--
-- Licensed to the Apache Software Foundation (ASF) under one or more
-- contributor license agreements.  See the NOTICE file distributed with
-- this work for additional information regarding copyright ownership.
-- The ASF licenses this file to You under the Apache License, Version 2.0
-- (the "License"); you may not use this file except in compliance with
-- the License.  You may obtain a copy of the License at
--
--     http://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS,
-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-- See the License for the specific language governing permissions and
-- limitations under the License.
--
local is_http = ngx.config.subsystem == "http"
local flatbuffers = require("flatbuffers")
local a6_method = require("A6.Method")
local prepare_conf_req = require("A6.PrepareConf.Req")
local prepare_conf_resp = require("A6.PrepareConf.Resp")
local http_req_call_req = require("A6.HTTPReqCall.Req")
local http_req_call_resp = require("A6.HTTPReqCall.Resp")
local http_req_call_action = require("A6.HTTPReqCall.Action")
local http_req_call_stop = require("A6.HTTPReqCall.Stop")
local http_req_call_rewrite = require("A6.HTTPReqCall.Rewrite")
local http_resp_call_req = require("A6.HTTPRespCall.Req")
local http_resp_call_resp = require("A6.HTTPRespCall.Resp")
local extra_info = require("A6.ExtraInfo.Info")
local extra_info_req = require("A6.ExtraInfo.Req")
local extra_info_var = require("A6.ExtraInfo.Var")
local extra_info_resp = require("A6.ExtraInfo.Resp")
local extra_info_reqbody = require("A6.ExtraInfo.ReqBody")
local extra_info_respbody = require("A6.ExtraInfo.RespBody")
local text_entry = require("A6.TextEntry")
local err_resp = require("A6.Err.Resp")
local err_code = require("A6.Err.Code")
local constants = require("apisix.constants")
local core = require("apisix.core")
local helper = require("apisix.plugins.ext-plugin.helper")
local process, ngx_pipe, events
if is_http then
    process = require("ngx.process")
    ngx_pipe = require("ngx.pipe")
    events = require("apisix.events")
end
local resty_lock = require("resty.lock")
local resty_signal = require "resty.signal"
local bit = require("bit")
local band = bit.band
local lshift = bit.lshift
local rshift = bit.rshift
local ffi = require("ffi")
local ffi_str = ffi.string
local socket_tcp = ngx.socket.tcp
local worker_id = ngx.worker.id
local ngx_timer_at = ngx.timer.at
local exiting = ngx.worker.exiting
local str_byte = string.byte
local str_format = string.format
local str_lower = string.lower
local str_sub = string.sub
local error = error
local ipairs = ipairs
local pairs = pairs
local tostring = tostring
local type = type
local ngx = ngx


local events_list
local exclude_resp_header = {
    ["connection"] = true,
    ["content-length"] = true,
    ["transfer-encoding"] = true,
    ["location"] = true,
    ["server"] = true,
    ["www-authenticate"] = true,
    ["content-encoding"] = true,
    ["content-type"] = true,
    ["content-location"] = true,
    ["content-language"] = true,
}

local function new_lrucache()
    return core.lrucache.new({
        type = "plugin",
        invalid_stale = true,
        ttl = helper.get_conf_token_cache_time(),
    })
end
local lrucache = new_lrucache()

local shdict_name = "ext-plugin"
local shdict = ngx.shared[shdict_name]

local schema = {
    type = "object",
    properties = {
        conf = {
            type = "array",
            items = {
                type = "object",
                properties = {
                    name = {
                        type = "string",
                        maxLength = 128,
                        minLength = 1
                    },
                    value = {
                        type = "string",
                    },
                },
                required = {"name", "value"}
            },
            minItems = 1,
        },
        allow_degradation = {type = "boolean", default = false}
    },
}

local _M = {
    schema = schema,
}
local builder = flatbuffers.Builder(0)


local send
do
    local hdr_buf = ffi.new("unsigned char[4]")
    local buf = core.table.new(2, 0)
    local MAX_DATA_SIZE = lshift(1, 24) - 1

    function send(sock, ty, data)
        hdr_buf[0] = ty

        local len = #data

        core.log.info("sending rpc type: ", ty, " data length: ", len)

        if len > MAX_DATA_SIZE then
            return nil, str_format("the max length of data is %d but got %d", MAX_DATA_SIZE, len)
        end

        -- length is sent as big endian
        for i = 3, 1, -1 do
            hdr_buf[i] = band(len, 255)
            len = rshift(len, 8)
        end

        buf[1] = ffi_str(hdr_buf, 4)
        buf[2] = data
        return sock:send(buf)
    end
end
_M.send = send


local err_to_msg
do
    local map = {
        [err_code.BAD_REQUEST] = "bad request",
        [err_code.SERVICE_UNAVAILABLE] = "service unavailable",
        [err_code.CONF_TOKEN_NOT_FOUND] = "conf token not found",
    }

    function err_to_msg(resp)
        local buf = flatbuffers.binaryArray.New(resp)
        local resp = err_resp.GetRootAsResp(buf, 0)
        local code = resp:Code()
        return map[code] or str_format("unknown err %d", code)
    end
end


local function receive(sock)
    local hdr, err = sock:receive(4)
    if not hdr then
        return nil, err
    end
    if #hdr ~= 4 then
        return nil, "header too short"
    end

    local ty = str_byte(hdr, 1)
    local resp
    local hi, mi, li = str_byte(hdr, 2, 4)
    local len = 256 * (256 * hi + mi) + li

    core.log.info("receiving rpc type: ", ty, " data length: ", len)

    if len > 0 then
        resp, err = sock:receive(len)
        if not resp then
            return nil, err
        end
        if #resp ~= len then
            return nil, "data truncated"
        end
    end

    if ty == constants.RPC_ERROR then
        return nil, err_to_msg(resp)
    end

    return ty, resp
end
_M.receive = receive


local generate_id
do
    local count = 0
    local MAX_COUNT = lshift(1, 22)

    function generate_id()
        local wid = worker_id()
        local id = lshift(wid, 22) + count
        count = count + 1
        if count == MAX_COUNT then
            count = 0
        end
        return id
    end
end


local encode_a6_method
do
    local map = {
        GET = a6_method.GET,
        HEAD = a6_method.HEAD,
        POST = a6_method.POST,
        PUT = a6_method.PUT,
        DELETE = a6_method.DELETE,
        MKCOL = a6_method.MKCOL,
        COPY = a6_method.COPY,
        MOVE = a6_method.MOVE,
        OPTIONS = a6_method.OPTIONS,
        PROPFIND = a6_method.PROPFIND,
        PROPPATCH = a6_method.PROPPATCH,
        LOCK = a6_method.LOCK,
        UNLOCK = a6_method.UNLOCK,
        PATCH = a6_method.PATCH,
        TRACE = a6_method.TRACE,
    }

    function encode_a6_method(name)
        return map[name]
    end
end


local function build_args(builder, key, val)
    local name = builder:CreateString(key)
    local value
    if val ~= true then
        value = builder:CreateString(val)
    end

    text_entry.Start(builder)
    text_entry.AddName(builder, name)
    if val ~= true then
        text_entry.AddValue(builder, value)
    end
    return text_entry.End(builder)
end


local function build_headers(var, builder, key, val)
    if key == "host" then
        val = var.upstream_host
    end

    local name = builder:CreateString(key)
    local value = builder:CreateString(val)

    text_entry.Start(builder)
    text_entry.AddName(builder, name)
    text_entry.AddValue(builder, value)
    return text_entry.End(builder)
end


local function handle_extra_info(ctx, input)
    -- exact request
    local buf = flatbuffers.binaryArray.New(input)
    local req = extra_info_req.GetRootAsReq(buf, 0)

    local res
    local info_type = req:InfoType()
    if info_type == extra_info.Var then
        local info = req:Info()
        local var_req = extra_info_var.New()
        var_req:Init(info.bytes, info.pos)

        local var_name = var_req:Name()
        res = ctx.var[var_name]
    elseif info_type == extra_info.ReqBody then
        local info = req:Info()
        local reqbody_req = extra_info_reqbody.New()
        reqbody_req:Init(info.bytes, info.pos)

        local err
        res, err = core.request.get_body()
        if err then
            core.log.error("failed to read request body: ", err)
        end
    elseif info_type == extra_info.RespBody then
        local ext_res = ctx.runner_ext_response
        if ext_res then
            local info = req:Info()
            local respbody_req = extra_info_respbody.New()
            respbody_req:Init(info.byte, info.pos)

            local chunks = {}
            local err = helper.response_reader(ext_res.body_reader, function (chunk, chunks)
                -- When the upstream response is chunked type,
                -- we will receive the complete response body
                -- before sending it to the runner program
                -- to reduce the number of RPC calls.
                core.table.insert_tail(chunks, chunk)
            end, chunks)
            if err then
                -- TODO: send RPC_ERROR to runner
                core.log.error(err)
            else
                res = core.table.concat(chunks)
                ctx.runner_ext_response_body = chunks
            end
        else
            core.log.error("failed to read response body: not exits")
        end
    else
        return nil, "unsupported info type: " .. info_type
    end

    -- build response
    builder:Clear()

    local packed_res
    if res then
        -- ensure to pass the res in string type
        res = tostring(res)
        packed_res = builder:CreateByteVector(res)
    end
    extra_info_resp.Start(builder)
    if packed_res then
        extra_info_resp.AddResult(builder, packed_res)
    end
    local resp = extra_info_resp.End(builder)
    builder:Finish(resp)
    return builder:Output()
end


local function fetch_token(key)
    if shdict then
        return shdict:get(key)
    else
        core.log.error('shm "ext-plugin" not found')
        return nil
    end
end


local function store_token(key, token)
    if shdict then
        local exp = helper.get_conf_token_cache_time()
        -- early expiry, lrucache in critical state sends prepare_conf_req as original behaviour
        exp = exp * 0.9
        local success, err, forcible = shdict:set(key, token, exp)
        if not success then
            core.log.error("ext-plugin:failed to set conf token, err: ", err)
        end
        if forcible then
            core.log.warn("ext-plugin:set valid items forcibly overwritten")
        end
    else
        core.log.error('shm "ext-plugin" not found')
    end
end


local function flush_token()
    if shdict then
        core.log.warn("flush conf token in shared dict")
        shdict:flush_all()
    else
        core.log.error('shm "ext-plugin" not found')
    end
end


local rpc_call
local rpc_handlers = {
    nil,
    function (conf, ctx, sock, unique_key)
        local token = fetch_token(unique_key)
        if token then
            core.log.info("fetch token from shared dict, token: ", token)
            return token
        end

        local lock, err = resty_lock:new(shdict_name)
        if not lock then
            return nil, "failed to create lock: " .. err
        end

        local elapsed, err = lock:lock("prepare_conf")
        if not elapsed then
            return nil, "failed to acquire the lock: " .. err
        end

        local token = fetch_token(unique_key)
        if token then
            lock:unlock()
            core.log.info("fetch token from shared dict, token: ", token)
            return token
        end

        builder:Clear()

        local key = builder:CreateString(unique_key)
        local conf_vec
        if conf.conf then
            local len = #conf.conf
            local textEntries = core.table.new(len, 0)
            for i = 1, len do
                local name = builder:CreateString(conf.conf[i].name)
                local value = builder:CreateString(conf.conf[i].value)
                text_entry.Start(builder)
                text_entry.AddName(builder, name)
                text_entry.AddValue(builder, value)
                local c = text_entry.End(builder)
                textEntries[i] = c
            end
            prepare_conf_req.StartConfVector(builder, len)
            for i = len, 1, -1 do
                builder:PrependUOffsetTRelative(textEntries[i])
            end
            conf_vec = builder:EndVector(len)
        end

        prepare_conf_req.Start(builder)
        prepare_conf_req.AddKey(builder, key)
        if conf_vec then
            prepare_conf_req.AddConf(builder, conf_vec)
        end
        local req = prepare_conf_req.End(builder)
        builder:Finish(req)

        local ok, err = send(sock, constants.RPC_PREPARE_CONF, builder:Output())
        if not ok then
            lock:unlock()
            return nil, "failed to send RPC_PREPARE_CONF: " .. err
        end

        local ty, resp = receive(sock)
        if ty == nil then
            lock:unlock()
            return nil, "failed to receive RPC_PREPARE_CONF: " .. resp
        end

        if ty ~= constants.RPC_PREPARE_CONF then
            lock:unlock()
            return nil, "failed to receive RPC_PREPARE_CONF: unexpected type " .. ty
        end

        local buf = flatbuffers.binaryArray.New(resp)
        local pcr = prepare_conf_resp.GetRootAsResp(buf, 0)
        token = pcr:ConfToken()

        core.log.notice("get conf token: ", token, " conf: ", core.json.delay_encode(conf.conf))
        store_token(unique_key, token)

        lock:unlock()

        return token
    end,
    function (conf, ctx, sock, entry)
        local lrucache_id = core.lrucache.plugin_ctx_id(ctx, entry)
        local token, err = core.lrucache.plugin_ctx(lrucache, ctx, entry, rpc_call,
                                                    constants.RPC_PREPARE_CONF, conf, ctx,
                                                    lrucache_id)
        if not token then
            return nil, err
        end

        builder:Clear()
        local var = ctx.var

        local uri
        if var.upstream_uri == "" then
            -- use original uri instead of rewritten one
            uri = var.uri
        else
            uri = var.upstream_uri

            -- the rewritten one may contain new args
            local index = core.string.find(uri, "?")
            if index then
                local raw_uri = uri
                uri = str_sub(raw_uri, 1, index - 1)
                core.request.set_uri_args(ctx, str_sub(raw_uri, index + 1))
            end
        end

        local path = builder:CreateString(uri)

        local bin_addr = var.binary_remote_addr
        local src_ip = builder:CreateByteVector(bin_addr)

        local args = core.request.get_uri_args(ctx)
        local textEntries = {}
        for key, val in pairs(args) do
            local ty = type(val)
            if ty == "table" then
                for _, v in ipairs(val) do
                    core.table.insert(textEntries, build_args(builder, key, v))
                end
            else
                core.table.insert(textEntries, build_args(builder, key, val))
            end
        end
        local len = #textEntries
        http_req_call_req.StartArgsVector(builder, len)
        for i = len, 1, -1 do
            builder:PrependUOffsetTRelative(textEntries[i])
        end
        local args_vec = builder:EndVector(len)

        local hdrs = core.request.headers(ctx)
        core.table.clear(textEntries)
        for key, val in pairs(hdrs) do
            local ty = type(val)
            if ty == "table" then
                for _, v in ipairs(val) do
                    core.table.insert(textEntries, build_headers(var, builder, key, v))
                end
            else
                core.table.insert(textEntries, build_headers(var, builder, key, val))
            end
        end
        local len = #textEntries
        http_req_call_req.StartHeadersVector(builder, len)
        for i = len, 1, -1 do
            builder:PrependUOffsetTRelative(textEntries[i])
        end
        local hdrs_vec = builder:EndVector(len)

        local id = generate_id()
        local method = var.method

        http_req_call_req.Start(builder)
        http_req_call_req.AddId(builder, id)
        http_req_call_req.AddConfToken(builder, token)
        http_req_call_req.AddSrcIp(builder, src_ip)
        http_req_call_req.AddPath(builder, path)
        http_req_call_req.AddArgs(builder, args_vec)
        http_req_call_req.AddHeaders(builder, hdrs_vec)
        http_req_call_req.AddMethod(builder, encode_a6_method(method))

        local req = http_req_call_req.End(builder)
        builder:Finish(req)

        local ok, err = send(sock, constants.RPC_HTTP_REQ_CALL, builder:Output())
        if not ok then
            return nil, "failed to send RPC_HTTP_REQ_CALL: " .. err
        end

        local ty, resp
        while true do
            ty, resp = receive(sock)
            if ty == nil then
                return nil, "failed to receive RPC_HTTP_REQ_CALL: " .. resp
            end

            if ty ~= constants.RPC_EXTRA_INFO then
                break
            end

            local out, err = handle_extra_info(ctx, resp)
            if not out then
                return nil, "failed to handle RPC_EXTRA_INFO: " .. err
            end

            local ok, err = send(sock, constants.RPC_EXTRA_INFO, out)
            if not ok then
                return nil, "failed to reply RPC_EXTRA_INFO: " .. err
            end
        end

        if ty ~= constants.RPC_HTTP_REQ_CALL then
            return nil, "failed to receive RPC_HTTP_REQ_CALL: unexpected type " .. ty
        end

        local buf = flatbuffers.binaryArray.New(resp)
        local call_resp = http_req_call_resp.GetRootAsResp(buf, 0)
        local action_type = call_resp:ActionType()
        if action_type == http_req_call_action.Stop then
            local action = call_resp:Action()
            local stop = http_req_call_stop.New()
            stop:Init(action.bytes, action.pos)

            local len = stop:HeadersLength()
            if len > 0 then
                local stop_resp_headers = {}
                for i = 1, len do
                    local entry = stop:Headers(i)
                    local name = str_lower(entry:Name())
                    if stop_resp_headers[name] == nil then
                        core.response.set_header(name, entry:Value())
                        stop_resp_headers[name] = true
                    else
                        core.response.add_header(name, entry:Value())
                    end
                end
            end

            local body
            local len = stop:BodyLength()
            if len > 0 then
                -- TODO: support empty body
                body = stop:BodyAsString()
            end
            local code = stop:Status()
            -- avoid using 0 as the default http status code
            if code == 0 then
                 code = 200
            end
            return true, nil, code, body
        end

        if action_type == http_req_call_action.Rewrite then
            local action = call_resp:Action()
            local rewrite = http_req_call_rewrite.New()
            rewrite:Init(action.bytes, action.pos)

            local path = rewrite:Path()
            if path then
                path = core.utils.uri_safe_encode(path)
                var.upstream_uri = path
            end

            local len = rewrite:HeadersLength()
            if len > 0 then
                for i = 1, len do
                    local entry = rewrite:Headers(i)
                    local name = entry:Name()
                    core.request.set_header(ctx, name, entry:Value())

                    if str_lower(name) == "host" then
                        var.upstream_host = entry:Value()
                    end
                end
            end

            local body_len = rewrite:BodyLength()
            if body_len > 0 then
                local body = rewrite:BodyAsString()
                ngx.req.read_body()
                ngx.req.set_body_data(body)
            end

            local len = rewrite:RespHeadersLength()
            if len > 0 then
                local rewrite_resp_headers = {}
                for i = 1, len do
                    local entry = rewrite:RespHeaders(i)
                    local name = str_lower(entry:Name())
                    if exclude_resp_header[name] == nil then
                        if rewrite_resp_headers[name] == nil then
                            core.response.set_header(name, entry:Value())
                            rewrite_resp_headers[name] = true
                        else
                            core.response.add_header(name, entry:Value())
                        end
                    end
                end
            end

            local len = rewrite:ArgsLength()
            if len > 0 then
                local changed = {}
                for i = 1, len do
                    local entry = rewrite:Args(i)
                    local name = entry:Name()
                    local value = entry:Value()
                    if value == nil then
                        args[name] = nil

                    else
                        if changed[name] then
                            if type(args[name]) == "table" then
                                core.table.insert(args[name], value)
                            else
                                args[name] = {args[name], entry:Value()}
                            end
                        else
                            args[name] = entry:Value()
                        end

                        changed[name] = true
                    end
                end

                core.request.set_uri_args(ctx, args)

                if path then
                    var.upstream_uri = path .. '?' .. var.args
                end
            end
        end

        return true
    end,
    nil, -- ignore RPC_EXTRA_INFO, already processed during RPC_HTTP_REQ_CALL interaction
    function (conf, ctx, sock, entry)
        local lrucache_id = core.lrucache.plugin_ctx_id(ctx, entry)
        local token, err = core.lrucache.plugin_ctx(lrucache, ctx, entry, rpc_call,
                                                    constants.RPC_PREPARE_CONF, conf, ctx,
                                                    lrucache_id)
        if not token then
            return nil, err
        end

        builder:Clear()
        local var = ctx.var

        local res = ctx.runner_ext_response
        local textEntries = {}
        local hdrs = res.headers
        for key, val in pairs(hdrs) do
            local ty = type(val)
            if ty == "table" then
                for _, v in ipairs(val) do
                    core.table.insert(textEntries, build_headers(var, builder, key, v))
                end
            else
                core.table.insert(textEntries, build_headers(var, builder, key, val))
            end
        end
        local len = #textEntries
        http_resp_call_req.StartHeadersVector(builder, len)
        for i = len, 1, -1 do
            builder:PrependUOffsetTRelative(textEntries[i])
        end
        local hdrs_vec = builder:EndVector(len)

        local id = generate_id()
        local status = res.status

        http_resp_call_req.Start(builder)
        http_resp_call_req.AddId(builder, id)
        http_resp_call_req.AddStatus(builder, status)
        http_resp_call_req.AddConfToken(builder, token)
        http_resp_call_req.AddHeaders(builder, hdrs_vec)

        local req = http_resp_call_req.End(builder)
        builder:Finish(req)

        local ok, err = send(sock, constants.RPC_HTTP_RESP_CALL, builder:Output())
        if not ok then
            return nil, "failed to send RPC_HTTP_RESP_CALL: " .. err
        end

        local ty, resp
        while true do
            ty, resp = receive(sock)
            if ty == nil then
                return nil, "failed to receive RPC_HTTP_REQ_CALL: " .. resp
            end

            if ty ~= constants.RPC_EXTRA_INFO then
                break
            end

            local out, err = handle_extra_info(ctx, resp)
            if not out then
                return nil, "failed to handle RPC_EXTRA_INFO: " .. err
            end

            local ok, err = send(sock, constants.RPC_EXTRA_INFO, out)
            if not ok then
                return nil, "failed to reply RPC_EXTRA_INFO: " .. err
            end
        end

        if ty ~= constants.RPC_HTTP_RESP_CALL then
            return nil, "failed to receive RPC_HTTP_RESP_CALL: unexpected type " .. ty
        end

        local buf = flatbuffers.binaryArray.New(resp)
        local call_resp = http_resp_call_resp.GetRootAsResp(buf, 0)
        local len = call_resp:HeadersLength()
        if len > 0 then
            local resp_headers = {}
            for i = 1, len do
                local entry = call_resp:Headers(i)
                local name = str_lower(entry:Name())
                if resp_headers[name] == nil then
                    core.response.set_header(name, entry:Value())
                    resp_headers[name] = true
                else
                    core.response.add_header(name, entry:Value())
                end
            end
        else
            -- Filter out origin headeres
            for k, v in pairs(res.headers) do
                if not exclude_resp_header[str_lower(k)] then
                    core.response.set_header(k, v)
                end
            end
        end

        local body
        local len = call_resp:BodyLength()
        if len > 0 then
            -- TODO: support empty body
            body = call_resp:BodyAsString()
        end
        local code = call_resp:Status()
        core.log.info("recv resp, code: ", code, " body: ", body, " len: ", len)

        if code == 0 then
            -- runner changes body only, we should set code.
            code = body and res.status or nil
        end

        return true, nil, code, body
    end
}


rpc_call = function (ty, conf, ctx, ...)
    local path = helper.get_path()

    local sock = socket_tcp()
    sock:settimeouts(1000, 60000, 60000)
    local ok, err = sock:connect(path)
    if not ok then
        return nil, "failed to connect to the unix socket " .. path .. ": " .. err
    end

    local res, err, code, body = rpc_handlers[ty + 1](conf, ctx, sock, ...)
    if not res then
        sock:close()
        return nil, err
    end

    local ok, err = sock:setkeepalive(180 * 1000, 32)
    if not ok then
        core.log.info("failed to setkeepalive: ", err)
    end

    return res, nil, code, body
end


local function recreate_lrucache()
    flush_token()

    if lrucache then
        core.log.warn("flush conf token lrucache")
    end

    lrucache = new_lrucache()
end


function _M.communicate(conf, ctx, plugin_name, rpc_cmd)
    local ok, err, code, body
    local tries = 0
    local ty = rpc_cmd and rpc_cmd or constants.RPC_HTTP_REQ_CALL
    while tries < 3 do
        tries = tries + 1
        ok, err, code, body = rpc_call(ty, conf, ctx, plugin_name)
        if ok then
            if code then
                return code, body
            end

            return
        end

        if not core.string.find(err, "conf token not found") then
            core.log.error(err)
            if conf.allow_degradation then
                core.log.warn("Plugin Runner is wrong, allow degradation")
                return
            end
            return 503
        end

        core.log.warn("refresh cache and try again")
        recreate_lrucache()
    end

    core.log.error(err)
    if conf.allow_degradation then
        core.log.warn("Plugin Runner is wrong after " .. tries .. " times retry, allow degradation")
        return
    end
    return 503
end


local function must_set(env, value)
    local ok, err = core.os.setenv(env, value)
    if not ok then
        error(str_format("failed to set %s: %s", env, err), 2)
    end
end


local function spawn_proc(cmd)
    must_set("APISIX_CONF_EXPIRE_TIME", helper.get_conf_token_cache_time())
    must_set("APISIX_LISTEN_ADDRESS", helper.get_path())

    local opt = {
        merge_stderr = true,
    }
    local proc, err = ngx_pipe.spawn(cmd, opt)
    if not proc then
        error(str_format("failed to start %s: %s", core.json.encode(cmd), err))
        -- TODO: add retry
    end

    proc:set_timeouts(nil, nil, nil, 0)
    return proc
end


local runner
local function setup_runner(cmd)

    ngx_timer_at(0, function(premature)
        if premature then
            return
        end

        runner = spawn_proc(cmd)

        while not exiting() do
            while true do
                -- drain output
                local max = 3800 -- smaller than Nginx error log length limit
                local data, err = runner:stdout_read_any(max)
                if not data then
                    if exiting() then
                        return
                    end

                    if err == "closed" then
                        break
                    end
                else
                    -- we log stdout here just for debug or test
                    -- the runner itself should log to a file
                    core.log.warn(data)
                end
            end

            local ok, reason, status = runner:wait()
            if not ok then
                core.log.warn("runner exited with reason: ", reason, ", status: ", status)
            end

            runner = nil
            local ok, err = events:post(events_list._source, events_list.runner_exit)
            if not ok then
                core.log.error("post event failure with ", events_list._source, ", error: ", err)
            end

            core.log.warn("respawn runner 3 seconds later with cmd: ", core.json.encode(cmd))
            core.utils.sleep(3)
            core.log.warn("respawning new runner...")
            runner = spawn_proc(cmd)
        end
    end)
end


function _M.init_worker()
    local local_conf = core.config.local_conf()
    local cmd = core.table.try_read_attr(local_conf, "ext-plugin", "cmd")
    if not cmd then
        return
    end

    events_list = events:event_list(
        "process_runner_exit_event",
        "runner_exit"
    )

    -- flush cache when runner exited
    events:register(recreate_lrucache, events_list._source, events_list.runner_exit)

    -- note that the runner is run under the same user as the Nginx master
    if process.type() == "privileged agent" then
        setup_runner(cmd)
    end
end


function _M.exit_worker()
    if process.type() == "privileged agent" and runner then
        -- We need to send SIGTERM in the exit_worker phase, as:
        -- 1. privileged agent doesn't support graceful exiting when I write this
        -- 2. better to make it work without graceful exiting
        local pid = runner:pid()
        core.log.notice("terminate runner ", pid, " with SIGTERM")
        local num = resty_signal.signum("TERM")
        runner:kill(num)

        -- give 1s to clean up the mess
        core.os.waitpid(pid, 1)
        -- then we KILL it via gc finalizer
    end
end


return _M