225 lines
7.1 KiB
Python
225 lines
7.1 KiB
Python
#!/usr/bin/env python
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'''
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Utilities to provide various misc functions.
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'''
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import aiohttp
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import asyncio
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from bs4 import BeautifulSoup
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import urllib.error
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from urllib.parse import urljoin, urlsplit
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import urllib.request
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import urllib.robotparser
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class AsyncCrawler(object):
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'''
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docstring
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'''
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def __init__(self, baseurl=None, robots=None, concurrency=None):
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self.baseurl = baseurl
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self.robots = robots
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self.crawled = set()
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self.headers = {'Accept-Encoding': 'gzip, deflate',
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'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/61.0'}
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self.client_session = None
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self.semaphore = asyncio.BoundedSemaphore(concurrency)
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async def crawl_url(self, url=None):
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'''
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Crawls the given URL and finds all new URLs in the initial page.
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'''
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urls = []
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source = await self.get_source(url)
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if source:
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urls = self.find_all_urls(source)
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return urls
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def validate_url(self, url=None):
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'''
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Ensures we have a valid URL to crawl and that the site's robots.txt
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allows it.
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'''
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# ensure the URL is in a sane format
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url = standardise_url(url=url, base_url=self.baseurl)
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if url and self.robots.check(url=url):
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return url
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else:
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return False
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async def get_source(self, url=None):
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'''
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Obtains the URL's source, provided it is HTML. Usage of semaphores
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ensures only a certain number of coroutines can run at once.
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'''
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async with self.semaphore:
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async with self.client_session.head(url, timeout=5) as head:
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try:
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data = await head.read()
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except Exception as e:
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print(e)
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if 'text/html' in head.headers['Content-Type']:
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async with self.client_session.get(url, timeout=5) as resp:
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try:
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source = await resp.read()
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return source
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except Exception:
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return None
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def find_all_urls(self, source=None):
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'''
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Find all URLs in a page's source. Returns a list of URLs which have
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been validated as local to the starting URL.
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'''
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urls = []
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html = BeautifulSoup(source, 'lxml')
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hrefs = html.find_all('a', href=True)
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# build a set of URLs which are valid and haven't been crawled yet
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for href in hrefs:
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url = self.validate_url(url=href['href'])
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if url and url not in self.crawled:
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urls.append(url)
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return urls
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async def run(self, urls=None):
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'''
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Crawls a batch of URLs of any size (resource usage is bounded by n
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semaphores (where n = concurrency). Returns a set of URLs to be added
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to the list of URLs which need to be crawled (find_all_urls only returns
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unseen URLs).
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'''
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tasks = []
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all_urls = set()
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for url in urls:
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# mark the URL as seen.
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self.crawled.add(url)
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# create an coroutine to crawl the URL.
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tasks.append(self.crawl_url(url))
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# wait for all tasks to complete.
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for task in asyncio.as_completed(tasks):
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urls = None
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try:
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# completed.append((await task))
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urls = await task
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except Exception as e:
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print(e)
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# add the URLs to a set to be returned.
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if urls:
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for url in urls:
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print('Found: {0}'.format(url))
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all_urls.add(url)
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return all_urls
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async def main(self):
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'''
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Runs a crawl with batches of URLs. Once complete returns a list of all
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crawled URLs.
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'''
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self.client_session = aiohttp.ClientSession(headers=self.headers)
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to_crawl = []
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to_crawl.append(self.baseurl)
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print('Crawling: {0}'.format(self.baseurl))
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while len(to_crawl) > 0:
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discovered_urls = await self.run(urls=to_crawl)
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# empty toe crawl list and then add all newly discovered URLs for
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# the next iteration.
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to_crawl.clear()
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to_crawl.extend(discovered_urls)
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# close the ssions once all URLs have been crawled.
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await self.client_session.close()
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return self.crawled
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class RobotsTxt(object):
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'''
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needs a docstring
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'''
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def __init__(self, base_url=None):
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'''
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Manually retrieve robots.txt to allow us to set the user-agent (works
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around sites which disallow access to robots.txt without a sane
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user-agent).
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'''
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self.base_url = base_url
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self.headers = {'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/61.0'}
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robots_url = urljoin(self.base_url, 'robots.txt')
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request = urllib.request.Request(robots_url, headers=self.headers)
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robots = urllib.robotparser.RobotFileParser()
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robots.set_url(robots_url)
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try:
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response = urllib.request.urlopen(request, timeout=5)
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except urllib.error.HTTPError:
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# if robots.txt doesn't exist then allow all URLs to be crawled.
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robots.allow_all = True
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else:
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data = response.read()
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decoded_data = data.decode("utf-8").splitlines()
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robots.parse(decoded_data)
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self.robots = robots
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def check(self, url):
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'''
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Test if robots allows us to crawl that URL.
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'''
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return self.robots.can_fetch("*", url)
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def standardise_url(url=None, base_url=None):
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'''
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If `base_url` is None then we attempt to standarise the URL to ensure it can
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be prepended to relative URLs. If no scheme has been provided then we default
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to http as any sane https-only site should 301 redirect http > https.
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If `base_url` is set, we standardise URLs to strip queries and fragments (we
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don't want to scrape in-page anchors etc). Any relative URLs will be appended
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to the base url.
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Returns a standardised URL as a string.
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'''
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default_proto = 'http'
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delim = '://'
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file_extensions = ('/', 'htm', 'html', 'xhtml', 'php', 'asp', 'aspx', 'cfm')
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split_url = urlsplit(url)
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if not base_url:
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# This will sanitise the initial url provided by the user.
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if split_url.scheme and split_url.scheme.startswith('http'):
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return "".join([split_url.scheme, delim, split_url.netloc])
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elif (split_url.path and not split_url.scheme and not split_url.netloc):
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return "".join([default_proto, delim, split_url.path])
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else:
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# if url.endswith(file_extensions):
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# Sanitise discovered URLs. We already expect them in the format
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# protocol://base_url/path
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if url.startswith('/'):
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return urljoin(base_url, split_url.path)
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elif url.startswith(base_url):
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return "".join([split_url.scheme, delim, split_url.netloc, split_url.path])
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return None
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