Donut now tests amount written should match expected amount to write

pkg/storage/donut/v1/donut.go

@@ -19,6 +19,7 @@ package v1
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"io"
 
 	"github.com/minio-io/minio/pkg/utils/checksum/crc32c"
@@ -101,10 +102,13 @@ func Write(target io.Writer, reader io.Reader, length uint64) error {
 	checksumChannel := make(chan checksumValue)
 	go generateChecksum(sumReader, checksumChannel)
 	teeReader := io.TeeReader(reader, sumWriter)
-	_, err = io.Copy(target, teeReader)
+	dataLength, err := io.Copy(target, teeReader)
 	if err != nil {
 		return err
 	}
+	if uint64(dataLength) != length {
+		return errors.New("Specified data length and amount written mismatched")
+	}
 	sumWriter.Close()
 	dataChecksum := <-checksumChannel
 	if dataChecksum.err != nil {

pkg/storage/donut/v1/donut_test.go

@@ -124,3 +124,9 @@ func (s *MySuite) TestSingleWrite(c *C) {
 	// ensure no extra data is in the file
 	c.Assert(testBuffer.Len(), Equals, 0)
 }
+
+func (s *MySuite) TestLengthMismatchInWrite(c *C) {
+	var testData bytes.Buffer
+	err := Write(&testData, bytes.NewBufferString("hello, world"), 5)
+	c.Assert(err, Not(IsNil))
+}