Fragment reader implemented

pkg/storage/donut/fragment/fragment1/fragment.go

@@ -146,6 +146,68 @@ func Write(target io.Writer, reader io.Reader, length uint64) error {
 	return nil
 }
 
+// Reads a donut fragment
+func Read(reader io.Reader) (io.Reader, error) {
+	header, err := ReadHeader(reader)
+	if err != nil {
+		return nil, err
+	}
+
+	sumReader, sumWriter := io.Pipe()
+
+	teeReader := io.TeeReader(reader, sumWriter)
+
+	defer sumWriter.Close()
+	checksumChannel := make(chan checksumValue)
+	go generateChecksum(sumReader, checksumChannel)
+
+	data := make([]byte, header.DataLength)
+	teeReader.Read(data)
+	sumWriter.Close()
+
+	// read crc
+	footerBuffer := make([]byte, 80)
+	reader.Read(footerBuffer)
+	expectedCrc := binary.LittleEndian.Uint32(footerBuffer[:4])
+
+	actualCrc := crc32c.Sum32(footerBuffer[4:])
+	if expectedCrc != actualCrc {
+		// TODO perhaps we should return data and still report error?
+		return nil, errors.New("Expected CRC doesn't match for footer")
+	}
+
+	footer := DonutFrameFooter{}
+	err = binary.Read(bytes.NewBuffer(footerBuffer[4:]), binary.LittleEndian, &footer)
+	if err != nil {
+		return nil, err
+	}
+
+	return bytes.NewBuffer(data), nil
+}
+
+// Reads the header of a donut
+func ReadHeader(reader io.Reader) (header DonutFrameHeader, err error) {
+	headerSlice := make([]byte, 32)
+	headerLength, err := reader.Read(headerSlice)
+	if err != nil {
+		return header, err
+	}
+	if headerLength != 32 {
+		return header, errors.New("EOF found while reading donut header")
+	}
+	actualCrc := crc32c.Sum32(headerSlice[:24])
+
+	expectedCrc := binary.LittleEndian.Uint32(headerSlice[24:28])
+
+	if actualCrc != expectedCrc {
+		return header, errors.New("CRC for donut did not match")
+	}
+
+	err = binary.Read(bytes.NewBuffer(headerSlice[0:24]), binary.LittleEndian, &header)
+
+	return header, nil
+}
+
 type checksumValue struct {
 	checksum Sha512
 	err      error

pkg/storage/donut/fragment/fragment1/fragment_test.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"crypto/sha512"
 	"encoding/binary"
+	"io"
 	"testing"
 
 	"github.com/minio-io/minio/pkg/utils/checksum/crc32c"
@@ -115,6 +116,23 @@ func (s *MySuite) TestLengthMismatchInWrite(c *C) {
 	c.Assert(err, Not(IsNil))
 }
 
+func (s *MySuite) TestWriteAndRead(c *C) {
+	testData := "Hello, World"
+	testLength := uint64(len(testData))
+	var testBuffer bytes.Buffer
+	err := Write(&testBuffer, bytes.NewBufferString(testData), testLength)
+	c.Assert(err, IsNil)
+
+	testReader, err := Read(&testBuffer)
+	c.Assert(err, IsNil)
+
+	var actualData bytes.Buffer
+	length, err := io.Copy(&actualData, testReader)
+	c.Assert(int64(len(testData)), Equals, length)
+
+	c.Assert([]byte(testData), DeepEquals, actualData.Bytes())
+}
+
 var buf = make([]byte, 1024*1024*8)
 
 func benchmarkSize(b *testing.B, size int) {