feat(server): online session history with configurable stats window (#1243)

Add persisted online sessions, configurable retention and online history statistics with lifecycle, recovery, timezone and concurrency regression coverage.

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

service/singleton/online_history_retention_test.go

@@ -0,0 +1,63 @@
+package singleton
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/nezhahq/nezha/model"
+	"github.com/stretchr/testify/require"
+)
+
+func TestOnlineHistoryPruneWaitsForRetentionCommit(t *testing.T) {
+	for _, saveFails := range []bool{true, false} {
+		t.Run(map[bool]string{true: "failed_save", false: "successful_save"}[saveFails], func(t *testing.T) {
+			setupOnlineHistoryTestDB(t)
+			previous := Conf
+			Conf = &ConfigClass{Config: &model.Config{}}
+			Conf.OnlineStatsDays = 30
+			t.Cleanup(func() { Conf = previous })
+			now := time.Now().UTC()
+			row := model.OnlineSession{ServerID: 1, StartedAt: now.AddDate(0, 0, -15), EndedAt: now.AddDate(0, 0, -14)}
+			require.NoError(t, DB.Create(&row).Error)
+			saveEntered := make(chan struct{})
+			releaseSave := make(chan struct{})
+			saved := make(chan error, 1)
+			days := 7
+			go func() {
+				saved <- Conf.CommitOnlineHistoryRetention(&days, func() error {
+					close(saveEntered)
+					<-releaseSave
+					if saveFails {
+						return errors.New("retention save unavailable")
+					}
+					return nil
+				})
+			}()
+			<-saveEntered
+			pruneStarted := make(chan struct{})
+			pruned := make(chan struct{})
+			go func() { close(pruneStarted); PruneOnlineSessions(); close(pruned) }()
+			<-pruneStarted
+			premature := false
+			select {
+			case <-pruned:
+				premature = true
+			case <-time.After(100 * time.Millisecond):
+			}
+			close(releaseSave)
+			err := <-saved
+			<-pruned
+			require.False(t, premature, "pruning must not read an uncommitted retention policy")
+			if saveFails {
+				require.ErrorContains(t, err, "retention save unavailable")
+				require.Equal(t, 30, Conf.OnlineHistoryRetentionDays())
+				require.Equal(t, int64(1), countOnlineSessions(t, "id = ?", row.ID))
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, 7, Conf.OnlineHistoryRetentionDays())
+				require.Equal(t, int64(0), countOnlineSessions(t, "id = ?", row.ID))
+			}
+		})
+	}
+}