPU usage percentage using cached previous measurements.
+// It uses the specified cache time interval to determine the time window for calculation.
+// Returns the CPU usage percentage (0-100) and any error encountered.
+func getCpuPercent(cacheTimeMs uint16) (float64, error) {
+	times, err := cpu.Times(false)
+	if err != nil || len(times) == 0 {
+		return 0, err
+	}
+	// if cacheTimeMs is not in lastCpuTimes, use 60000 as fallback lastCpuTime
+	if _, ok := lastCpuTimes[cacheTimeMs]; !ok {
+		lastCpuTimes[cacheTimeMs] = lastCpuTimes[60000]
+	}
+	delta := calculateBusy(lastCpuTimes[cacheTimeMs], times[0])
+	lastCpuTimes[cacheTimeMs] = times[0]
+	return delta, nil
+}
+
+// calculateBusy calculates the CPU busy percentage between two time points.
+// It computes the ratio of busy time to total time elapsed between t1 and t2,
+// returning a percentage clamped between 0 and 100.
+func calculateBusy(t1, t2 cpu.TimesStat) float64 {
+	t1All, t1Busy := getAllBusy(t1)
+	t2All, t2Busy := getAllBusy(t2)
+
+	if t2Busy <= t1Busy {
+		return 0
+	}
+	if t2All <= t1All {
+		return 100
+	}
+	return math.Min(100, math.Max(0, (t2Busy-t1Busy)/(t2All-t1All)*100))
+}
+
+// getAllBusy calculates the total CPU time and busy CPU time from CPU times statistics.
+// On Linux, it excludes guest and guest_nice time from the total to match kernel behavior.
+// Returns total CPU time and busy CPU time (total minus idle and I/O wait time).
+func getAllBusy(t cpu.TimesStat) (float64, float64) {
+	tot := t.Total()
+	if runtime.GOOS == "linux" {
+		tot -= t.Guest     // Linux 2.6.24+
+		tot -= t.GuestNice // Linux 3.2.0+
+	}
+
+	busy := tot - t.Idle - t.Iowait
+
+	return tot, busy
+}