config: move snapshot related code into utils

Config's box.cfg applier scans snapshot_dir in order to find out,
whether recovery is going to be done. It's needed in order to determine,
whether the instance should be started into ro mode firstly.

Let's move info about snapshot into separate file in utils. The commit
also introduces snapshot_path, which will be used in the following
commits in order to validate names.

Needed for #8978

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

src/box/CMakeLists.txt

@@ -54,6 +54,7 @@ lua_source(lua_sources lua/config/source/env.lua          config_source_env_lua)
 lua_source(lua_sources lua/config/source/file.lua         config_source_file_lua)
 lua_source(lua_sources lua/config/utils/log.lua           config_utils_log_lua)
 lua_source(lua_sources lua/config/utils/schema.lua        config_utils_schema_lua)
+lua_source(lua_sources lua/config/utils/snapshot.lua      config_utils_snapshot_lua)
 lua_source(lua_sources lua/config/utils/tabulate.lua      config_utils_tabulate_lua)
 
 if (ENABLE_CONFIG_EXTRAS)

src/box/lua/config/applier/box_cfg.lua

@@ -1,7 +1,7 @@
-local fio = require('fio')
 local fiber = require('fiber')
 local log = require('internal.config.utils.log')
 local instance_config = require('internal.config.instance_config')
+local snapshot = require('internal.config.utils.snapshot')
 
 local function peer_uri(configdata, peer_name)
     local iconfig = configdata._peers[peer_name].iconfig_def
@@ -69,55 +69,6 @@ local function log_destination(log)
     end
 end
 
--- Determine where snapshot should reside based on the given
--- configuration.
---
--- To be called before first box.cfg().
-local function effective_snapshot_dir(configdata)
-    -- The snapshot directory has a default value in the schema
-    -- (it is a string). So, it can't be nil or box.NULL.
-    local snap_dir = configdata:get('snapshot.dir', {use_default = true})
-    assert(snap_dir ~= nil)
-
-    -- If the path is absolute, just return it.
-    --
-    -- This check is necessary due to fio.pathjoin() peculiars,
-    -- see gh-8816.
-    if snap_dir:startswith('/') then
-        return snap_dir
-    end
-
-    -- We assume that the startup working directory is the current
-    -- working directory. IOW, that this function is called before
-    -- first box.cfg() call. Let's verify it.
-    assert(type(box.cfg) == 'function')
-
-    -- If the snapshot directory is not absolute, it is relative
-    -- to the working directory.
-    --
-    -- Determine an absolute path to the configured working
-    -- directory considering that it may be relative to the
-    -- working directory at the startup moment.
-    local work_dir = configdata:get('process.work_dir', {use_default = true})
-    if work_dir == nil then
-        work_dir = '.'
-    end
-    work_dir = fio.abspath(work_dir)
-
-    -- Now we know the absolute path to the configured working
-    -- directory. Let's determine the snapshot directory path.
-    return fio.abspath(fio.pathjoin(work_dir, snap_dir))
-end
-
--- Determine whether the instance will be started from an existing
--- snapshot.
---
--- To be called before first box.cfg().
-local function has_snapshot(configdata)
-    local pattern = fio.pathjoin(effective_snapshot_dir(configdata), '*.snap')
-    return #fio.glob(pattern) > 0
-end
-
 -- Returns nothing or {needs_retry = true}.
 local function apply(config)
     local configdata = config._configdata
@@ -266,7 +217,8 @@ local function apply(config)
         local am_i_bootstrap_leader = false
         if is_startup then
             local instance_name = configdata:names().instance_name
-            am_i_bootstrap_leader = not has_snapshot(configdata) and
+            am_i_bootstrap_leader =
+                snapshot.get_path(configdata._iconfig_def) == nil and
                 instance_name == configdata:bootstrap_leader_name()
             box_cfg.read_only = not am_i_bootstrap_leader
         end
@@ -382,7 +334,7 @@ local function apply(config)
     if is_startup and failover ~= 'election' and failover ~= 'supervised' then
         local configured_as_rw = not box_cfg.read_only
         local in_replicaset = #configdata:peers() > 1
-        local has_snap = has_snapshot(configdata)
+        local has_snap = snapshot.get_path(configdata._iconfig_def) ~= nil
 
         -- Require at least one writable instance in the
         -- replicaset if the instance is to be bootstrapped (has

src/box/lua/config/utils/snapshot.lua

@@ -0,0 +1,67 @@
+local fio = require('fio')
+local instance_config = require('internal.config.instance_config')
+
+local snapshot_path = nil
+
+-- Determine where snapshot should reside based on the given
+-- configuration.
+--
+-- To be called before first box.cfg().
+local function effective_snapshot_dir(iconfig)
+    assert(iconfig ~= nil)
+    -- The snapshot directory has a default value in the schema
+    -- (it is a string). So, it can't be nil or box.NULL.
+    local snap_dir = instance_config:get(iconfig, 'snapshot.dir')
+    assert(snap_dir ~= nil)
+
+    -- If the path is absolute, just return it.
+    --
+    -- This check is necessary due to fio.pathjoin() peculiars,
+    -- see gh-8816.
+    if snap_dir:startswith('/') then
+        return snap_dir
+    end
+
+    -- We assume that the startup working directory is the current
+    -- working directory. IOW, that this function is called before
+    -- first box.cfg() call. Let's verify it.
+    assert(type(box.cfg) == 'function')
+
+    -- If the snapshot directory is not absolute, it is relative
+    -- to the working directory.
+    --
+    -- Determine an absolute path to the configured working
+    -- directory considering that it may be relative to the
+    -- working directory at the startup moment.
+    local work_dir = instance_config:get(iconfig, 'process.work_dir')
+    if work_dir == nil then
+        work_dir = '.'
+    end
+    work_dir = fio.abspath(work_dir)
+
+    -- Now we know the absolute path to the configured working
+    -- directory. Let's determine the snapshot directory path.
+    return fio.abspath(fio.pathjoin(work_dir, snap_dir))
+end
+
+-- Determine whether the instance will be recovered from an existing
+-- snapshot and return its path. Should be called before box.cfg.
+--
+-- To be called before first box.cfg().
+local function get_snapshot_path(iconfig)
+    assert(type(box.cfg) == 'function')
+    if snapshot_path == nil then
+        local snap_dir = effective_snapshot_dir(iconfig)
+        local glob = fio.glob(fio.pathjoin(snap_dir, '*.snap'))
+        if #glob > 0 then
+            table.sort(glob)
+            snapshot_path = glob[#glob]
+        end
+    end
+
+    return snapshot_path
+end
+
+return {
+    get_path = get_snapshot_path,
+}

src/box/lua/init.c

@@ -155,6 +155,7 @@ extern char session_lua[],
 	config_source_file_lua[],
 	config_utils_log_lua[],
 	config_utils_schema_lua[],
+	config_utils_snapshot_lua[],
 	config_utils_tabulate_lua[]
 #if ENABLE_CONFIG_EXTRAS
 	,
@@ -335,6 +336,10 @@ static const char *lua_sources[] = {
 	"internal.config.instance_config",
 	config_instance_config_lua,
 
+	"config/utils/snapshot",
+	"internal.config.utils.snapshot",
+	config_utils_snapshot_lua,
+
 	"config/cluster_config",
 	"internal.config.cluster_config",
 	config_cluster_config_lua,