#!/home/spc/web/Lua/bin/lua
-- ************************************************************************
--
--    Main program
--    Copyright 2018 by Sean Conner.  All Rights Reserved.
--
--    This program is free software: you can redistribute it and/or modify
--    it under the terms of the GNU General Public License as published by
--    the Free Software Foundation, either version 3 of the License, or
--    (at your option) any later version.
--
--    This program is distributed in the hope that it will be useful,
--    but WITHOUT ANY WARRANTY; without even the implied warranty of
--    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--    GNU General Public License for more details.
--
--    You should have received a copy of the GNU General Public License
--    along with this program.  If not, see <http://www.gnu.org/licenses/>.
--
--    Comments, questions and criticisms can be sent to: sean@conman.org
--
-- ************************************************************************
-- luacheck: ignore 611
-- RFC-3875
-- RFC-8484
-- https://daniel.haxx.se/blog/2018/06/03/inside-firefoxs-doh-engine/

local syslog  = require "org.conman.syslog"
local dns     = require "org.conman.dns"
local base64  = require "org.conman.base64"()
local httpret = require "org.conman.const.http-response"
local lpeg    = require "lpeg"

-- **********************************************************************

local function output(status,data)
  if not data then
    io.stdout:write(string.format([[
Status: %d
Content-Length: 0

]],status))
  else
    io.stdout:write(string.format([[
Status: %d
Content-Type: application/dns-message
Content-Length: %d

%s]],status,#data,data))
  end
end

-- **********************************************************************

local function dns_query(query)
  local q = dns.decode(query)
  if q then
    syslog(
        'notice',
        "%s host=%q question.type=%s rc=%d age=%d",
        "POST",
        q.question.name,
        q.question.type,
        0,
        0
    )
  end
  
  local reply = dns.query('127.0.0.1',query)
  
  if not reply then
    output(httpret.CLIENT.TIMEOUT)
  else
    output(httpret.SUCCESS.OKAY,reply)
  end
end

-- **********************************************************************

local query_string do
  local xdigit = lpeg.locale().xdigit
  local char   = lpeg.P"%" * lpeg.C(xdigit * xdigit)
               / function(c)
                   return string.char(tonumber(c,16))
                 end
               + lpeg.R"!~"
  local name   = lpeg.Cs((char - (lpeg.P"=" + lpeg.P"&"))^1)
  local value  = lpeg.P"=" * lpeg.Cs((char - lpeg.P"&")^1)
               + lpeg.Cc""
  
  query_string = lpeg.Cf(
                          lpeg.Ct"" * lpeg.Cg(name * value * lpeg.P"&"^-1)^0,
                           function(result,n,v)
                             if result and not result[n] then
                               result[n] = v
                               return result
                             else
                               return false
                             end
                           end
                         )
end

-- **********************************************************************

local function http_get()
  local vars = query_string:match(os.getenv "QUERY_STRING")
  if vars and vars['dns'] then
    dns_query(base64:decode(vars['dns']))
  else
    output(httpret.CLIENT.BADREQ)
  end
end

-- **********************************************************************

local function http_post()
  if os.getenv("CONTENT_TYPE") ~= "application/dns-message" then
    output(httpret.CLIENT.MEDIATYPE)
    return
  end
  
  local len = tonumber(os.getenv("CONTENT_LENGTH"))
  if not len then
    output(httpret.CLIENT.LENGTHREQ)
    return
  end
  
  dns_query(io.stdin:read(len))
end

-- **********************************************************************

syslog.open("DNSoverHTTP/2-3","user")

local method = os.getenv("REQUEST_METHOD")

if method == "POST" then
  http_post()
elseif method == "GET" then
  http_get()
else
  output(httpret.SERVER.NOTIMP) -- per RFC-3875 s6.3.3
end

os.exit(0,true)