fix(GODT-1615): Fix too many SQL variables error

Perform paged loading of snapshot state from the database to avoid
SQL error.

This patch also adds an utility to to fill the database with many
messages and invoke `Flush()` after they have all been submitted.

Testing large mailboxes can cause the CI to timeout, specially on
windows (>10 min), therefore the test is added as a benchmark instead.

internal/backend/snapshot.go

@@ -28,11 +28,24 @@ func newSnapshot(ctx context.Context, state *State, mbox *ent.Mailbox) (*snapsho
 		messages: newMsgList(),
 	}
 
-	msgUIDs, err := mbox.QueryUIDs().
-		WithMessage(func(query *ent.MessageQuery) { query.WithFlags() }).
-		All(ctx)
-	if err != nil {
-		return nil, err
+	var msgUIDs []*ent.UID
+
+	const limit = 16000
+
+	for offset := 0; ; offset += limit {
+		list, err := mbox.QueryUIDs().
+			WithMessage(func(query *ent.MessageQuery) { query.WithFlags() }).Offset(offset).Limit(limit).
+			All(ctx)
+
+		if err != nil {
+			return nil, err
+		}
+
+		if len(list) == 0 {
+			break
+		}
+
+		msgUIDs = append(msgUIDs, list...)
 	}
 
 	for _, msgUID := range msgUIDs {

tests/benchmark_big_mailbox_test.go

@@ -0,0 +1,20 @@
+package tests
+
+import (
+	"fmt"
+	"testing"
+)
+
+func BenchmarkBigMailboxStatus(b *testing.B) {
+	b.Run("status", func(b *testing.B) {
+		runOneToOneTestWithAuth(b, defaultServerOptions(b), func(c *testConnection, s *testSession) {
+			mboxID := s.mailboxCreated("user", []string{"mbox"})
+
+			ids := s.batchMessageCreated("user", mboxID, 32515, func(n int) ([]byte, []string) {
+				return []byte(fmt.Sprintf(`To: %[email protected]`, n)), []string{}
+			})
+
+			c.Cf(`A001 STATUS %v (MESSAGES)`, "mbox").Sx(fmt.Sprintf(`MESSAGES %v`, len(ids))).OK(`A001`)
+		})
+	})
+}

tests/session_test.go

@@ -166,6 +166,31 @@ func (s *testSession) messageCreated(user, mailboxID string, literal []byte, fla
 	return messageID
 }
 
+func (s *testSession) batchMessageCreated(user string, mailboxID string, count int, createMessage func(int) ([]byte, []string)) []string {
+	var messageIDs []string
+
+	for i := 0; i < count; i++ {
+		messageID := utils.NewRandomMessageID()
+
+		literal, flags := createMessage(i)
+
+		require.NoError(s.tb, s.conns[s.userIDs[user]].MessageCreated(
+			imap.Message{
+				ID:    messageID,
+				Flags: imap.NewFlagSetFromSlice(flags),
+				Date:  time.Now(),
+			},
+			literal,
+			[]string{mailboxID},
+		))
+
+		messageIDs = append(messageIDs, messageID)
+	}
+	s.conns[s.userIDs[user]].Flush()
+
+	return messageIDs
+}
+
 func (s *testSession) messageCreatedFromFile(user, mailboxID, path string, flags ...string) string {
 	literal, err := os.ReadFile(path)
 	require.NoError(s.tb, err)