This snippet tests how smtp client (curl internally) handles error messages from smtp server

smtp.lua

#!/usr/bin/env tarantool

local socket = require('socket')
local log = require('log')

local vars = {}

local function smtp_server(s)
    s:write('220 localhost ESMTP Tarantool\r\n')
    local l
    local mail = {rcpt = {}}
    while true do
        l = s:read('\r\n')
        if l:find('EHLO') then
            s:write('250-localhost Hello localhost.lan [127.0.0.1]\r\n')
            s:write('250-SIZE 52428800\r\n')
            s:write('250-8BITMIME\r\n')
            s:write('250-PIPELINING\r\n')
            s:write('250-CHUNKING\r\n')
            s:write('250-PRDR\r\n')
            s:write('250 HELP\r\n')
        elseif l:find('MAIL FROM:') then
            mail.from = l:sub(11):sub(1, -3)
            s:write('250 OK\r\n')
        elseif l:find('RCPT TO:') then
            local rcpt = l:sub(9):sub(1, -3)
            mail.rcpt[#mail.rcpt + 1] = rcpt

            -- Parse adresses like <510@tarantool.io>
            local status = tonumber(rcpt:lower():match('^<(%-?%d+).*@'))
            if status and status > 100 and status < 600 then
                s:write(tostring(status)
                    .. ' Reply code was extracted from recipient address\r\n')
            else
                s:write('250 OK\r\n')
            end
        elseif l == 'DATA\r\n' then
            s:write('354 Enter message, ending with "." on a line by itself\r\n')
            while true do
                local l = s:read('\r\n')
                if l == '.\r\n' then
                    break
                end
                mail.text = (mail.text or '') .. l
            end
            log.info('Got mail:\n\n%s', require('yaml').encode(mail))
            s:write('250 OK\r\n')
        elseif l:find('QUIT') then
            s:write('221 Bye\r\n')
            return
        elseif l ~= nil then
            s:write('502 Not implemented')
        else
            log.error('Error while reading from socket...')
            return
        end
    end
end

local function init()
    -- TODO: Wrap it with background module
    socket.tcp_server(
            os.getenv('SMTP_LISTEN') or '0.0.0.0',
            os.getenv('SMTP_PORT') or '2500',
            smtp_server
    )
end

init()
local fiber = require('fiber')
local yaml = require('yaml')
local client = require('smtp').new()
fiber.sleep(1)
local ok, res = pcall(client.request, client, 'smtp://localhost:2500', 'from@tarantool.io', 'nulldev@tarantool.io', 'Hi there!')
if ok then
    print('SUCCESS, ', yaml.encode(res))
else
    print('FAIL, ', yaml.encode(res))
end
ok, res = pcall(client.request, client, 'smtp://localhost:2500', 'from@tarantool.io', '500@tarantool.io', 'Hi there!')
if ok then
    print('SUCCESS, ', yaml.encode(res))
else
    print('FAIL, ', yaml.encode(res))
end

os.exit(1)