RomanNum3ral
/
scrapy
mirror of https://github.com/scrapy/scrapy.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity
scrapy/docs/topics/downloader-middleware.rst

14 KiB
Raw Blame History

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> </head>

Downloader Middleware

The downloader middleware is a framework of hooks into Scrapy's request/response processing. It's a light, low-level system for globally altering Scrapy's requests and responses.

Activating a downloader middleware

To activate a downloader middleware component, add it to the :setting:`DOWNLOADER_MIDDLEWARES` setting, which is a dict whose keys are the middleware class paths and their values are the middleware orders.

System Message: ERROR/3 (<stdin>, line 16); backlink

Unknown interpreted text role "setting".

Here's an example:

DOWNLOADER_MIDDLEWARES = {
    'myproject.middlewares.CustomDownloaderMiddleware': 543,
}

The :setting:`DOWNLOADER_MIDDLEWARES` setting is merged with the :setting:`DOWNLOADER_MIDDLEWARES_BASE` setting defined in Scrapy (and not meant to be overridden) and then sorted by order to get the final sorted list of enabled middlewares: the first middleware is the one closer to the engine and the last is the one closer to the downloader.

System Message: ERROR/3 (<stdin>, line 26); backlink

Unknown interpreted text role "setting".

System Message: ERROR/3 (<stdin>, line 26); backlink

Unknown interpreted text role "setting".

To decide which order to assign to your middleware see the :setting:`DOWNLOADER_MIDDLEWARES_BASE` setting and pick a value according to where you want to insert the middleware. The order does matter because each middleware performs a different action and your middleware could depend on some previous (or subsequent) middleware being applied.

System Message: ERROR/3 (<stdin>, line 32); backlink

Unknown interpreted text role "setting".

If you want to disable a builtin middleware (the ones defined in :setting:`DOWNLOADER_MIDDLEWARES_BASE` and enabled by default) you must define it in your project :setting:`DOWNLOADER_MIDDLEWARES` setting and assign None as its value. For example, if you want to disable the off-site middleware:

System Message: ERROR/3 (<stdin>, line 38); backlink

Unknown interpreted text role "setting".

System Message: ERROR/3 (<stdin>, line 38); backlink

Unknown interpreted text role "setting".
DOWNLOADER_MIDDLEWARES = {
    'myproject.middlewares.CustomDownloaderMiddleware': 543,
    'scrapy.contrib.downloadermiddleware.useragent.UserAgentMiddleware': None,
}

Finally, keep in mind that some middlewares may need to be enabled through a particular setting. See each middleware documentation for more info.

Writing your own downloader middleware

Writing your own downloader middleware is easy. Each middleware component is a single Python class that defines one or more of the following methods:

System Message: ERROR/3 (<stdin>, line 57)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware

System Message: ERROR/3 (<stdin>, line 61)

Unknown directive type "method".

.. method:: process_request(request, spider)

   This method is called for each request that goes through the download
   middleware.

   :meth:`process_request` should return either ``None``, a
   :class:`~scrapy.http.Response` object, or a :class:`~scrapy.http.Request`
   object.

   If returns ``None``, Scrapy will continue processing this request, executing all
   other middlewares until, finally, the appropriate downloader handler is called
   the request performed (and its response downloaded).

   If returns a :class:`~scrapy.http.Response` object, Scrapy won't bother
   calling ANY other request or exception middleware, or the appropriate
   download function; it'll return that Response. Response middleware is
   always called on every response.

   If returns a :class:`~scrapy.http.Request` object, the returned request will be
   re-scheduled (in the Scheduler) to be downloaded in the future. The callback of
   the original request will always be called. If the new request has a callback
   it will be called with the response downloaded, and the output of that callback
   will then be passed to the original callback. If the new request doesn't have a
   callback, the response downloaded will be just passed to the original request
   callback.

   If returns an :exc:`~scrapy.core.exceptions.IgnoreRequest` exception, the
   entire request will be dropped completely and its callback never called.

   :param request: the request being processed
   :type request: :class:`~scrapy.http.Request` object

   :param spider: the spider for which this request is intended
   :type spider: :class:`~scrapy.spider.BaseSpider` object

System Message: ERROR/3 (<stdin>, line 96)

Unknown directive type "method".

.. method:: process_response(request, response, spider)

   meth:`process_response` should return a :class:`~scrapy.http.Response`
   object or raise a :exc:`~scrapy.core.exceptions.IgnoreRequest` exception.

   If returns a :class:`~scrapy.http.Response` (it could be the same given
   response, or a brand-new one) that response will continue to be processed
   with the :meth:`process_response` of the next middleware in the pipeline.

   If returns an :exc:`~scrapy.core.exceptions.IgnoreRequest` exception, the
   response will be dropped completely and its callback never called.

   :param request: the request that originated the response
   :type request: is a :class:`~scrapy.http.Request` object

   :param reponse: the response being processed
   :type response: :class:`~scrapy.http.Response` object

   :param spider: the spider for which this response is intended
   :type spider: :class:`~scrapy.spider.BaseSpider` object

System Message: ERROR/3 (<stdin>, line 117)

Unknown directive type "method".

.. method:: process_download_exception(request, exception, spider)

   Scrapy calls :meth:`process_download_exception` when a download handler
   or a :meth:`process_request` (from a downloader middleware) raises an
   exception.

   :meth:`process_download_exception` should return either ``None``,
   :class:`~scrapy.http.Response` or :class:`~scrapy.http.Request` object.

   If it returns ``None``, Scrapy will continue processing this exception,
   executing any other exception middleware, until no middleware is left and
   the default exception handling kicks in.

   If it returns a :class:`~scrapy.http.Response` object, the response middleware
   kicks in, and won't bother calling any other exception middleware.

   If it returns a :class:`~scrapy.http.Request` object, returned request is
   used to instruct a immediate redirection. Redirection is handled inside
   middleware scope, and the original request won't finish until redirected
   request is completed. This stop :meth:`process_download_exception`
   middleware as returning Response would do.

   :param request: the request that generated the exception
   :type request: is a :class:`~scrapy.http.Request` object

   :param exception: the raised exception
   :type exception: a ``Exception`` object

   :param spider: the spider for which this request is intended
   :type spider: :class:`~scrapy.spider.BaseSpider` object

Built-in downloader middleware reference

This page describes all downloader middleware components that come with Scrapy. For information on how to use them and how to write your own downloader middleware, see the :ref:`downloader middleware usage guide <topics-downloader-middleware>`.

System Message: ERROR/3 (<stdin>, line 153); backlink

Unknown interpreted text role "ref".

For a list of the components enabled by default (and their orders) see the :setting:`DOWNLOADER_MIDDLEWARES_BASE` setting.

System Message: ERROR/3 (<stdin>, line 158); backlink

Unknown interpreted text role "setting".

CookiesMiddleware

System Message: ERROR/3 (<stdin>, line 164)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.cookies
   :synopsis: Cookies Downloader Middleware

This middleware enables working with sites that need cookies.

DefaultHeadersMiddleware

System Message: ERROR/3 (<stdin>, line 174)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.defaultheaders
   :synopsis: Default Headers Downloader Middleware

This middleware sets all default requests headers specified in the :setting:`DEFAULT_REQUEST_HEADERS` setting.

System Message: ERROR/3 (<stdin>, line 179); backlink

Unknown interpreted text role "setting".

HttpAuthMiddleware

System Message: ERROR/3 (<stdin>, line 185)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.httpauth
   :synopsis: HTTP Auth downloader middleware

This middleware authenticates all requests generated from certain spiders using Basic access authentication (aka. HTTP auth).

To enable HTTP authentication from certain spiders set the http_user and http_pass attributes of those spiders.

Example:

class SomeIntranetSiteSpider(CrawlSpider):

    http_user = 'someuser'
    http_pass = 'somepass'
    domain_name = 'intranet.example.com'

    # .. rest of the spider code omitted ...

HttpCacheMiddleware

System Message: ERROR/3 (<stdin>, line 211)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.httpcache
   :synopsis: HTTP Cache downloader middleware

This middleware provides low-level cache to all HTTP requests and responses. Every request and its corresponding response are cached and then, when that same request is seen again, the response is returned without transferring anything from the Internet.

The HTTP cache is useful for testing spiders faster (without having to wait for downloads every time) and for trying your spider off-line when you don't have an Internet connection.

The :class:`HttpCacheMiddleware` can be configured through the following settings (see the settings documentation for more info):

System Message: ERROR/3 (<stdin>, line 225); backlink

Unknown interpreted text role "class".

HttpCompressionMiddleware

System Message: ERROR/3 (<stdin>, line 242)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.httpcompression
   :synopsis: Http Compression Middleware

This middleware allows compressed (gzip, deflate) traffic to be sent/received from web sites.

HttpProxyMiddleware

System Message: ERROR/3 (<stdin>, line 253)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.httpproxy
   :synopsis: Http Proxy Middleware

System Message: ERROR/3 (<stdin>, line 256)

Unknown directive type "versionadded".

.. versionadded:: 0.8

This middleware sets the HTTP proxy to use for requests, by setting the proxy meta value to :class:`~scrapy.http.Request` objects.

System Message: ERROR/3 (<stdin>, line 260); backlink

Unknown interpreted text role "class".

Like the Python standard library modules urllib and urllib2 it obeys the following enviroment variables:

  • http_proxy
  • https_proxy
  • no_proxy

RedirectMiddleware

System Message: ERROR/3 (<stdin>, line 276)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.redirect
   :synopsis: Redirection Middleware

This middlware handles redirection of requests based on response status and meta-refresh html tag.

The :class:`RedirectMiddleware` can be configured through the following settings (see the settings documentation for more info):

System Message: ERROR/3 (<stdin>, line 284); backlink

Unknown interpreted text role "class".

RetryMiddleware

System Message: ERROR/3 (<stdin>, line 294)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.retry
   :synopsis: Retry Middleware

A middlware to retry failed requests that are potentially caused by temporary problems such as a connection timeout or HTTP 500 error.

Failed pages are collected on the scraping process and rescheduled at the end, once the spider has finished crawling all regular (non failed) pages. Once there is no more failed pages to retry this middleware sends a signal (retry_complete), so other extensions could connect to that signal.

The :class:`RetryMiddleware` can be configured through the following settings (see the settings documentation for more info):

System Message: ERROR/3 (<stdin>, line 307); backlink

Unknown interpreted text role "class".

About HTTP errors to consider:

You may want to remove 400 from RETRY_HTTP_CODES, if you stick to the HTTP protocol. It's included by default because it's a common code used to indicate server overload, which would be something we want to retry.

RobotsTxtMiddleware

System Message: ERROR/3 (<stdin>, line 322)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.robotstxt
   :synopsis: robots.txt middleware

This middleware filters out requests forbidden by the robots.txt exclusion standard.

To make sure Scrapy respects robots.txt make sure the middleware is enabled amd the :setting:`ROBOTSTXT_OBEY` setting is enabled.

System Message: ERROR/3 (<stdin>, line 330); backlink

Unknown interpreted text role "setting".

Warning

Keep in mind that, if you crawl using multiple concurrent requests per domain, Scrapy could still download some forbidden pages if they were requested before the robots.txt file was downloaded. This is a known limitation of the current robots.txt middleware and will be fixed in the future.

DownloaderStats

System Message: ERROR/3 (<stdin>, line 342)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.stats
   :synopsis: Downloader Stats Middleware

Middleware that store stats of all requests, responses and exceptions that pass through it.

To use this middleware you must enable the :setting:`DOWNLOADER_STATS` setting.

System Message: ERROR/3 (<stdin>, line 350); backlink

Unknown interpreted text role "setting".

UserAgentMiddleware

System Message: ERROR/3 (<stdin>, line 356)

Unknown directive type "module".

.. module:: scrapy.contrib.downloadermiddleware.useragent
   :synopsis: User Agent Middleware

Middleware that allows spiders to override the default user agent.

In order for a spider to override the default user agent, its user_agent attribute must be set.

</html>