how does scrapy-splash handle infinite scrolling?

Question

I want to reverse engineering the contents generated by scrolling down in the webpage. The problem is in the url https://www.crowdfunder.com/user/following_page/80159?user_id=80159&limit=0&per_page=20&screwrand=933. screwrand doesn't seem to follow any pattern, so the reversing the urls don't work. I'm considering the automatic rendering using Splash. How to use Splash to scroll like browsers? Thanks a lot! Here are the codes for two request:

request1 = scrapy_splash.SplashRequest(
    'https://www.crowdfunder.com/user/following/{}'.format(user_id),
     self.parse_follow_relationship,
     args={'wait':2},
     meta={'user_id':user_id, 'action':'following'},
     endpoint='http://192.168.99.100:8050/render.html')

yield request1

request2 = scrapy_splash.SplashRequest(
    'https://www.crowdfunder.com/user/following_user/80159?user_id=80159&limit=0&per_page=20&screwrand=76',
    self.parse_tmp,
    meta={'user_id':user_id, 'action':'following'},
    endpoint='http://192.168.99.100:8050/render.html')

yield request2

ajax request shown in browser console

Answer 1

To scroll a page you can write a custom rendering script (see http://splash.readthedocs.io/en/stable/scripting-tutorial.html), something like this:

function main(splash)
    local num_scrolls = 10
    local scroll_delay = 1.0

    local scroll_to = splash:jsfunc("window.scrollTo")
    local get_body_height = splash:jsfunc(
        "function() {return document.body.scrollHeight;}"
    )
    assert(splash:go(splash.args.url))
    splash:wait(splash.args.wait)

    for _ = 1, num_scrolls do
        scroll_to(0, get_body_height())
        splash:wait(scroll_delay)
    end        
    return splash:html()
end

To render this script use 'execute' endpoint instead of render.html endpoint:

script = """<Lua script> """
scrapy_splash.SplashRequest(url, self.parse,
                            endpoint='execute', 
                            args={'wait':2, 'lua_source': script}, ...)

Answer 2

Thanks Mikhail, I tried your scroll script, and it worked, but I also notice that your script scroll too much one time, some js have no time too render and is skipped, so I do some little change as follow:

function main(splash)
        local num_scrolls = 10
        local scroll_delay = 1

        local scroll_to = splash:jsfunc("window.scrollTo")
        local get_body_height = splash:jsfunc(
            "function() {return document.body.scrollHeight;}"
        )
        assert(splash:go(splash.args.url))
        splash:wait(splash.args.wait)

        for _ = 1, num_scrolls do
            local height = get_body_height()
            for i = 1, 10 do
                scroll_to(0, height * i/10)
                splash:wait(scroll_delay/10)
            end
        end        
        return splash:html()
end