-- SPDX-License-Identifier: GPL-3.0-or-later

local debug = require('debug')
local ffi = require('ffi')
local kluautil = require('kluautil')
local krprint = require("krprint")

-- Units
kB = 1024
MB = 1024*kB
GB = 1024*MB
-- Time
sec = 1000
second = sec
minute = 60 * sec
min = minute
hour = 60 * minute
day = 24 * hour

-- Logging

-- from syslog.h
LOG_CRIT	= 2
LOG_ERR		= 3
LOG_WARNING	= 4
LOG_NOTICE	= 5
LOG_INFO	= 6
LOG_DEBUG	= 7

local function curr_file() return debug.getinfo(4,'S').source end
local function curr_line() return debug.getinfo(4,'l').currentline end

local function log_fmt(grp, level, fmt, ...)
	ffi.C.kr_log_fmt(grp, level,
			'CODE_FILE='..curr_file(), 'CODE_LINE='..curr_line(), 'CODE_FUNC=',
			'[%-6s] %s\n', ffi.C.kr_log_grp2name(grp), string.format(fmt, ...))
end

function log_req(req, qry_uid, indent, grp, fmt, ...)
	ffi.C.kr_log_req1(req, qry_uid, indent, grp, ffi.C.kr_log_grp2name(grp),
		'%s\n', string.format(fmt, ...))
end

function log_qry(qry, grp, fmt, ...)
	ffi.C.kr_log_q1(qry, grp, ffi.C.kr_log_grp2name(grp),
		'%s\n', string.format(fmt, ...))
end

function panic(fmt, ...)
        print(debug.traceback('error occurred here (config filename:lineno is '
                .. 'at the bottom, if config is involved):', 2))
        error(string.format('ERROR: '.. fmt, ...), 0)
end

function log_error(grp, fmt, ...)
	log_fmt(grp, LOG_ERR, fmt, ...)
end

function log_warn(grp, fmt, ...)
	log_fmt(grp, LOG_WARNING, fmt, ...)
end

function log_notice(grp, fmt, ...)
	log_fmt(grp, LOG_NOTICE, fmt, ...)
end

function log_info(grp, fmt, ...)
	log_fmt(grp, LOG_INFO, fmt, ...)
end

function log_debug(grp, fmt, ...)
	log_fmt(grp, LOG_DEBUG, fmt, ...)
end

function log(fmt, ...)
	log_notice(ffi.C.LOG_GRP_MODULE, fmt, ...)
end

-- Resolver bindings
kres = require('kres')
if rawget(kres, 'str2dname') ~= nil then
	todname = kres.str2dname
end

worker.resolve_pkt = function (pkt, options, finish, init)
	options = kres.mk_qflags(options)
	local task = ffi.C.worker_resolve_start(pkt, options)

	-- Deal with finish and init callbacks
	if finish ~= nil then
		local finish_cb
		finish_cb = ffi.cast('trace_callback_f',
			function (req)
				jit.off(true, true) -- JIT for (C -> lua)^2 nesting isn't allowed
				finish(req.answer, req)
				finish_cb:free()
			end)
		task.ctx.req.trace_finish = finish_cb
	end
	if init ~= nil then
		init(task.ctx.req)
	end

	return ffi.C.worker_resolve_exec(task, pkt) == 0
end

worker.resolve = function (qname, qtype, qclass, options, finish, init)
	-- Alternatively use named arguments
	if type(qname) == 'table' then
		local t = qname
		qname = t.name
		qtype = t.type
		qclass = t.class
		options = t.options
		finish = t.finish
		init = t.init
	end
	qtype = qtype or kres.type.A
	qclass = qclass or kres.class.IN
	options = kres.mk_qflags(options)
	-- LATER: nicer errors for rubbish in qname, qtype, qclass?
	local pkt = ffi.C.worker_resolve_mk_pkt(qname, qtype, qclass, options)
	if pkt == nil then
		panic('failure in worker.resolve(); probably invalid qname "%s"', qname)
	end
	local ret = worker.resolve_pkt(pkt, options, finish, init)
	ffi.C.knot_pkt_free(pkt);
	return ret
end
resolve = worker.resolve

-- Shorthand for aggregated per-worker information
worker.info = function ()
	local t = worker.stats()
	t.pid = worker.pid
	return t
end

-- Resolver mode of operation
local current_mode = 'normal'
local mode_table = { normal=0, strict=1, permissive=2 }
function mode(m)
	if not m then return current_mode end
	if not mode_table[m] then error('unsupported mode: '..m) end
	-- Update current operation mode
	current_mode = m
	option('STRICT', current_mode == 'strict')
	option('PERMISSIVE', current_mode == 'permissive')
	return true
end

-- Trivial option alias
function reorder_RR(val)
	return option('REORDER_RR', val)
end

-- Get/set resolver options via name (string)
function option(name, val)
	local flags = kres.context().options;
	-- Note: no way to test existence of flags[name] but we want error anyway.
	name = string.upper(name) -- convenience
	if val ~= nil then
		if (val ~= true) and (val ~= false) then
			panic('invalid option value: ' .. tostring(val))
		end
		flags[name] = val;
	end
	return flags[name];
end

-- Function aliases
-- `env.VAR returns os.getenv(VAR)`
env = {}
setmetatable(env, {
	__index = function (_, k) return os.getenv(k) end
})

debugging = {}
setmetatable(debugging, {
	__index = function(_, k)
		if k == 'assertion_abort' then return ffi.C.kr_dbg_assertion_abort
		elseif k == 'assertion_fork' then return ffi.C.kr_dbg_assertion_fork
		else panic('invalid debugging option: ' .. tostring(k))
		end
	end,
	__newindex = function(_, k, v)
		if k == 'assertion_abort' then ffi.C.kr_dbg_assertion_abort = v
		elseif k == 'assertion_fork' then ffi.C.kr_dbg_assertion_fork = v
		else panic('invalid debugging option: ' .. tostring(k))
		end
	end
})

-- Quick access to interfaces
-- `net.<iface>` => `net.interfaces()[iface]`
-- `net = {addr1, ..}` => `net.listen(name, addr1)`
-- `net.ipv{4,6} = {true, false}` => enable/disable IPv{4,6}
setmetatable(net, {
	__index = function (t, k)
		local v = rawget(t, k)
		if v then return v
		elseif k == 'ipv6' then return not option('NO_IPV6')
		elseif k == 'ipv4' then return not option('NO_IPV4')
		else return net.interfaces()[k]
		end
	end,
	__newindex = function (t,k,v)
		if     k == 'ipv6' then return option('NO_IPV6', not v)
		elseif k == 'ipv4' then return option('NO_IPV4', not v)
		else
			local iname = rawget(net.interfaces(), v)
			if iname then t.listen(iname)
			else t.listen(v)
			end
		end
	end
})

-- Syntactic sugar for module loading
-- `modules.<name> = <config>`
setmetatable(modules, {
	__newindex = function (_, k, v)
		if type(k) == 'number' then
			k, v = v, nil
		end
		if not rawget(_G, k) then
			modules.load(k)
			k = string.match(k, '[%w_]+')
			local mod = _G[k]
			local config = mod and rawget(mod, 'config')
			if mod ~= nil and config ~= nil then
				if k ~= v then config(v)
				else           config()
				end
			end
		end
	end
})

-- Set up lua table for a C module. (Internal function.)
function modules_create_table_for_c(kr_module_ud)
	local kr_module = ffi.cast('struct kr_module **', kr_module_ud)[0]
	--- Set up the global table named according to the module.
	if kr_module.config == nil and kr_module.props == nil then
		return
	end
	local module = {}
	local module_name = ffi.string(kr_module.name)
	_G[module_name] = module

	--- Construct lua functions for properties.
	if kr_module.props ~= nil then
		local i = 0
		while true do
			local prop = kr_module.props[i]
			local cb = prop.cb
			if cb == nil then break; end
			module[ffi.string(prop.name)] =
				function (arg) -- lua wrapper around kr_prop_cb function typedef
					local arg_conv
					if type(arg) == 'table' or type(arg) == 'boolean' then
						arg_conv = tojson(arg)
					elseif arg ~= nil then
						arg_conv = tostring(arg)
					end
					local ret_cstr = cb(ffi.C.the_engine, kr_module, arg_conv)
					if ret_cstr == nil then
						return nil
					end
					-- LATER(optim.): superfluous copying
					local ret_str = ffi.string(ret_cstr)
					-- This is a bit ugly, but the API is that invalid JSON
					-- should be just returned as string :-(
					local status, ret = pcall(fromjson, ret_str)
					if not status then ret = ret_str end
					ffi.C.free(ret_cstr)
					return ret
				end
			i = i + 1
		end
	end

	--- Construct lua function for config().
	if kr_module.config ~= nil then
		module.config =
			function (arg)
				local arg_conv
				if type(arg) == 'table' or type(arg) == 'boolean' then
					arg_conv = tojson(arg)
				elseif arg ~= nil then
					arg_conv = tostring(arg)
				end
				return kr_module.config(kr_module, arg_conv)
			end
	end

	--- Add syntactic sugar for get() and set() properties.
	--- That also "catches" any commands like `moduleName.foo = bar`.
	local m_index, m_newindex
	local get_f = rawget(module, 'get')
	if get_f ~= nil then
		m_index = function (_, key)
			return get_f(key)
		end
	else
		m_index = function ()
			error('module ' .. module_name .. ' does not support indexing syntax sugar')
		end
	end
	local set_f = rawget(module, 'set')
	if set_f ~= nil then
		m_newindex = function (_, key, value)
			-- This will produce a nasty error on some non-string parameters.
			-- Still, we already use it with integer values, e.g. in predict module :-/
			return set_f(key .. ' ' .. value)
		end
	else
		m_newindex = function ()
			error('module ' .. module_name .. ' does not support assignment syntax sugar')
		end
	end
	setmetatable(module, {
		-- note: the two functions only get called for *missing* indices
		__index = m_index,
		__newindex = m_newindex,
	})
end

local layer_ctx = ffi.C.kr_layer_t_static
-- Utilities internal for lua layer glue; see ../ffimodule.c
modules_ffi_layer_wrap1 = function (layer_cb)
	return layer_cb(layer_ctx.state, layer_ctx.req)
end
modules_ffi_layer_wrap2 = function (layer_cb)
	return layer_cb(layer_ctx.state, layer_ctx.req, layer_ctx.pkt)
end
modules_ffi_layer_wrap_checkout = function (layer_cb)
	return layer_cb(layer_ctx.state, layer_ctx.req, layer_ctx.pkt,
					layer_ctx.dst, layer_ctx.is_stream)
end
modules_ffi_wrap_modcb = function (cb, kr_module_ud) -- this one isn't for layer
	local kr_module = ffi.cast('struct kr_module **', kr_module_ud)[0]
	return cb(kr_module)
end

-- Return filesystem size where the cache resides.
cache.fssize = function ()
	local path = cache.current_storage or '.'
	-- As it is now, `path` may or may not include the lmdb:// prefix.
	if string.sub(path, 1, 7) == 'lmdb://' then
		path = string.sub(path, 8)
	end
	if #path == 0 then
		path = '.'
	end
	local size = tonumber(ffi.C.kr_fssize(path))
	if size < 0 then
		panic('cache.fssize(): %s', kres.strerror(size))
	else
		return size
	end
end

cache.clear = function (name, exact_name, rr_type, chunk_size, callback, prev_state)
	if name == nil or (name == '.' and not exact_name) then
		-- keep same output format as for 'standard' clear
		local total_count = cache.count()
		if not cache.clear_everything() then
			error('unable to clear everything')
		end
		return {count = total_count}
	end
	-- Check parameters, in order, and set defaults if missing.
	local dname = kres.str2dname(name)
	if not dname then error('cache.clear(): incorrect name passed') end
	if exact_name == nil then exact_name = false end
	if type(exact_name) ~= 'boolean'
		then error('cache.clear(): incorrect exact_name passed') end

	local cach = kres.context().cache;
	local rettable = {}
	-- Apex warning.  If the caller passes a custom callback,
	-- we assume they are advanced enough not to need the check.
	-- The point is to avoid repeating the check in each callback iteration.
	if callback == nil then
		local apex_array = ffi.new('knot_dname_t *[1]')  -- C: dname **apex_array
		local ret = ffi.C.kr_cache_closest_apex(cach, dname, false, apex_array)
		if ret < 0 then
			error(kres.strerror(ret)) end
		if not ffi.C.knot_dname_is_equal(apex_array[0], dname) then
			local apex_str = kres.dname2str(apex_array[0])
			rettable.not_apex = 'to clear proofs of non-existence call '
				.. 'cache.clear(\'' .. tostring(apex_str) ..'\')'
			rettable.subtree = apex_str
		end
		ffi.C.free(apex_array[0])
	end

	if rr_type ~= nil then
		-- Special case, without any subtree searching.
		if not exact_name
			then error('cache.clear(): specifying rr_type only supported with exact_name') end
		if chunk_size or callback
			then error('cache.clear(): chunk_size and callback parameters not supported with rr_type') end
		local ret = ffi.C.kr_cache_remove(cach, dname, rr_type)
		if ret < 0 then error(kres.strerror(ret)) end
		return {count = 1}
	end

	if chunk_size == nil then chunk_size = 100 end
	if type(chunk_size) ~= 'number' or chunk_size <= 0
		then error('cache.clear(): chunk_size has to be a positive integer') end

	-- Do the C call, and add chunk_size warning.
	rettable.count = ffi.C.kr_cache_remove_subtree(cach, dname, exact_name, chunk_size)
	if rettable.count == chunk_size then
		local msg_extra = ''
		if callback == nil then
			msg_extra = '; the default callback will continue asynchronously'
		end
		rettable.chunk_limit = 'chunk size limit reached' .. msg_extra
	end

	-- Default callback function: repeat after 1ms
	if callback == nil then callback =
		function (cbname, cbexact_name, cbrr_type, cbchunk_size, cbself, cbprev_state, cbrettable)
			if cbrettable.count < 0 then error(kres.strerror(cbrettable.count)) end
			if cbprev_state == nil then cbprev_state = { round = 0 } end
			if type(cbprev_state) ~= 'table'
				then error('cache.clear() callback: incorrect prev_state passed') end
			cbrettable.round = cbprev_state.round + 1
			if (cbrettable.count == cbchunk_size) then
				event.after(1, function ()
						cache.clear(cbname, cbexact_name, cbrr_type, cbchunk_size, cbself, cbrettable)
					end)
			elseif cbrettable.round > 1 then
				log_info(ffi.C.LOG_GRP_CACHE, 'asynchronous cache.clear(\'' .. cbname .. '\', '
				    .. tostring(cbexact_name) .. ') finished')
			end
			return cbrettable
		end
	end
	return callback(name, exact_name, rr_type, chunk_size, callback, prev_state, rettable)
end
-- Syntactic sugar for cache
-- `cache[x] -> cache.get(x)`
-- `cache.{size|storage} = value`
setmetatable(cache, {
	__index = function (t, k)
		local res = rawget(t, k)
		if not res and not rawget(t, 'current_size') then return res end
		-- Beware: t.get returns empty table on failure to find.
		-- That would be confusing here (breaking kresc), so return nil instead.
		res = t.get(k)
		if res and next(res) ~= nil then return res else return nil end
	end,
	__newindex = function (t,k,v)
		-- Defaults
		local storage = rawget(t, 'current_storage')
		if not storage then storage = 'lmdb://' end
		local size = rawget(t, 'current_size')
		if not size then size = 10*MB end
		-- Declarative interface for cache
		if     k == 'size'    then t.open(v, storage)
		elseif k == 'storage' then t.open(size, v) end
	end
})

-- Make sandboxed environment
local function make_sandbox(defined)
	local __protected = {
		worker = true, env = true, debugging = true, modules = true,
		cache = true, net = true, trust_anchors = true
	}

	-- Compute and export the list of top-level names (hidden otherwise)
	local nl = ""
	for n in pairs(defined) do
		nl = nl .. n .. "\n"
	end

	return setmetatable({ __orig_name_list = nl }, {
		__index = defined,
		__newindex = function (_, k, v)
			if __protected[k] then
				for k2,v2 in pairs(v) do
					defined[k][k2] = v2
				end
			else
				defined[k] = v
			end
		end
	})
end

-- Compatibility sandbox
_G = make_sandbox(getfenv(0))
setfenv(0, _G)

-- Load default modules
trust_anchors = require('trust_anchors')
modules.load('ta_update')
modules.load('ta_signal_query')
modules.load('policy')
modules.load('priming')
modules.load('detect_time_skew')
modules.load('detect_time_jump')
modules.load('ta_sentinel')
modules.load('edns_keepalive')
modules.load('refuse_nord')
modules.load('watchdog')
modules.load('extended_error')

-- Load keyfile_default
trust_anchors.add_file('/opt/local/var/lib/knot-resolver/root.ds', false)

local function eval_cmd_compile(line, mode)
	-- Compatibility sandbox code loading
	local function load_code(code)
	    if getfenv then -- Lua 5.1
	        return loadstring(code)
	    else            -- Lua 5.2+
	        return load(code, nil, 't', _ENV)
	    end
	end

	-- See `ENGINE_EVAL_MODE_MAP(XX)` C-macro for possible values
	local err, chunk
	if mode == "LUA_TABLE" then
		chunk, err = load_code('return table_print(('..line..'))')
	elseif mode == "RAW" then
		chunk, err = load_code('return ('..line..')')
	elseif mode == "JSON" then
		chunk, err = load_code('return tojson(('..line..'))')
	else
		return nil, "invalid mode"
	end

	if err then
		chunk, err = load_code(line)
	end
	return chunk, err
end

-- Interactive command evaluation
function eval_cmd(line, mode)
	local chunk, err = eval_cmd_compile(line, mode)
	if not err then
		return chunk()
	else
		error(err)
	end
end

-- Pretty printing
local pprint = require('krprint').pprint
function table_print(...)
	local strs = {}
	local nargs = select('#', ...)
	if nargs == 0 then
		return nil
	end
	for n=1,nargs do
		local arg = select(n, ...)
		local arg_str = pprint(arg)
		if nargs > 1 then
			table.insert(strs, string.format("%s\t-- result # %d", arg_str, n))
		else
			table.insert(strs, arg_str)
		end
	end
	return table.concat(strs, '\n')
end

-- This extends the worker module to allow asynchronous execution of functions and nonblocking I/O.
-- The current implementation combines cqueues for Lua interface, and event.socket() in order to not
-- block resolver engine while waiting for I/O or timers.
--
local has_cqueues, cqueues = pcall(require, 'cqueues')
if has_cqueues then

	-- Export the asynchronous sleep function
	worker.sleep = cqueues.sleep

	-- Create metatable for workers to define the API
	-- It can schedule multiple cqueues and yield execution when there's a wait for blocking I/O or timer
	local asynchronous_worker_mt = {
		work = function (self)
			local ok, err, _, co = self.cq:step(0)
			if not ok then
				log_warn(ffi.C.LOG_GRP_SYSTEM, '%s error: %s %s', self.name or 'worker', err, debug.traceback(co))
			end
			-- Reschedule timeout or create new one
			local timeout = self.cq:timeout()
			if timeout then
				-- Throttle timeouts to avoid too frequent wakeups
				if timeout == 0 then timeout = 0.00001 end
				-- Convert from seconds to duration
				timeout = timeout * sec
				if not self.next_timeout then
					self.next_timeout = event.after(timeout, self.on_step)
				else
					event.reschedule(self.next_timeout, timeout)
				end
			else -- Cancel running timeout when there is no next deadline
				if self.next_timeout then
					event.cancel(self.next_timeout)
					self.next_timeout = nil
				end
			end
		end,
		wrap = function (self, f)
			self.cq:wrap(f)
		end,
		loop = function (self)
			self.on_step = function () self:work() end
			self.event_fd = event.socket(self.cq:pollfd(), self.on_step)
		end,
		close = function (self)
			if self.event_fd then
				event.cancel(self.event_fd)
				self.event_fd = nil
			end
		end,
	}

	-- Implement the coroutine worker with cqueues
	local function worker_new (name)
		return setmetatable({name = name, cq = cqueues.new()}, { __index = asynchronous_worker_mt })
	end

	-- Create a default background worker
	worker.bg_worker = worker_new('worker.background')
	worker.bg_worker:loop()

	-- Wrap a function for asynchronous execution
	function worker.coroutine (f)
		worker.bg_worker:wrap(f)
	end
else
	-- Disable asynchronous execution
	local function disabled ()
		error('Lua library cqueues is required for asynchronous execution (luaJIT requires library for Lua 5.1)')
	end
	worker.sleep = disabled
	worker.map = disabled
	worker.coroutine = disabled
	worker.bg_worker = setmetatable({}, { __index = disabled })
end

-- Global commands for map()

-- must be public because it is called from eval_cmd()
-- when map() commands are read from control socket
function _map_luaobj_call_wrapper(cmd)
	local func = eval_cmd_compile(cmd, "RAW")
	local ret = kluautil.kr_table_pack(xpcall(func, debug.traceback))
	local ok, serial = pcall(krprint.serialize_lua, ret, 'error')
	if not ok then
		log_error(ffi.C.LOG_GRP_SYSTEM, 'failed to serialize map() response %s (%s)',
			table_print(ret), serial)
		return krprint.serialize_lua(
			kluautil.kr_table_pack(false, "returned values cannot be serialized: "
				.. serial))
	else
		return serial
	end
end

local function _sock_errmsg(path, desc)
	return string.format(
		'map() error while communicating with %s: %s',
		path, desc)
end

local function _sock_check(sock, call, params, path, desc)
	local errprefix = _sock_errmsg(path, desc) .. ': '
	local retvals = kluautil.kr_table_pack(pcall(call, unpack(params)))
	local ok = retvals[1]
	if not ok then
		error(errprefix .. tostring(retvals[2]))
	end
	local rerr, werr = sock:error()
	if rerr or werr then
		error(string.format('%sread error %s; write error %s', errprefix, rerr, werr))
	end
	if retvals[2] == nil then
		error(errprefix .. 'unexpected nil result')
	end
	return unpack(retvals, 2, retvals.n)
end

local function _sock_assert(condition, path, desc)
	if not condition then
		error(_sock_errmsg(path, desc))
	end
end

local function map_send_recv(cmd, path)
	local bit = require('bit')
	local socket = require('cqueues.socket')
	local s = socket.connect({ path = path })
	s:setmaxerrs(0)
	s:setmode('bn', 'bn')
	local status, err = pcall(s.connect, s)
	if not status then
		log_error(ffi.C.LOG_GRP_NETWORK, 'map() error while connecting to control socket %s: '
			.. '%s (ignoring this socket)', path, err)
		return nil
	end
	local ret = _sock_check(s, s.write, {s, '__binary\n'}, path,
		'write __binary')
	_sock_assert(ret, path,
		'write __binary result')
	local recv = _sock_check(s, s.read, {s, 2}, path,
		'read reply to __binary')
	_sock_assert(recv and recv == '> ', path,
		'unexpected reply to __binary')
	_sock_check(s, s.write, {s, cmd..'\n'}, path,
		'command write')
	recv = _sock_check(s, s.read, {s, 4}, path,
		'response length read')
	_sock_assert(recv and #recv == 4, path,
		'length of response length preamble does not match')
	local len = tonumber(recv:byte(1))
	for i=2,4 do
		len = bit.bor(bit.lshift(len, 8), tonumber(recv:byte(i)))
	end
	ret = _sock_check(s, s.read, {s, len}, path,
		'read response')
	_sock_assert(ret and #ret == len, path,
		'actual response length does not match length in preamble')
	s:close()
	return ret
end

-- internal use only
-- Call cmd on each instance via control sockets.
-- @param format - "luaobj" if individual results should be Lua objects
--               - "strings" for eval_cmd output for each instance
-- @returns table with results, one item per instance + key n=number of instances
--          (order of return values is undefined)
-- @throws Lua error if:
--         - communication failed in the middle of transaction
--         - a result is not serializable
--         - individual call throws an error
--         - number of return values != 1 per instance per call
--         - cmd execution state is undefined after an error
-- Connection errors at the beginning are ignored to paper over leftover dead sockets.
function map(cmd, format)
	local local_sockets = {}
	local results = {}

	if (type(cmd) ~= 'string') then
		panic('map() command must be a string') end
	if string.find(cmd, '\n', 1, true) then
		panic('map() command cannot contain literal \\n, escape it with \\010') end
	if (#cmd <= 0) then
		panic('map() command must be non-empty') end
	-- syntax check on input command to detect typos early
	local chunk, err = eval_cmd_compile(cmd, "LUA_TABLE")
	if not chunk then
		panic('failure when compiling map() command: %s', err)
	end

	format = format or 'luaobj'
	if (format ~= 'luaobj' and format ~= 'strings') then
		panic('map() output format must be luaobj or strings') end
	if format == 'luaobj' then
		cmd = '_map_luaobj_call_wrapper([=====[' .. cmd .. ']=====])'
	end

	-- find out control socket paths
	for _,v in pairs(net.list()) do
		if (v['kind'] == 'control') and (v['transport']['family'] == 'unix') then
			table.insert(local_sockets, string.match(v['transport']['path'], '^.*/([^/]+)$'))
		end
	end
	local filetab = kluautil.list_dir(worker.control_path)
	if next(filetab) == nil then
		panic('no control sockets found in directory %s',
			worker.control_path)
	end

	local result_count = 0
	-- finally execute it on all instances
	for _, file in ipairs(filetab) do
		local local_exec = false
		for _, lsoc in ipairs(local_sockets) do
			if file == lsoc then
				local_exec = true
			end
		end
		local path = worker.control_path..file
		local path_name = (local_exec and 'this instance') or path
		log_info(ffi.C.LOG_GRP_SYSTEM, 'executing map() on %s: command %s', path_name, cmd)
		local ret
		if local_exec then
			ret = eval_cmd(cmd, "LUA_TABLE")
		else
			ret = map_send_recv(cmd, path)
			-- skip dead sockets (leftovers from dead instances)
			if ret == nil then
				goto continue
			end
		end
		result_count = result_count + 1
		-- return value is output from eval_cmd
		-- i.e. string including "quotes" and Lua escaping in between
		assert(type(ret) == 'string', 'map() protocol error, '
			.. 'string not retured by follower')
		assert(#ret >= 2 and
			string.sub(ret, 1, 1) == "'"
			and string.sub(ret, -1, -1) == "'",
			'map() protocol error, value returned by follower does '
			.. 'not look like a string')
		-- deserialize string: remove "quotes" and de-escape bytes
		ret = krprint.deserialize_lua(ret)
		if format == 'luaobj' then
			-- ret should be table with xpcall results serialized into string
			ret = krprint.deserialize_lua(ret)
			assert(type(ret) == 'table', 'map() protocol error, '
				.. 'table with results not retured by follower')
			if (ret.n ~= 2) then
				log_error(ffi.C.LOG_GRP_SYSTEM, 'got unsupported map() response: %s', table_print(ret))
				panic('unexpected number of return values in map() response: '
					.. 'only single return value is allowed, '
					.. 'use kluautil.kr_table_pack() helper')
			end
			local ok, retval = ret[1], ret[2]
			if ok == false then
				panic('error when executing map() command on control socket %s: '
					.. '%s. command execution state is now undefined!',
					path, retval)
			end
			-- drop wrapper table and return only the actual return value
			ret = retval
		end
		results[result_count] = ret
		::continue::
	end
	results.n = result_count
	return results
end
