smtp_stls.lua

-- Enable STARTTLS support for SMTP

local smtp = require("socket.smtp")
local socket = require("socket")
local ssl = require("ssl")

local _M = smtp
local metat = { __index = {} }

local function augment(obj, mt)
  local orig_mt = getmetatable(obj).__index

  for name, method in pairs(mt.__index) do
    if type(method) == "function" then
      orig_mt[name] = method
    end
  end
end

function metat.__index:starttls(params, domain, ext)
  -- enforce client mode
  params.mode = "client"
  -- fallback protocol
  params.protocol = params.protocol or "any"

  if string.find(ext, "STARTTLS") then
    self.try(self.tp:command("STARTTLS"))
    self.try(self.tp:check("2.."))

    local timeout = self.tp.c:gettimeout()
    -- wrap the connection
    self.tp.c = self.try(ssl.wrap(self.tp.c, params))
    -- inherit original socket's connect timeout
    self.tp.c:settimeout(timeout)

    self.try(self.tp.c:dohandshake())
    -- resend EHLO on success
    self.try(self.tp:command("EHLO", domain))
    return socket.skip(1, self.try(self.tp:check("2..")))
  else
    self.try(nil, "STARTTLS not supported")
  end
end

-- override original socket.smtp.send to inject STARTTLS
_M.send = socket.protect(function(ms)
  local s = _M.open(ms.server, ms.port, ms.create)

  augment(s, metat)

  local ext = s:greet(ms.domain)

  if ms.starttls and ms.domain then
    ext = s:starttls(ms.tls_params, ms.domain, ext)
  end

  s:auth(ms.user, ms.password, ext)
  s:send(ms)
  s:quit()
  return s:close()
end)

return _M