Add real+shadow recovery

db.go

@@ -1,6 +1,7 @@
 package litestream
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -36,6 +37,7 @@ type DB struct {
 	walHeader         *sqlite.WALHeader
 	processedWALByteN int64  // bytes copied to shadow WAL
 	pendingWALByteN   int64  // bytes pending copy to shadow WAL
+	checksum          uint64 // running checksum on real WAL
 
 	ctx    context.Context
 	cancel func()
@@ -84,6 +86,48 @@ func (db *DB) ActiveShadowWALPath() string {
 	return filepath.Join(db.ShadowWALDir(), ActiveWALName)
 }
 
+// LastShadowWALPath returns the active shadow WAL or the last snapshotted shadow WAL path.
+// Returns an empty string if no shadow WAL files exist.
+func (db *DB) LastShadowWALPath() (string, error) {
+	// Return active shadow WAL if it exists.
+	if _, err := os.Stat(db.ActiveShadowWALPath()); err == nil {
+		return db.ActiveShadowWALPath(), nil
+	} else if !os.IsNotExist(err) {
+		return "", nil
+	}
+
+	// Otherwise search for the largest shadow WAL file.
+	f, err := os.Open(db.ShadowWALDir())
+	if os.IsNotExist(err) {
+		return "", nil
+	} else if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	var filename string
+	for {
+		fis, err := f.Readdir(512)
+		if err != nil {
+			return "", err
+		}
+
+		for _, fi := range fis {
+			if !strings.HasSuffix(fi.Name(), WALExt) {
+				continue
+			} else if filename == "" || fi.Name() > filename {
+				filename = fi.Name()
+			}
+		}
+	}
+
+	// Return an error if there is no shadow WAL files.
+	if filename == "" {
+		return "", os.ErrNotExist
+	}
+	return filepath.Join(db.ShadowWALDir(), filename), nil
+}
+
 // LogPath returns the path to the internal log directory.
 func (db *DB) LogPath() string {
 	return filepath.Join(db.MetaPath(), LogFilename)
@@ -163,49 +207,7 @@ func (db *DB) recover() error {
 // recoverRealWALOnly copies the real WAL to the active shadow WAL.
 func (db *DB) recoverRealWALOnly() error {
 	db.logger.Printf("recovering: real WAL only")
-
+	return db.sync()
-	// Open real WAL to read from.
-	r, err := os.Open(db.WALPath())
-	if err != nil {
-		return fmt.Errorf("cannot open wal: %w", err)
-	}
-	defer r.Close()
-
-	// Read header from real WAL.
-	var hdr sqlite.WALHeader
-	if _, err := hdr.ReadFrom(r); os.IsNotExist(err) {
-		return nil
-	} else if err != nil {
-		return err
-	}
-
-	// Create a new shadow WAL file.
-	w, err := db.createActiveShadowWAL(hdr)
-	if err != nil {
-		return fmt.Errorf("cannot create active shadow wal: %w", err)
-	}
-	defer w.Close()
-
-	// Read from real WAL and copy to shadow WAL.
-	buf := make([]byte, hdr.PageSize)
-	for {
-		// Read frame header & data from real WAL.
-		var fhdr sqlite.WALFrameHeader
-		if _, err := fhdr.ReadFrom(r); err != nil {
-			return fmt.Errorf("cannot read frame header: %w", err)
-		} else if _, err := io.ReadFull(r, buf); err != nil {
-			return fmt.Errorf("cannot read frame: %w", err)
-		}
-
-		// Copy to the shadow WAL.
-		if _, err := fhdr.WriteTo(w); err != nil {
-			return fmt.Errorf("cannot write frame to shadow: %w", err)
-		} else if _, err := w.Write(buf); err != nil {
-			return fmt.Errorf("cannot write frame to shadow: %w", err)
-		}
-	}
-
-	return nil
 }
 
 // walExists returns true if the real WAL exists.
@@ -238,32 +240,6 @@ func (db *DB) shadowWALExists() (bool, error) {
 	}
 }
 
-// createActiveShadowWAL creates a new shadow WAL file with the given header.
-func (db *DB) createActiveShadowWAL(hdr sqlite.WALHeader) (f *os.File, err error) {
-	if f, err = os.OpenFile(db.ActiveShadowWALPath(), os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600); err != nil {
-		return nil, err
-	}
-
-	// Attempt to clean up if shadow WAL creation fails.
-	defer func() {
-		if err != nil {
-			f.Close()
-			os.Remove(f.Name())
-		}
-	}()
-
-	// Clear some fields from header that we won't use for the shadow WAL.
-	hdr = ClearShadowWALHeader(hdr)
-
-	// Write header & save it to the DB to ensure new WAL header writes match.
-	if _, err := hdr.WriteTo(f); err != nil {
-		return nil, err
-	}
-	db.walHeader = &hdr
-
-	return f, nil
-}
-
 // recoverShadowWALOnly verifies the last page in the shadow WAL matches the
 // contents of the database page.
 func (db *DB) recoverShadowWALOnly() error {
@@ -274,7 +250,131 @@ func (db *DB) recoverShadowWALOnly() error {
 // recoverRealAndShadowWALs verifies the last page of the real & shadow WALs match.
 func (db *DB) recoverRealAndShadowWALs() error {
 	db.logger.Printf("recovering: real & shadow WAL")
-	panic("TODO")
+
+	// Read WAL header from shadow WAL.
+	lastShadowWALPath, err := db.LastShadowWALPath()
+	if err != nil {
+		return fmt.Errorf("cannot find last shadow wal path: %w", err)
+	}
+	hdr, err := readFileWALHeader(lastShadowWALPath)
+	if err != nil {
+		return fmt.Errorf("cannot read last shadow wal header: %w", err)
+	}
+	db.walHeader = &hdr
+
+	// Read last pages from shadow WAL & real WAL and ensure they match.
+	if fhdr0, data0, err := readLastWALPage(lastShadowWALPath); err != nil {
+		return fmt.Errorf("cannot read last shadow wal page: %w", err)
+	} else if fhdr1, data1, err := readLastWALPage(db.WALPath()); err != nil {
+		return fmt.Errorf("cannot read last shadow wal page: %w", err)
+	} else if fhdr0 != fhdr1 {
+		return fmt.Errorf("last frame header mismatch: %#v != %#v", fhdr0, fhdr1)
+	} else if !bytes.Equal(data0, data1) {
+		return fmt.Errorf("last frame data mismatch")
+	} else {
+		db.checksum = fhdr1.Checksum
+	}
+
+	// Update position within real WAL.
+	fi, err := os.Stat(db.WALPath())
+	if err != nil {
+		return fmt.Errorf("cannot stat wal: %w", err)
+	}
+	db.processedWALByteN = fi.Size()
+	db.pendingWALByteN = 0
+
+	return nil
+}
+
+// Sync synchronizes the real WAL to the shadow WAL.
+func (db *DB) Sync() error {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	return db.sync()
+}
+
+func (db *DB) sync() (err error) {
+	db.logger.Printf("sync: begin")
+	defer func() {
+		db.logger.Printf("sync: end: err=%v", err)
+	}()
+
+	// Open real WAL to read from.
+	r, err := os.Open(db.WALPath())
+	if err != nil {
+		return fmt.Errorf("cannot open wal: %w", err)
+	} else if _, err := r.Seek(db.processedWALByteN, io.SeekStart); err != nil {
+		return fmt.Errorf("cannot seek wal: %w", err)
+	}
+	defer r.Close()
+
+	// TODO: Verify all frames are valid & committed before copy.
+
+	// Read header if we are at the beginning of the WAL.
+	if db.processedWALByteN == 0 {
+		var hdr sqlite.WALHeader
+		if _, err := hdr.ReadFrom(r); err != nil {
+			return fmt.Errorf("cannot read wal header: %w", err)
+		}
+
+		// Save checksum to verify later pages in WAL.
+		db.checksum = hdr.Checksum
+
+		// Clear out salt & checksum from header for shadow WAL.
+		hdr = ClearShadowWALHeader(hdr)
+		db.walHeader = &hdr
+	}
+
+	// Open shadow WAL to copy to.
+	w, err := os.OpenFile(db.ActiveShadowWALPath(), os.O_RDWR|os.O_CREATE|os.O_APPEND, 0600)
+	if err != nil {
+		return fmt.Errorf("cannot open active shadow wal: %w", err)
+	}
+	defer w.Close()
+
+	// If we are at the start of a new shadow WAL, write a header.
+	if n, err := w.Seek(0, io.SeekCurrent); err != nil {
+		return fmt.Errorf("cannot seek shadow wal: %w", err)
+	} else if n == 0 {
+		db.logger.Printf("sync: new shadow wal, writing header: magic=%x page-size=%d", db.walHeader.Magic, db.walHeader.PageSize)
+		if _, err := db.walHeader.WriteTo(w); err != nil {
+			return fmt.Errorf("cannot write shadow wal header: %w", err)
+		}
+	}
+
+	// Read from real WAL and copy to shadow WAL.
+	buf := make([]byte, db.walHeader.PageSize)
+	for db.pendingWALByteN != 0 {
+		// Read frame header & data from real WAL.
+		var fhdr sqlite.WALFrameHeader
+		if _, err := fhdr.ReadFrom(r); err == io.EOF {
+			break
+		} else if err != nil {
+			return fmt.Errorf("cannot read frame header: %w", err)
+		} else if _, err := io.ReadFull(r, buf); err != nil {
+			return fmt.Errorf("cannot read frame: %w", err)
+		}
+
+		db.logger.Printf("sync: copy frame: pgno=%d pageN=%d salt=%x checksum=%x",
+			fhdr.Pgno,
+			fhdr.PageN,
+			fhdr.Salt,
+			fhdr.Checksum,
+		)
+
+		// Copy to the shadow WAL.
+		if _, err := fhdr.WriteTo(w); err != nil {
+			return fmt.Errorf("cannot write frame to shadow: %w", err)
+		} else if _, err := w.Write(buf); err != nil {
+			return fmt.Errorf("cannot write frame to shadow: %w", err)
+		}
+
+		byteN := int64(sqlite.WALFrameHeaderSize + len(buf))
+		db.processedWALByteN += byteN
+		db.pendingWALByteN -= byteN
+	}
+
+	return nil
 }
 
 // Close stops management of the database.
@@ -340,6 +440,7 @@ func (db *DB) setHeader(page []byte) {
 func (db *DB) AddPendingWALByteN(n int64) {
 	db.mu.Lock()
 	defer db.mu.Unlock()
+	db.logger.Printf("write: n=%d pending=%d", n, db.pendingWALByteN)
 	db.pendingWALByteN += n
 }
 
@@ -366,3 +467,52 @@ func ClearShadowWALHeader(hdr sqlite.WALHeader) sqlite.WALHeader {
 	hdr.Checksum = 0
 	return hdr
 }
+
+// readLastWALPage reads the last frame header & data from a WAL file.
+func readLastWALPage(path string) (fhdr sqlite.WALFrameHeader, data []byte, err error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return fhdr, data, err
+	}
+	defer f.Close()
+
+	// Determine WAL file size.
+	fi, err := f.Stat()
+	if err != nil {
+		return fhdr, data, err
+	}
+
+	// Read WAL header to determine page size.
+	var hdr sqlite.WALHeader
+	if _, err := hdr.ReadFrom(f); err != nil {
+		return fhdr, data, fmt.Errorf("cannot read wal header: %w", err)
+	}
+
+	// WAL file size must be divisible by frame size (minus the header).
+	if (fi.Size()-sqlite.WALHeaderSize)%(sqlite.WALFrameHeaderSize+int64(hdr.PageSize)) != 0 {
+		return fhdr, data, fmt.Errorf("partial wal record: path=%s sz=%d", path, fi.Size())
+	}
+
+	// Seek to last frame and read header & data.
+	data = make([]byte, hdr.PageSize)
+	if _, err := f.Seek(sqlite.WALFrameHeaderSize+int64(hdr.PageSize), io.SeekStart); err != nil {
+		return fhdr, data, fmt.Errorf("cannot seek: %w", err)
+	} else if _, err := fhdr.ReadFrom(f); err != nil {
+		return fhdr, data, fmt.Errorf("cannot read frame header: %w", err)
+	} else if _, err := io.ReadFull(f, data); err != nil {
+		return fhdr, data, fmt.Errorf("cannot read frame data: %w", err)
+	}
+	return fhdr, data, nil
+}
+
+// readFileWALHeader reads the WAL header from file.
+func readFileWALHeader(path string) (hdr sqlite.WALHeader, err error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return hdr, err
+	}
+	defer f.Close()
+
+	_, err = hdr.ReadFrom(f)
+	return hdr, err
+}

handle.go

@@ -37,6 +37,9 @@ func NewHandle(n *Node, f *os.File) *Handle {
 
 // Release closes the underlying file descriptor.
 func (h *Handle) Release(ctx context.Context, req *fuse.ReleaseRequest) (err error) {
+	if err := h.node.Sync(); err != nil {
+		return err
+	}
 	return h.f.Close()
 }
 
@@ -90,6 +93,9 @@ func (h *Handle) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.W
 
 // Flush is called when a file handle is synced to disk. Implements fs.HandleFlusher.
 func (h *Handle) Flush(ctx context.Context, req *fuse.FlushRequest) (err error) {
+	if err := h.node.Sync(); err != nil {
+		return err
+	}
 	return h.f.Sync()
 }
 

node.go

@@ -56,6 +56,11 @@ func (n *Node) srcpath() string {
 	return filepath.Join(n.fs.TargetPath, n.path)
 }
 
+// IsWAL returns true if node path has a "-wal" suffix.
+func (n *Node) IsWAL() bool {
+	return strings.HasSuffix(n.path, sqlite.WALSuffix)
+}
+
 // DB returns the DB object associated with the node, if any.
 // If node points to a "-wal" file then the associated DB is returned.
 func (n *Node) DB() *DB {
@@ -65,6 +70,25 @@ func (n *Node) DB() *DB {
 	return n.fs.DB(n.path)
 }
 
+// Sync synchronizes the data to the shadow WAL if this node is the WAL.
+func (n *Node) Sync() (err error) {
+	println("dbg/node.sync")
+	// Ignore if this is not the WAL.
+	if !n.IsWAL() {
+		println("dbg/node.sync.notwal", n.path)
+		return nil
+	}
+
+	// Ignore if the node is not a managed db.
+	db := n.DB()
+	if db == nil {
+		println("dbg/node.sync.notmanaged", n.path)
+		return nil
+	}
+
+	return db.Sync()
+}
+
 func (n *Node) Attr(ctx context.Context, a *fuse.Attr) (err error) {
 	fi, err := os.Stat(n.srcpath())
 	if err != nil {
@@ -312,6 +336,11 @@ func (n *Node) Mknod(ctx context.Context, req *fuse.MknodRequest) (_ fs.Node, er
 }
 
 func (n *Node) Fsync(ctx context.Context, req *fuse.FsyncRequest) (err error) {
+	// Synchronize to shadow WAL.
+	if err := n.Sync(); err != nil {
+		return err
+	}
+
 	f, err := os.Open(n.srcpath())
 	if err != nil {
 		return err