storage: check backoff errors

Before this patch, it was possible to get a successful storage info
response, while some replicas still could be treated as erroneous
(backoff) by vshard ro calls.

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 * Explicitly forbid datetime interval conditions (#373).
 * Storage initialization is now asynchronous by default for Tarantool 3.0+ (#412).
+* Additionally check backoff error on storage info fetch (#427).
 
 ### Fixed
 * Working with datetime conditions in case of non-indexed fields or

crud/storage_info.lua

@@ -67,18 +67,22 @@ function storage_info.call(opts)
                 is_master = master == replica
             }
 
-            local ok, res = pcall(replica.conn.call, replica.conn, CRUD_STORAGE_INFO_FUNC_NAME,
-                                  {}, async_opts)
-            if ok then
-                futures_by_replicas[replica_id] = res
+            if replica.backoff_err ~= nil then
+                replica_state_by_id[replica_id].message = tostring(replica.backoff_err)
             else
-                local err_msg = string.format("Error getting storage info for %s", replica_id)
-                if res ~= nil then
-                    log.error("%s: %s", err_msg, res)
-                    replica_state_by_id[replica_id].message = tostring(res)
+                local ok, res = pcall(replica.conn.call, replica.conn, CRUD_STORAGE_INFO_FUNC_NAME,
+                                      {}, async_opts)
+                if ok then
+                    futures_by_replicas[replica_id] = res
                 else
-                    log.error(err_msg)
-                    replica_state_by_id[replica_id].message = err_msg
+                    local err_msg = string.format("Error getting storage info for %s", replica_id)
+                    if res ~= nil then
+                        log.error("%s: %s", err_msg, res)
+                        replica_state_by_id[replica_id].message = tostring(res)
+                    else
+                        log.error(err_msg)
+                        replica_state_by_id[replica_id].message = err_msg
+                    end
                 end
             end
         end