# 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 `DOWNLOADER_MIDDLEWARES` setting, which is a dict whose keys are the middleware class paths and their values are the middleware orders.

Here’s an example:

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

The `DOWNLOADER_MIDDLEWARES` setting is merged with the `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. In other words, the `process_request()` method of each middleware will be invoked in increasing middleware order (100, 200, 300, …) and the `process_response()` method of each middleware will be invoked in decreasing order.

To decide which order to assign to your middleware see the `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.

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

    DOWNLOADER_MIDDLEWARES = {
        "myproject.middlewares.CustomDownloaderMiddleware": 543,
        "scrapy.downloadermiddlewares.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

Each downloader middleware is a Python class that defines one or more of the methods defined below.

The main entry point is the `from_crawler` class method, which receives a `Crawler` instance. The `Crawler` object gives you access, for example, to the settings.

class scrapy.downloadermiddlewares.DownloaderMiddleware

  Note

  Any of the downloader middleware methods may also return a deferred.

  process_request(request, spider)

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

    `process_request()` should either: return `None`, return a `Response` object, return a `Request` object, or raise `IgnoreRequest`.

    If it 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 it returns a `Response` object, Scrapy won’t bother calling any other `process_request()` or `process_exception()` methods, or the appropriate download function; it’ll return that response. The `process_response()` methods of installed middleware is always called on every response.

    If it returns a `Request` object, Scrapy will stop calling `process_request()` methods and reschedule the returned request. Once the newly returned request is performed, the appropriate middleware chain will be called on the downloaded response.

    If it raises an `IgnoreRequest` exception, the `process_exception()` methods of installed downloader middleware will be called. If none of them handle the exception, the errback function of the request (`Request.errback`) is called. If no code handles the raised exception, it is ignored and not logged (unlike other exceptions).

    Parameters:

      - request (`Request` object) – the request being processed

      - spider (`Spider` object) – the spider for which this request is intended

  process_response(request, response, spider)

    `process_response()` should either: return a `Response` object, return a `Request` object or raise a `IgnoreRequest` exception.

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

    If it returns a `Request` object, the middleware chain is halted and the returned request is rescheduled to be downloaded in the future. This is the same behavior as if a request is returned from `process_request()`.

    If it raises an `IgnoreRequest` exception, the errback function of the request (`Request.errback`) is called. If no code handles the raised exception, it is ignored and not logged (unlike other exceptions).

    Parameters:

      - request (is a `Request` object) – the request that originated the response

      - response (`Response` object) – the response being processed

      - spider (`Spider` object) – the spider for which this response is intended

  process_exception(request, exception, spider)

    Scrapy calls `process_exception()` when a download handler or a `process_request()` (from a downloader middleware) raises an exception (including an `IgnoreRequest` exception)

    `process_exception()` should return: either `None`, a `Response` object, or a `Request` object.

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

    If it returns a `Response` object, the `process_response()` method chain of installed middleware is started, and Scrapy won’t bother calling any other `process_exception()` methods of middleware.

    If it returns a `Request` object, the returned request is rescheduled to be downloaded in the future. This stops the execution of `process_exception()` methods of the middleware the same as returning a response would.

    Parameters:

      - request (is a `Request` object) – the request that generated the exception

      - exception (an `Exception` object) – the raised exception

      - spider (`Spider` object) – the spider for which this request is intended

  from_crawler(cls, crawler)

    If present, this classmethod is called to create a middleware instance from a `Crawler`. It must return a new instance of the middleware. Crawler object provides access to all Scrapy core components like settings and signals; it is a way for middleware to access them and hook its functionality into Scrapy.

    Parameters:

      crawler (`Crawler` object) – crawler that uses this middleware

## 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 downloader middleware usage guide.

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

### CookiesMiddleware

class scrapy.downloadermiddlewares.cookies.CookiesMiddleware

  This middleware enables working with sites that require cookies, such as those that use sessions. It keeps track of cookies sent by web servers, and sends them back on subsequent requests (from that spider), just like web browsers do.

  Caution

  When non-UTF8 encoded byte sequences are passed to a `Request`, the `CookiesMiddleware` will log a warning. Refer to Advanced customization to customize the logging behaviour.

  Caution

  Cookies set via the `Cookie` header are not considered by the CookiesMiddleware. If you need to set cookies for a request, use the `Request.cookies` parameter. This is a known current limitation that is being worked on.

The following settings can be used to configure the cookie middleware:

- `COOKIES_ENABLED`

- `COOKIES_DEBUG`

#### Multiple cookie sessions per spider

There is support for keeping multiple cookie sessions per spider by using the `cookiejar` Request meta key. By default it uses a single cookie jar (session), but you can pass an identifier to use different ones.

For example:

    for i, url in enumerate(urls):
        yield scrapy.Request(url, meta={"cookiejar": i}, callback=self.parse_page)

Keep in mind that the `cookiejar` meta key is not “sticky”. You need to keep passing it along on subsequent requests. For example:

    def parse_page(self, response):
        # do some processing
        return scrapy.Request(
            "http://www.example.com/otherpage",
            meta={"cookiejar": response.meta["cookiejar"]},
            callback=self.parse_other_page,
        )

#### COOKIES_ENABLED

Default: `True`

Whether to enable the cookies middleware. If disabled, no cookies will be sent to web servers.

Notice that despite the value of `COOKIES_ENABLED` setting if `Request.``meta['dont_merge_cookies']` evaluates to `True` the request cookies will not be sent to the web server and received cookies in `Response` will not be merged with the existing cookies.

For more detailed information see the `cookies` parameter in `Request`.

#### COOKIES_DEBUG

Default: `False`

If enabled, Scrapy will log all cookies sent in requests (i.e. `Cookie` header) and all cookies received in responses (i.e. `Set-Cookie` header).

Here’s an example of a log with `COOKIES_DEBUG` enabled:

    2011-04-06 14:35:10-0300 [scrapy.core.engine] INFO: Spider opened
    2011-04-06 14:35:10-0300 [scrapy.downloadermiddlewares.cookies] DEBUG: Sending cookies to: <GET http://www.diningcity.com/netherlands/index.html>
            Cookie: clientlanguage_nl=en_EN
    2011-04-06 14:35:14-0300 [scrapy.downloadermiddlewares.cookies] DEBUG: Received cookies from: <200 http://www.diningcity.com/netherlands/index.html>
            Set-Cookie: JSESSIONID=B~FA4DC0C496C8762AE4F1A620EAB34F38; Path=/
            Set-Cookie: ip_isocode=US
            Set-Cookie: clientlanguage_nl=en_EN; Expires=Thu, 07-Apr-2011 21:21:34 GMT; Path=/
    2011-04-06 14:49:50-0300 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://www.diningcity.com/netherlands/index.html> (referer: None)
    [...]

### DefaultHeadersMiddleware

class scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware

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

### DownloadTimeoutMiddleware

class scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware

  This middleware sets the download timeout for requests specified in the `DOWNLOAD_TIMEOUT` setting or `download_timeout` spider attribute.

Note

You can also set download timeout per-request using `download_timeout` Request.meta key; this is supported even when DownloadTimeoutMiddleware is disabled.

### HttpAuthMiddleware

class scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware

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

  To enable HTTP authentication for a spider, set the `http_user` and `http_pass` spider attributes to the authentication data and the `http_auth_domain` spider attribute to the domain which requires this authentication (its subdomains will be also handled in the same way). You can set `http_auth_domain` to `None` to enable the authentication for all requests but you risk leaking your authentication credentials to unrelated domains.

  Warning

  In previous Scrapy versions HttpAuthMiddleware sent the authentication data with all requests, which is a security problem if the spider makes requests to several different domains. Currently if the `http_auth_domain` attribute is not set, the middleware will use the domain of the first request, which will work for some spiders but not for others. In the future the middleware will produce an error instead.

  Example:

      from scrapy.spiders import CrawlSpider

      class SomeIntranetSiteSpider(CrawlSpider):
          http_user = "someuser"
          http_pass = "somepass"
          http_auth_domain = "intranet.example.com"
          name = "intranet.example.com"

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

### HttpCacheMiddleware

class scrapy.downloadermiddlewares.httpcache.HttpCacheMiddleware

  This middleware provides low-level cache to all HTTP requests and responses. It has to be combined with a cache storage backend as well as a cache policy.

  Scrapy ships with the following HTTP cache storage backends:

  > - Filesystem storage backend (default)

  > - DBM storage backend

  You can change the HTTP cache storage backend with the `HTTPCACHE_STORAGE` setting. Or you can also implement your own storage backend.

  Scrapy ships with two HTTP cache policies:

  > - RFC2616 policy

  > - Dummy policy (default)

  You can change the HTTP cache policy with the `HTTPCACHE_POLICY` setting. Or you can also implement your own policy.

  You can also avoid caching a response on every policy using `dont_cache` meta key equals `True`.

#### Dummy policy (default)

class scrapy.extensions.httpcache.DummyPolicy

  This policy has no awareness of any HTTP Cache-Control directives. Every request and its corresponding response are cached. When the same request is seen again, the response is returned without transferring anything from the Internet.

  The Dummy policy is useful for testing spiders faster (without having to wait for downloads every time) and for trying your spider offline, when an Internet connection is not available. The goal is to be able to “replay” a spider run exactly as it ran before.

#### RFC2616 policy

class scrapy.extensions.httpcache.RFC2616Policy

  This policy provides a RFC2616 compliant HTTP cache, i.e. with HTTP Cache-Control awareness, aimed at production and used in continuous runs to avoid downloading unmodified data (to save bandwidth and speed up crawls).

  What is implemented:

  - Do not attempt to store responses/requests with `no-store` cache-control directive set

  - Do not serve responses from cache if `no-cache` cache-control directive is set even for fresh responses

  - Compute freshness lifetime from `max-age` cache-control directive

  - Compute freshness lifetime from `Expires` response header

  - Compute freshness lifetime from `Last-Modified` response header (heuristic used by Firefox)

  - Compute current age from `Age` response header

  - Compute current age from `Date` header

  - Revalidate stale responses based on `Last-Modified` response header

  - Revalidate stale responses based on `ETag` response header

  - Set `Date` header for any received response missing it

  - Support `max-stale` cache-control directive in requests

  This allows spiders to be configured with the full RFC2616 cache policy, but avoid revalidation on a request-by-request basis, while remaining conformant with the HTTP spec.

  Example:

  Add `Cache-Control: max-stale=600` to Request headers to accept responses that have exceeded their expiration time by no more than 600 seconds.

  See also: RFC2616, 14.9.3

  What is missing:

  - `Pragma: no-cache` support https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.1

  - `Vary` header support https://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.6

  - Invalidation after updates or deletes https://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.10

  - … probably others ..

#### Filesystem storage backend (default)

class scrapy.extensions.httpcache.FilesystemCacheStorage

  File system storage backend is available for the HTTP cache middleware.

  Each request/response pair is stored in a different directory containing the following files:

  - `request_body` - the plain request body

  - `request_headers` - the request headers (in raw HTTP format)

  - `response_body` - the plain response body

  - `response_headers` - the request headers (in raw HTTP format)

  - `meta` - some metadata of this cache resource in Python `repr()` format (grep-friendly format)

  - `pickled_meta` - the same metadata in `meta` but pickled for more efficient deserialization

  The directory name is made from the request fingerprint (see `scrapy.utils.request.fingerprint`), and one level of subdirectories is used to avoid creating too many files into the same directory (which is inefficient in many file systems). An example directory could be:

      /path/to/cache/dir/example.com/72/72811f648e718090f041317756c03adb0ada46c7

#### DBM storage backend

class scrapy.extensions.httpcache.DbmCacheStorage

  A DBM storage backend is also available for the HTTP cache middleware.

  By default, it uses the `dbm`, but you can change it with the `HTTPCACHE_DBM_MODULE` setting.

#### Writing your own storage backend

You can implement a cache storage backend by creating a Python class that defines the methods described below.

class scrapy.extensions.httpcache.CacheStorage
  open_spider(spider)

    This method gets called after a spider has been opened for crawling. It handles the `open_spider` signal.

    Parameters:

      spider (`Spider` object) – the spider which has been opened

  close_spider(spider)

    This method gets called after a spider has been closed. It handles the `close_spider` signal.

    Parameters:

      spider (`Spider` object) – the spider which has been closed

  retrieve_response(spider, request)

    Return response if present in cache, or `None` otherwise.

    Parameters:

      - spider (`Spider` object) – the spider which generated the request

      - request (`Request` object) – the request to find cached response for

  store_response(spider, request, response)

    Store the given response in the cache.

    Parameters:

      - spider (`Spider` object) – the spider for which the response is intended

      - request (`Request` object) – the corresponding request the spider generated

      - response (`Response` object) – the response to store in the cache

In order to use your storage backend, set:

- `HTTPCACHE_STORAGE` to the Python import path of your custom storage class.

#### HTTPCache middleware settings

The `HttpCacheMiddleware` can be configured through the following settings:

##### HTTPCACHE_ENABLED

Default: `False`

Whether the HTTP cache will be enabled.

##### HTTPCACHE_EXPIRATION_SECS

Default: `0`

Expiration time for cached requests, in seconds.

Cached requests older than this time will be re-downloaded. If zero, cached requests will never expire.

##### HTTPCACHE_DIR

Default: `'httpcache'`

The directory to use for storing the (low-level) HTTP cache. If empty, the HTTP cache will be disabled. If a relative path is given, is taken relative to the project data dir. For more info see: Default structure of Scrapy projects.

##### HTTPCACHE_IGNORE_HTTP_CODES

Default: `[]`

Don’t cache response with these HTTP codes.

##### HTTPCACHE_IGNORE_MISSING

Default: `False`

If enabled, requests not found in the cache will be ignored instead of downloaded.

##### HTTPCACHE_IGNORE_SCHEMES

Default: `['file']`

Don’t cache responses with these URI schemes.

##### HTTPCACHE_STORAGE

Default: `'scrapy.extensions.httpcache.FilesystemCacheStorage'`

The class which implements the cache storage backend.

##### HTTPCACHE_DBM_MODULE

Default: `'dbm'`

The database module to use in the DBM storage backend. This setting is specific to the DBM backend.

##### HTTPCACHE_POLICY

Default: `'scrapy.extensions.httpcache.DummyPolicy'`

The class which implements the cache policy.

##### HTTPCACHE_GZIP

Default: `False`

If enabled, will compress all cached data with gzip. This setting is specific to the Filesystem backend.

##### HTTPCACHE_ALWAYS_STORE

Default: `False`

If enabled, will cache pages unconditionally.

A spider may wish to have all responses available in the cache, for future use with `Cache-Control: max-stale`, for instance. The DummyPolicy caches all responses but never revalidates them, and sometimes a more nuanced policy is desirable.

This setting still respects `Cache-Control: no-store` directives in responses. If you don’t want that, filter `no-store` out of the Cache-Control headers in responses you feed to the cache middleware.

##### HTTPCACHE_IGNORE_RESPONSE_CACHE_CONTROLS

Default: `[]`

List of Cache-Control directives in responses to be ignored.

Sites often set “no-store”, “no-cache”, “must-revalidate”, etc., but get upset at the traffic a spider can generate if it actually respects those directives. This allows to selectively ignore Cache-Control directives that are known to be unimportant for the sites being crawled.

We assume that the spider will not issue Cache-Control directives in requests unless it actually needs them, so directives in requests are not filtered.

### HttpCompressionMiddleware

class scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware

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

  This middleware also supports decoding brotli-compressed as well as zstd-compressed responses, provided that brotli or zstandard is installed, respectively.

#### HttpCompressionMiddleware Settings

##### COMPRESSION_ENABLED

Default: `True`

Whether the Compression middleware will be enabled.

### HttpProxyMiddleware

class scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware

  This middleware sets the HTTP proxy to use for requests, by setting the `proxy` meta value for `Request` objects.

  Like the Python standard library module `urllib.request`, it obeys the following environment variables:

  - `http_proxy`

  - `https_proxy`

  - `no_proxy`

  You can also set the meta key `proxy` per-request, to a value like `http://some_proxy_server:port` or `http://username:password@some_proxy_server:port`. Keep in mind this value will take precedence over `http_proxy`/`https_proxy` environment variables, and it will also ignore `no_proxy` environment variable.

### OffsiteMiddleware

class scrapy.downloadermiddlewares.offsite.OffsiteMiddleware

  Added in version 2.11.2.

  Filters out Requests for URLs outside the domains covered by the spider.

  This middleware filters out every request whose host names aren’t in the spider’s `allowed_domains` attribute. All subdomains of any domain in the list are also allowed. E.g. the rule `www.example.org` will also allow `bob.www.example.org` but not `www2.example.com` nor `example.com`.

  When your spider returns a request for a domain not belonging to those covered by the spider, this middleware will log a debug message similar to this one:

      DEBUG: Filtered offsite request to 'offsite.example': <GET http://offsite.example/some/page.html>

  To avoid filling the log with too much noise, it will only print one of these messages for each new domain filtered. So, for example, if another request for `offsite.example` is filtered, no log message will be printed. But if a request for `other.example` is filtered, a message will be printed (but only for the first request filtered).

  If the spider doesn’t define an `allowed_domains` attribute, or the attribute is empty, the offsite middleware will allow all requests.

  If the request has the `dont_filter` attribute set, the offsite middleware will allow the request even if its domain is not listed in allowed domains.

### RedirectMiddleware

class scrapy.downloadermiddlewares.redirect.RedirectMiddleware

  This middleware handles redirection of requests based on response status.

The urls which the request goes through (while being redirected) can be found in the `redirect_urls` `Request.meta` key.

The reason behind each redirect in `redirect_urls` can be found in the `redirect_reasons` `Request.meta` key. For example: `[301, 302, 307, 'meta refresh']`.

The format of a reason depends on the middleware that handled the corresponding redirect. For example, `RedirectMiddleware` indicates the triggering response status code as an integer, while `MetaRefreshMiddleware` always uses the `'meta refresh'` string as reason.

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

- `REDIRECT_ENABLED`

- `REDIRECT_MAX_TIMES`

If `Request.meta` has `dont_redirect` key set to True, the request will be ignored by this middleware.

If you want to handle some redirect status codes in your spider, you can specify these in the `handle_httpstatus_list` spider attribute.

For example, if you want the redirect middleware to ignore 301 and 302 responses (and pass them through to your spider) you can do this:

    class MySpider(CrawlSpider):
        handle_httpstatus_list = [301, 302]

The `handle_httpstatus_list` key of `Request.meta` can also be used to specify which response codes to allow on a per-request basis. You can also set the meta key `handle_httpstatus_all` to `True` if you want to allow any response code for a request.

#### RedirectMiddleware settings

##### REDIRECT_ENABLED

Default: `True`

Whether the Redirect middleware will be enabled.

##### REDIRECT_MAX_TIMES

Default: `20`

The maximum number of redirections that will be followed for a single request. If maximum redirections are exceeded, the request is aborted and ignored.

### MetaRefreshMiddleware

class scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware

  This middleware handles redirection of requests based on meta-refresh html tag.

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

- `METAREFRESH_ENABLED`

- `METAREFRESH_IGNORE_TAGS`

- `METAREFRESH_MAXDELAY`

This middleware obey `REDIRECT_MAX_TIMES` setting, `dont_redirect`, `redirect_urls` and `redirect_reasons` request meta keys as described for `RedirectMiddleware`

#### MetaRefreshMiddleware settings

##### METAREFRESH_ENABLED

Default: `True`

Whether the Meta Refresh middleware will be enabled.

##### METAREFRESH_IGNORE_TAGS

Default: `[]`

Meta tags within these tags are ignored.

Changed in version 2.0: The default value of `METAREFRESH_IGNORE_TAGS` changed from `["script", "noscript"]` to `[]`.

Changed in version 2.11.2: The default value of `METAREFRESH_IGNORE_TAGS` changed from `[]` to `["noscript"]`.

##### METAREFRESH_MAXDELAY

Default: `100`

The maximum meta-refresh delay (in seconds) to follow the redirection. Some sites use meta-refresh for redirecting to a session expired page, so we restrict automatic redirection to the maximum delay.

### RetryMiddleware

class scrapy.downloadermiddlewares.retry.RetryMiddleware

  A middleware 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.

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

- `RETRY_ENABLED`

- `RETRY_TIMES`

- `RETRY_HTTP_CODES`

- `RETRY_EXCEPTIONS`

If `Request.meta` has `dont_retry` key set to True, the request will be ignored by this middleware.

To retry requests from a spider callback, you can use the `get_retry_request()` function:

scrapy.downloadermiddlewares.retry.get_retry_request(request: Request, *, spider: Spider, reason: str | Exception | type[Exception] = 'unspecified', max_retry_times: int | None = None, priority_adjust: int | None = None, logger: Logger = <Logger scrapy.downloadermiddlewares.retry (WARNING)>, stats_base_key: str = 'retry') → Request | None

  Returns a new `Request` object to retry the specified request, or `None` if retries of the specified request have been exhausted.

  For example, in a `Spider` callback, you could use it as follows:

      def parse(self, response):
          if not response.text:
              new_request_or_none = get_retry_request(
                  response.request,
                  spider=self,
                  reason='empty',
              )
              return new_request_or_none

  spider is the `Spider` instance which is asking for the retry request. It is used to access the settings and stats, and to provide extra logging context (see `logging.debug()`).

  reason is a string or an `Exception` object that indicates the reason why the request needs to be retried. It is used to name retry stats.

  max_retry_times is a number that determines the maximum number of times that request can be retried. If not specified or `None`, the number is read from the `max_retry_times` meta key of the request. If the `max_retry_times` meta key is not defined or `None`, the number is read from the `RETRY_TIMES` setting.

  priority_adjust is a number that determines how the priority of the new request changes in relation to request. If not specified, the number is read from the `RETRY_PRIORITY_ADJUST` setting.

  logger is the logging.Logger object to be used when logging messages

  stats_base_key is a string to be used as the base key for the retry-related job stats

#### RetryMiddleware Settings

##### RETRY_ENABLED

Default: `True`

Whether the Retry middleware will be enabled.

##### RETRY_TIMES

Default: `2`

Maximum number of times to retry, in addition to the first download.

Maximum number of retries can also be specified per-request using `max_retry_times` attribute of `Request.meta`. When initialized, the `max_retry_times` meta key takes higher precedence over the `RETRY_TIMES` setting.

##### RETRY_HTTP_CODES

Default: `[500, 502, 503, 504, 522, 524, 408, 429]`

Which HTTP response codes to retry. Other errors (DNS lookup issues, connections lost, etc) are always retried.

In some cases you may want to add 400 to `RETRY_HTTP_CODES` because it is a common code used to indicate server overload. It is not included by default because HTTP specs say so.

##### RETRY_EXCEPTIONS

Default:

    [
        'twisted.internet.defer.TimeoutError',
        'twisted.internet.error.TimeoutError',
        'twisted.internet.error.DNSLookupError',
        'twisted.internet.error.ConnectionRefusedError',
        'twisted.internet.error.ConnectionDone',
        'twisted.internet.error.ConnectError',
        'twisted.internet.error.ConnectionLost',
        'twisted.internet.error.TCPTimedOutError',
        'twisted.web.client.ResponseFailed',
        IOError,
        'scrapy.core.downloader.handlers.http11.TunnelError',
    ]

List of exceptions to retry.

Each list entry may be an exception type or its import path as a string.

An exception will not be caught when the exception type is not in `RETRY_EXCEPTIONS` or when the maximum number of retries for a request has been exceeded (see `RETRY_TIMES`). To learn about uncaught exception propagation, see `process_exception()`.

##### RETRY_PRIORITY_ADJUST

Default: `-1`

Adjust retry request priority relative to original request:

- a positive priority adjust means higher priority.

- a negative priority adjust (default) means lower priority.

### RobotsTxtMiddleware

class scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware

  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 and the `ROBOTSTXT_OBEY` setting is enabled.

  The `ROBOTSTXT_USER_AGENT` setting can be used to specify the user agent string to use for matching in the robots.txt file. If it is `None`, the User-Agent header you are sending with the request or the `USER_AGENT` setting (in that order) will be used for determining the user agent to use in the robots.txt file.

  This middleware has to be combined with a robots.txt parser.

  Scrapy ships with support for the following robots.txt parsers:

  - Protego (default)

  - RobotFileParser

  - Robotexclusionrulesparser

  You can change the robots.txt parser with the `ROBOTSTXT_PARSER` setting. Or you can also implement support for a new parser.

If `Request.meta` has `dont_obey_robotstxt` key set to True the request will be ignored by this middleware even if `ROBOTSTXT_OBEY` is enabled.

Parsers vary in several aspects:

- Language of implementation

- Supported specification

- Support for wildcard matching

- Usage of length based rule: in particular for `Allow` and `Disallow` directives, where the most specific rule based on the length of the path trumps the less specific (shorter) rule

Performance comparison of different parsers is available at the following link.

#### Protego parser

Based on Protego:

- implemented in Python

- is compliant with Google’s Robots.txt Specification

- supports wildcard matching

- uses the length based rule

Scrapy uses this parser by default.

#### RobotFileParser

Based on `RobotFileParser`:

- is Python’s built-in robots.txt parser

- is compliant with Martijn Koster’s 1996 draft specification

- lacks support for wildcard matching

- doesn’t use the length based rule

It is faster than Protego and backward-compatible with versions of Scrapy before 1.8.0.

In order to use this parser, set:

- `ROBOTSTXT_PARSER` to `scrapy.robotstxt.PythonRobotParser`

#### Robotexclusionrulesparser

Based on Robotexclusionrulesparser:

- implemented in Python

- is compliant with Martijn Koster’s 1996 draft specification

- supports wildcard matching

- doesn’t use the length based rule

In order to use this parser:

- Install `Robotexclusionrulesparser` by running `pip install robotexclusionrulesparser`

- Set `ROBOTSTXT_PARSER` setting to `scrapy.robotstxt.RerpRobotParser`

#### Implementing support for a new parser

You can implement support for a new robots.txt parser by subclassing the abstract base class `RobotParser` and implementing the methods described below.

class scrapy.robotstxt.RobotParser
  abstract allowed(url: str | bytes, user_agent: str | bytes) → bool

    Return `True` if `user_agent` is allowed to crawl `url`, otherwise return `False`.

    Parameters:

      - url (str or bytes) – Absolute URL

      - user_agent (str or bytes) – User agent

  abstract classmethod from_crawler(crawler: Crawler, robotstxt_body: bytes) → Self

    Parse the content of a robots.txt file as bytes. This must be a class method. It must return a new instance of the parser backend.

    Parameters:

      - crawler (`Crawler` instance) – crawler which made the request

      - robotstxt_body (bytes) – content of a robots.txt file.

### DownloaderStats

class scrapy.downloadermiddlewares.stats.DownloaderStats

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

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

### UserAgentMiddleware

class scrapy.downloadermiddlewares.useragent.UserAgentMiddleware

  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.

### AjaxCrawlMiddleware

class scrapy.downloadermiddlewares.ajaxcrawl.AjaxCrawlMiddleware

  Middleware that finds ‘AJAX crawlable’ page variants based on meta-fragment html tag.

  Note

  Scrapy finds ‘AJAX crawlable’ pages for URLs like `'http://example.com/!#foo=bar'` even without this middleware. AjaxCrawlMiddleware is necessary when URL doesn’t contain `'!#'`. This is often a case for ‘index’ or ‘main’ website pages.

#### AjaxCrawlMiddleware Settings

##### AJAXCRAWL_ENABLED

Default: `False`

Whether the AjaxCrawlMiddleware will be enabled. You may want to enable it for broad crawls.

#### HttpProxyMiddleware settings

##### HTTPPROXY_ENABLED

Default: `True`

Whether or not to enable the `HttpProxyMiddleware`.

##### HTTPPROXY_AUTH_ENCODING

Default: `"latin-1"`

The default encoding for proxy authentication on `HttpProxyMiddleware`.