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