scrapyjs 0.1.1

JavaScript support for Scrapy using Splash

This library provides Scrapy+JavaScript integration using Splash. The license is BSD 3-clause.

Installation

Install ScrapyJS using pip:

$ pip install scrapyjs

ScrapyJS uses Splash HTTP API, so you also need a Splash instance. Usually to install & run Splash something like this is enough:

$ docker run -p 8050:8050 scrapinghub/splash

Check Splash install docs for more info.

Scrapy+Splash

To process JavaScript from Scrapy spiders one can use Splash HTTP API directly, without SrapyJS. For example, let’s fetch HTML of a webpage, as returned by a browser:

import json

import scrapy
from scrapy.http.headers import Headers

RENDER_HTML_URL = "http://127.0.0.1:8050/render.html"

class MySpider(scrapy.Spider):
    start_urls = ["http://example.com", "http://example.com/foo"]

    def start_requests(self):
        for url in self.start_urls:
            body = json.dumps({"url": url, "wait": 0.5})
            headers = Headers({'Content-Type': 'application/json'})
            yield scrapy.Request(RENDER_HTML_URL, self.parse, method="POST",
                                 body=body, headers=headers)

    def parse(self, response):
        # response.body is a result of render.html call; it
        # contains HTML processed by a browser.
        # ...

It was easy enough, but the code has some problems:

1. There is a bit of biolerplate.

2. As seen by Scrapy, we’re sending requests to RENDER_HTML_URL instead of the target URLs. It affects concurrency and politeness settings: CONCURRENT_REQUESTS_PER_DOMAIN, DOWNLOAD_DELAY, etc could work in unexpected way as delays and concurrency settings are no longer per-domain.

3. Some options depend on each other - for example, if you use timeout Splash option then you may want to set download_timeout scrapy.Request meta key as well.

ScrapyJS utlities allow to handle such edge cases and reduce the boilerplate.

Configuration

1. Put Splash server address to settings.py of your Scrapy project like this:

   SPLASH_URL = 'http://192.168.59.103:8050'

2. Enable the middleware by adding it to DOWNLOADER_MIDDLEWARES:

   DOWNLOADER_MIDDLEWARES = {
       'scrapyjs.SplashMiddleware': 725,
   }

   Order 725 is just before HttpProxyMiddleware (750) in default scrapy settings.

3. You also have to set a custom DUPEFILTER_CLASS:

   DUPEFILTER_CLASS = 'scrapyjs.SplashAwareDupeFilter'

4. If you use Scrapy HTTP cache then a custom cache storage backend is required. ScrapyJS provides a subclass of scrapy.contrib.httpcache.FilesystemCacheStorage:

   HTTPCACHE_STORAGE = 'scrapyjs.SplashAwareFSCacheStorage'

   If you use other cache storage then it is necesary to subclass it and replace all scrapy.util.request.request_fingerprint calls with scrapyjs.splash_request_fingerprint.

Note

Steps (3) and (4) are necessary because Scrapy doesn’t provide a way to override request fingerprints calculation algorithm globally; this could change in future.

Usage

To render the requests with Splash use ‘splash’ Request meta key:

yield Request(url, self.parse_result, meta={
    'splash': {
        'args': {
            # set rendering arguments here
            'html': 1,
            'png': 1,

            # 'url' is prefilled from request url
        },

        # optional parameters
        'endpoint': 'render.json',  # optional; default is render.json
        'splash_url': '<url>',      # overrides SPLASH_URL
        'slot_policy': scrapyjs.SlotPolicy.PER_DOMAIN,
    }
})

• meta['splash']['args'] contains arguments sent to Splash. ScrapyJS adds request.url to these arguments automatically.

• meta['splash']['endpoint'] is the Splash endpoint to use. By default render.json is used.

  See Splash HTTP API docs for a full list of available endpoints and parameters.

• meta['splash']['splash_url'] allows to override Splash URL set in settings.py.

• meta['splash']['slot_policy'] allows to customize how concurrency & politeness are maintained for Splash requests.

  Currently there are 3 policies available:

  1. scrapyjs.SlotPolicy.PER_DOMAIN (default) - send Splash requests to downloader slots based on URL being rendered. It is useful if you want to maintain per-domain politeness & concurrency settings.

  2. scrapyjs.SlotPolicy.SINGLE_SLOT - send all Splash requests to a single downloader slot. It is useful if you want to throttle requests to Splash.

  3. scrapyjs.SlotPolicy.SCRAPY_DEFAULT - don’t do anything with slots. It is similar to SINGLE_SLOT policy, but can be different if you access other services on the same address as Splash.

Examples

Get HTML contents:

import scrapy

class MySpider(scrapy.Spider):
    start_urls = ["http://example.com", "http://example.com/foo"]

    def start_requests(self):
        for url in self.start_urls:
            yield scrapy.Request(url, self.parse, meta={
                'splash': {
                    'endpoint': 'render.html',
                    'args': {'wait': 0.5}
                }
            })

    def parse(self, response):
        # response.body is a result of render.html call; it
        # contains HTML processed by a browser.
        # ...

Get HTML contents and a screenshot:

import json
import base64
import scrapy

class MySpider(scrapy.Spider):

    # ...
        yield scrapy.Request(url, self.parse_result, meta={
            'splash': {
                'args': {
                    'html': 1,
                    'png': 1,
                    'width': 600,
                    'render_all': 1,
                }
            }
        })

    # ...
    def parse_result(self, response):
        data = json.loads(response.body_as_unicode())
        body = data['html']
        png_bytes = base64.b64decode(data['png'])
        # ...

Run a simple Splash Lua Script:

import json
import base64

class MySpider(scrapy.Spider):

    # ...
        script = """
        function main(splash)
            assert(splash:go(splash.args.url))
            return splash:evaljs("document.title")
        end
        """
        yield scrapy.Request(url, self.parse_result, meta={
            'splash': {
                'args': {'lua_source': script},
                'endpoint': 'execute',
            }
        })

    # ...
    def parse_response(self, response):
        doc_title = response.body_as_unicode()
        # ...

Contributing

Source code and bug tracker are on github: https://github.com/scrapinghub/scrapyjs

To run tests, install “tox” Python package and then run tox command from the source checkout.