feat: network monitoring from agents (#2266, #1911)

Co-authored-by: Sven van Ginkel <svenvanginkel@icloud.com>
Co-authored-by: xiaomiku01 <xiaomiku01@outlook.com>

internal/alerts/network_monitor_cache.go

@@ -0,0 +1,79 @@
+package alerts
+
+import (
+	"sync"
+
+	"github.com/pocketbase/dbx"
+	"github.com/pocketbase/pocketbase/core"
+)
+
+// networkMonitorCache keeps just the enabled monitor IDs and probe intervals
+// needed for the alert fast path. Names and targets are read only on transitions.
+// Returned maps are immutable; configuration changes invalidate the whole entry.
+type networkMonitorCache struct {
+	app     core.App
+	mu      sync.RWMutex
+	systems map[string]map[string]int
+}
+
+func newNetworkMonitorCache(app core.App) *networkMonitorCache {
+	c := &networkMonitorCache{app: app, systems: make(map[string]map[string]int)}
+	invalidate := func(e *core.RecordEvent) error {
+		c.invalidate(e.Record.GetString("system"))
+		return e.Next()
+	}
+	app.OnRecordAfterCreateSuccess("network_monitors").BindFunc(invalidate)
+	app.OnRecordAfterDeleteSuccess("network_monitors").BindFunc(invalidate)
+	app.OnRecordAfterUpdateSuccess("network_monitors").BindFunc(func(e *core.RecordEvent) error {
+		old := e.Record.Original()
+		// Realtime metric saves also invoke this hook. They must not evict config.
+		if old.GetString("system") != e.Record.GetString("system") ||
+			old.GetBool("enabled") != e.Record.GetBool("enabled") ||
+			old.GetInt("interval") != e.Record.GetInt("interval") {
+			c.invalidate(old.GetString("system"))
+			c.invalidate(e.Record.GetString("system"))
+		}
+		return e.Next()
+	})
+	app.OnRecordAfterDeleteSuccess("systems").BindFunc(func(e *core.RecordEvent) error {
+		c.invalidate(e.Record.Id)
+		return e.Next()
+	})
+	return c
+}
+
+func (c *networkMonitorCache) invalidate(systemID string) {
+	c.mu.Lock()
+	delete(c.systems, systemID)
+	c.mu.Unlock()
+}
+
+func (c *networkMonitorCache) get(systemID string) (map[string]int, error) {
+	c.mu.RLock()
+	monitors, ok := c.systems[systemID]
+	c.mu.RUnlock()
+	if ok {
+		return monitors, nil
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if monitors, ok := c.systems[systemID]; ok {
+		return monitors, nil
+	}
+	// Keep the lock through the load so a concurrent config change cannot be
+	// invalidated first and then overwritten by the older query result.
+	var rows []struct {
+		ID       string `db:"id"`
+		Interval int    `db:"interval"`
+	}
+	if err := c.app.DB().Select("id", "interval").From("network_monitors").
+		Where(dbx.HashExp{"system": systemID, "enabled": true}).All(&rows); err != nil {
+		return nil, err
+	}
+	monitors = make(map[string]int, len(rows))
+	for _, row := range rows {
+		monitors[row.ID] = row.Interval
+	}
+	c.systems[systemID] = monitors
+	return monitors, nil
+}