Recovery fixes

- Don't create files when reading them
- Don't remove lock on db.Open errors

datalog.go

@@ -79,7 +79,7 @@ func parseSegmentName(name string) (uint16, uint64, error) {
 }
 
 func (dl *datalog) openSegment(name string, id uint16, seqID uint64) (*segment, error) {
-	f, err := openFile(dl.opts.FileSystem, name, false)
+	f, err := openFile(dl.opts.FileSystem, name, openFileFlags{})
 	if err != nil {
 		return nil, err
 	}

db.go

@@ -64,12 +64,6 @@ func Open(path string, opts *Options) (*DB, error) {
 		}
 		return nil, errors.Wrap(err, "creating lock file")
 	}
-	clean := lock.Unlock
-	defer func() {
-		if clean != nil {
-			_ = clean()
-		}
-	}()
 
 	if acquiredExistingLock {
 		// Lock file already existed, but the process managed to acquire it.
@@ -121,7 +115,6 @@ func Open(path string, opts *Options) (*DB, error) {
 		db.startBackgroundWorker()
 	}
 
-	clean = nil
 	return db, nil
 }
 

file.go

@@ -14,10 +14,20 @@ type file struct {
 	size int64
 }
 
-func openFile(fsyst fs.FileSystem, name string, truncate bool) (*file, error) {
-	flag := os.O_CREATE | os.O_RDWR
-	if truncate {
-		flag |= os.O_TRUNC
+type openFileFlags struct {
+	truncate bool
+	readOnly bool
+}
+
+func openFile(fsyst fs.FileSystem, name string, flags openFileFlags) (*file, error) {
+	var flag int
+	if flags.readOnly {
+		flag = os.O_RDONLY
+	} else {
+		flag = os.O_CREATE | os.O_RDWR
+		if flags.truncate {
+			flag |= os.O_TRUNC
+		}
 	}
 	fi, err := fsyst.OpenFile(name, flag, os.FileMode(0640))
 	f := &file{}

gobfile.go

@@ -7,7 +7,7 @@ import (
 )
 
 func readGobFile(fsys fs.FileSystem, name string, v interface{}) error {
-	f, err := openFile(fsys, name, false)
+	f, err := openFile(fsys, name, openFileFlags{readOnly: true})
 	if err != nil {
 		return err
 	}
@@ -17,7 +17,7 @@ func readGobFile(fsys fs.FileSystem, name string, v interface{}) error {
 }
 
 func writeGobFile(fsys fs.FileSystem, name string, v interface{}) error {
-	f, err := openFile(fsys, name, true)
+	f, err := openFile(fsys, name, openFileFlags{truncate: true})
 	if err != nil {
 		return err
 	}

index.go

@@ -38,11 +38,11 @@ type indexMeta struct {
 type matchKeyFunc func(slot) (bool, error)
 
 func openIndex(opts *Options) (*index, error) {
-	main, err := openFile(opts.FileSystem, indexMainName, false)
+	main, err := openFile(opts.FileSystem, indexMainName, openFileFlags{})
 	if err != nil {
 		return nil, errors.Wrap(err, "opening main index")
 	}
-	overflow, err := openFile(opts.FileSystem, indexOverflowName, false)
+	overflow, err := openFile(opts.FileSystem, indexOverflowName, openFileFlags{})
 	if err != nil {
 		_ = main.Close()
 		return nil, errors.Wrap(err, "opening overflow index")