bash netcat

#!/bin/bash

RCON_AUTH=3
RCON_CMD=2

declare -A decode_msg

function switchEndian
{
  printf %s ${1} | grep -o .. | tac | tr -d '\n'
  return 0
}

function intToHex
{
  printf %.8X ${1}
  return 0
}

function hexToInt
{
  echo "ibase=16; "${1} | bc
  return 0
}

function intToHex_SE
{
  echo $(switchEndian $(intToHex ${1}))
  return 0
}

function hexToInt_SE
{
  echo $(hexToInt $(switchEndian ${1}))
  return 0
}

function helper
{
  echo ${1} | sed -e 's/\(..\)/\\x\1/g'
  return 0
}

function rcon_build_msg
{
  # {1} = ident
  # {2} = type
  # {3} = payload

  if [[ "${#@}" -ne 3 ]]
  then
    echo "Error using rcon_build_msg" >&2
    return 1
  fi

  local msg_size=$(helper $(intToHex_SE $(( 10 + ${#3}))))
  local msg_body=$(helper $(intToHex_SE "${1}"))$(helper $(intToHex_SE "${2}"))"${3}""\\00\\00"

  echo "${msg_size}""${msg_body}"
  return 0
}

function rcon_sendMsg
{
  # ${1} = message

  if [[ "${#@}" -ne 1 ]]
  then
    echo "Error rcon_sendMsg" >&2
    return 1
  fi

  echo -ne "${1}" >"${rcon_pIn}"
  return 0
}

function rcon_readByte
{
  dd if=${rcon_pOut} bs=1 count=${1} 2>/dev/null | xxd -ps  | tr 'a-z' 'A-Z'
  return 0
}

function rcon_readMsg
{
  local msgSize=$(rcon_readByte "4")
  local msgBody=$(rcon_readByte $(hexToInt_SE ${msgSize}))
  echo ${msgSize}${msgBody}
  return 0
}

function rcon_decodeMsg
{
  if [[ "${#@}" -ne 1 ]]
  then
    return 1
  fi

  decode_msg["size"]=$(hexToInt_SE ${1:0:8})
  decode_msg["ident"]=$(hexToInt_SE ${1:8:8})
  decode_msg["type"]=$(hexToInt_SE ${1:16:8})
  decode_msg["payload"]=$( echo ${1:24:-4} | xxd -p -r )

  return 0
}

function rcon_connect
{
  # {1} = host
  # {2} = port
  # {3} = password

  ident=42
  local msg=""
  local response=""

  if [[ "${#@}" -ne 3 ]]
  then
    echo "Usage: rcon_connect host port password" >&2
  fi

  netcat -nq 1 "${1}" "${2}" <"${rcon_pIn}" >"${rcon_pOut}" &
  local res=${!}

  exec {hold_pIn}>"${rcon_pIn}"
  exec {hold_pOut}<"${rcon_pOut}"

  ps -p "${res}" >/dev/null

  if [[ $? -ne 0 ]]
  then
    echo "Error netcat" >&2
    return 1
  fi

  msg=$(rcon_build_msg "${ident}" "${RCON_AUTH}" "${3}")
  rcon_sendMsg "${msg}"
  response=$(rcon_readMsg)
  rcon_decodeMsg "${response}"

  if [[ ${decode_msg["ident"]} -ne "${ident}" ]]
  then
    echo "Authentification failed" >&2
    return 1
  fi
  return 0
}

rcon_pIn=$(mktemp -u)
mkfifo "${rcon_pIn}"

rcon_pOut=$(mktemp -u)
mkfifo "${rcon_pOut}"

ident=0
response=""

rcon_connect "127.0.0.1" "25575" "password"
if [[ "${?}" -eq 0 && "${ident}" -gt 0 ]]
then
  msg=$(rcon_build_msg "${ident}" "${RCON_CMD}" "save-off")
  rcon_sendMsg "${msg}"
  response=$(rcon_readMsg)
  rcon_decodeMsg "${response}"
  echo ${decode_msg["payload"]}

  if [[ "${decode_msg["payload"]}" == "Disabled"* ]]
  then
    msg=$(rcon_build_msg "${ident}" "${RCON_CMD}" "save-all")
    rcon_sendMsg "${msg}"
    response=$(rcon_readMsg)
    rcon_decodeMsg "${response}"
    echo "${decode_msg["payload"]}"

    if [[ "${decode_msg["payload"]}" == *"Save complete." ]]
    then
      echo "TODO: BACKUP"
    fi

    msg=$(rcon_build_msg "${ident}" "${RCON_CMD}" "save-on")
    rcon_sendMsg "${msg}"
    response=$(rcon_readMsg)
    rcon_decodeMsg "${response}"
    echo "${decode_msg["payload"]}"
  fi
fi