libs/common: Refactor tempfile code into its own file

libs/common/os.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"os/exec"
 	"os/signal"
-	"path/filepath"
 	"strings"
 	"syscall"
 )
@@ -124,60 +123,6 @@ func MustWriteFile(filePath string, contents []byte, mode os.FileMode) {
 	}
 }
 
-// WriteFileAtomic creates a temporary file with data and the perm given and
-// swaps it atomically with filename if successful.
-func WriteFileAtomic(filename string, data []byte, perm os.FileMode) error {
-	var (
-		dir      = filepath.Dir(filename)
-		tempFile = filepath.Join(dir, "write-file-atomic-"+RandStr(32))
-		// Override in case it does exist, create in case it doesn't and force kernel
-		// flush, which still leaves the potential of lingering disk cache.
-		flag = os.O_WRONLY | os.O_CREATE | os.O_SYNC | os.O_TRUNC
-	)
-
-	f, err := os.OpenFile(tempFile, flag, perm)
-	if err != nil {
-		return err
-	}
-	// Clean up in any case. Defer stacking order is last-in-first-out.
-	defer os.Remove(f.Name())
-	defer f.Close()
-
-	if n, err := f.Write(data); err != nil {
-		return err
-	} else if n < len(data) {
-		return io.ErrShortWrite
-	}
-	// Close the file before renaming it, otherwise it will cause "The process 
-	// cannot access the file because it is being used by another process." on windows.
-	f.Close()
-
-	return os.Rename(f.Name(), filename)
-}
-
-//--------------------------------------------------------------------------------
-
-func Tempfile(prefix string) (*os.File, string) {
-	file, err := ioutil.TempFile("", prefix)
-	if err != nil {
-		PanicCrisis(err)
-	}
-	return file, file.Name()
-}
-
-func Tempdir(prefix string) (*os.File, string) {
-	tempDir := os.TempDir() + "/" + prefix + RandStr(12)
-	err := EnsureDir(tempDir, 0700)
-	if err != nil {
-		panic(Fmt("Error creating temp dir: %v", err))
-	}
-	dir, err := os.Open(tempDir)
-	if err != nil {
-		panic(Fmt("Error opening temp dir: %v", err))
-	}
-	return dir, tempDir
-}
-
 //--------------------------------------------------------------------------------
 
 func Prompt(prompt string, defaultValue string) (string, error) {

libs/common/tempfile.go

@@ -0,0 +1,63 @@
+package common
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// WriteFileAtomic creates a temporary file with data and the perm given and
+// swaps it atomically with filename if successful.
+func WriteFileAtomic(filename string, data []byte, perm os.FileMode) error {
+	var (
+		dir = filepath.Dir(filename)
+		// Create in case it doesn't exist and force kernel
+		// flush, which still leaves the potential of lingering disk cache.
+		// Never overwrites files
+		flag = os.O_WRONLY | os.O_CREATE | os.O_SYNC | os.O_TRUNC | os.O_EXCL
+	)
+
+	tempFile := filepath.Join(dir, "write-file-atomic-"+RandStr(32))
+	f, err := os.OpenFile(tempFile, flag, perm)
+	if err != nil {
+		return err
+	}
+	// Clean up in any case. Defer stacking order is last-in-first-out.
+	defer os.Remove(f.Name())
+	defer f.Close()
+
+	if n, err := f.Write(data); err != nil {
+		return err
+	} else if n < len(data) {
+		return io.ErrShortWrite
+	}
+	// Close the file before renaming it, otherwise it will cause "The process
+	// cannot access the file because it is being used by another process." on windows.
+	f.Close()
+
+	return os.Rename(f.Name(), filename)
+}
+
+//--------------------------------------------------------------------------------
+
+func Tempfile(prefix string) (*os.File, string) {
+	file, err := ioutil.TempFile("", prefix)
+	if err != nil {
+		PanicCrisis(err)
+	}
+	return file, file.Name()
+}
+
+func Tempdir(prefix string) (*os.File, string) {
+	tempDir := os.TempDir() + "/" + prefix + RandStr(12)
+	err := EnsureDir(tempDir, 0700)
+	if err != nil {
+		panic(Fmt("Error creating temp dir: %v", err))
+	}
+	dir, err := os.Open(tempDir)
+	if err != nil {
+		panic(Fmt("Error opening temp dir: %v", err))
+	}
+	return dir, tempDir
+}