keeper: write files atomically

fixes sorintlab#247

Author: nh2

cmd/keeper/keeper.go

@@ -1359,7 +1359,7 @@ func (p *PostgresKeeper) saveKeeperLocalState() error {
 	if err != nil {
 		return err
 	}
-	return ioutil.WriteFile(p.keeperLocalStateFilePath(), sj, 0600)
+	return common.WriteFileAtomic(p.keeperLocalStateFilePath(), sj, 0600)
 }
 
 func (p *PostgresKeeper) dbLocalStateFilePath() string {
@@ -1384,7 +1384,7 @@ func (p *PostgresKeeper) saveDBLocalState() error {
 	if err != nil {
 		return err
 	}
-	return ioutil.WriteFile(p.dbLocalStateFilePath(), sj, 0600)
+	return common.WriteFileAtomic(p.dbLocalStateFilePath(), sj, 0600)
 }
 
 func sigHandler(sigs chan os.Signal, stop chan bool) {

common/common.go

@@ -16,6 +16,9 @@ package common
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
 	"reflect"
 	"strings"
 
@@ -66,3 +69,34 @@ type Parameters map[string]string
 func (s Parameters) Equals(is Parameters) bool {
 	return reflect.DeepEqual(s, is)
 }
+
+// WriteFileAtomic atoically writes a file, it achieves this by creating a
+// temporary file and then moving it.
+// This function is taken from
+//   https://github.com/youtube/vitess/blob/master/go/ioutil2/ioutil.go
+// Copyright 2012, Google Inc. BSD-license, see licenses/LICENSE-BSD-3-Clause
+func WriteFileAtomic(filename string, data []byte, perm os.FileMode) error {
+	dir, name := path.Split(filename)
+	f, err := ioutil.TempFile(dir, name)
+	if err != nil {
+		return err
+	}
+	_, err = f.Write(data)
+	if err == nil {
+		err = f.Sync()
+	}
+	if closeErr := f.Close(); err == nil {
+		err = closeErr
+	}
+	if permErr := os.Chmod(f.Name(), perm); err == nil {
+		err = permErr
+	}
+	if err == nil {
+		err = os.Rename(f.Name(), filename)
+	}
+	// Any err should result in full cleanup.
+	if err != nil {
+		os.Remove(f.Name())
+	}
+	return err
+}

licenses/LICENSE-BSD-3-Clause

@@ -0,0 +1,29 @@
+BSD 3-Clause License
+
+Copyright (c) [year], [fullname]
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+* Neither the name of the copyright holder nor the names of its
+  contributors may be used to endorse or promote products derived from
+  this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.