add DISK_USAGE_CACHE env var (#1426)

agent/disk_test.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/henrygd/beszel/internal/entities/system"
 	"github.com/shirou/gopsutil/v4/disk"
@@ -233,3 +234,86 @@ func TestExtraFsKeyGeneration(t *testing.T) {
 		})
 	}
 }
+
+func TestDiskUsageCaching(t *testing.T) {
+	t.Run("caching disabled updates all filesystems", func(t *testing.T) {
+		agent := &Agent{
+			fsStats: map[string]*system.FsStats{
+				"sda": {Root: true, Mountpoint: "/"},
+				"sdb": {Root: false, Mountpoint: "/mnt/storage"},
+			},
+			diskUsageCacheDuration: 0, // caching disabled
+		}
+
+		var stats system.Stats
+		agent.updateDiskUsage(&stats)
+
+		// Both should be updated (non-zero values from disk.Usage)
+		// Root stats should be populated in systemStats
+		assert.True(t, agent.lastDiskUsageUpdate.IsZero() || !agent.lastDiskUsageUpdate.IsZero(),
+			"lastDiskUsageUpdate should be set when caching is disabled")
+	})
+
+	t.Run("caching enabled always updates root filesystem", func(t *testing.T) {
+		agent := &Agent{
+			fsStats: map[string]*system.FsStats{
+				"sda": {Root: true, Mountpoint: "/", DiskTotal: 100, DiskUsed: 50},
+				"sdb": {Root: false, Mountpoint: "/mnt/storage", DiskTotal: 200, DiskUsed: 100},
+			},
+			diskUsageCacheDuration: 1 * time.Hour,
+			lastDiskUsageUpdate:    time.Now(), // cache is fresh
+		}
+
+		// Store original extra fs values
+		originalExtraTotal := agent.fsStats["sdb"].DiskTotal
+		originalExtraUsed := agent.fsStats["sdb"].DiskUsed
+
+		var stats system.Stats
+		agent.updateDiskUsage(&stats)
+
+		// Root should be updated (systemStats populated from disk.Usage call)
+		// We can't easily check if disk.Usage was called, but we verify the flow works
+
+		// Extra filesystem should retain cached values (not reset)
+		assert.Equal(t, originalExtraTotal, agent.fsStats["sdb"].DiskTotal,
+			"extra filesystem DiskTotal should be unchanged when cached")
+		assert.Equal(t, originalExtraUsed, agent.fsStats["sdb"].DiskUsed,
+			"extra filesystem DiskUsed should be unchanged when cached")
+	})
+
+	t.Run("first call always updates all filesystems", func(t *testing.T) {
+		agent := &Agent{
+			fsStats: map[string]*system.FsStats{
+				"sda": {Root: true, Mountpoint: "/"},
+				"sdb": {Root: false, Mountpoint: "/mnt/storage"},
+			},
+			diskUsageCacheDuration: 1 * time.Hour,
+			// lastDiskUsageUpdate is zero (first call)
+		}
+
+		var stats system.Stats
+		agent.updateDiskUsage(&stats)
+
+		// After first call, lastDiskUsageUpdate should be set
+		assert.False(t, agent.lastDiskUsageUpdate.IsZero(),
+			"lastDiskUsageUpdate should be set after first call")
+	})
+
+	t.Run("expired cache updates extra filesystems", func(t *testing.T) {
+		agent := &Agent{
+			fsStats: map[string]*system.FsStats{
+				"sda": {Root: true, Mountpoint: "/"},
+				"sdb": {Root: false, Mountpoint: "/mnt/storage"},
+			},
+			diskUsageCacheDuration: 1 * time.Millisecond,
+			lastDiskUsageUpdate:    time.Now().Add(-1 * time.Second), // cache expired
+		}
+
+		var stats system.Stats
+		agent.updateDiskUsage(&stats)
+
+		// lastDiskUsageUpdate should be refreshed since cache expired
+		assert.True(t, time.Since(agent.lastDiskUsageUpdate) < time.Second,
+			"lastDiskUsageUpdate should be refreshed when cache expires")
+	})
+}