add atomic file ops

1 files changed, 63 insertions, 0 deletions

diff --git a/skate/atomic/file.go b/skate/atomic/file.go
new file mode 100644
index 0000000..1b9bf25
--- /dev/null
+++ b/skate/atomic/file.go
@@ -0,0 +1,63 @@
+package atomic
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+)
+
+// WriteFileReader writes data from a reader atomically into filename.
+func WriteFileReader(filename string, r io.Reader, perm os.FileMode) error {
+	dir, name := path.Split(filename)
+	f, err := ioutil.TempFile(dir, name)
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(f, r)
+	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
+}
+
+// WriteFileAtomic writes the data to a temp file and atomically move if
+// everything else succeeds.
+func WriteFile(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
+}