50-motd-news

#!/bin/sh
#
#    50-motd-news - print the live news from the Ubuntu wire
#    Copyright (C) 2016-2017 Canonical Ltd.
#    Copyright (C) 2016-2017 Dustin Kirkland
#
#    Authors: Dustin Kirkland <kirkland@canonical.com>
#
#    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 2 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, write to the Free Software Foundation, Inc.,
#    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

##############################################################################
# This program could be rewritten in C or Golang for faster performance.
# Or it could be rewritten in Python or another higher level language
# for more modularity.
# However, I've insisted on shell here for transparency!
#                                                                     - Dustin
##############################################################################

# Source the local configuration
[ -r /etc/default/motd-news ] && . /etc/default/motd-news

# Exit immediately, unless we're enabled
# This makes this script very easy to disable in /etc/default/motd-news configuration
[ "$ENABLED" = "1" ] || exit 0

# Ensure sane defaults
[ -n "$URLS" ] || URLS="https://motd.ubuntu.com"
[ -n "$WAIT" ] || WAIT=5
[ -n "$CACHE" ] || CACHE="/var/cache/motd-news"
[ "$1" = "--force" ] && FORCED=1

# Ensure we print safely, maximum of the first 10 lines,
# maximum of the first 80 chars per line, no control chars
safe_print() {
    cat "$1" | head -n 10 | tr -d '\000-\011\013\014\016-\037' | cut -c -80
}


# If we're not forcing an update, and we have a cached motd-news file,
# then just print it and exit as quickly as possible, for login performance.
# Note that systemd should keep this cache file up to date, asynchronously
if [ "$FORCED" != "1" ]; then
    if [ -r $CACHE ]; then
        echo
        safe_print $CACHE
    else
        : > $CACHE
    fi
    exit 0
fi

# If we've made it here, we've been given the --force argument,
# probably from the systemd motd-news.service.  Let's update...

# Generate our temp files, clean up when done
NEWS=$(mktemp) || exit 1
ERR=$(mktemp) || exit 1
CLOUD=$(mktemp) || exit 1
trap "rm -f $NEWS $ERR $CLOUD" HUP INT QUIT ILL TRAP KILL BUS TERM

# Construct a user agent, similar to Firefox/Chrome/Safari/IE to
# ensure a proper, tailored, accurate message of the day

# Curl browser version, for debug purposes
curl_ver="$(dpkg -l curl | awk '$1 == "ii" { print($3); exit(0); }')"

# Distribution version, for messages releated to this Ubuntu release
. /etc/lsb-release
lsb=$(echo "$DISTRIB_DESCRIPTION" | sed -e "s/ /\//g")
codename="$DISTRIB_CODENAME"

# Kernel version and CPU type, for messages related to a particular revision or hardware
platform="$(uname -o)/$(uname -r)/$(uname -m)"
arch="$(uname -m)"
cpu="$(grep -m1 "^model name" /proc/cpuinfo | sed -e "s/.*: //" -e "s:\s\+:/:g")"
cloud_id="unknown"
if [ -x /usr/bin/cloud-id ]; then
    /usr/bin/cloud-id > "$CLOUD" 2>/dev/null
    if [ $? -eq 0 ]; then
        # sanitize it a bit, just in case
        cloud_id=$(cut -c -40 "${CLOUD}" | tr -c -d '[:alnum:]')
        if [ -z "${cloud_id}" ]; then
            cloud_id="unknown"
        fi
    fi
fi

# Some messages may only be pertinent before or after some amount of uptime
read up idle < /proc/uptime
uptime="uptime/$up/$idle"

# Piece together the user agent
USER_AGENT="curl/$curl_ver $lsb $platform $cpu $uptime cloud_id/$cloud_id"

# Loop over any configured URLs
for u in $URLS; do
    # Ensure https:// protocol, for security reasons
    case $u in
        https://*)
            true
        ;;
        https://motd.ubuntu.com)
            u="$u/$codename/$arch"
        ;;
        *)
            continue
        ;;
    esac
    # If we're forced, set the wait to much higher (1 minute)
    [ "$FORCED" = "1" ] && WAIT=60
    # Fetch and print the news motd
    if curl --connect-timeout "$WAIT" --max-time "$WAIT" -A "$USER_AGENT" -o- "$u" >"$NEWS" 2>"$ERR"; then
        echo
        # At most, 10 lines of text, remove control characters, print at most 80 characters per line
        safe_print "$NEWS"
        # Try to update the cache
        safe_print "$NEWS" 2>/dev/null >$CACHE || true
    else
        : > "$CACHE"
    fi
done
rm -f "$NEWS" "$ERR" "$CLOUD"
exit 0