Time travel pragma.

embed/bcw2/build.sh

@@ -23,6 +23,7 @@ if [[ "$OSTYPE" == "msys" || "$OSTYPE" == "cygwin" ]]; then
 	MSYS_NO_PATHCONV=1 nmake /f makefile.msc sqlite3.c "OPTS=-DSQLITE_ENABLE_UPDATE_DELETE_LIMIT -DSQLITE_ENABLE_ORDERED_SET_AGGREGATES"
 else
 	sh configure --enable-update-limit
+	make verify-source
 	OPTS=-DSQLITE_ENABLE_ORDERED_SET_AGGREGATES make sqlite3.c
 fi
 cd ~-

litestream/vfs.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -62,8 +63,10 @@ type liteFile struct {
 	db       *liteDB
 	conn     *sqlite3.Conn
 	pages    *pageIndex
+	syncTime time.Time
 	txid     ltx.TXID
 	pageSize uint32
+	locked   bool
 }
 
 func (f *liteFile) Close() error { return nil }
@@ -71,10 +74,11 @@ func (f *liteFile) Close() error { return nil }
 func (f *liteFile) ReadAt(p []byte, off int64) (n int, err error) {
 	ctx := f.context()
 	pages, txid := f.pages, f.txid
-	if pages == nil {
+	if pages == nil && f.syncTime.IsZero() {
 		pages, txid, err = f.db.pollReplica(ctx)
 	}
 	if err != nil {
+		f.db.opts.Logger.Error("poll replica", "error", err)
 		return 0, err
 	}
 
@@ -135,14 +139,25 @@ func (f *liteFile) Size() (size int64, err error) {
 
 func (f *liteFile) Lock(lock vfs.LockLevel) (err error) {
 	if lock >= vfs.LOCK_RESERVED {
+		// notest // OPEN_READONLY
 		return sqlite3.IOERR_LOCK
 	}
-	f.pages, f.txid, err = f.db.pollReplica(f.context())
+	if f.syncTime.IsZero() {
+		f.pages, f.txid, err = f.db.pollReplica(f.context())
+	}
+	if err != nil {
+		f.db.opts.Logger.Error("poll replica", "error", err)
+	} else {
+		f.locked = true
+	}
 	return err
 }
 
 func (f *liteFile) Unlock(lock vfs.LockLevel) error {
-	f.pages, f.txid = nil, 0
+	if f.syncTime.IsZero() {
+		f.pages, f.txid = nil, 0
+	}
+	f.locked = false
 	return nil
 }
 
@@ -166,7 +181,6 @@ func (f *liteFile) Pragma(name, value string) (string, error) {
 	case "litestream_txid":
 		txid := f.txid
 		if txid == 0 {
-			// Outside transaction.
 			f.db.mtx.Lock()
 			txid = f.db.txids[0]
 			f.db.mtx.Unlock()
@@ -179,11 +193,45 @@ func (f *liteFile) Pragma(name, value string) (string, error) {
 		f.db.mtx.Unlock()
 
 		if lastPoll.IsZero() {
-			// Never polled successfully.
 			return "-1", nil
 		}
 		lag := time.Since(lastPoll) / time.Second
 		return strconv.FormatInt(int64(lag), 10), nil
+
+	case "litestream_time":
+		if value == "" {
+			syncTime := f.syncTime
+			if syncTime.IsZero() {
+				f.db.mtx.Lock()
+				syncTime = f.db.lastInfo
+				f.db.mtx.Unlock()
+			}
+			if syncTime.IsZero() {
+				return "latest", nil
+			}
+			return syncTime.Format(time.RFC3339Nano), nil
+		}
+
+		if !f.locked {
+			return "", sqlite3.MISUSE
+		}
+
+		if strings.EqualFold(value, "latest") {
+			f.syncTime = time.Time{}
+			f.pages, f.txid = nil, 0
+			return "", nil
+		}
+
+		syncTime, err := sqlite3.TimeFormatAuto.Decode(value)
+		if err != nil {
+			return "", err
+		}
+
+		err = f.buildIndex(f.context(), syncTime)
+		if err != nil {
+			f.db.opts.Logger.Error("build index", "error", err)
+		}
+		return "", err
 	}
 
 	return "", sqlite3.NOTFOUND
@@ -200,27 +248,53 @@ func (f *liteFile) context() context.Context {
 	return context.Background()
 }
 
+func (f *liteFile) buildIndex(ctx context.Context, syncTime time.Time) error {
+	// Build the index from scratch from a Litestream restore plan.
+	infos, err := litestream.CalcRestorePlan(ctx, f.db.client, 0, syncTime, f.db.opts.Logger)
+	if err != nil {
+		if !errors.Is(err, litestream.ErrTxNotAvailable) {
+			return fmt.Errorf("calc restore plan: %w", err)
+		}
+		return nil
+	}
+
+	var txid ltx.TXID
+	var pages *pageIndex
+	for _, info := range infos {
+		pages, err = fetchPageIndex(ctx, pages, f.db.client, info)
+		if err != nil {
+			return err
+		}
+		txid = max(txid, info.MaxTXID)
+	}
+	f.syncTime = syncTime
+	f.pages = pages
+	f.txid = txid
+	return nil
+}
+
 type liteDB struct {
 	client   litestream.ReplicaClient
 	opts     ReplicaOptions
 	cache    pageCache
 	pages    *pageIndex // +checklocks:mtx
 	lastPoll time.Time  // +checklocks:mtx
+	lastInfo time.Time  // +checklocks:mtx
 	txids    levelTXIDs // +checklocks:mtx
 	mtx      sync.Mutex
 }
 
-func (f *liteDB) buildIndex(ctx context.Context) error {
+func (d *liteDB) buildIndex(ctx context.Context) error {
-	f.mtx.Lock()
+	d.mtx.Lock()
-	defer f.mtx.Unlock()
+	defer d.mtx.Unlock()
 
 	// Skip if we already have an index.
-	if f.pages != nil {
+	if d.pages != nil {
 		return nil
 	}
 
 	// Build the index from scratch from a Litestream restore plan.
-	infos, err := litestream.CalcRestorePlan(ctx, f.client, 0, time.Time{}, f.opts.Logger)
+	infos, err := litestream.CalcRestorePlan(ctx, d.client, 0, time.Time{}, d.opts.Logger)
 	if err != nil {
 		if !errors.Is(err, litestream.ErrTxNotAvailable) {
 			return fmt.Errorf("calc restore plan: %w", err)
@@ -229,47 +303,46 @@ func (f *liteDB) buildIndex(ctx context.Context) error {
 	}
 
 	for _, info := range infos {
-		err := f.updateInfo(ctx, info)
+		err := d.updateInfo(ctx, info)
 		if err != nil {
 			return err
 		}
 	}
 
-	f.lastPoll = time.Now()
+	d.lastPoll = time.Now()
 	return nil
 }
 
-func (f *liteDB) pollReplica(ctx context.Context) (*pageIndex, ltx.TXID, error) {
+func (d *liteDB) pollReplica(ctx context.Context) (*pageIndex, ltx.TXID, error) {
-	f.mtx.Lock()
+	d.mtx.Lock()
-	defer f.mtx.Unlock()
+	defer d.mtx.Unlock()
 
 	// Limit polling interval.
-	if time.Since(f.lastPoll) < f.opts.PollInterval {
+	if time.Since(d.lastPoll) < d.opts.PollInterval {
-		return f.pages, f.txids[0], nil
+		return d.pages, d.txids[0], nil
 	}
 
 	for level := range []int{0, 1, litestream.SnapshotLevel} {
-		if err := f.updateLevel(ctx, level); err != nil {
+		if err := d.updateLevel(ctx, level); err != nil {
-			f.opts.Logger.Error("cannot poll replica", "error", err)
 			return nil, 0, err
 		}
 	}
 
-	f.lastPoll = time.Now()
+	d.lastPoll = time.Now()
-	return f.pages, f.txids[0], nil
+	return d.pages, d.txids[0], nil
 }
 
-// +checklocks:f.mtx
+// +checklocks:d.mtx
-func (f *liteDB) updateLevel(ctx context.Context, level int) error {
+func (d *liteDB) updateLevel(ctx context.Context, level int) error {
 	var nextTXID ltx.TXID
 	// Snapshots must start from scratch,
 	// other levels can start from where they were left.
 	if level != litestream.SnapshotLevel {
-		nextTXID = f.txids[level] + 1
+		nextTXID = d.txids[level] + 1
 	}
 
 	// Start reading from the next LTX file after the current position.
-	itr, err := f.client.LTXFiles(ctx, level, nextTXID, false)
+	itr, err := d.client.LTXFiles(ctx, level, nextTXID, false)
 	if err != nil {
 		return fmt.Errorf("ltx files: %w", err)
 	}
@@ -280,11 +353,11 @@ func (f *liteDB) updateLevel(ctx context.Context, level int) error {
 		info := itr.Item()
 
 		// Skip LTX files already fully loaded into the index.
-		if info.MaxTXID <= f.txids[level] {
+		if info.MaxTXID <= d.txids[level] {
 			continue
 		}
 
-		err := f.updateInfo(ctx, info)
+		err := d.updateInfo(ctx, info)
 		if err != nil {
 			return err
 		}
@@ -295,26 +368,41 @@ func (f *liteDB) updateLevel(ctx context.Context, level int) error {
 	return itr.Close()
 }
 
-// +checklocks:f.mtx
+// +checklocks:d.mtx
-func (f *liteDB) updateInfo(ctx context.Context, info *ltx.FileInfo) error {
+func (d *liteDB) updateInfo(ctx context.Context, info *ltx.FileInfo) error {
-	idx, err := litestream.FetchPageIndex(ctx, f.client, info)
+	pages, err := fetchPageIndex(ctx, d.pages, d.client, info)
 	if err != nil {
-		return fmt.Errorf("fetch page index: %w", err)
+		return err
+	}
+
+	// Track the MaxTXID for each level.
+	maxTXID := &d.txids[info.Level]
+	*maxTXID = max(*maxTXID, info.MaxTXID)
+	d.txids[0] = max(d.txids[0], *maxTXID)
+	if d.lastInfo.Before(info.CreatedAt) {
+		d.lastInfo = info.CreatedAt
+	}
+	d.pages = pages
+	return nil
+}
+
+func fetchPageIndex(
+	ctx context.Context, pages *pageIndex,
+	client litestream.ReplicaClient, info *ltx.FileInfo) (*pageIndex, error) {
+
+	idx, err := litestream.FetchPageIndex(ctx, client, info)
+	if err != nil {
+		return nil, fmt.Errorf("fetch page index: %w", err)
 	}
 
 	// Replace pages in the index with new pages.
 	for k, v := range idx {
 		// Patch avoids mutating the index for an unmodified page.
-		f.pages = f.pages.Patch(k, func(node *pageIndex) (ltx.PageIndexElem, bool) {
+		pages = pages.Patch(k, func(node *pageIndex) (ltx.PageIndexElem, bool) {
 			return v, node == nil || v != node.Value()
 		})
 	}
-
+	return pages, nil
-	// Track the MaxTXID for each level.
-	maxTXID := &f.txids[info.Level]
-	*maxTXID = max(*maxTXID, info.MaxTXID)
-	f.txids[0] = max(f.txids[0], *maxTXID)
-	return nil
 }
 
 // Type aliases; these are a mouthful.

vfs/vfs.go

@@ -329,9 +329,9 @@ func vfsFileControlImpl(ctx context.Context, mod api.Module, file File, op _Fcnt
 
 	case _FCNTL_PRAGMA:
 		if file, ok := file.(FilePragma); ok {
+			var value string
 			ptr := util.Read32[ptr_t](mod, pArg+1*ptrlen)
 			name := util.ReadString(mod, ptr, _MAX_SQL_LENGTH)
-			var value string
 			if ptr := util.Read32[ptr_t](mod, pArg+2*ptrlen); ptr != 0 {
 				value = util.ReadString(mod, ptr, _MAX_SQL_LENGTH)
 			}