minor bug fixes to file installer

dropship/installer.go

@@ -4,6 +4,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 // Installer is an interface that allows different methods of writing
@@ -13,7 +14,7 @@ type Installer interface {
 }
 
 func moveOld(dest string) error {
-	return os.Rename(dest, filepath.Join(dest, ".old"))
+	return os.Rename(dest, strings.Join([]string{dest, "old"}, "."))
 }
 
 func cleanup(dest string, err error) error {

dropship/installer_file.go

@@ -10,9 +10,13 @@ import (
 type FileInstaller struct{}
 
 func (i FileInstaller) Install(dest string, f io.Reader) (count int, err error) {
-	err = moveOld(dest)
-	if err != nil {
-		return 0, err
+	// if file exists lets move it so we can recover on failure
+	if _, err := os.Stat(dest); err == nil {
+		err = moveOld(dest)
+		if err != nil {
+			return 0, err
+		}
+		defer cleanup(dest, err)
 	}
 
 	if f == nil {

dropship/installer_file_test.go

@@ -3,6 +3,8 @@ package dropship
 import (
 	"bytes"
 	"io"
+	"io/ioutil"
+	"os"
 	"testing"
 )
 
@@ -21,7 +23,13 @@ func TestInstallFile(t *testing.T) {
 
 	var fileInstaller FileInstaller
 	for _, test := range cases {
-		count, err := fileInstaller.Install("/tmp/test.txt", test.file)
+		dir, err := ioutil.TempDir(".", "test")
+		if err != nil {
+			t.Error(err)
+		}
+		defer os.RemoveAll(dir)
+
+		count, err := fileInstaller.Install(dir+"/test.txt", test.file)
 		if err != test.err {
 			t.Errorf("Install: Expected error to equal %v got: %v", test.err, err)
 		}