entrypoint.sh

#!/usr/bin/env bash
#
# ehough/docker-nfs-server: A lightweight, robust, flexible, and containerized NFS server.
#
# https://hub.docker.com/r/erichough/nfs-server
# https://github.com/ehough/docker-nfs-server
#
# Copyright (C) 2017-2020  Eric D. Hough
#
# 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/>.

######################################################################################
### constants
######################################################################################

readonly ENV_VAR_NFS_DISABLE_VERSION_3='NFS_DISABLE_VERSION_3'
readonly ENV_VAR_NFS_SERVER_THREAD_COUNT='NFS_SERVER_THREAD_COUNT'
readonly ENV_VAR_NFS_ENABLE_KERBEROS='NFS_ENABLE_KERBEROS'
readonly ENV_VAR_NFS_PORT_MOUNTD='NFS_PORT_MOUNTD'
readonly ENV_VAR_NFS_PORT='NFS_PORT'
readonly ENV_VAR_NFS_PORT_STATD_IN='NFS_PORT_STATD_IN'
readonly ENV_VAR_NFS_PORT_STATD_OUT='NFS_PORT_STATD_OUT'
readonly ENV_VAR_NFS_VERSION='NFS_VERSION'
readonly ENV_VAR_NFS_LOG_LEVEL='NFS_LOG_LEVEL'

readonly DEFAULT_NFS_PORT=2049
readonly DEFAULT_NFS_PORT_MOUNTD=32767
readonly DEFAULT_NFS_PORT_STATD_IN=32765
readonly DEFAULT_NFS_PORT_STATD_OUT=32766
readonly DEFAULT_NFS_VERSION='4.2'

readonly PATH_BIN_EXPORTFS='/usr/sbin/exportfs'
readonly PATH_BIN_IDMAPD='/usr/sbin/rpc.idmapd'
readonly PATH_BIN_MOUNTD='/usr/sbin/rpc.mountd'
readonly PATH_BIN_NFSD='/usr/sbin/rpc.nfsd'
readonly PATH_BIN_RPCBIND='/sbin/rpcbind'
readonly PATH_BIN_RPC_SVCGSSD='/usr/sbin/rpc.svcgssd'
readonly PATH_BIN_STATD='/sbin/rpc.statd'

readonly PATH_FILE_ETC_EXPORTS='/etc/exports'
readonly PATH_FILE_ETC_IDMAPD_CONF='/etc/idmapd.conf'
readonly PATH_FILE_ETC_KRB5_CONF='/etc/krb5.conf'
readonly PATH_FILE_ETC_KRB5_KEYTAB='/etc/krb5.keytab'

readonly MOUNT_PATH_NFSD='/proc/fs/nfsd'
readonly MOUNT_PATH_RPC_PIPEFS='/var/lib/nfs/rpc_pipefs'

readonly REGEX_EXPORTS_LINES_TO_SKIP='^\s*#|^\s*$'

readonly LOG_LEVEL_INFO='INFO'
readonly LOG_LEVEL_DEBUG='DEBUG'

readonly STATE_LOG_LEVEL='log_level'
readonly STATE_IS_LOGGING_DEBUG='is_logging_debug'
readonly STATE_IS_LOGGING_INFO='is_logging_info'
readonly STATE_NFSD_THREAD_COUNT='nfsd_thread_count'
readonly STATE_NFSD_PORT='nfsd_port'
readonly STATE_MOUNTD_PORT='mountd_port'
readonly STATE_STATD_PORT_IN='statd_port_in'
readonly STATE_STATD_PORT_OUT='statd_port_out'
readonly STATE_NFS_VERSION='nfs_version'

# "state" is our only global variable, which is an associative array of normalized data
declare -A state


######################################################################################
### logging
######################################################################################

log() {

  echo "----> $1"
}

log_warning() {

  log "WARNING: $1"
}

log_error() {

  log ''
  log "ERROR: $1"
  log ''
}

log_header() {

  echo "
==================================================================
      ${1^^}
=================================================================="
}


######################################################################################
### error handling
######################################################################################

bail() {

  log_error "$1"
  exit 1
}

on_failure() {

  # shellcheck disable=SC2181
  if [[ $? -eq 0 ]]; then
    return
  fi

  case "$1" in
    warn)
      log_warning "$2"
      ;;
    stop)
      log_error "$2"
      stop
      ;;
    *)
      bail "$2"
      ;;
  esac
}


######################################################################################
### process control
######################################################################################

term_process() {

  local -r base=$(basename "$1")
  local -r pid=$(pidof "$base")

  if [[ -n $pid ]]; then
    log "terminating $base"
    kill "$pid"
    on_failure warn "unable to terminate $base"
  else
    log "$base was not running"
  fi
}


######################################################################################
### teardown
######################################################################################

stop_mount() {

  local -r path=$1
  local -r type=$(basename "$path")

  if mount | grep -Eq ^"$type on $path\\s+"; then

    local args=()
    if is_logging_debug; then
      args+=('-v')
      log "un-mounting $type filesystem from $path"
    fi
    args+=("$path")

    umount "${args[@]}"
    on_failure warn "unable to un-mount $type filesystem from $path"

  else
    log "no active mount at $path"
  fi
}

stop_nfsd() {

  log 'terminating nfsd'
  $PATH_BIN_NFSD 0
  on_failure warn 'unable to terminate nfsd. if it had started already, check Docker host for lingering [nfsd] processes'
}

stop_exportfs() {

  local args=('-ua')
  if is_logging_debug; then
    args+=('-v')
  fi

  log 'un-exporting filesystem(s)'
  $PATH_BIN_EXPORTFS "${args[@]}"
  on_failure warn 'unable to un-export filesystem(s)'
}

stop() {

  log_header 'terminating ...'

  if is_kerberos_requested; then
    term_process "$PATH_BIN_RPC_SVCGSSD"
  fi

  stop_nfsd

  if is_idmapd_requested; then
    term_process "$PATH_BIN_IDMAPD"
  fi

  if is_nfs3_enabled; then
    term_process "$PATH_BIN_STATD"
  fi

  term_process "$PATH_BIN_MOUNTD"
  stop_exportfs
  term_process "$PATH_BIN_RPCBIND"
  stop_mount "$MOUNT_PATH_NFSD"
  stop_mount "$MOUNT_PATH_RPC_PIPEFS"

  log_header 'terminated'

  exit 0
}


######################################################################################
### runtime environment detection
######################################################################################

is_kerberos_requested() {

  [[ -n "${!ENV_VAR_NFS_ENABLE_KERBEROS}" ]] && return 0 || return 1
}

is_nfs3_enabled() {

  [[ -z "${!ENV_VAR_NFS_DISABLE_VERSION_3}" ]] && return 0 || return 1
}

is_idmapd_requested() {

  [[ -f "$PATH_FILE_ETC_IDMAPD_CONF" ]] && return 0 || return 1
}

is_logging_debug() {

  [[ -n ${state[$STATE_IS_LOGGING_DEBUG]} ]] && return 0 || return 1
}

is_kernel_module_loaded() {

  local -r module=$1

  if lsmod | grep -Eq "^$module\\s+" || [[ -d "/sys/module/$module" ]]; then

    if is_logging_debug; then
      log "kernel module $module is loaded"
    fi
    return 0
  fi

  log "kernel module $module is missing"
  return 1
}

is_granted_linux_capability() {

  if capsh --print | grep -Eq "^Current: ?=? .*,?${1}(,|$)"; then
    return 0
  fi

  return 1
}


######################################################################################
### runtime configuration assertions
######################################################################################

assert_file_provided() {

  if [[ ! -f "$1" ]]; then
    bail "please provide $1 to the container"
  fi
}

assert_kernel_mod() {

  local -r module=$1

  if is_kernel_module_loaded "$module"; then
    return
  fi

  if [[ ! -d /lib/modules ]] || ! is_granted_linux_capability 'sys_module'; then
    bail "$module module is not loaded in the Docker host's kernel (try: modprobe $module)"
  fi

  log "attempting to load kernel module $module"
  modprobe -v "$module"
  on_failure bail "unable to dynamically load kernel module $module. try modprobe $module on the Docker host"

  if ! is_kernel_module_loaded "$module"; then
    bail "modprobe claims that it loaded kernel module $module, but it still appears to be missing"
  fi
}

assert_port() {

  local -r variable_name=$1
  local -r value=${!variable_name}

  if [[ -n "$value" && ( "$value" -lt 1 || "$value" -gt 65535 ) ]]; then
    bail "please set $variable_name to an integer between 1 and 65535 inclusive"
  fi
}


######################################################################################
### initialization
######################################################################################

init_state_logging() {

  # if the user didn't request a specific log level, the default is INFO
  local incoming_log_level="${!ENV_VAR_NFS_LOG_LEVEL:-$LOG_LEVEL_INFO}"
  local -r normalized_log_level="${incoming_log_level^^}"

  if ! echo "$normalized_log_level" | grep -Eq 'DEBUG|INFO'; then
    bail "the only acceptable values for $ENV_VAR_NFS_LOG_LEVEL are: DEBUG, INFO"
  fi

  state[$STATE_LOG_LEVEL]=$normalized_log_level;
  state[$STATE_IS_LOGGING_INFO]=1

  if [[ $normalized_log_level = "$LOG_LEVEL_DEBUG" ]]; then
    state[$STATE_IS_LOGGING_DEBUG]=1
    log "log level set to $LOG_LEVEL_DEBUG"
  fi
}

init_state_nfsd_thread_count() {

  local count

  if [[ -n "${!ENV_VAR_NFS_SERVER_THREAD_COUNT}" ]]; then

    count="${!ENV_VAR_NFS_SERVER_THREAD_COUNT}"

    if [[ $count -lt 1 ]]; then
      bail "please set $ENV_VAR_NFS_SERVER_THREAD_COUNT to a positive integer"
    fi

    if is_logging_debug; then
      log "will use requested rpc.nfsd thread count of $count"
    fi

  else

    count="$(grep -Ec ^processor /proc/cpuinfo)"
    on_failure bail "unable to detect CPU count. set $ENV_VAR_NFS_SERVER_THREAD_COUNT environment variable"

    if is_logging_debug; then
      log "will use $count rpc.nfsd server thread(s) (1 thread per CPU)"
    fi

  fi

  state[$STATE_NFSD_THREAD_COUNT]=$count
}

init_state_ports() {

  assert_port "$ENV_VAR_NFS_PORT"
  assert_port "$ENV_VAR_NFS_PORT_MOUNTD"
  assert_port "$ENV_VAR_NFS_PORT_STATD_IN"
  assert_port "$ENV_VAR_NFS_PORT_STATD_OUT"

  state[$STATE_NFSD_PORT]=${!ENV_VAR_NFS_PORT:-$DEFAULT_NFS_PORT}
  state[$STATE_MOUNTD_PORT]=${!ENV_VAR_NFS_PORT_MOUNTD:-$DEFAULT_NFS_PORT_MOUNTD}
  state[$STATE_STATD_PORT_IN]=${!ENV_VAR_NFS_PORT_STATD_IN:-$DEFAULT_NFS_PORT_STATD_IN}
  state[$STATE_STATD_PORT_OUT]=${!ENV_VAR_NFS_PORT_STATD_OUT:-$DEFAULT_NFS_PORT_STATD_OUT}
}

init_state_nfs_version() {

  local -r requested_version="${!ENV_VAR_NFS_VERSION:-$DEFAULT_NFS_VERSION}"

  echo "$requested_version" | grep -Eq '^3$|^4(\.[1-2])?$'
  on_failure bail "please set $ENV_VAR_NFS_VERSION to one of: 4.2, 4.1, 4, 3"

  if ! is_nfs3_enabled && [[ "$requested_version" = '3' ]]; then
    bail 'you cannot simultaneously enable and disable NFS version 3'
  fi

  state[$STATE_NFS_VERSION]=$requested_version
}

init_trap() {

  trap stop SIGTERM SIGINT
}

init_exports() {

  # first, see if it's bind-mounted
  if mount | grep -Eq "^[^ ]+ on $PATH_FILE_ETC_EXPORTS type "; then

    if is_logging_debug; then
      log "$PATH_FILE_ETC_EXPORTS is bind-mounted"
    fi

  # maybe it's baked-in to the image
  elif [[ -f $PATH_FILE_ETC_EXPORTS && -r $PATH_FILE_ETC_EXPORTS && -s $PATH_FILE_ETC_EXPORTS ]]; then

    if is_logging_debug; then
      log "$PATH_FILE_ETC_EXPORTS is baked into the image"
    fi

  # fall back to environment variables
  else

    local count_valid_exports=0
    local exports=''
    local candidate_export_vars
    local candidate_export_var

    # collect all candidate environment variable names
    candidate_export_vars=$(compgen -A variable | grep -E 'NFS_EXPORT_[0-9]+' | sort)
    on_failure bail 'failed to detect NFS_EXPORT_* variables'

    if [[ -z "$candidate_export_vars" ]]; then
      bail "please provide $PATH_FILE_ETC_EXPORTS to the container or set at least one NFS_EXPORT_* environment variable"
    fi

    log "building $PATH_FILE_ETC_EXPORTS from environment variables"

    for candidate_export_var in $candidate_export_vars; do

      local line="${!candidate_export_var}"

      # skip comments and empty lines
      if [[ "$line" =~ $REGEX_EXPORTS_LINES_TO_SKIP ]]; then
        log_warning "skipping $candidate_export_var environment variable since it contains only whitespace or a comment"
        continue;
      fi

      local line_as_array
      read -r -a line_as_array <<< "$line"
      local dir="${line_as_array[0]}"

      if [[ ! -d "$dir" ]]; then
        log_warning "skipping $candidate_export_var environment variable since $dir is not a container directory"
        continue
      fi

      if [[ $count_valid_exports -gt 0 ]]; then
        exports=$exports$'\n'
      fi

      exports=$exports$line

      (( count_valid_exports++ ))

    done

    log "collected $count_valid_exports valid export(s) from NFS_EXPORT_* environment variables"

    if [[ $count_valid_exports -eq 0 ]]; then
      bail 'no valid exports'
    fi

    echo "$exports" > $PATH_FILE_ETC_EXPORTS
    on_failure bail "unable to write to $PATH_FILE_ETC_EXPORTS"
  fi

  # make sure we have at least one export
  grep -Evq "$REGEX_EXPORTS_LINES_TO_SKIP" $PATH_FILE_ETC_EXPORTS
  on_failure bail "$PATH_FILE_ETC_EXPORTS has no exports"
}

init_runtime_assertions() {

  # check kernel modules
  assert_kernel_mod nfs
  assert_kernel_mod nfsd

  # perform Kerberos assertions
  if is_kerberos_requested; then

    assert_file_provided "$PATH_FILE_ETC_KRB5_KEYTAB"
    assert_file_provided "$PATH_FILE_ETC_KRB5_CONF"

    assert_kernel_mod rpcsec_gss_krb5
  fi
}


######################################################################################
### boot helpers
######################################################################################

boot_helper_mount() {

  local -r path=$1
  local -r type=$(basename "$path")
  local args=('-t' "$type" "$path")

  if is_logging_debug; then
    args+=('-vvv')
    log "mounting $type filesystem onto $path"
  fi

  mount "${args[@]}"
  on_failure stop "unable to mount $type filesystem onto $path"
}

boot_helper_start_daemon() {

  local -r msg="$1"
  local -r daemon="$2"
  shift 2
  local -r daemon_args=("$@")

  log "$msg"
  "$daemon" "${daemon_args[@]}"
  on_failure stop "$daemon failed"
}

boot_helper_start_non_daemon() {

  local -r msg="$1"
  local -r process="$2"
  shift 2
  local -r process_args=("$@")

  log "$msg"
  "$process" "${process_args[@]}" &

  local -r bg_pid=$!

  # somewhat arbitrary assumption that if the process isn't dead already, it will die within a millisecond. for our
  # purposes this works just fine, but if someone has a better solution please open a PR.
  sleep .001
  kill -0 $bg_pid 2> /dev/null
  on_failure stop "$process failed"
}

######################################################################################
### primary boot
######################################################################################

boot_main_mounts() {

  # http://wiki.linux-nfs.org/wiki/index.php/Nfsv4_configuration
  boot_helper_mount "$MOUNT_PATH_RPC_PIPEFS"
  boot_helper_mount "$MOUNT_PATH_NFSD"
}

boot_main_exportfs() {

  local args=('-ar')
  if is_logging_debug; then
    args+=('-v')
  fi

  boot_helper_start_daemon 'starting exportfs' $PATH_BIN_EXPORTFS "${args[@]}"
}

boot_main_mountd() {

  # https://linux.die.net/man/8/rpc.mountd
  #
  # --debug  turn on debugging. Valid kinds are: all, auth, call, general and parse.
  # --port   specifies the port number used for RPC listener sockets

  local args=("-N 2 -N 3 -V 4")
  if is_logging_debug; then
    args+=('--debug' 'all')
  fi

  # yes, rpc.mountd is required even for NFS v4: https://forums.gentoo.org/viewtopic-p-7724856.html#7724856
  boot_helper_start_daemon "starting rpc.mountd on port $port" $PATH_BIN_MOUNTD "${args[@]}"
}

boot_main_rpcbind() {

  # https://linux.die.net/man/8/rpcbind
  #
  # -d  run in debug mode. in this mode, rpcbind will not fork when it starts, will print additional information during
  #     operation, and will abort on certain errors if -a is also specified. with this option, the name-to-address
  #     translation consistency checks are shown in detail
  # -s  cause rpcbind to change to the user daemon as soon as possible. this causes rpcbind to use non-privileged ports
  #     for outgoing connections, preventing non-privileged clients from using rpcbind to connect to services from a
  #     privileged port

  local args=('-s')
  if is_logging_debug; then
    arg+=('-d')
  fi
  # boot_helper_start_daemon 'starting rpcbind' $PATH_BIN_RPCBIND "${args[@]}"
}

boot_main_idmapd() {

  if ! is_idmapd_requested; then
    return
  fi

  # https://linux.die.net/man/8/rpc.idmapd
  #
  # -S  Server-only: perform no idmapping for any NFS client, even if one is detected
  # -v  increases the verbosity level (can be specified multiple times
  # -f  runs rpc.idmapd in the foreground and prints all output to the terminal

  local args=('-S')
  local func=boot_helper_start_daemon
  if is_logging_debug; then
    args+=('-vvv' '-f')
    func=boot_helper_start_non_daemon
  fi

  $func 'starting rpc.idmapd' $PATH_BIN_IDMAPD "${args[@]}"
}

boot_main_statd() {

  if ! is_nfs3_enabled; then
    return
  fi

  # https://linux.die.net/man/8/rpc.statd
  #
  # --no-syslog      causes rpc.statd to write log messages on stderr instead of to the system log, if the -F option was
  #                  also specified
  # --foreground     keeps rpc.statd attached to its controlling terminal so that NSM operation can be monitored
  #                  directly or run under a debugger. if this option is not specified, rpc.statd backgrounds itself
  #                  soon after it starts
  # --no-notify      prevents rpc.statd from running the sm-notify command when it starts up, preserving the existing
  #                  NSM state number and monitor list
  # --outgoing-port  specifies the source port number the sm-notify command should use when sending reboot notifications
  # --port           specifies the port number used for RPC listener sockets

  local -r port_in="${state[$STATE_STATD_PORT_IN]}"
  local -r port_out="${state[$STATE_STATD_PORT_OUT]}"
  local args=('--no-notify' '--port' "$port_in" '--outgoing-port' "$port_out")
  local func=boot_helper_start_daemon

  if is_logging_debug; then
    args+=('--no-syslog' '--foreground')
    func=boot_helper_start_non_daemon
  fi

  $func "starting rpc.statd on port $port_in (outgoing from port $port_out)" $PATH_BIN_STATD "${args[@]}"
}

boot_main_nfsd() {

  # https://linux.die.net/man/8/rpc.nfsd
  #
  # --debug  enable logging of debugging messages
  # --port   specify a diferent port to listen on for NFS requests. by default, rpc.nfsd will listen on port 2049
  # --tcp    explicitly enable TCP connections from clients
  # --udp    explicitly enable UCP connections from clients
  # nproc    specify the number of NFS server threads. by default, just one thread is started. however, for optimum
  #          performance several threads should be used. the actual figure depends on the number of and the work load
  #          created by the NFS clients, but a useful starting point is 8 threads. effects of modifying that number can
  #          be checked using the nfsstat(8) program

  local args=("-N 3 -V 4 --grace-time 10")

  if is_logging_debug; then
    args+=('--debug')
  fi

  boot_helper_start_daemon "starting rpc.nfsd on port $port with $threads server thread(s) with $args args" $PATH_BIN_NFSD "${args[@]}"
}

boot_main_svcgssd() {

  if ! is_kerberos_requested; then
    return
  fi

  # https://linux.die.net/man/8/rpc.svcgssd
  #
  # -f  runs rpc.svcgssd in the foreground and sends output to stderr (as opposed to syslogd)
  # -v  increases the verbosity of the output (can be specified multiple times)
  # -r  if the rpcsec_gss library supports setting debug level, increases the verbosity of the output (can be specified
  #     multiple times)
  # -i  if the nfsidmap library supports setting debug level, increases the verbosity of the output (can be specified
  #     multiple times)

  local args=('-f')
  if is_logging_debug; then
    args+=('-vvv' '-rrr' '-iii')
  fi

  boot_helper_start_non_daemon 'starting rpc.svcgssd' $PATH_BIN_RPC_SVCGSSD "${args[@]}"
}


######################################################################################
### boot summary
######################################################################################

summarize_nfs_versions() {

  local -r reqd_version="${state[$STATE_NFS_VERSION]}"
  local versions=''

  case "$reqd_version" in
    4\.2)
      versions='4.2, 4.1, 4'
      ;;
    4\.1)
      versions='4.1, 4'
      ;;
    4)
      versions='4'
      ;;
    *)
      versions='3'
      ;;
  esac

  if is_nfs3_enabled && [[ "$reqd_version" =~ ^4 ]]; then
    versions="$versions, 3"
  fi

  log "list of enabled NFS protocol versions: $versions"
}

summarize_exports() {

  log 'list of container exports:'

  # if debug is enabled, read /var/lib/nfs/etab as it contains the "real" export data. but it also contains more
  # information that most people will usually need to see
  local file_to_read="$PATH_FILE_ETC_EXPORTS"
  if is_logging_debug; then
    file_to_read='/var/lib/nfs/etab'
  fi

  while read -r export; do

    # skip comments and empty lines
    if [[ "$export" =~ $REGEX_EXPORTS_LINES_TO_SKIP ]]; then
      continue;
    fi

    # log it w/out leading and trailing whitespace
    log "  $(echo -e "$export" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//')"

  done < "$file_to_read"
}

summarize_ports() {

  local -r port_nfsd="${state[$STATE_NFSD_PORT]}"
  local -r port_mountd="${state[$STATE_MOUNTD_PORT]}"
  local -r port_statd_in="${state[$STATE_STATD_PORT_IN]}"

  if ! is_nfs3_enabled; then
    log "list of container ports that should be exposed: $port_nfsd (TCP)"
  else
    log 'list of container ports that should be exposed:'
    log '  111 (TCP and UDP)'
    log "  $port_nfsd (TCP and UDP)"
    log "  $port_statd_in (TCP and UDP)"
    log "  $port_mountd (TCP and UDP)"
  fi
}


######################################################################################
### main routines
######################################################################################

init() {

  log_header 'setting up ...'

  init_state_logging
  init_state_nfsd_thread_count
  init_state_ports
  init_state_nfs_version
  init_exports
  init_runtime_assertions
  init_trap

  log 'setup complete'
}

boot() {

  log_header 'starting services ...'

  boot_main_mounts
  boot_main_rpcbind
  boot_main_exportfs
  boot_main_mountd
  boot_main_statd
  boot_main_idmapd
  boot_main_nfsd
  boot_main_svcgssd

  log 'all services started normally'
}

summarize() {

  log_header 'server startup complete'

  summarize_nfs_versions
  summarize_exports
  summarize_ports
}

hangout() {

  log_header 'ready and waiting for NFS client connections'

  # wait forever or until we get SIGTERM or SIGINT
  # https://stackoverflow.com/a/41655546/229920
  # https://stackoverflow.com/a/27694965/229920
  while :; do sleep 2073600 & wait; done
}

main() {

  init
  boot
  summarize
  hangout
}

main