[#63] Add fast multipart upload

Add new flag to object tree meta `isCombined` that means
the object payload is list of parts that forms real payload.
Set this attribute when complete multipart upload not to do unnecessary copying.

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/layer/object.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -32,6 +33,14 @@ type (
 		// payload range
 		off, ln uint64
 
+		objInfo *data.ObjectInfo
+		bktInfo *data.BucketInfo
+	}
+
+	getFrostFSParams struct {
+		// payload range
+		off, ln uint64
+
 		oid     oid.ID
 		bktInfo *data.BucketInfo
 	}
@@ -98,9 +107,55 @@ func (n *layer) objectHead(ctx context.Context, bktInfo *data.BucketInfo, idObj
 	return res.Head, nil
 }
 
+func (n *layer) initObjectPayloadReader(ctx context.Context, p getParams) (io.Reader, error) {
+	if _, isCombined := p.objInfo.Headers[MultipartObjectSize]; !isCombined {
+		return n.initFrostFSObjectPayloadReader(ctx, getFrostFSParams{
+			off:     p.off,
+			ln:      p.ln,
+			oid:     p.objInfo.ID,
+			bktInfo: p.bktInfo,
+		})
+	}
+
+	combinedObj, err := n.objectGet(ctx, p.bktInfo, p.objInfo.ID)
+	if err != nil {
+		return nil, fmt.Errorf("get combined object '%s': %w", p.objInfo.ID.EncodeToString(), err)
+	}
+
+	var parts []*data.PartInfo
+	if err = json.Unmarshal(combinedObj.Payload(), &parts); err != nil {
+		return nil, fmt.Errorf("unmarshal combined object parts: %w", err)
+	}
+
+	isEncrypted := FormEncryptionInfo(p.objInfo.Headers).Enabled
+	objParts := make([]partObj, len(parts))
+	for i, part := range parts {
+		size := part.Size
+		if isEncrypted {
+			if size, err = sio.EncryptedSize(part.Size); err != nil {
+				return nil, fmt.Errorf("compute encrypted size: %w", err)
+			}
+		}
+
+		objParts[i] = partObj{
+			OID:  part.OID,
+			Size: size,
+		}
+	}
+
+	return &multiObjectReader{
+		ctx:   ctx,
+		off:   p.off,
+		ln:    p.ln,
+		layer: n,
+		parts: objParts,
+		prm:   getFrostFSParams{bktInfo: p.bktInfo},
+	}, nil
+}
+
 // initializes payload reader of the FrostFS object.
 // Zero range corresponds to full payload (panics if only offset is set).
-func (n *layer) initObjectPayloadReader(ctx context.Context, p getParams) (io.Reader, error) {
+func (n *layer) initFrostFSObjectPayloadReader(ctx context.Context, p getFrostFSParams) (io.Reader, error) {
 	prm := PrmObjectRead{
 		Container:    p.bktInfo.CID,
 		Object:       p.oid,
@@ -250,6 +305,7 @@ func (n *layer) PutObject(ctx context.Context, p *PutObjectParams) (*data.Extend
 			Size:     size,
 		},
 		IsUnversioned: !bktSettings.VersioningEnabled(),
+		IsCombined:    p.Header[MultipartObjectSize] != "",
 	}
 
 	if newVersion.ID, err = n.treeService.AddVersion(ctx, p.BktInfo, newVersion); err != nil {