Resume curl download with filename detection and resume on libssl error

resume.sh

# Retries a command a with backoff.
#
# The retry count is given by ATTEMPTS (default 5), the
# initial backoff timeout is given by TIMEOUT in seconds
# (default 1.)
#
# Successive backoffs double the timeout.
#
# Beware of set -e killing your whole script!
#
# https://coderwall.com/p/--eiqg/exponential-backoff-in-bash
function with_backoff {
  local max_attempts=${ATTEMPTS-5}
  local timeout=${TIMEOUT-1}
  local attempt=0
  local exitCode=0

  while [[ $attempt < $max_attempts ]]
  do
    "$@"
    exitCode=$?

    if [[ $exitCode == 0 ]]
    then
      break
    fi

    echo "Failure! Retrying in $timeout.." 1>&2
    sleep $timeout
    attempt=$(( attempt + 1 ))
    timeout=$(( timeout * 2 ))
  done

  if [[ $exitCode != 0 ]]
  then
    echo "You've failed me for the last time! ($@)" 1>&2
  fi

  return $exitCode
}

urldecode() {
    # urldecode <string>

    local url_encoded="${1//+/ }"
    printf '%b' "${url_encoded//%/\\x}"
}

#https://stackoverflow.com/a/26500519/3896616
resume() {
    local url=${1:?"Error: Missing url"}
    local file=${2}

    # try to detect file name from http headers
    if [[ -z "$file" ]]; then
        local header="$(curl -sI "$url" | tr -d '\r')"
        file="$(echo "$header" | sed -nE "s/.*filename.?=(.*'')?(.*)$/\2/p")"
        if [[ -z "$file" ]]; then
            file="$(echo "$header" | grep -o -E 'Location:.*$')"
            if [[ -n "$file" ]]; then
                file=$(basename "${file#Location\:}")
            fi
            file=$(urldecode $file)
        fi
    fi

    # fallback to filename from url
    if [[ -z "$file" ]]; then
        file="$(basename $1 | cut -d \? -f 1)"
        file=$(urldecode $file)
    fi

    with_backoff curl --speed-limit 0 --speed-limit 60 -C - -o "$file" "$url"
}