connpool: mode option for call()

This patch adds a "mode" option to experimental.call(). This option
allows to execute a function on instances with desired RO status.

Part of #9930

NO_DOC=will be added later
NO_CHANGELOG=will be added later

src/box/lua/experimental/connpool.lua

@@ -192,9 +192,22 @@ local function filter(opts)
     return dynamic_candidates
 end
 
-local function get_connection(all_candidates, prefer_local)
-    local candidates = table.copy(all_candidates)
-    if prefer_local ~= false then
+local function get_connection(opts)
+    local mode = nil
+    if opts.mode == 'ro' or opts.mode == 'rw' then
+        mode = opts.mode
+    end
+    local candidates_opts = {
+        labels = opts.labels,
+        roles = opts.roles,
+        mode = mode,
+    }
+    local candidates = filter(candidates_opts)
+    if next(candidates) == nil then
+        return nil, "no candidates are available with these conditions"
+    end
+
+    if opts.prefer_local ~= false then
         local candidate_idx = nil
         for n, candidate in ipairs(candidates) do
             if candidate == box.info.name then
@@ -219,14 +232,15 @@ local function get_connection(all_candidates, prefer_local)
             return conn
         end
     end
-    return nil
+    return nil, "connection to candidates failed"
 end
 
 local function call(func_name, args, opts)
     checks('string', '?table', {
         labels = '?table',
         roles = '?table',
         prefer_local = '?boolean',
+        mode = '?string',
         -- The following options passed directly to net.box.call().
         timeout = '?',
         buffer = '?',
@@ -235,23 +249,21 @@ local function call(func_name, args, opts)
         is_async = '?boolean',
     })
     opts = opts or {}
+    if opts.mode ~= nil and opts.mode ~= 'ro' and opts.mode ~= 'rw' then
+        local msg = 'Expected nil, "ro" or "rw", got "%s"'
+        error(msg:format(opts.mode), 0)
+    end
 
-    local candidates_opts = {
+    local conn_opts = {
         labels = opts.labels,
         roles = opts.roles,
+        prefer_local = opts.prefer_local,
+        mode = opts.mode,
     }
-    local candidates = filter(candidates_opts)
-    if next(candidates) == nil then
-        local msg = "Couldn't execute function %s: no candidates are " ..
-                    "available with these conditions"
-        error(msg:format(func_name), 0)
-    end
-
-    local conn = get_connection(candidates, opts.prefer_local)
+    local conn, err = get_connection(conn_opts)
     if conn == nil then
-        local msg = "Couldn't execute function %s: connection to " ..
-                    "candidates failed"
-        error(msg:format(func_name), 0)
+        local msg = "Couldn't execute function %s: %s"
+        error(msg:format(func_name, err), 0)
     end
 
     local net_box_call_opts = {

test/config-luatest/rpc_test.lua

@@ -426,3 +426,96 @@ g.test_call = function(g)
     g.server_3:exec(check)
     g.server_4:exec(check)
 end
+
+g.test_call_mode = function(g)
+    local dir = treegen.prepare_directory(g, {}, {})
+    local config = [[
+    credentials:
+      users:
+        guest:
+          roles: [super]
+
+    iproto:
+      listen:
+        - uri: 'unix/:./{{ instance_name }}.iproto'
+
+    roles: [one]
+
+    groups:
+      group-001:
+        replicasets:
+          replicaset-001:
+            instances:
+              instance-001:
+                database:
+                  mode: rw
+                labels:
+                  l1: 'first'
+              instance-002: {}
+          replicaset-002:
+            replication:
+              failover: manual
+            leader: 'instance-003'
+            instances:
+              instance-003: {}
+              instance-004:
+                labels:
+                  l1: 'first'
+    ]]
+    treegen.write_script(dir, 'config.yaml', config)
+
+    local role = string.dump(function()
+        local function f()
+            return box.info.name
+        end
+
+        rawset(_G, 'f', f)
+
+        return {
+            stop = function() end,
+            apply = function() end,
+            validate = function() end,
+        }
+    end)
+    treegen.write_script(dir, 'one.lua', role)
+
+    local opts = {
+        env = {LUA_PATH = os.environ()['LUA_PATH']},
+        config_file = 'config.yaml',
+        chdir = dir,
+    }
+    g.server_1 = server:new(fun.chain(opts, {alias = 'instance-001'}):tomap())
+    g.server_2 = server:new(fun.chain(opts, {alias = 'instance-002'}):tomap())
+    g.server_3 = server:new(fun.chain(opts, {alias = 'instance-003'}):tomap())
+    g.server_4 = server:new(fun.chain(opts, {alias = 'instance-004'}):tomap())
+
+    g.server_1:start({wait_until_ready = false})
+    g.server_2:start({wait_until_ready = false})
+    g.server_3:start({wait_until_ready = false})
+    g.server_4:start({wait_until_ready = false})
+
+    g.server_1:wait_until_ready()
+    g.server_2:wait_until_ready()
+    g.server_3:wait_until_ready()
+    g.server_4:wait_until_ready()
+
+    local function check()
+        local connpool = require('experimental.connpool')
+        local opts = {
+            labels = {l1 = 'first'},
+            mode = 'rw',
+        }
+        t.assert_equals(connpool.call('f', nil, opts), 'instance-001')
+
+        opts = {
+            mode = 'ro',
+        }
+        local exp_list = {'instance-002', 'instance-004'}
+        t.assert_items_include(exp_list, {connpool.call('f', nil, opts)})
+    end
+
+    g.server_1:exec(check)
+    g.server_2:exec(check)
+    g.server_3:exec(check)
+    g.server_4:exec(check)
+end