Seek to offset 0 after Truncate() (#5375)

cmd/format-fs.go

@@ -17,7 +17,6 @@
 package cmd
 
 import (
-	"encoding/json"
 	"fmt"
 	"io"
 	"os"
@@ -74,30 +73,11 @@ func newFormatFSV2() (format *formatFSV2) {
 	return f
 }
 
-// Save to fs format.json
-func formatFSSave(f *os.File, data interface{}) error {
-	b, err := json.Marshal(data)
-	if err != nil {
-		return errors2.Trace(err)
-	}
-	if err = f.Truncate(0); err != nil {
-		return errors2.Trace(err)
-	}
-	if _, err = f.Seek(0, io.SeekStart); err != nil {
-		return err
-	}
-	_, err = f.Write(b)
-	if err != nil {
-		return errors2.Trace(err)
-	}
-	return nil
-}
-
 // Returns the field formatMetaV1.Format i.e the string "fs" which is never likely to change.
 // We do not use this function in XL to get the format as the file is not fcntl-locked on XL.
 func formatMetaGetFormatBackendFS(r io.ReadSeeker) (string, error) {
 	format := &formatMetaV1{}
-	if err := jsonLoadFromSeeker(r, format); err != nil {
+	if err := jsonLoad(r, format); err != nil {
 		return "", err
 	}
 	if format.Version == formatMetaVersionV1 {
@@ -109,7 +89,7 @@ func formatMetaGetFormatBackendFS(r io.ReadSeeker) (string, error) {
 // Returns formatFS.FS.Version
 func formatFSGetVersion(r io.ReadSeeker) (string, error) {
 	format := &formatFSVersionDetect{}
-	if err := jsonLoadFromSeeker(r, format); err != nil {
+	if err := jsonLoad(r, format); err != nil {
 		return "", err
 	}
 	return format.FS.Version, nil
@@ -135,7 +115,7 @@ func formatFSMigrateV1ToV2(wlk *lock.LockedFile, fsPath string) error {
 		return err
 	}
 
-	return formatFSSave(wlk.File, newFormatFSV2())
+	return jsonSave(wlk.File, newFormatFSV2())
 }
 
 // Migrate the "fs" backend.
@@ -190,7 +170,7 @@ func createFormatFS(fsFormatPath string) error {
 		return nil
 	}
 
-	return formatFSSave(lk.File, newFormatFSV1())
+	return jsonSave(lk.File, newFormatFSV1())
 }
 
 // This function returns a read-locked format.json reference to the caller.

cmd/fs-v1-metadata.go

@@ -17,7 +17,6 @@
 package cmd
 
 import (
-	"encoding/json"
 	"io"
 	"io/ioutil"
 	"os"
@@ -127,22 +126,14 @@ func (m fsMetaV1) ToObjectInfo(bucket, object string, fi os.FileInfo) ObjectInfo
 }
 
 func (m *fsMetaV1) WriteTo(lk *lock.LockedFile) (n int64, err error) {
-	var metadataBytes []byte
-	metadataBytes, err = json.Marshal(m)
+	if err = jsonSave(lk, m); err != nil {
+		return 0, err
+	}
+	fi, err := lk.Stat()
 	if err != nil {
-		return 0, errors.Trace(err)
+		return 0, err
 	}
-
-	if err = lk.Truncate(0); err != nil {
-		return 0, errors.Trace(err)
-	}
-
-	if _, err = lk.Write(metadataBytes); err != nil {
-		return 0, errors.Trace(err)
-	}
-
-	// Success.
-	return int64(len(metadataBytes)), nil
+	return fi.Size(), nil
 }
 
 func parseFSVersion(fsMetaBuf []byte) string {

cmd/object-api-multipart-common.go

@@ -84,20 +84,14 @@ func (u *uploadsV1) IsEmpty() bool {
 }
 
 func (u *uploadsV1) WriteTo(lk *lock.LockedFile) (n int64, err error) {
-	// Serialize to prepare to write to disk.
-	var uplBytes []byte
-	uplBytes, err = json.Marshal(u)
+	if err = jsonSave(lk, u); err != nil {
+		return 0, err
+	}
+	fi, err := lk.Stat()
 	if err != nil {
-		return 0, errors.Trace(err)
+		return 0, err
 	}
-	if err = lk.Truncate(0); err != nil {
-		return 0, errors.Trace(err)
-	}
-	_, err = lk.Write(uplBytes)
-	if err != nil {
-		return 0, errors.Trace(err)
-	}
-	return int64(len(uplBytes)), nil
+	return fi.Size(), nil
 }
 
 func (u *uploadsV1) ReadFrom(lk *lock.LockedFile) (n int64, err error) {

cmd/utils.go

@@ -265,9 +265,31 @@ func NewCustomHTTPTransport() http.RoundTripper {
 }
 
 // Load the json (typically from disk file).
-func jsonLoadFromSeeker(r io.ReadSeeker, data interface{}) error {
+func jsonLoad(r io.ReadSeeker, data interface{}) error {
 	if _, err := r.Seek(0, io.SeekStart); err != nil {
 		return err
 	}
 	return json.NewDecoder(r).Decode(data)
 }
+
+// Save to disk file in json format.
+func jsonSave(f interface {
+	io.WriteSeeker
+	Truncate(int64) error
+}, data interface{}) error {
+	b, err := json.Marshal(data)
+	if err != nil {
+		return err
+	}
+	if err = f.Truncate(0); err != nil {
+		return err
+	}
+	if _, err = f.Seek(0, io.SeekStart); err != nil {
+		return err
+	}
+	_, err = f.Write(b)
+	if err != nil {
+		return err
+	}
+	return nil
+}

cmd/utils_test.go

@@ -365,18 +365,47 @@ func TestContains(t *testing.T) {
 	}
 }
 
-// Test jsonLoadFromSeeker.
-func TestJSONLoadFromSeeker(t *testing.T) {
+// Test jsonLoad.
+func TestJSONLoad(t *testing.T) {
 	format := newFormatFSV1()
 	b, err := json.Marshal(format)
 	if err != nil {
 		t.Fatal(err)
 	}
 	var gotFormat formatFSV1
-	if err = jsonLoadFromSeeker(bytes.NewReader(b), &gotFormat); err != nil {
+	if err = jsonLoad(bytes.NewReader(b), &gotFormat); err != nil {
 		t.Fatal(err)
 	}
 	if *format != gotFormat {
-		t.Fatal("jsonLoadFromSeeker() failed to decode json")
+		t.Fatal("jsonLoad() failed to decode json")
+	}
+}
+
+// Test jsonSave.
+func TestJSONSave(t *testing.T) {
+	f, err := ioutil.TempFile("", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(f.Name())
+
+	// Test to make sure formatFSSave overwrites and does not append.
+	format := newFormatFSV1()
+	if err = jsonSave(f, format); err != nil {
+		t.Fatal(err)
+	}
+	fi1, err := f.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = jsonSave(f, format); err != nil {
+		t.Fatal(err)
+	}
+	fi2, err := f.Stat()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if fi1.Size() != fi2.Size() {
+		t.Fatal("Size should not differ after jsonSave()", fi1.Size(), fi2.Size(), f.Name())
 	}
 }