Adding read header for erasure

pkg/storage/donut/erasure/erasure1/erasure.go

@@ -22,6 +22,11 @@ import (
 	"encoding/gob"
 	"errors"
 	"io"
+	"strconv"
+)
+
+const (
+	Version = uint32(1)
 )
 
 // DataHeader represents the structure serialized to gob.
@@ -84,7 +89,7 @@ func Write(target io.Writer, key string, part uint8, length uint32, k, m uint8,
 	encoder.Encode(header)
 
 	// write version
-	binary.Write(target, binary.LittleEndian, uint32(1))
+	binary.Write(target, binary.LittleEndian, uint32(Version))
 
 	// write encoded header
 	if _, err := io.Copy(target, &headerBuffer); err != nil {
@@ -96,3 +101,18 @@ func Write(target io.Writer, key string, part uint8, length uint32, k, m uint8,
 	}
 	return nil
 }
+
+// Read an erasure block
+func ReadHeader(reader io.Reader) (dataHeader DataHeader, err error) {
+	versionArray := make([]byte, 4)
+	if err := binary.Read(reader, binary.LittleEndian, versionArray); err != nil {
+		return dataHeader, err
+	}
+	version := binary.LittleEndian.Uint32(versionArray)
+	if version > Version || version == 0 {
+		return dataHeader, errors.New("Unknown version: " + strconv.FormatUint(uint64(version), 10))
+	}
+	decoder := gob.NewDecoder(reader)
+	err = decoder.Decode(&dataHeader)
+	return dataHeader, err
+}

pkg/storage/donut/erasure/erasure1/erasure_test.go

@@ -66,3 +66,25 @@ func (s *MySuite) TestSingleWrite(c *C) {
 	c.Assert(actualData.Bytes(), DeepEquals, []byte(testData))
 	c.Assert(err, IsNil)
 }
+
+func (s *MySuite) TestReadWrite(c *C) {
+	var testBuffer bytes.Buffer
+	testData := "Hello, World"
+	testHeader := DataHeader{
+		Key:              "testobj",
+		ChunkIndex:       1,
+		OriginalLength:   uint32(len(testData)),
+		EncoderK:         8,
+		EncoderM:         8,
+		EncoderTechnique: Cauchy,
+	}
+
+	err := Write(&testBuffer, testHeader.Key, testHeader.ChunkIndex, testHeader.OriginalLength, testHeader.EncoderK, testHeader.EncoderM, testHeader.EncoderTechnique, bytes.NewBufferString(testData))
+	c.Assert(err, IsNil)
+
+	header, err := ReadHeader(&testBuffer)
+	c.Assert(err, IsNil)
+	c.Assert(header, DeepEquals, testHeader)
+	c.Assert(testBuffer.Len(), Equals, len(testData))
+	c.Assert(testBuffer.Bytes(), DeepEquals, []byte(testData))
+}