env/bin/rfcopen.sh

#!/bin/sh
# rfcopen
# Written in 2019-2020 by Lucas
# CC0 1.0 Universal/Public domain - No rights reserved
#
# To the extent possible under law, the author(s) have dedicated all
# copyright and related and neighboring rights to this software to the
# public domain worldwide. This software is distributed without any
# warranty. You should have received a copy of the CC0 Public Domain
# Dedication along with this software. If not, see
# <http://creativecommons.org/publicdomain/zero/1.0/>.

usage()
{
	printf "Usage: %s [-T] rfc-number\n" "${0##*/}" >&2
	exit 1
}

err()
{
	printf "%s: %s\n" "${0##*/}" "$*" >&2
	exit 1
}

fetch_file()
{
	# Assumes utility supports `-o output_file`
	case $(uname) in
	OpenBSD)
		$torsocks ftp -MV "$@"
		;;
	*)
		$torsocks curl -fLSs "$@"
		;;
	esac
}

tonumber()
{
	printf "%u" "$1" 2>/dev/null
}

: ${RFCDIR:=~/doc/rfc}

torsocks=torsocks
while getopts T flag; do
	case $flag in
	T)	torsocks= ;;
	*)	usage ;;
	esac
done
shift $((OPTIND - 1))

[ $# -eq 1 ] && [ -n "$1" ] && n=$(tonumber "$1") || usage
rfcfile=$RFCDIR/rfc$n.txt
url=https://tools.ietf.org/rfc/rfc$n.txt

mkdir -p "$RFCDIR"
if [ ! -f "$rfcfile" ]; then
	fetch_file -o "$rfcfile" "$url" || err "couldn't fetch RFC $n"
fi
${PAGER:-more} "$rfcfile"