retry/retry

#!/usr/bin/env sh

GETOPT_BIN=$IN_GETOPT_BIN
GETOPT_BIN=${GETOPT_BIN:-getopt}

__sleep_amount() {
  if [ -n "$constant_sleep" ]; then
    sleep_time=$constant_sleep
  else
    #TODO: check for awk
    #TODO: check if user would rather use one of the other possible dependencies: python, ruby, bc, dc
    sleep_time=$(awk "BEGIN {t = $min_sleep * $(((1 << (_retry_attempts - 1)))); print (t > $max_sleep ? $max_sleep : t)}")
  fi
}

__log_out() {
  echo "$1" 1>&2
}

# Parameters: max_tries min_sleep max_sleep constant_sleep fail_script EXECUTION_COMMAND
retry() {
  _retry_max_tries="$1"
  shift
  _retry_min_sleep="$1"
  shift
  _retry_max_sleep="$1"
  shift
  _retry_constant_sleep="$1"
  shift
  _retry_fail_script="$1"
  shift
  if [ -n "$VERBOSE" ]; then
    __log_out "Retry Parameters: max_tries=$_retry_max_tries min_sleep=$_retry_min_sleep max_sleep=$_retry_max_sleep constant_sleep=$_retry_constant_sleep"
    if [ -n "$_retry_fail_script" ]; then __log_out "Fail script: $_retry_fail_script"; fi
    __log_out ""
    __log_out "Execution Command: $*"
    __log_out ""
  fi

  _retry_attempts=0
  _retry_return_code=1

  while [ "$_retry_return_code" -ne 0 ] && [ "$_retry_attempts" -le "$_retry_max_tries" ]; do
    if [ $_retry_attempts -gt 0 ]; then
      __sleep_amount
      __log_out "Before retry #$_retry_attempts: sleeping $sleep_time seconds"
      sleep "$sleep_time"
    fi

    P="$1"
    #for param in "${@:2}"; do P="$P '$param'"; done
    #TODO: replace single quotes in each arg with '"'"' ?
    export RETRY_ATTEMPT=$_retry_attempts
    sh -c "$P"
    _retry_return_code=$?
    #__log_out "Process returned $_retry_return_code on attempt $_retry_attempts"
    if [ $_retry_return_code -eq 127 ]; then
      # command not found
      exit $_retry_return_code
    elif [ $_retry_return_code -ne 0 ]; then
      _retry_attempts=$((_retry_attempts + 1))
    fi
  done

  if [ "$_retry_attempts" -gt "$_retry_max_tries" ]; then
    if [ -n "$_retry_fail_script" ]; then
      __log_out "Retries exhausted, running fail script"
      eval "$_retry_fail_script"
    else
      __log_out "Retries exhausted"
    fi
  fi

  exit $_retry_return_code
}

help() {
  _help_retry=$(basename "$0")
  cat <<EOF
Usage: $_help_retry [options] -- execute command
-h, -?, --help
-v, --verbose                    Verbose output
-t, --tries=#                    Set max retries: Default 10
-s, --sleep=secs                 Constant sleep amount (seconds)
-m, --min=secs                   Exponential Backoff: minimum sleep amount (seconds): Default 0.3
-x, --max=secs                   Exponential Backoff: maximum sleep amount (seconds): Default 60
-f, --fail="script +cmds"        Fail Script: run in case of final failure
EOF
}

# show help for no arguments if stdin is a terminal
if { [ -z "$1" ] && [ -t 0 ]; } || [ "$1" = '-h' ] || [ "$1" = '-?' ] || [ "$1" = '--help' ]; then
  help
  exit 0
fi

$GETOPT_BIN --test >/dev/null
if [ $? -ne 4 ]; then
  echo "I’m sorry, 'getopt --test' failed in this environment. Please load GNU getopt."
  exit 1
fi

OPTIONS=vt:s:m:x:f:
LONGOPTIONS=verbose,tries:,sleep:,min:,max:,fail:

PARSED=$($GETOPT_BIN --options="$OPTIONS" --longoptions="$LONGOPTIONS" --name "$0" -- "$@")
# shellcheck disable=SC2181
if [ $? -ne 0 ]; then
  # e.g. $? == 1
  #  then getopt has complained about wrong arguments to stdout
  exit 2
fi
# read getopt’s output this way to handle the quoting right:
eval set -- "$PARSED"

max_tries=10
min_sleep=0.3
max_sleep=60.0
constant_sleep=
fail_script=

# now enjoy the options in order and nicely split until we see --
while true; do
  case "$1" in
  -v | --verbose)
    VERBOSE=true
    shift
    ;;
  -t | --tries)
    max_tries="$2"
    shift 2
    ;;
  -s | --sleep)
    constant_sleep="$2"
    shift 2
    ;;
  -m | --min)
    min_sleep="$2"
    shift 2
    ;;
  -x | --max)
    max_sleep="$2"
    shift 2
    ;;
  -f | --fail)
    fail_script="$2"
    shift 2
    ;;
  --)
    shift
    break
    ;;
  *)
    echo "Programming error"
    exit 3
    ;;
  esac
done

retry "$max_tries" "$min_sleep" "$max_sleep" "$constant_sleep" "$fail_script" "$@"