[#874] engine: Check object existance concurrently

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/blobstor/exists.go

@@ -3,6 +3,7 @@ package blobstor
 import (
 	"context"
 	"encoding/hex"
+	"errors"
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
@@ -57,27 +58,30 @@ func (b *BlobStor) Exists(ctx context.Context, prm common.ExistsPrm) (common.Exi
 	// error     | found       | log the error, return true, nil
 	// error     | not found   | return the error
 	// error     | error       | log the first error, return the second
-	var errors []error
+	var storageErrors []error
 	for i := range b.storage {
 		res, err := b.storage[i].Storage.Exists(ctx, prm)
 		if err == nil && res.Exists {
 			exists = true
 			return res, nil
 		} else if err != nil {
-			errors = append(errors, err)
+			if errors.Is(err, context.Canceled) {
+				return common.ExistsRes{}, err
+			}
+			storageErrors = append(storageErrors, err)
 		}
 	}
 
-	if len(errors) == 0 {
+	if len(storageErrors) == 0 {
 		return common.ExistsRes{}, nil
 	}
 
-	for _, err := range errors[:len(errors)-1] {
+	for _, err := range storageErrors[:len(storageErrors)-1] {
 		b.log.Warn(logs.BlobstorErrorOccurredDuringObjectExistenceChecking,
 			zap.Stringer("address", prm.Address),
 			zap.String("error", err.Error()),
 			zap.String("trace_id", tracingPkg.GetTraceID(ctx)))
 	}
 
-	return common.ExistsRes{}, errors[len(errors)-1]
+	return common.ExistsRes{}, storageErrors[len(storageErrors)-1]
 }