Safer file io for configuration files

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

ioutils/fswriters_test.go

@@ -0,0 +1,31 @@
+package ioutils
+
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestAtomicWriteToFile(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "atomic-writers-test")
+	if err != nil {
+		t.Fatalf("Error when creating temporary directory: %s", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	expected := []byte("barbaz")
+	if err := AtomicWriteFile(filepath.Join(tmpDir, "foo"), expected, 0600); err != nil {
+		t.Fatalf("Error writing to file: %v", err)
+	}
+
+	actual, err := ioutil.ReadFile(filepath.Join(tmpDir, "foo"))
+	if err != nil {
+		t.Fatalf("Error reading from file: %v", err)
+	}
+
+	if bytes.Compare(actual, expected) != 0 {
+		t.Fatalf("Data mismatch, expected %q, got %q", expected, actual)
+	}
+}