systemd user-unit file for Minecraft server

minecraft@.service

# ~/.config/systemd/user/minecraft@.service

# Setup:
#	loginctl enable-linger "${USER}"
#	systemctl --user daemon-reload
#	ln -sfv ../../jars/paper.jar /var/minecraft/servers/survival/server.jar
#	systemctl --user enable --now minecraft@"$(systemd-escape /var/minecraft/servers/survival)".service

[Unit]
Description=Minecraft Server (%I)
After=network.target

[Service]
Type=simple
WorkingDirectory=%I
KillSignal=SIGINT
#ExecStart=sh start.sh
ExecStart=java -jar server.jar
SuccessExitStatus=INT SIGINT 130
# https://serverfault.com/a/800631/175102
Restart=always
RestartSec=90
StartLimitIntervalSec=400
StartLimitBurst=3

[Install]
WantedBy=default.target

paper-fetch.py

#!/usr/bin/env python3
import urllib3, json, sys, logging, os, errno, hashlib
# you might need to run one of these first:
#	apt install python3-urllib3
#	python3 -m pip install urllib3
#	python3 -m pip install --user urllib3
#	dnf install python3-urllib3

logging.basicConfig(stream=sys.stderr, level=logging.INFO)
http = urllib3.PoolManager(headers={'user-agent': '"https://gist.github.com/JamesTheAwesomeDude/7a582af73448e330fc7bcfb5efef68d1"/2022.03.15'})

def getjson(url, *, suppress_error=False, http=http):
	r = http.request('GET', url)
	data = json.load(r)
	if not suppress_error:
		if ('error' in data) and (data['error'] is not None):
			raise RuntimeError(data['error'])
		if r.status != 200:
			raise urllib3.exceptions.HTTPError(r.status)
	return data

if len(sys.argv) > 1:
	version = sys.argv[-1]
else:
	version = getjson("https://papermc.io/api/v2/projects/paper")['versions'][-1]
	# this does NOT need to be refactored, I think; it's already sorted:
	# https://github.com/PaperMC/bibliothek/blob/8b388693ee68df59852773f640c98f54e457b275/src/main/java/io/papermc/bibliothek/controller/v2/ProjectController.java#L107

logging.debug(f"version = {version}")

build = getjson(f"https://papermc.io/api/v2/projects/paper/versions/{version}")['builds'][-1]
#TODO: does this need to be refactored? It's unclear whether being-sorted is part of the promise:
# https://github.com/PaperMC/bibliothek/blob/8b388693ee68df59852773f640c98f54e457b275/src/main/java/io/papermc/bibliothek/controller/v2/VersionController.java#L112
logging.debug(f"build = {build}")

application = getjson(f"https://papermc.io/api/v2/projects/paper/versions/{version}/builds/{build}")['downloads']['application']

fname = application['name']
sha256sum_good = application['sha256']

logging.debug(f"sha256 = {sha256sum_good}")

if os.path.exists(fname) and '-f' not in sys.argv:
	raise FileExistsError(errno.EEXIST, os.strerror(errno.EEXIST), fname)

logging.info(f"Downloading version {version}, build #{build} (to {fname})...")
with open(fname + '.part', 'wb') as f,\
     http.request('GET', f"https://papermc.io/api/v2/projects/paper/versions/{version}/builds/{build}/downloads/{fname}", preload_content=False) as r:
	hash = hashlib.sha256()
	for chunk in r.stream():
		f.write(chunk)
		hash.update(chunk)
	sha256sum = hash.hexdigest()

if sha256sum == sha256sum_good:
	logging.info(f"SHA256 OK: {fname} [{sha256sum}]")
	os.replace(fname + '.part', fname)
	print("You should run:\n\tln -svf %s %s\n\tsystemctl --user restart \"minecraft@$(systemd-escape \"${PWD}\").service\"" % (repr(fname), repr('server.jar')))
else:
	raise AssertionError(f"File is corrupted.\nexpected: {sha256sum_good}\ngot:      {sha256sum}")