api: added future/response releasing methods

Added method Release to Future and Response's interface,
that allows to free used data directly by calling.
Used to reduce allocations in creating and using SelectResponse.

Closes #493

Author: ermyar

request.go

@@ -620,11 +620,11 @@ func (req *SelectRequest) Context(ctx context.Context) *SelectRequest {
 
 // Response creates a response for the SelectRequest.
 func (req *SelectRequest) Response(header Header, body io.Reader) (Response, error) {
-	baseResp, err := createBaseResponse(header, body)
+	SelectResp, err := createSelectResponse(header, body)
 	if err != nil {
 		return nil, err
 	}
-	return &SelectResponse{baseResponse: *baseResp}, nil
+	return SelectResp, nil
 }
 
 // InsertRequest helps you to create an insert request object for execution

response.go

@@ -3,6 +3,7 @@ package tarantool
 import (
 	"fmt"
 	"io"
+	"sync"
 
 	"github.com/tarantool/go-iproto"
 	"github.com/vmihailenco/msgpack/v5"
@@ -676,9 +677,38 @@ func (resp *baseResponse) Header() Header {
 	return resp.header
 }
 
+var selectResponsePool *sync.Pool = &sync.Pool{
+	New: func() interface{} {
+		return &SelectResponse{}
+	},
+}
+
+func createSelectResponse(header Header, body io.Reader) (*SelectResponse, error) {
+	resp := selectResponsePool.Get().(*SelectResponse)
+	if body == nil {
+		resp.header = header
+		return resp, nil
+	}
+	if buf, ok := body.(*smallBuf); ok {
+		resp.header = header
+		resp.buf.b = buf.b
+		resp.buf.p = buf.p
+		return resp, nil
+	}
+	data, err := io.ReadAll(body)
+	if err != nil {
+		return resp, err
+	}
+	resp.header = header
+	resp.buf.b = data
+	return resp, nil
+}
+
 func (resp *SelectResponse) Release() {
 	resp.baseResponse.Release()
 	resp.pos = nil
+
+	selectResponsePool.Put(resp)
 }
 
 // Pos returns a position descriptor of the last selected tuple for the SelectResponse.