[#205] object: Initial EC implementation

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

object/erasurecode/split.go

@@ -0,0 +1,69 @@
+package erasurecode
+
+import (
+	"crypto/ecdsa"
+
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+)
+
+// Split splits fully formed object into multiple chunks.
+func (c *Constructor) Split(obj *objectSDK.Object, key *ecdsa.PrivateKey) ([]*objectSDK.Object, error) {
+	c.clear()
+
+	header, err := obj.CutPayload().Marshal()
+	if err != nil {
+		return nil, err
+	}
+
+	headerShards, err := c.encodeRaw(header)
+	if err != nil {
+		return nil, err
+	}
+	payloadShards, err := c.encodeRaw(obj.Payload())
+	if err != nil {
+		return nil, err
+	}
+
+	parts := make([]*objectSDK.Object, len(payloadShards))
+	parent, _ := obj.ID()
+	for i := range parts {
+		chunk := objectSDK.New()
+		copyRequiredFields(chunk, obj)
+		chunk.SetPayload(payloadShards[i])
+		chunk.SetPayloadSize(uint64(len(payloadShards[i])))
+
+		ec := objectSDK.NewECHeader(parent, uint32(i), uint32(len(payloadShards)), headerShards[i], uint32(len(header)))
+		chunk.SetECHeader(ec)
+		if err := setIDWithSignature(chunk, key); err != nil {
+			return nil, err
+		}
+
+		parts[i] = chunk
+	}
+	return parts, nil
+}
+
+func setIDWithSignature(obj *objectSDK.Object, key *ecdsa.PrivateKey) error {
+	if err := objectSDK.CalculateAndSetID(obj); err != nil {
+		return err
+	}
+
+	objectSDK.CalculateAndSetPayloadChecksum(obj)
+
+	if key == nil {
+		return nil
+	}
+
+	return objectSDK.CalculateAndSetSignature(*key, obj)
+}
+
+func (c *Constructor) encodeRaw(data []byte) ([][]byte, error) {
+	shards, err := c.enc.Split(data)
+	if err != nil {
+		return nil, err
+	}
+	if err := c.enc.Encode(shards); err != nil {
+		return nil, err
+	}
+	return shards, nil
+}