---
-- A library implementing a minor subset of the IMAP protocol, currently the
-- CAPABILITY, LOGIN and AUTHENTICATE functions. The library was initially
-- written by Brandon Enright and later extended and converted to OO-form by
-- Patrik Karlsson <patrik@cqure.net>
--
-- The library consists of a <code>Helper</code>, class which is the main
-- interface for script writers, and the <code>IMAP</code> class providing
-- all protocol-level functionality.
--
-- The following example illustrates the recommended use of the library:
-- <code>
-- local helper = imap.Helper:new(host, port)
-- helper:connect()
-- helper:login("user","password","PLAIN")
-- helper:close()
-- </code>
--
-- @copyright Same as Nmap--See https://nmap.org/book/man-legal.html
-- @author Brandon Enright
-- @author Patrik Karlsson

-- Version 0.2
-- Revised 07/15/2011 - v0.2 - added the IMAP and Helper classes
--                             added support for LOGIN and AUTHENTICATE
--                             <patrik@cqure.net>

local base64 = require "base64"
local comm = require "comm"
local sasl = require "sasl"
local stdnse = require "stdnse"
local table = require "table"
_ENV = stdnse.module("imap", stdnse.seeall)


IMAP = {

  --- Creates a new instance of the IMAP class
  --
  -- @param host table as received by the script action method
  -- @param port table as received by the script action method
  -- @param options table containing options, currently
  --  <code>timeout<code> - number containing the seconds to wait for
  --                        a response
  new = function(self, host, port, options)
    local o = {
      host = host,
      port = port,
      counter = 1,
      timeout = ( options and options.timeout ) or 10000
    }
    setmetatable(o, self)
    self.__index = self
    return o
  end,

  --- Receives a response from the IMAP server
  --
  -- @return status true on success, false on failure
  -- @return data string containing the received data
  receive = function(self)
    local data = ""
    repeat
      local status, tmp = self.socket:receive_buf("\r\n", false)
      if( not(status) ) then return false, tmp end
      data = data .. tmp
    until( tmp:match(("^A%04d"):format(self.counter - 1)) or tmp:match("^%+"))

    return true, data
  end,

  --- Sends a request to the IMAP server
  --
  -- @param cmd string containing the command to send to the server eg.
  --            eg. (AUTHENTICATE, LOGIN)
  -- @param params string containing the command parameters
  -- @return true on success, false on failure
  -- @return err string containing the error if status was false
  send = function(self, cmd, params)
    local data
    if ( not(params) ) then
      data = ("A%04d %s\r\n"):format(self.counter, cmd)
    else
      data = ("A%04d %s %s\r\n"):format(self.counter, cmd, params)
    end
    local status, err = self.socket:send(data)
    if ( not(status) ) then return false, err end
    self.counter = self.counter + 1
    return true
  end,

  --- Connect to the server
  --
  -- @return status true on success, false on failure
  -- @return banner string containing the server banner
  connect = function(self)
    local socket, banner, opt = comm.tryssl( self.host, self.port, "", { request_timeout=self.timeout, recv_before=true } )
    if ( not(socket) or not(banner) ) then return false, "ERROR: Failed to connect to server" end
    self.socket = socket
    return true, banner
  end,

  --- Authenticate to the server (non PLAIN text mode)
  -- Currently supported algorithms are CRAM-MD5 and CRAM-SHA1
  --
  -- @param username string containing the username
  -- @param pass string containing the password
  -- @param mech string containing a authentication mechanism, currently
  --             CRAM-MD5 or CRAM-SHA1
  -- @return status true if login was successful, false on failure
  -- @return err string containing the error message if status was false
  authenticate = function(self, username, pass, mech)
    assert( mech == "NTLM" or
      mech == "DIGEST-MD5" or
      mech == "CRAM-MD5" or
      mech == "PLAIN",
      "Unsupported authentication mechanism")

    local status, err = self:send("AUTHENTICATE", mech)

    if( not(status) ) then return false, "ERROR: Failed to send data" end

    local status, data = self:receive()
    if( not(status) ) then return false, "ERROR: Failed to receive challenge" end

    if ( mech == "NTLM" ) then
      -- sniffed of the wire, seems to always be the same
      -- decodes to some NTLMSSP blob greatness
      status, data = self.socket:send("TlRMTVNTUAABAAAAB7IIogYABgA3AAAADwAPACgAAAAFASgKAAAAD0FCVVNFLUFJUi5MT0NBTERPTUFJTg==\r\n")
      if ( not(status) ) then return false, "ERROR: Failed to send NTLM packet" end
      status, data = self:receive()
      if ( not(status) ) then return false, "ERROR: Failed to receive NTLM challenge" end
    end

    if ( data:match(("^A%04d "):format(self.counter-1)) ) then
      return false, "ERROR: Authentication mechanism not supported"
    end

    local digest, auth_data
    if ( not(data:match("^+")) ) then
      return false, "ERROR: Failed to receive proper response from server"
    end
    data = base64.dec(data:match("^+ (.*)"))

    -- All mechanisms expect username and pass
    -- add the otheronce for those who need them
    local mech_params = { username, pass, data, "imap" }
    auth_data = sasl.Helper:new(mech):encode(table.unpack(mech_params))
    auth_data = base64.enc(auth_data) .. "\r\n"

    status, data = self.socket:send(auth_data)
    if( not(status) ) then return false, "ERROR: Failed to send data" end

    status, data = self:receive()
    if( not(status) ) then return false, "ERROR: Failed to receive data" end

    if ( mech == "DIGEST-MD5" ) then
      local rspauth = data:match("^+ (.*)")
      if ( rspauth ) then
        rspauth = base64.dec(rspauth)
        status, data = self.socket:send("\r\n")
        status, data = self:receive()
      end
    end
    if ( data:match(("^A%04d OK"):format(self.counter - 1)) ) then
      return true
    end
    return false, "Login failed"
  end,

  --- Login to the server using PLAIN text authentication
  --
  -- @param username string containing the username
  -- @param password string containing the password
  -- @return status true on success, false on failure
  -- @return err string containing the error message if status was false
  login = function(self, username, password)
    local status, err = self:send("LOGIN", ("\"%s\" \"%s\""):format(username, password))
    if( not(status) ) then return false, "ERROR: Failed to send data" end

    local status, data = self:receive()
    if( not(status) ) then return false, "ERROR: Failed to receive data" end

    if ( data:match(("^A%04d OK"):format(self.counter - 1)) ) then
      return true
    end
    return false, "Login failed"
  end,

  --- Retrieves a list of server capabilities (eg. supported authentication
  --  mechanisms, QUOTA, UIDPLUS, ACL ...)
  --
  -- @return status true on success, false on failure
  -- @return capas array containing the capabilities that are supported
  capabilities = function(self)
    local capas = {}
    local proto = (self.port.version and self.port.version.service_tunnel == "ssl" and "ssl") or "tcp"
    local status, err = self:send("CAPABILITY")
    if( not(status) ) then return false, err end

    local status, line = self:receive()
    if (not(status)) then
      capas.CAPABILITY = false
    else
      while status do
        if ( line:match("^%*%s+CAPABILITY") ) then
          line = line:gsub("^%*%s+CAPABILITY", "")
          for capability in line:gmatch("[%w%+=-]+") do
            capas[capability] = true
          end
          break
        end
        status, line = self.socket:receive()
      end
    end
    return true, capas
  end,

  --- Closes the connection to the IMAP server
  -- @return true on success, false on failure
  close = function(self) return self.socket:close() end

}


-- The helper class, that servers as interface to script writers
Helper = {

  -- @param host table as received by the script action method
  -- @param port table as received by the script action method
  -- @param options table containing options, currently
  -- <code>timeout<code> -  number containing the seconds to wait for
  --                        a response
  new = function(self, host, port, options)
    local o = { client = IMAP:new( host, port, options ) }
    setmetatable(o, self)
    self.__index = self
    return o
  end,

  --- Connects to the IMAP server
  -- @return status true on success, false on failure
  connect = function(self)
    return self.client:connect()
  end,

  --- Login to the server using either plain-text or using the authentication
  -- mechanism provided in the mech argument.
  --
  -- @param username string containing the username
  -- @param password string containing the password
  -- @param mech [optional] containing the authentication mechanism to use
  -- @return status true on success, false on failure
  login = function(self, username, password, mech)
    if ( not(mech) or mech == "LOGIN" ) then
      return self.client:login(username, password)
    else
      return self.client:authenticate(username, password, mech)
    end
  end,

  --- Retrieves a list of server capabilities (eg. supported authentication
  --  mechanisms, QUOTA, UIDPLUS, ACL ...)
  --
  -- @return status true on success, false on failure
  -- @return capas array containing the capabilities that are supported
  capabilities = function(self)
    return self.client:capabilities()
  end,

  --- Closes the connection to the IMAP server
  -- @return true on success, false on failure
  close = function(self)
    return self.client:close()
  end,

}

return _ENV;
