satellite/buckets: handle bucket exists better

In some rare cases when two entities are trying to create the same
bucket at the same time it's possible that we will return internal
error instead of `bucket already exists`. It's because we are not
handling correctly DB error about constraint error. This change checks
if while inserting bucket into DB we got constraint error and propagate
correct error to metainfo API.

Change-Id: Ie6fd2c943b864b4ea7d71e4a162e74dc3510e386

satellite/buckets/db.go

@@ -25,6 +25,9 @@ var (
 
 	// ErrBucketNotFound is an error class for non-existing bucket.
 	ErrBucketNotFound = errs.Class("bucket not found")
+
+	// ErrBucketAlreadyExists is used to indicate that bucket already exists.
+	ErrBucketAlreadyExists = errs.Class("bucket already exists")
 )
 
 // Bucket contains information about a specific bucket.

satellite/metainfo/endpoint_bucket.go

@@ -114,6 +114,10 @@ func (endpoint *Endpoint) CreateBucket(ctx context.Context, req *pb.BucketCreate
 
 	bucket, err := endpoint.buckets.CreateBucket(ctx, bucketReq)
 	if err != nil {
+		if buckets.ErrBucketAlreadyExists.Has(err) {
+			return nil, rpcstatus.Error(rpcstatus.AlreadyExists, "bucket already exists")
+		}
+
 		endpoint.log.Error("error while creating bucket", zap.String("bucketName", bucketReq.Name), zap.Error(err))
 		return nil, rpcstatus.Error(rpcstatus.Internal, "unable to create bucket")
 	}

satellite/satellitedb/bucketsdb.go

@@ -51,6 +51,9 @@ func (db *bucketsDB) CreateBucket(ctx context.Context, bucket buckets.Bucket) (_
 		optionalFields,
 	)
 	if err != nil {
+		if dbx.IsConstraintError(err) {
+			return buckets.Bucket{}, buckets.ErrBucketAlreadyExists.New("")
+		}
 		return buckets.Bucket{}, buckets.ErrBucket.Wrap(err)
 	}