[#373] blobstor: Add metrics

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"
+	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor/common"
@@ -17,6 +18,14 @@ import (
 // Returns any error encountered that did not allow
 // to completely check object existence.
 func (b *BlobStor) Exists(ctx context.Context, prm common.ExistsPrm) (common.ExistsRes, error) {
+	var (
+		exists    = false
+		startedAt = time.Now()
+	)
+	defer func() {
+		b.metrics.Exists(time.Since(startedAt), exists, prm.StorageID != nil)
+	}()
+
 	ctx, span := tracing.StartSpanFromContext(ctx, "BlobStor.Exists",
 		trace.WithAttributes(
 			attribute.String("address", prm.Address.EncodeToString()),
@@ -29,9 +38,13 @@ func (b *BlobStor) Exists(ctx context.Context, prm common.ExistsPrm) (common.Exi
 
 	if prm.StorageID != nil {
 		if len(prm.StorageID) == 0 {
-			return b.storage[len(b.storage)-1].Storage.Exists(ctx, prm)
+			res, err := b.storage[len(b.storage)-1].Storage.Exists(ctx, prm)
+			exists = err == nil && res.Exists
+			return res, err
 		}
-		return b.storage[0].Storage.Exists(ctx, prm)
+		res, err := b.storage[0].Storage.Exists(ctx, prm)
+		exists = err == nil && res.Exists
+		return res, err
 	}
 
 	// If there was an error during existence check below,
@@ -47,6 +60,7 @@ func (b *BlobStor) Exists(ctx context.Context, prm common.ExistsPrm) (common.Exi
 	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)