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version.go
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version.go
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// Copyright 2016 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
package engine
import (
"encoding/json"
"fmt"
"io/ioutil"
"os"
"path/filepath"
)
type storageVersion int
const (
versionNoFile storageVersion = iota
versionBeta20160331
)
const (
versionFilename = "COCKROACHDB_VERSION"
versionFilenameTemp = "COCKROACHDB_VERSION_TEMP"
versionMinimum = versionNoFile
versionCurrent = versionBeta20160331
)
// Version stores all the version information for all stores and is used as
// the format for the version file.
type Version struct {
Version storageVersion
}
// getVersionFilename returns the filename for the version file stored in the
// data directory.
func getVersionFilename(dir string) string {
return filepath.Join(dir, versionFilename)
}
// getVersion returns the current on disk cockroach version from the version
// file in the passed in directory. If there is no version file yet, it
// returns 0.
func getVersion(dir string) (storageVersion, error) {
filename := getVersionFilename(dir)
b, err := ioutil.ReadFile(filename)
if err != nil {
if os.IsNotExist(err) {
return versionNoFile, nil
}
return 0, err
}
var ver Version
if err := json.Unmarshal(b, &ver); err != nil {
return 0, fmt.Errorf("version file %s is not formatted correctly; %s", filename, err)
}
return ver.Version, nil
}
// writeVersionFile overwrites the version file to contain the latest version.
func writeVersionFile(dir string) error {
tempFilename := filepath.Join(dir, versionFilenameTemp)
filename := getVersionFilename(dir)
b, err := json.Marshal(Version{versionCurrent})
if err != nil {
return err
}
// First write to a temp file.
if err := ioutil.WriteFile(tempFilename, b, 0644); err != nil {
return err
}
// Atomically rename the file to overwrite the version file on disk.
return os.Rename(tempFilename, filename)
}