Atomic writes

cmd/cloudinit/cloudinit.go

@@ -18,7 +18,6 @@ package cloudinit
 import (
 	"errors"
 	"flag"
-	"io/ioutil"
 	"os"
 	"strings"
 	"sync"
@@ -40,6 +39,7 @@ import (
 	"github.com/coreos/coreos-cloudinit/system"
 	"github.com/rancher/netconf"
 	rancherConfig "github.com/rancher/os/config"
+	"github.com/rancher/os/util"
 )
 
 const (
@@ -71,13 +71,13 @@ func saveFiles(cloudConfigBytes, scriptBytes []byte, metadata datasource.Metadat
 
 	if len(scriptBytes) > 0 {
 		log.Infof("Writing to %s", rancherConfig.CloudConfigScriptFile)
-		if err := ioutil.WriteFile(rancherConfig.CloudConfigScriptFile, scriptBytes, 500); err != nil {
+		if err := util.WriteFileAtomic(rancherConfig.CloudConfigScriptFile, scriptBytes, 500); err != nil {
 			log.Errorf("Error while writing file %s: %v", rancherConfig.CloudConfigScriptFile, err)
 			return err
 		}
 	}
 
-	if err := ioutil.WriteFile(rancherConfig.CloudConfigBootFile, cloudConfigBytes, 400); err != nil {
+	if err := util.WriteFileAtomic(rancherConfig.CloudConfigBootFile, cloudConfigBytes, 400); err != nil {
 		return err
 	}
 	log.Infof("Written to %s:\n%s", rancherConfig.CloudConfigBootFile, string(cloudConfigBytes))
@@ -87,7 +87,7 @@ func saveFiles(cloudConfigBytes, scriptBytes []byte, metadata datasource.Metadat
 		return err
 	}
 
-	if err = ioutil.WriteFile(rancherConfig.MetaDataFile, metaDataBytes, 400); err != nil {
+	if err = util.WriteFileAtomic(rancherConfig.MetaDataFile, metaDataBytes, 400); err != nil {
 		return err
 	}
 	log.Infof("Written to %s:\n%s", rancherConfig.MetaDataFile, string(metaDataBytes))

cmd/cloudinit/gce.go

@@ -1,11 +1,11 @@
 package cloudinit
 
 import (
-	"io/ioutil"
 	"strings"
 
 	log "github.com/Sirupsen/logrus"
 	yaml "github.com/cloudfoundry-incubator/candiedyaml"
+	"github.com/rancher/os/util"
 	"google.golang.org/cloud/compute/metadata"
 )
 
@@ -111,7 +111,7 @@ func (cc *GceCloudConfig) getMergedUserData() ([]byte, error) {
 }
 
 func writeFile(filename string, data []byte) error {
-	if err := ioutil.WriteFile(filename, data, 400); err != nil {
+	if err := util.WriteFileAtomic(filename, data, 400); err != nil {
 		log.Errorf("Could not write file %v", err)
 		return err
 	}

cmd/control/config.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/codegangsta/cli"
 	"github.com/rancher/os/config"
+	"github.com/rancher/os/util"
 )
 
 func configSubcommands() []cli.Command {
@@ -202,7 +203,7 @@ func export(c *cli.Context) error {
 	if output == "" {
 		fmt.Println(content)
 	} else {
-		err := ioutil.WriteFile(output, []byte(content), 0400)
+		err := util.WriteFileAtomic(output, []byte(content), 0400)
 		if err != nil {
 			log.Fatal(err)
 		}

cmd/control/tlsconf.go

@@ -10,6 +10,7 @@ import (
 	"github.com/codegangsta/cli"
 	machineUtil "github.com/docker/machine/utils"
 	"github.com/rancher/os/config"
+	"github.com/rancher/os/util"
 )
 
 const (
@@ -79,11 +80,11 @@ func writeCerts(generateServer bool, hostname []string, cfg *config.CloudConfig,
 		return err
 	}
 
-	if err := ioutil.WriteFile(certPath, []byte(cfg.Rancher.Docker.ServerCert), 0400); err != nil {
+	if err := util.WriteFileAtomic(certPath, []byte(cfg.Rancher.Docker.ServerCert), 0400); err != nil {
 		return err
 	}
 
-	return ioutil.WriteFile(keyPath, []byte(cfg.Rancher.Docker.ServerKey), 0400)
+	return util.WriteFileAtomic(keyPath, []byte(cfg.Rancher.Docker.ServerKey), 0400)
 
 }
 
@@ -117,11 +118,11 @@ func writeCaCerts(cfg *config.CloudConfig, caCertPath, caKeyPath string) error {
 		return err
 	}
 
-	if err := ioutil.WriteFile(caCertPath, []byte(cfg.Rancher.Docker.CACert), 0400); err != nil {
+	if err := util.WriteFileAtomic(caCertPath, []byte(cfg.Rancher.Docker.CACert), 0400); err != nil {
 		return err
 	}
 
-	if err := ioutil.WriteFile(caKeyPath, []byte(cfg.Rancher.Docker.CAKey), 0400); err != nil {
+	if err := util.WriteFileAtomic(caKeyPath, []byte(cfg.Rancher.Docker.CAKey), 0400); err != nil {
 		return err
 	}
 

config/disk.go

@@ -239,7 +239,7 @@ func WriteToFile(data interface{}, filename string) error {
 		return err
 	}
 
-	return ioutil.WriteFile(filename, content, 400)
+	return util.WriteFileAtomic(filename, content, 400)
 }
 
 func readConfig(bytes []byte, substituteMetadataVars bool, files ...string) (map[interface{}]interface{}, error) {

util/util.go

@@ -2,8 +2,10 @@ package util
 
 import (
 	"bytes"
-	"io"
+	"fmt"
+	"io/ioutil"
 	"os"
+	"path"
 	"strings"
 
 	yaml "github.com/cloudfoundry-incubator/candiedyaml"
@@ -29,23 +31,33 @@ func Contains(values []string, value string) bool {
 
 type ReturnsErr func() error
 
-func FileCopy(src, dest string) (err error) {
+func FileCopy(src, dest string) error {
-	in, err := os.Open(src)
+	data, err := ioutil.ReadFile(src)
 	if err != nil {
 		return err
 	}
-	defer func() { err = in.Close() }()
+	return WriteFileAtomic(dest, data, 0666)
+}
 
-	out, err := os.Create(dest)
+func WriteFileAtomic(filename string, data []byte, perm os.FileMode) error {
+	dir, file := path.Split(filename)
+	tempFile, err := ioutil.TempFile(dir, fmt.Sprintf(".%s", file))
 	if err != nil {
 		return err
 	}
-	defer func() { err = out.Close() }()
+	defer os.Remove(tempFile.Name())
 
-	if _, err := io.Copy(out, in); err != nil {
+	if _, err := tempFile.Write(data); err != nil {
 		return err
 	}
-	return
+	if err := tempFile.Close(); err != nil {
+		return err
+	}
+	if err := os.Chmod(tempFile.Name(), perm); err != nil {
+		return err
+	}
+
+	return os.Rename(tempFile.Name(), filename)
 }
 
 func Convert(from, to interface{}) error {