Scrapy & JavaScript integration through Splash
This library provides Scrapy and JavaScript integration using Splash. The license is BSD 3-clause.
Installation
Install scrapy-splash using pip:
$ pip install scrapy-splash
Scrapy-Splash 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.
Configuration
Add the Splash server address to
settings.py
of your Scrapy project like this:SPLASH_URL = 'http://192.168.59.103:8050'
Enable the Splash middleware by adding it to
DOWNLOADER_MIDDLEWARES
in yoursettings.py
file and changing HttpCompressionMiddleware priority:DOWNLOADER_MIDDLEWARES = { 'scrapy_splash.SplashCookiesMiddleware': 723, 'scrapy_splash.SplashMiddleware': 725, 'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware': 810, }
Order 723 is just before HttpProxyMiddleware (750) in default scrapy settings.
HttpCompressionMiddleware priority should be changed in order to allow advanced response processing; see scrapy/scrapy#1895 for details.
Enable
SplashDeduplicateArgsMiddleware
by adding it toSPIDER_MIDDLEWARES
in yoursettings.py
:SPIDER_MIDDLEWARES = { 'scrapy_splash.SplashDeduplicateArgsMiddleware': 100, }
This middleware is needed to support
cache_args
feature; it allows to save disk space by not storing duplicate Splash arguments multiple times in a disk request queue. If Splash 2.1+ is used the middleware also allows to save network traffic by not sending these duplicate arguments to Splash server multiple times.Set a custom
DUPEFILTER_CLASS
:DUPEFILTER_CLASS = 'scrapy_splash.SplashAwareDupeFilter'
If you use Scrapy HTTP cache then a custom cache storage backend is required. scrapy-splash provides a subclass of
scrapy.contrib.httpcache.FilesystemCacheStorage
:HTTPCACHE_STORAGE = 'scrapy_splash.SplashAwareFSCacheStorage'
If you use other cache storage then it is necesary to subclass it and replace all
scrapy.util.request.request_fingerprint
calls withscrapy_splash.splash_request_fingerprint
.
Note
Steps (4) and (5) are necessary because Scrapy doesn't provide a way to override request fingerprints calculation algorithm globally; this could change in future.
There are also some additional options available.
Put them into your settings.py
if you want to change the defaults:
SPLASH_COOKIES_DEBUG
isFalse
by default. Set toTrue
to enable debugging cookies in theSplashCookiesMiddleware
. This option is similar toCOOKIES_DEBUG
for the built-in scarpy cookies middleware: it logs sent and received cookies for all requests.SPLASH_LOG_400
isTrue
by default - it instructs to log all 400 errors from Splash. They are important because they show errors occurred when executing the Splash script. Set it toFalse
to disable this logging.SPLASH_SLOT_POLICY
isscrapy_splash.SlotPolicy.PER_DOMAIN
by default. It specifies how concurrency & politeness are maintained for Splash requests, and specify the default value forslot_policy
argument forSplashRequest
, which is described below.
Usage
Requests
The easiest way to render requests with Splash is to
use scrapy_splash.SplashRequest
:
yield SplashRequest(url, self.parse_result, args={ # optional; parameters passed to Splash HTTP API 'wait': 0.5, # 'url' is prefilled from request url # 'http_method' is set to 'POST' for POST requests # 'body' is set to request body for POST requests }, endpoint='render.json', # optional; default is render.html splash_url='<url>', # optional; overrides SPLASH_URL slot_policy=scrapy_splash.SlotPolicy.PER_DOMAIN, # optional )
Alternatively, you can use regular scrapy.Request and
'splash'
Request meta key:
yield scrapy.Request(url, self.parse_result, meta={ 'splash': { 'args': { # set rendering arguments here 'html': 1, 'png': 1, # 'url' is prefilled from request url # 'http_method' is set to 'POST' for POST requests # 'body' is set to request body for POST requests }, # optional parameters 'endpoint': 'render.json', # optional; default is render.json 'splash_url': '<url>', # optional; overrides SPLASH_URL 'slot_policy': scrapy_splash.SlotPolicy.PER_DOMAIN, 'splash_headers': {}, # optional; a dict with headers sent to Splash 'dont_process_response': True, # optional, default is False 'dont_send_headers': True, # optional, default is False 'magic_response': False, # optional, default is True } })
Use request.meta['splash']
API in middlewares or when scrapy.Request
subclasses are used (there is also SplashFormRequest
described below).
For example, meta['splash']
allows to create a middleware which enables
Splash for all outgoing requests by default.
SplashRequest
is a convenient utility to fill request.meta['splash']
;
it should be easier to use in most cases. For each request.meta['splash']
key there is a corresponding SplashRequest
keyword argument: for example,
to set meta['splash']['args']
use SplashRequest(..., args=myargs)
.
meta['splash']['args']
contains arguments sent to Splash. scrapy-splash adds some default keys/values toargs
:- 'url' is set to request.url;
- 'http_method' is set to 'POST' for POST requests;
- 'body' is set to to request.body for POST requests.
You can override default values by setting them explicitly.
Note that by default Scrapy escapes URL fragments using AJAX escaping scheme. If you want to pass a URL with a fragment to Splash then set
url
inargs
dict manually. This is handled automatically if you useSplashRequest
, but you need to keep that in mind if you use rawmeta['splash']
API.Splash 1.8+ is required to handle POST requests; in earlier Splash versions 'http_method' and 'body' arguments are ignored. If you work with
/execute
endpoint and want to support POST requests you have to handlehttp_method
andbody
arguments in your Lua script manually.meta['splash']['cache_args']
is a list of argument names to cache on Splash side. These arguments are sent to Splash only once, then cached values are used; it allows to save network traffic and decreases request queue disk memory usage. Usecache_args
only for large arguments which don't change with each request;lua_source
is a good candidate (if you don't use string formatting to build it). Splash 2.1+ is required for this feature to work.meta['splash']['endpoint']
is the Splash endpoint to use. In case of SplashRequest render.html is used by default. If you're using raw scrapy.Request then render.json is a default (for historical reasons). It is better to always pass endpoint explicitly.See Splash HTTP API docs for a full list of available endpoints and parameters.
meta['splash']['splash_url']
overrides the Splash URL set insettings.py
.meta['splash']['splash_headers']
allows to add or change headers which are sent to Splash server. Note that this option is not for setting headers which are sent to the remote website.meta['splash']['slot_policy']
customize how concurrency & politeness are maintained for Splash requests.Currently there are 3 policies available:
scrapy_splash.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.scrapy_splash.SlotPolicy.SINGLE_SLOT
- send all Splash requests to a single downloader slot. It is useful if you want to throttle requests to Splash.scrapy_splash.SlotPolicy.SCRAPY_DEFAULT
- don't do anything with slots. It is similar toSINGLE_SLOT
policy, but can be different if you access other services on the same address as Splash.
meta['splash']['dont_process_response']
- when set to True, SplashMiddleware won't change the response to a custom scrapy.Response subclass. By default for Splash requests one of SplashResponse, SplashTextResponse or SplashJsonResponse is passed to the callback.meta['splash']['dont_send_headers']
: by default scrapy-splash passes request headers to Splash in 'headers' JSON POST field. For all render.xxx endpoints it means Scrapy header options are respected by default (http://splash.readthedocs.org/en/stable/api.html#arg-headers). In Lua scripts you can useheaders
argument ofsplash:go
to apply the passed headers:splash:go{url, headers=splash.args.headers}
.Set 'dont_send_headers' to True if you don't want to pass
headers
to Splash.meta['splash']['http_status_from_error_code']
- set response.status to HTTP error code whenassert(splash:go(..))
fails; it requiresmeta['splash']['magic_response']=True
.http_status_from_error_code
option is False by default if you use raw meta API; SplashRequest sets it to True by default.meta['splash']['magic_response']
- when set to True and a JSON response is received from Splash, several attributes of the response (headers, body, url, status code) are filled using data returned in JSON:- response.headers are filled from 'headers' keys;
- response.url is set to the value of 'url' key;
- response.body is set to the value of 'html' key, or to base64-decoded value of 'body' key;
- response.status is set to the value of 'http_status' key.
When
meta['splash']['http_status_from_error_code']
is True andassert(splash:go(..))
fails with an HTTP error response.status is also set to HTTP error code.
This option is set to True by default if you use SplashRequest.
render.json
andexecute
endpoints may not have all the necessary keys/values in the response. For non-JSON endpoints, only url is filled, regardless of themagic_response
setting.
Use scrapy_splash.SplashFormRequest
if you want to make a FormRequest
via splash. It accepts the same arguments as SplashRequest
,
and also formdata
, like FormRequest
from scrapy:
>>> SplashFormRequest('http://example.com', formdata={'foo': 'bar'}) <POST http://example.com>
SplashFormRequest.from_response
is also supported, and works as described
in scrapy documentation.
Responses
scrapy-splash returns Response subclasses for Splash requests:
- SplashResponse is returned for binary Splash responses - e.g. for /render.png responses;
- SplashTextResponse is returned when the result is text - e.g. for /render.html responses;
- SplashJsonResponse is returned when the result is a JSON object - e.g. for /render.json responses or /execute responses when script returns a Lua table.
To use standard Response classes set meta['splash']['dont_process_response']=True
or pass dont_process_response=True
argument to SplashRequest.
All these responses set response.url
to the URL of the original request
(i.e. to the URL of a website you want to render), not to the URL of the
requested Splash endpoint. "True" URL is still available as
response.real_url
.
SplashJsonResponse provide extra features:
response.data
attribute contains response data decoded from JSON; you can access it likeresponse.data['html']
.- If Splash session handling is configured, you can access current cookies
as
response.cookiejar
; it is a CookieJar instance. - If Scrapy-Splash response magic is enabled in request (default),
several response attributes (headers, body, url, status code)
are set automatically from original response body:
- response.headers are filled from 'headers' keys;
- response.url is set to the value of 'url' key;
- response.body is set to the value of 'html' key, or to base64-decoded value of 'body' key;
- response.status is set from the value of 'http_status' key.
When respone.body
is updated in SplashJsonResponse
(either from 'html' or from 'body' keys) familiar response.css
and response.xpath
methods are available.
To turn off special handling of JSON result keys either set
meta['splash']['magic_response']=False
or pass magic_response=False
argument to SplashRequest.
Session Handling
Splash itself is stateless - each request starts from a clean state. In order to support sessions the following is required:
- client (Scrapy) must send current cookies to Splash;
- Splash script should make requests using these cookies and update them from HTTP response headers or JavaScript code;
- updated cookies should be sent back to the client;
- client should merge current cookies wiht the updated cookies.
For (2) and (3) Splash provides splash:get_cookies()
and
splash:init_cookies()
methods which can be used in Splash Lua scripts.
scrapy-splash provides helpers for (1) and (4): to send current cookies
in 'cookies' field and merge cookies back from 'cookies' response field
set request.meta['splash']['session_id']
to the session
identifier. If you only want a single session use the same session_id
for
all request; any value like '1' or 'foo' is fine.
For scrapy-splash session handling to work you must use /execute
endpoint
and a Lua script which accepts 'cookies' argument and returns 'cookies'
field in the result:
function main(splash) splash:init_cookies(splash.args.cookies) -- ... your script return { cookies = splash:get_cookies(), -- ... other results, e.g. html } end
SplashRequest sets session_id
automatically for /execute
endpoint,
i.e. cookie handling is enabled by default if you use SplashRequest,
/execute
endpoint and a compatible Lua rendering script.
If you want to start from the same set of cookies, but then 'fork' sessions
set request.meta['splash']['new_session_id']
in addition to
session_id
. Request cookies will be fetched from cookiejar session_id
,
but response cookies will be merged back to the new_session_id
cookiejar.
Standard Scrapy cookies
argument can be used with SplashRequest
to add cookies to the current Splash cookiejar.
Examples
Get HTML contents:
import scrapy from scrapy_splash import SplashRequest class MySpider(scrapy.Spider): start_urls = ["http://example.com", "http://example.com/foo"] def start_requests(self): for url in self.start_urls: yield SplashRequest(url, self.parse, 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 from scrapy_splash import SplashRequest class MySpider(scrapy.Spider): # ... splash_args = { 'html': 1, 'png': 1, 'width': 600, 'render_all': 1, } yield SplashRequest(url, self.parse_result, endpoint='render.json', args=splash_args) # ... def parse_result(self, response): # magic responses are turned ON by default, # so the result under 'html' key is available as response.body html = response.body # you can also query the html result as usual title = response.css('title').extract_first() # full decoded JSON data is available as response.data: png_bytes = base64.b64decode(response.data['png']) # ...
Run a simple Splash Lua Script:
import json import base64 from scrapy_splash import SplashRequest class MySpider(scrapy.Spider): # ... script = """ function main(splash) assert(splash:go(splash.args.url)) return splash:evaljs("document.title") end """ yield SplashRequest(url, self.parse_result, endpoint='execute', args={'lua_source': script}) # ... def parse_result(self, response): doc_title = response.body_as_unicode() # ...
More complex Splash Lua Script example - get a screenshot of an HTML element by its CSS selector (it requires Splash 2.1+). Note how are arguments passed to the script:
import json import base64 from scrapy_splash import SplashRequest script = """ -- Arguments: -- * url - URL to render; -- * css - CSS selector to render; -- * pad - screenshot padding size. -- this function adds padding around region function pad(r, pad) return {r[1]-pad, r[2]-pad, r[3]+pad, r[4]+pad} end -- main script function main(splash) -- this function returns element bounding box local get_bbox = splash:jsfunc([[ function(css) { var el = document.querySelector(css); var r = el.getBoundingClientRect(); return [r.left, r.top, r.right, r.bottom]; } ]]) assert(splash:go(splash.args.url)) assert(splash:wait(0.5)) -- don't crop image by a viewport splash:set_viewport_full() local region = pad(get_bbox(splash.args.css), splash.args.pad) return splash:png{region=region} end """ class MySpider(scrapy.Spider): # ... yield SplashRequest(url, self.parse_element_screenshot, endpoint='execute', args={ 'lua_source': script, 'pad': 32, 'css': 'a.title' } ) # ... def parse_element_screenshot(self, response): image_data = response.body # binary image data in PNG format # ...
Use a Lua script to get an HTML response with cookies, headers, body
and method set to correct values; lua_source
argument value is cached
on Splash server and is not sent with each request (it requires Splash 2.1+):
import scrapy from scrapy_splash import SplashRequest script = """ function main(splash) splash:init_cookies(splash.args.cookies) assert(splash:go{ splash.args.url, headers=splash.args.headers, http_method=splash.args.http_method, body=splash.args.body, }) assert(splash:wait(0.5)) local entries = splash:history() local last_response = entries[#entries].response return { url = splash:url(), headers = last_response.headers, http_status = last_response.status, cookies = splash:get_cookies(), html = splash:html(), } end """ class MySpider(scrapy.Spider): # ... yield SplashRequest(url, self.parse_result, endpoint='execute', cache_args=['lua_source'], args={'lua_source': script}, headers={'X-My-Header': 'value'}, ) def parse_result(self, response): # here response.body contains result HTML; # response.headers are filled with headers from last # web page loaded to Splash; # cookies from all responses and from JavaScript are collected # and put into Set-Cookie response header, so that Scrapy # can remember them.
HTTP Basic Auth
If you need HTTP Basic Authentication to access Splash, use Scrapy's HttpAuthMiddleware.
Another option is meta['splash']['splash_headers']
: it allows to set
custom headers which are sent to Splash server; add Authorization header
to splash_headers
if HttpAuthMiddleware doesn't fit for some reason.
Why not use the Splash HTTP API directly?
The obvious alternative to scrapy-splash would be to send requests directly to the Splash HTTP API. Take a look at the example below and make sure to read the observations after it:
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}, sort_keys=True) 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 works and is easy enough, but there are some issues that you should be aware of:
- There is a bit of boilerplate.
- 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 behave in unexpected ways since delays and concurrency settings are no longer per-domain. - As seen by Scrapy, response.url is an URL of the Splash server.
scrapy-splash fixes it to be an URL of a requested page.
"Real" URL is still available as
response.real_url
. - 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. - It is easy to get it subtly wrong - e.g. if you won't use
sort_keys=True
argument when preparing JSON body then binary POST body content could vary even if all keys and values are the same, and it means dupefilter and cache will work incorrectly. - Default Scrapy duplication filter doesn't take Splash specifics in account. For example, if an URL is sent in a JSON POST request body Scrapy will compute request fingerprint without canonicalizing this URL.
- Splash Bad Request (HTTP 400) errors are hard to debug because by default
response content is not displayed by Scrapy. SplashMiddleware logs content
of HTTP 400 Splash responses by default (it can be turned off by setting
SPLASH_LOG_400 = False
option). - Cookie handling is tedious to implement, and you can't use Scrapy built-in Cookie middleware to handle cookies when working with Splash.
- Large Splash arguments which don't change with every request
(e.g.
lua_source
) may take a lot of space when saved to Scrapy disk request queues.scrapy-splash
provides a way to store such static parameters only once. - Splash 2.1+ provides a way to save network traffic by caching large
static arguments on server, but it requires client support: client should
send proper
save_args
andload_args
values and handle HTTP 498 responses.
scrapy-splash utlities allow to handle such edge cases and reduce the boilerplate.
Contributing
Source code and bug tracker are on github: https://github.com/scrapy-plugins/scrapy-splash
To run tests, install "tox" Python package and then run tox
command
from the source checkout.