pferd/PFERD/http_crawler.py

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import asyncio
from pathlib import PurePath
from typing import Optional
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import aiohttp
from .config import Config
from .crawler import Crawler, CrawlerSection
from .logging import log
from .utils import fmt_real_path
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from .version import NAME, VERSION
class HttpCrawler(Crawler):
COOKIE_FILE = PurePath(".cookies")
def __init__(
self,
name: str,
section: CrawlerSection,
config: Config,
) -> None:
super().__init__(name, section, config)
self._cookie_jar_path = self._output_dir.resolve(self.COOKIE_FILE)
self._output_dir.register_reserved(self.COOKIE_FILE)
self._authentication_id = 0
self._authentication_lock = asyncio.Lock()
self._current_cookie_jar: Optional[aiohttp.CookieJar] = None
self._request_count = 0
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async def _current_auth_id(self) -> int:
"""
Returns the id for the current authentication, i.e. an identifier for the last
successful call to [authenticate].
This method must be called before any request that might authenticate is made, so the
HttpCrawler can properly track when [authenticate] can return early and when actual
authentication is necessary.
"""
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# We acquire the lock here to ensure we wait for any concurrent authenticate to finish.
# This should reduce the amount of requests we make: If an authentication is in progress
# all future requests wait for authentication to complete.
async with self._authentication_lock:
self._request_count += 1
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return self._authentication_id
async def authenticate(self, caller_auth_id: int) -> None:
"""
Starts the authentication process. The main work is offloaded to _authenticate, which
you should overwrite in a subclass if needed. This method should *NOT* be overwritten.
The [caller_auth_id] should be the result of a [_current_auth_id] call made *before*
the request was made. This ensures that authentication is not performed needlessly.
"""
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async with self._authentication_lock:
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# Another thread successfully called authenticate in-between
# We do not want to perform auth again, so we return here. We can
# assume the other thread suceeded as authenticate will throw an error
# if it failed and aborts the crawl process.
if caller_auth_id != self._authentication_id:
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return
await self._authenticate()
self._authentication_id += 1
# Saving the cookies after the first auth ensures we won't need to re-authenticate
# on the next run, should this one be aborted or crash
await self._save_cookies()
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async def _authenticate(self) -> None:
"""
Performs authentication. This method must only return normally if authentication suceeded.
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In all other cases it must either retry internally or throw a terminal exception.
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"""
raise RuntimeError("_authenticate() was called but crawler doesn't provide an implementation")
async def _save_cookies(self) -> None:
log.explain_topic("Saving cookies")
if not self._current_cookie_jar:
log.explain("No cookie jar, save aborted")
return
try:
self._current_cookie_jar.save(self._cookie_jar_path)
log.explain(f"Cookies saved to {fmt_real_path(self._cookie_jar_path)}")
except Exception:
log.warn(f"Failed to save cookies to {fmt_real_path(self._cookie_jar_path)}")
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async def run(self) -> None:
self._current_cookie_jar = aiohttp.CookieJar()
self._request_count = 0
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try:
self._current_cookie_jar.load(self._cookie_jar_path)
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except Exception:
pass
async with aiohttp.ClientSession(
headers={"User-Agent": f"{NAME}/{VERSION}"},
cookie_jar=self._current_cookie_jar,
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) as session:
self.session = session
try:
await super().run()
finally:
del self.session
log.explain_topic(f"Total amount of HTTP requests: {self._request_count}")
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# They are saved in authenticate, but a final save won't hurt
await self._save_cookies()