How does Scrapy automatically log in during the crawling process?

How does Scrapy automatically log in during the crawling process?

When crawling website data, some websites require user login authentication to browse specific pages or obtain more data. At the same time, for some data that can only be obtained after logging in, crawler engineers often use some automated operations to simulate logging in to the website to collect crawler data. In this article, we will detail how to implement automatic login functionality in Scrapy.

1. Create login spider

Create a new spider and name it "login_spider". The purpose of this spider is to complete the simulated login work, that is, to complete the user login work before the crawler starts.

2. Create login form

Find the form on the login page and view the html code of the form.
Find the fields that need to be filled in (name attribute), such as "username", "password", etc., and copy them.
Use the Selector method to find the input tags corresponding to these fields, use the extract() method to obtain their values, and assign them to the corresponding key values.

    def parse(self,response):
        return scrapy.FormRequest.from_response(
            response,
            formdata={'username': 'your_username', 'password': 'your_password'},
            callback=self.start_scraping
        )

3. Write the callback function when the login spider starts running

What the login callback function here does is to obtain the cookie through the response with the login Token value, construct a new Request object and pass the cookie (header) value for use by subsequent business spiders.

    def start_scraping(self, response):
        # Get CSRF token
        token = response.css('input[name="csrf_token"]::attr(value)').extract_first()
        logging.info('CSRF token obtained: ' + token)

        # Create cookie dict
        cookie = response.headers.getlist('Set-Cookie')
        cookie = [str(c, 'utf-8') for c in cookie]
        cookie_dict = {
            str(c.split('; ')[0].split('=')[0]): str(c.split('; ')[0].split('=')[1])
            for c in cookie
        }

        # Store cookie dict in spider settings
        self.settings.set('COOKIE_DICT', cookie_dict, priority='cmdline')

        # Start scraping main website
        yield scrapy.Request(
            url='https://www.example.com/your/start/url/',
            callback=self.parse_homepage,
            headers={'Cookie': cookie}
        )

4. Use cookies to issue requests with user information

After logging in to the spider, call the start_requests method to send the first Request. Get the value of cookie_dict stored in the previous step from settings and pass it to the crawler using the headers parameter.

    def start_requests(self):
        cookie = self.settings.get('COOKIE_DICT')
        yield scrapy.Request(
            url='https://www.example.com/your/start/url/',
            callback=self.parse_homepage,
            headers={'Cookie': cookie},
            meta={'login': True}
        )

5. Create business spider

Use cookie information to access the real target page after login. In the customization of the business spider, all involved URLs that need to obtain cookie information are accessed using cookie information. The following is a simple business spider code

    class MySpider(scrapy.Spider):
    name = 'myspider'

    def start_requests(self):
        yield scrapy.Request('https://www.example.com/real-target-url/', callback=self.parse, headers={'Cookie': self.settings.get('COOKIE_DICT')})

    def parse(self, response):
        # Do whatever you want with the authenticated response

Through the above steps, we can use the Scrapy framework to implement the simulated login function. By carrying the cookie value, Scrapy can continue to capture data that requires login verification without logging out. Although there may be security issues in doing so, this solution is feasible when learning crawlers and conducting research for academic purposes.

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