282 lines
7.5 KiB
Python
282 lines
7.5 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 urllib.request
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import urllib.error
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import gzip
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import aiohttp
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import asyncio
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from bs4 import BeautifulSoup
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from urllib.parse import urljoin, urlsplit
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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.uncrawled = set()
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self.crawled = set()
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self.session = aiohttp.ClientSession()
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self.semaphore = asyncio.BoundedSemaphore(concurrency)
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# add the base URL to be crawled
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self.uncrawled.add(baseurl)
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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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def validate_url(self, url):
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'''
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Checks if the discovered URL is local to the base URL.
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'''
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# ensure the URL is in a sane format
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url = sanitise_url(url=url)
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if url.startswith(self.baseurl) and 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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def get_source(self, url):
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'''
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Obtains the page's source.
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'''
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pass
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return source
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def find_links(self, source):
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'''
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Find all links in a page's source.
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'''
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links = set()
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html = BeautifulSoup(source, 'lxml')
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hrefs = html.find_all('a', href=True)
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for href in hrefs:
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url = self.validate_url(url=href)
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if url:
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links.add(url)
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return links
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def run(self):
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'''
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function which runs the crawler
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'''
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pass
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for url in self.uncrawled:
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validated = validate_url(url=url)
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if validated:
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source = get_source(url=url)
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links = find_links(source=source)
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class UrlPool(object):
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'''
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Object to manage a pool of URLs.
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'''
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def __init__(self):
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self.pool = set()
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def check_duplicate(self, new_url):
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'''
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Checks if a URL exists in the current pool.
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'''
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if new_url in self.pool:
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return True
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else:
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return False
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def remove_from_pool(self):
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'''
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Remove a URL from the pool and return it to be crawled.
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'''
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return(self.pool.pop())
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def add_to_pool(self, url):
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self.pool.add(url)
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def list_pool(self):
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pool = self.pool
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return pool
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class WebPage(object):
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'''
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Object to manage common operations required to return
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the data from each individual page.
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'''
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# set a sane user-agent and request compression if available.
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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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def __init__(self, url=None, base_url=None, robots=None):
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self.url = url
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self.base_url = base_url
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self.robots = robots
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self.source = None
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self.urls_to_crawl = set()
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def get_source(self):
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'''
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Retrieve a page's source.
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'''
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request = urllib.request.Request(self.url, headers=self.headers)
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page = urllib.request.urlopen(request, timeout=5)
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# handle the content encoding in case it needs decompressing.
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if 'text/html' in page.info().get('Content-Type'):
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if page.info().get('Content-Encoding'):
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if page.info().get('Content-Encoding') == 'gzip':
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self.source = gzip.decompress(page.read())
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elif page.info().get('Content-Encoding') == 'deflate':
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self.source = page.read()
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else:
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self.source = page.read()
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def find_links(self):
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'''
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Find all URLs on a page and ensure they are absolute. If they are
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relative then they will be appended to the base URL.
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'''
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hrefs = set()
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soup = BeautifulSoup(self.source, 'lxml')
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links = soup.find_all('a', href=True)
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for link in links:
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if link['href'].startswith('/'):
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hrefs.add(urljoin(self.url, link['href']))
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else:
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hrefs.add(link['href'])
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self.discovered_hrefs = hrefs
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def parse_urls(self):
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'''
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Iterate through the list of discovered URLs and add them to the
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pool if they start with the base URL.
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'''
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for url in self.discovered_hrefs:
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if url.startswith(self.base_url) and self.robots.check(url):
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sanitised_url = sanitise_url(url=url)
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self.urls_to_crawl.add(sanitised_url)
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def list_urls(self):
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'''
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Returns all valid discovered URLs.
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'''
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return self.urls_to_crawl
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def run(self):
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'''
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Attempt to get the page's source and if successful, iterate through it
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to find any links we can crawl.
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'''
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try:
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self.get_source()
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except Exception:
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# skip if we didn't retrieve the source.
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pass
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if self.source:
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self.find_links()
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self.parse_urls()
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return True
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else:
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return False
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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.
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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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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 sanitise_url(url, base_url=False):
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'''
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If `base_url` is True, we attempt to standardise `url` to ensure it can be
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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 False, we sanitise URLs to strip queries and fragments (we
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don't want to scrape in-page anchors etc).
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Returns a sanitised URL as a string.
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'''
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default_proto = 'http'
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delim = '://'
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split_url = urlsplit(url)
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if base_url:
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# This will sanitise the initial url for the initial page crawl.
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if split_url.scheme and split_url.scheme.startswith('http'):
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sanitised_url = "".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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sanitised_url = "".join([default_proto, delim, split_url.path])
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else:
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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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sanitised_url = "".join([split_url.scheme, delim, split_url.netloc, split_url.path])
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return sanitised_url
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