Update filestore to first remove existing metadata before setting metadata.

This would let it remove corrupt or bad-state metadata.

Signed-off-by: Ying Li <ying.li@docker.com>

tuf/store/filestore.go

@@ -75,6 +75,9 @@ func (f *FilesystemStore) SetMeta(name string, meta []byte) error {
 		return err
 	}
 
+	// if something already exists, just delete it and re-write it
+	os.RemoveAll(path)
+
 	// Write the file to disk
 	if err = ioutil.WriteFile(path, meta, 0600); err != nil {
 		return err

tuf/store/filestore_test.go

@@ -4,6 +4,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -57,6 +58,24 @@ func TestSetMetaWithNoParentDirectory(t *testing.T) {
 	assert.Equal(t, testContent, content, "Content written to file was corrupted.")
 }
 
+// if something already existed there, remove it first and write a new file
+func TestSetMetaRemovesExistingFileBeforeWriting(t *testing.T) {
+	s, err := NewFilesystemStore(testDir, "metadata", "json", "targets")
+	assert.Nil(t, err, "Initializing FilesystemStore returned unexpected error: %v", err)
+	defer os.RemoveAll(testDir)
+
+	// make a directory where we want metadata to go
+	os.Mkdir(filepath.Join(testDir, "metadata", "root.json"), 0700)
+
+	testContent := []byte("test data")
+	err = s.SetMeta("root", testContent)
+	assert.NoError(t, err, "SetMeta returned unexpected error: %v", err)
+
+	content, err := ioutil.ReadFile(path.Join(testDir, "metadata", "root.json"))
+	assert.NoError(t, err, "Error reading file: %v", err)
+	assert.Equal(t, testContent, content, "Content written to file was corrupted.")
+}
+
 func TestGetMeta(t *testing.T) {
 	s, err := NewFilesystemStore(testDir, "metadata", "json", "targets")
 	assert.Nil(t, err, "Initializing FilesystemStore returned unexpected error: %v", err)