Sending new release notification (via email) for GitHub repos.

check_release.py

#!/usr/bin/env python3
"""GitHub New Release Checker

./check_release.py path/to/releases.ini

It fetches release tag from GitHub, then comparing it with the
old one in ini file. If tag changed, send a email to configured
address.
"""
import re
import sys
import logging
from smtplib import SMTP
from email.message import EmailMessage
from configparser import ConfigParser
import requests


URL_LATEST_RELEASE = 'https://github.com/{repo}/releases/latest'
RE_REPO_PATH = f'^[^/]+/[^/]+$'
RE_RELEASE_TAG = r'.*/releases/tag/(.*)$'

session = requests.session()

def get_release_tag(repo: str) -> str:
    resp = session.head(URL_LATEST_RELEASE.replace('{repo}', repo))
    location = resp.headers.get('location', '')
    match = re.match(RE_RELEASE_TAG, location)
    if match:
        return match.group(1)

def template_replace(template: str, kvs: dict) -> str:
    for key, value in kvs.items():
        template = template.replace(f'{{{key}}}', f'{value}')
    return template

def main():
    logging.basicConfig(
        level=logging.INFO,
        format='%(levelname)-s: %(message)s'
    )
    if len(sys.argv) != 2:
        print(f'Usage: {sys.argv[0]} path/to/releases.ini', file=sys.stderr)
        sys.exit(1)
    cfgfile = sys.argv[1]
    cfg = ConfigParser()
    cfg.read(cfgfile)

    changes = []
    for repo in cfg.sections():
        if not re.match(RE_REPO_PATH, repo):
            logging.warning('[%s] is not a GitHub repo, ignored.')
            continue
        logging.debug('Checking for %s...', repo)
        tag = get_release_tag(repo)
        if tag is None:
            logging.warning('Fail to get new release tag for %s', repo)
            continue
        old_tag = cfg[repo].get('tag')
        if tag == old_tag:
            logging.info('%s: %s no change', repo, tag)
            continue
        logging.info('%s: %s => %s', repo, old_tag, tag)
        cfg[repo]['tag'] = tag
        changes.append((repo, old_tag, tag))

    if not changes:
        logging.debug('No change, exit.')
        return

    logging.debug('Writing out new tags...')
    with open(cfgfile, 'w') as f:
        cfg.write(f)

    if 'smtp' not in cfg['DEFAULT'] or 'to' not in cfg['DEFAULT']:
        logging.debug('No email configured, exit.')
        return

    with SMTP(cfg['DEFAULT']['smtp']) as smtp:
        logging.debug('Sending email notifications...')
        for repo, old_tag, tag in changes:
            kws = dict(repo=repo, old_tag=old_tag, tag=tag)
            subject = template_replace(cfg['DEFAULT']['subject'], kws)
            content = template_replace(cfg['DEFAULT']['content'], kws)

            msg = EmailMessage()
            msg.set_content(content)
            msg['Subject'] = subject
            msg['From'] = cfg['DEFAULT']['from']
            msg['To'] = cfg['DEFAULT']['to']
            logging.info('Sending "%s"...', subject)
            smtp.send_message(msg)


if __name__ == '__main__':
    main()

release-checker.service

[Unit]
Description=Checking new release on GitHub repo

[Service]
Type=simple
User=EXAMPLE
Group=EXAMPLES
WorkingDirectory=/opt/check-release
ExecStart=/opt/check-release/check_release.py releases.ini

PrivateDevices=True
ProtectHome=True
NoNewPrivileges=True
ProtectSystem=strict
ReadWritePaths=/opt/check-release/releases.ini

release-checker.timer

[Unit]
Description=Checking new release every 3 hours

[Timer]
OnCalendar=00/3:00
RandomizedDelaySec=1h
AccuracySec=1h

[Install]
WantedBy=multi-user.target

releases.ini

[DEFAULT]
smtp = 127.0.0.1
from = Release Checker <releases@example.com>
to = you@example.com
subject = {repo} {tag} released
content = {repo}: {old_tag} => {tag}
    https://github.com/{repo}/releases/tag/{tag}

; add repos below
[tootsuite/mastodon]
[cternes/openkeepass]