Write repo file using atomicfile

This prevents clients from seeing half-written files because
on POSIX systems renaming a file is an atomic operation.

Drive-by: Add test for repo file permission.

glide.lock

@@ -102,6 +102,8 @@ imports:
   version: ba18e35c5c1b36ef6334cad706eb681153d2d379
 - name: github.com/exponent-io/jsonpath
   version: d6023ce2651d8eafb5c75bb0c7167536102ec9f5
+- name: github.com/facebookgo/atomicfile
+  version: 2de1f203e7d5e386a6833233882782932729f27e
 - name: github.com/facebookgo/symwalk
   version: 42004b9f322246749dd73ad71008b1f3160c0052
 - name: github.com/ghodss/yaml

glide.yaml

@@ -41,6 +41,7 @@ import:
 - package: github.com/gobwas/glob
   version: ^0.2.1
 - package: github.com/evanphx/json-patch
+- package: github.com/facebookgo/atomicfile
 - package: github.com/facebookgo/symwalk
 - package: github.com/BurntSushi/toml
   version: ~0.3.0

pkg/repo/repo.go

@@ -23,6 +23,7 @@ import (
 	"os"
 	"time"
 
+	"github.com/facebookgo/atomicfile"
 	"github.com/ghodss/yaml"
 )
 
@@ -134,9 +135,20 @@ func (r *RepoFile) Remove(name string) bool {
 
 // WriteFile writes a repositories file to the given path.
 func (r *RepoFile) WriteFile(path string, perm os.FileMode) error {
+	f, err := atomicfile.New(path, perm)
+	if err != nil {
+		return err
+	}
+
 	data, err := yaml.Marshal(r)
 	if err != nil {
 		return err
 	}
-	return ioutil.WriteFile(path, data, perm)
+
+	_, err = f.File.Write(data)
+	if err != nil {
+		return err
+	}
+
+	return f.Close()
 }

pkg/repo/repo_test.go

@@ -201,10 +201,18 @@ func TestWriteFile(t *testing.T) {
 		t.Errorf("failed to create test-file (%v)", err)
 	}
 	defer os.Remove(repoFile.Name())
-	if err := sampleRepository.WriteFile(repoFile.Name(), 744); err != nil {
+
+	fileMode := os.FileMode(0744)
+	if err := sampleRepository.WriteFile(repoFile.Name(), fileMode); err != nil {
 		t.Errorf("failed to write file (%v)", err)
 	}
 
+	info, _ := os.Stat(repoFile.Name())
+	mode := info.Mode()
+	if mode != fileMode {
+		t.Errorf("incorrect file mode: %s (expected %s)", mode, fileMode)
+	}
+
 	repos, err := LoadRepositoriesFile(repoFile.Name())
 	if err != nil {
 		t.Errorf("failed to load file (%v)", err)