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#!/usr/bin/env python3
# Arch Linux packages proxy
#
# Proxies requests, caching files with ".pkg.tar.*" suffix.
# If the cached file exists, serve that file.
# Otherwise, try to download file (as normally) and optionally cache it with
# ".download" extension. If the file exists and the file is not being
# downloaded, resume the download (Range requests).
import argparse
import http.server
import os
import re
import socket
from datetime import datetime
import requests
from contextlib import closing, contextmanager
import fcntl
DATE_FORMAT = '%a, %d %b %Y %H:%M:%S GMT'
def text_to_epoch(text):
return datetime.strptime(text, DATE_FORMAT).timestamp()
def epoch_to_text(epoch):
return datetime.fromtimestamp(epoch).strftime(DATE_FORMAT)
class BadRequest(Exception):
pass
class RequestHandler(http.server.BaseHTTPRequestHandler):
def send_ok(self, size, headers={}, upstream=None, range_offset=None):
if range_offset is None:
code = 200
else:
if size is None:
raise BadRequest("Content-Length missing in upstream response"
" for range request")
if range_offset >= size:
# TODO need different status code
raise BadRequest("416 Requested Range Not Satisfiable")
code = 206
content_range = "bytes %d-%d/%d" % (range_offset, size - 1, size)
headers["Content-Range"] = content_range
size -= range_offset
self.log_message('"%s" %d %s %s', self.requestline, code, size,
"HIT" if upstream is None else "MISS:%s" % (upstream,))
self.send_response_only(code)
if size is not None:
self.send_header('Content-Length', size)
for k, v in headers.items():
self.send_header(k, v)
self.end_headers()
def request_data(self, head_only=False, mtime_out=None, range_offset=None):
"""
Retrieves the full response body. The given "range_offset" serves only
as hint for the response to the client, it is not used with the upstream
request.
"""
method = "HEAD" if head_only else "GET"
streamable = not head_only
status_code = None
urls = list(self.get_upstream_urls())
# Try each upstream. If one fails, log it and try another. On success,
# return the response data. If all upstreams fail, fail the request.
for i, url in enumerate(urls):
with closing(requests.request(method, url, stream=streamable)) as r:
status_code = r.status_code
if status_code == 200:
yield from self.process_upstream_response(r, head_only,
mtime_out, i, range_offset)
return
self.log_message('"%s" %d - SKIP:%d', self.requestline,
status_code, i)
self.log_request(status_code)
self.send_response_only(status_code)
self.end_headers()
def process_upstream_response(self, r, head_only, mtime_out, upstream,
range_offset):
if r:
response_headers = {}
if 'Last-Modified' in r.headers:
try:
mtime = text_to_epoch(r.headers['Last-Modified'])
response_headers['Last-Modified'] = epoch_to_text(mtime)
if mtime_out:
mtime_out[0] = mtime
except ValueError:
self.log_error("Unable to parse Last-Modified header")
if 'Content-Length' in r.headers:
self.send_ok(int(r.headers['Content-Length']), response_headers,
upstream=upstream, range_offset=range_offset)
else:
self.send_ok(None, response_headers,
upstream=upstream, range_offset=range_offset)
if not head_only:
yield from r.iter_content(4096)
@contextmanager
def open_write_cache(self, path):
if self.server.is_readonly:
yield None
return
temp_path = path + ".download"
try:
with open(temp_path, 'wb') as f:
# Prevent concurrent writers
fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
yield f
except OSError as e:
self.log_error("Failed to create cache file %s: %s", temp_path, e)
yield None
def finish_cache(self, mtime):
path = self.get_local_path()
temp_path = path + ".download"
if mtime:
os.utime(temp_path, times=(mtime, mtime))
try:
os.rename(temp_path, path)
except OSError as e:
self.log_error("Failed to rename %s", temp_path)
try:
os.unlink(temp_path)
except OSError as e:
self.log_error("Failed to remove %s", temp_path)
def parse_range(self):
value = self.headers.get('Range')
if value is not None:
# Only support "continue" range requests, resuming previous
# download. Anything more complex is not needed at the moment.
m = re.match(r'bytes=(?P<from>\d+)-$', value)
if not m:
raise BadRequest("Unsupported range request: %s" % value)
return int(m.group("from"))
@staticmethod
def skip_range_chunk(chunk, skip_bytes):
if skip_bytes:
chunksize = len(chunk)
if chunksize > skip_bytes:
chunk = chunk[skip_bytes:]
skip_bytes = None
else:
chunk = b''
skip_bytes -= chunksize
return chunk, (skip_bytes or None)
@classmethod
def skip_range(cls, it, skip_bytes):
for chunk in it:
chunk, skip_bytes = cls.skip_range_chunk(chunk, skip_bytes)
if chunk:
yield chunk
def request_data_with_cache(self, head_only=False):
range_offset = self.parse_range()
if not self.is_cacheable():
# Not cacheable, directly obtain data and bypass cache
remote_data = self.request_data(range_offset=range_offset)
yield from self.skip_range(remote_data, range_offset)
return
path = self.get_local_path()
try:
# Try to open cached file and yield data from it
stat_info = os.stat(path)
if stat_info.st_size == 0:
# Treat empty files as missing.
raise FileNotFoundError
response_headers = {'Last-Modified':
epoch_to_text(stat_info.st_mtime)}
self.send_ok(stat_info.st_size, response_headers,
range_offset=range_offset)
if not head_only:
with open(path, 'rb') as f:
if range_offset:
f.seek(range_offset)
yield from f
except FileNotFoundError:
# File does not exist, so try to pipe upstream
# (optionally writing to cache file)
mtime_pointer = [None]
remote_data = self.request_data(head_only=head_only,
mtime_out=mtime_pointer, range_offset=range_offset)
if head_only:
list(remote_data) # consume yield and StopIteration
if not head_only and remote_data:
cache_ok = False
with self.open_write_cache(path) as cache_file:
cache_ok = cache_file is not None
if cache_ok:
# Overwrite the temporary cache file from begin to end,
# but do not write include the first "range_offset"
# bytes in the response.
skip = range_offset
for chunk in remote_data:
cache_file.write(chunk)
chunk, skip = self.skip_range_chunk(chunk, skip)
if chunk:
yield chunk
if cache_ok:
# Write was successful, now fix mtime and rename
self.finish_cache(mtime_pointer[0])
else:
# Cache file unavailable, just pass all data
yield from self.skip_range(remote_data, range_offset)
def do_GET(self):
try:
data = self.request_data_with_cache()
if data:
for chunk in data:
self.wfile.write(chunk)
except (BrokenPipeError, ConnectionResetError):
self.log_error("GET %s - (connection aborted)", self.path)
except BadRequest as e:
self.log_error("GET %s - Bad Request: %s", self.path, e)
self.send_response(400)
except Exception as e:
self.log_error("GET %s failed: %s", self.path, e)
import traceback; traceback.print_exc()
self.send_response(502)
def do_HEAD(self):
try:
list(self.request_data_with_cache(True))
except (BrokenPipeError, ConnectionResetError):
self.log_error("HEAD %s - (connection aborted)", self.path)
except BadRequest as e:
self.log_error("HEAD %s - Bad Request: %s", self.path, e)
self.send_response(400)
except Exception as e:
self.log_error("HEAD %s failed: %s", self.path, e)
import traceback; traceback.print_exc()
self.send_response(502)
def get_upstream_urls(self):
# If an old version is requested, retrieve the databases from the
# archive mirror and do not fallback.
if self.server.archive_url and self.is_date_sensitive_request():
yield self.server.archive_url + self.path
return
for prefix in self.server.mirrors:
yield prefix + self.path
def get_local_path(self):
filename = os.path.basename(self.path)
return os.path.join(self.server.cachedir, filename)
def is_cacheable(self):
"""Whether the requested file should be cached."""
# Support .pkg.tar.xz, .pkg.tar.zst, etc.
basename = os.path.splitext(self.path)[0]
return basename.endswith(".pkg.tar")
def is_date_sensitive_request(self):
"""Whether the resource is ephemeral."""
path = self.path
if path.endswith(".sig"):
path = path[:-4]
suffixes = [".db", ".files", ".abs.tar.gz"]
return any(path.endswith(suffix) for suffix in suffixes)
class SomeServer(http.server.HTTPServer):
def __init__(self, addr, handler, args):
self.allow_reuse_address = True
if ':' in addr[0]:
self.address_family = socket.AF_INET6
super().__init__(addr, handler)
self.cachedir = args.cachedir
self.is_readonly = args.readonly
self.mirrors = [m.rstrip('/') for m in args.mirrors]
if not args.date:
self.archive_url = None
else:
archive_mirror = "https://archive.archlinux.org/repos/"
self.archive_url = archive_mirror + args.date
self.mirrors.append(self.archive_url)
def dump_config(self):
yesno = lambda x: "yes" if x else "no"
print("Listen address: %s:%s" % self.socket.getsockname()[:2])
print("Cache directory: %s" % self.cachedir)
print("Read-only cache: %s" % yesno(self.is_readonly))
print("Using archive: %s" % yesno(self.archive_url))
print("Mirrors:")
for mirror in self.mirrors:
print(" %s" % mirror)
def mirror_url(string):
scheme = string.split(":", 1)[0]
if scheme not in ("http", "https"):
raise argparse.ArgumentTypeError("%s is not a valid URL" % string)
return string.rstrip("/") + "/"
def parse_date(string):
m = re.match(r'^(\d{4})([/-]?)(\d{2})\2(\d{2})$', string)
if not m:
raise argparse.ArgumentTypeError("%s is not a valid date" % string)
y, _, m, d = m.groups()
return "%s/%s/%s" % (y, m, d)
parser = argparse.ArgumentParser(
formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument("--readonly", action="store_true",
help="Do not write downloaded results to the cache directory")
parser.add_argument("--cachedir", default=os.getcwd(),
help="Cache directory")
parser.add_argument("--port", type=int, default=8001,
help="Listen port")
parser.add_argument("--date", type=parse_date,
help="Provide a repository snapshot from 'yyyy/mm/dd'")
parser.add_argument("--mirror", dest="mirrors", metavar='URL', nargs="+",
type=mirror_url, default=["https://mirror.nl.leaseweb.net/archlinux"],
help="Mirror list")
if __name__ == '__main__':
args = parser.parse_args()
addr = ('', args.port)
server = SomeServer(addr, RequestHandler, args)
server.dump_config()
server.serve_forever()
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