Bash script to automatically update qBittorrent port with a forwarded port from Gluetun

Dockerfile

# Make sure to bind mount the docker socket so docker commands work inside the container:
# -v /var/run/docker.sock:/var/run/docker.sock

FROM docker
RUN apk add bash curl perl
COPY update_port.sh .
ENTRYPOINT ["/update_port.sh"]

update_port.sh

#!/usr/bin/env bash

QBT_USERNAME=${QBT_USERNAME:-admin}
QBT_PASSWORD=${QBT_PASSWORD:-adminadmin}

QBT_URL=${QBT_URL:-http://localhost:8080}
GLUETUN_URL=${GLUETUN_URL:-http://localhost:8000}

LOG_LEVEL=${LOG_LEVEL:-info}

debug() {
  [[ $LOG_LEVEL == "debug" ]] && echo $@
}

log() {
  echo $@
}

err() {
  echo $@ >&2
}

COOKIE_JAR=$(mktemp)
login() {
  debug "logging in"
  body=$(curl -s "${QBT_URL}/api/v2/auth/login" \
    --fail-with-body \
    -c $COOKIE_JAR \
    --data-urlencode username=${QBT_USERNAME} \
    --data-urlencode password=${QBT_PASSWORD}
  )
  code=$?

  [[ $body == "Fails." ]] && return 1
  return $code
}

logout() {
  debug "logging out"
  curl -s "${QBT_URL}/api/v2/auth/logout" \
    -X POST \
    -b $COOKIE_JAR \
    -c $COOKIE_JAR \
    > /dev/null
}

isnumber() {
  [[ $1 =~ ^[0-9]+$ ]]
}

get_gluetun_port() {
  if ! port=$(curl -s --fail "${GLUETUN_URL}/v1/openvpn/portforwarded" | perl -ne '/"port":\s?(\d+)/ && print $1') ; then
    err "failed to read gluetun forwarded port"
    return 1
  fi

  if ! isnumber $port || ((port < 1024)) ; then
    err "port is not numeric or below 1024: $port"
    return 1
  fi

  echo -n $port
  return 0
}

get_current_qbt_port() {
  curl -s "${QBT_URL}/api/v2/app/preferences" \
    --fail-with-body \
    -b $COOKIE_JAR \
    -c $COOKIE_JAR \
  | perl -ne '/"listen_port":\s?(\d+),/ && print $1'
}

set_qbt_port() {
  body=$(printf '{"listen_port": %d}' "$1")

  curl "${QBT_URL}/api/v2/app/setPreferences" \
    --fail-with-body \
    -s \
    -X POST \
    -b $COOKIE_JAR \
    -c $COOKIE_JAR \
    --data-urlencode "json=${body}"
}

cleanup() {
  debug "EXIT: Running cleanup"
  logout
  rm -f $COOKIE_JAR
  pkill -P $$
}
trap cleanup SIGINT EXIT

show_help() {
  cat - <<EOF | fold -sw100
Usage: $0 [options]

  -h                  show help
  -i interval         automatically run at an interval (seconds)
  -c container_name   listen for Docker container \`start\` events of \`container_name\`

Note: options \`-i\` and \`-c\` can be used together to auto run on container start/restart, and run periodically. This is useful if Gluetun's internal healthcheck restarts the VPN (thereby rerolling the forwarded port) without restarting the container.
EOF
}

run() {
  if ! login ; then
    code=$?
    err "failed to login: $code"
    return $code
  fi
  debug "logged in"

  gluetun_port=$(get_gluetun_port)
  if [[ $? != 0 ]] ; then
    err "failed to get forwarded gluetun port"
    return 1
  fi
  debug "got gluetun port: $gluetun_port"

  if ! isnumber $gluetun_port ; then
    err "gluetun port is not a number"
    return 1
  fi

  if ! curr_qbt_port=$(get_current_qbt_port) ; then
    err "failed to read current qBittorrent port"
    return 1
  fi
  debug "got current qbittorrent port: $curr_qbt_port"

  if isnumber $curr_qbt_port && [[ $curr_qbt_port == $gluetun_port ]] ; then
    debug "ports match $curr_qbt_port $gluetun_port"
    return 0
  fi

  log "setting port to $gluetun_port"
  set_qbt_port $gluetun_port
  logout
}

run_interval() {
  interval=$1
  while : ; do
    run
    sleep $interval &
    wait $!
  done
}

run_watch_docker() {
  container_name=$1

  last=0

  while read type time container_name ; do
    # skip if it runs in quick succession. this could happen if the container gets into a crahsk loop
    if ((time - last < 30 )); then
      debug "Got \`$type\` less than 30 seconds after the previous. Skipping..."
      continue;
    fi
    last=$time

    log "Got \`$type\` for \`$container_name\`. Waiting 20 seconds before running"

    # wait 10 seconds so it can connect
    sleep 20
    run
  done < <(docker events --filter event=start --filter "container=${container_name}" --format "{{.Type}} {{.Time}} {{index .Actor.Attributes \"name\"}}")
}

trap run SIGHUP
if [[ $# == 0 ]] ; then
  run
  exit 0
fi

while getopts "hi:c:" arg ; do
  case $arg in
    h)
      show_help
      ;;

    i)
      log "Running every $OPTARG seconds"
      (run_interval "$OPTARG") &
      ;;

    c)
      log "Listening to Docker events of container: $OPTARG"
      (run_watch_docker "$OPTARG") &
      ;;

    *)
      ;;
  esac
done
shift $(($OPTIND -1))

[[ $LOG_LEVEL == "debug" ]] && jobs
wait -n