Script to download CurseForge modpacks

cfpackdl.py

from urllib import request
import argparse
import io
import json
import os
import sys
import time
import urllib
import urllib.parse
import zipfile

def main():
	parser = argparse.ArgumentParser(prog="cfpackdl")
	parser.add_argument(
		"-S", "--skip-on-error",
		action="store_true",
		help="Skip downloading a mod if it fails"
	)
	mode = parser.add_mutually_exclusive_group(required=True)
	mode.add_argument("--url", help="Download and process modpack zip file")
	mode.add_argument("--zip", help="Process a modpack zip you've already downloaded")
	args = parser.parse_args()

	def getZipReader():
		match [args.url, args.zip]:
			case [url, None]:
				if "curseforge.com/api/v1/mods" not in url:
					print('Pack zip URL should look like "https://www.curseforge.com/api/v1/mods/..."')
					print('(copy the manual download link, labeled "try again")')
					raise SystemExit(1)
				print("Downloading pack zip")
				return fetch(url)
			case [None, path]:
				if not os.path.isfile(path):
					print(f"Path {path} doesn't exist, or isn't a regular file")
					raise SystemExit(1)
				print(f"Reading pack from {path}")
				return open(path, "rb")
			case _:
				assert False, "argparse should prevent passing both --url and --zip"

	os.makedirs("mods", exist_ok = True)
	anySkipped = False
	with getZipReader() as rawZip:
		rawZip = io.BytesIO(rawZip.read())
		with zipfile.ZipFile(rawZip) as zip:
			print("Parsing manifest")
			manifest = None
			with zip.open("manifest.json", "r") as f:
				manifest = json.load(f)

			print("Downloading mods")
			for file in manifest["files"]:
				project = file["projectID"]
				file = file["fileID"]
				try:
					filename = downloadJar(project, file)
					print(f"=> downloaded {filename}")
				except Exception as err:
					if not args.skip_on_error:
						raise err
					print(f"=> skipped {filename} (could not download: {err})")
					anySkipped = True

			print("Unzipping config")
			configs = (f for f in zip.namelist() if f.startswith("overrides/"))
			for file in configs:
				path = file.split("/", 1)[1]
				dirname = os.path.dirname(path)
				if dirname != "":
					os.makedirs(os.path.dirname(path), exist_ok = True)
				with zip.open(file, "r") as src:
					with open(path, "wb") as dst:
						pipeFile(src, dst)
				print(f"=> unzipped {path}")

			mcInfo = manifest["minecraft"]
			print(f"\nMinecraft version {mcInfo['version']}")
			print("Recommended modloader version(s):")
			for loader in mcInfo["modLoaders"]:
				print(f"* {loader['id']}")

			print("\nDone!")
			if anySkipped:
				print("Warning: one or more files could not be downloaded!")

headers = {
	"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; rv:117.0) Gecko/20100101 Firefox/117.0"
}
def fetch(url):
	attempts = 5
	for attempt in range(attempts):
		try:
			req = request.Request(url, headers = headers)
			return request.urlopen(req, timeout = 10)
		except urllib.error.URLError as err:
			match err:
				case urllib.error.HTTPError():
					if err.code == 404:
						raise err
				case _:
					match err.reason:
						case TimeoutError():
							pass
						case _:
							raise err
			print(f"retrying... ({err})")
			time.sleep(1 + 2.5 * attempt)
	raise TimeoutError(f"Fetching `{url}` timed out after {attempts} attempts")

def downloadJar(project, file):
	url = f"https://www.curseforge.com/api/v1/mods/{project}/files/{file}/download"
	with fetch(url) as resp:
		(_, filename) = resp.url.rsplit("/", 1)
		# expand percent escapes
		filename = urllib.parse.parse_qsl(f"x={filename}")[0][1]

		path = f"mods/{filename}"
		if os.path.exists(path):
			print("...already downloaded")
			return filename
		with open(f"mods/{filename}", "wb") as f:
			pipeFile(resp, f)
		return filename

pipeBuf = bytearray(64 * 1024)
def pipeFile(src, dst):
	while True:
		len = src.readinto(pipeBuf)
		if len > 0:
			dst.write(pipeBuf[:len])
		else:
			break

if __name__ == "__main__":
	main()