dir package - to enforce dir RW lock by types (#332)

* save

* save

common/cli.go

@@ -44,10 +44,3 @@ func RootContext() (context.Context, context.CancelFunc) {
 	}()
 	return ctx, cancel
 }
-
-func MustExist(path string) {
-	const perm = 0764 // user rwx, group rw, other r
-	if err := os.MkdirAll(path, perm); err != nil {
-		panic(err)
-	}
-}

common/dir/rw_dir.go

@@ -0,0 +1,65 @@
+package dir
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"github.com/gofrs/flock"
+	"github.com/ledgerwatch/log/v3"
+)
+
+// Rw - type to represent Read-Write access to directory
+// if some code accept this typ - it can be sure: dir exists, no other process now write there
+// We have no specific Ro type, just use `string` for Ro directory path
+type Rw struct {
+	dirLock *flock.Flock // prevents concurrent use of instance directory
+	Path    string
+}
+
+func convertFileLockError(err error, dir string) error {
+	if errno, ok := err.(syscall.Errno); ok && dirInUseErrnos[uint(errno)] {
+		return fmt.Errorf("%w: %s\n", ErrDirUsed, dir)
+	}
+	return err
+}
+
+var dirInUseErrnos = map[uint]bool{11: true, 32: true, 35: true}
+
+var (
+	ErrDirUsed = errors.New("datadir already used by another process")
+)
+
+func OpenRw(dir string) (*Rw, error) {
+	MustExist(dir)
+
+	// Lock the instance directory to prevent concurrent use by another instance as well as
+	// accidental use of the instance directory as a database.
+	l := flock.New(filepath.Join(dir, "LOCK"))
+	locked, err := l.TryLock()
+	if err != nil {
+		return nil, convertFileLockError(err, dir)
+	}
+	if !locked {
+		return nil, fmt.Errorf("%w: %s\n", ErrDirUsed, dir)
+	}
+	return &Rw{dirLock: l, Path: dir}, nil
+}
+func (t *Rw) Close() {
+	// Release instance directory lock.
+	if t.dirLock != nil {
+		if err := t.dirLock.Unlock(); err != nil {
+			log.Error("Can't release snapshot dir lock", "err", err)
+		}
+		t.dirLock = nil
+	}
+}
+
+func MustExist(path string) {
+	const perm = 0764 // user rwx, group rw, other r
+	if err := os.MkdirAll(path, perm); err != nil {
+		panic(err)
+	}
+}

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/c2h5oh/datasize v0.0.0-20200825124411-48ed595a09d2
 	github.com/flanglet/kanzi-go v1.9.0
 	github.com/go-stack/stack v1.8.1
+	github.com/gofrs/flock v0.8.1
 	github.com/google/btree v1.0.1
 	github.com/grpc-ecosystem/go-grpc-middleware v1.3.0
 	github.com/hashicorp/golang-lru v0.5.5-0.20210104140557-80c98217689d

go.sum

@@ -33,6 +33,8 @@ github.com/go-logfmt/logfmt v0.4.0/go.mod h1:3RMwSq7FuexP4Kalkev3ejPJsZTpXXBr9+V
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
 github.com/go-stack/stack v1.8.1 h1:ntEHSVwIt7PNXNpgPmVfMrNhLtgjlmnZha2kOpuRiDw=
 github.com/go-stack/stack v1.8.1/go.mod h1:dcoOX6HbPZSZptuspn9bctJ+N/CnF5gGygcUP3XYfe4=
+github.com/gofrs/flock v0.8.1 h1:+gYjHKf32LDeiEEFhQaotPbLuUXjY5ZqxKgXy7n59aw=
+github.com/gofrs/flock v0.8.1/go.mod h1:F1TvTiK9OcQqauNUHlbJvyl9Qa1QvF/gOUDKA14jxHU=
 github.com/gogo/protobuf v1.3.2/go.mod h1:P1XiOD3dCwIKUDQYPy72D8LYyHL2YPYrpS2s69NZV8Q=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=