docs/topics/download-handlers.rst
.. _topics-download-handlers:
Download handlers are Scrapy :ref:components <topics-components> used to
download :ref:requests <topics-request-response> and produce responses from
them.
The :setting:DOWNLOAD_HANDLERS_BASE and :setting:DOWNLOAD_HANDLERS settings
tell Scrapy which handler is responsible for a given URL scheme. Their values
are merged into a mapping from scheme names to handler classes. When Scrapy
initializes it creates instances of all configured download handlers (except
for :ref:lazy ones <lazy-download-handlers>) and stores them in a similar
mapping. When Scrapy needs to download a request it extracts the scheme from
its URL, finds the handler for this scheme, passes the request to it and gets a
response from it. If there is no handler for the scheme, the request is not
downloaded and a :exc:~scrapy.exceptions.NotSupported exception is raised.
The :setting:DOWNLOAD_HANDLERS_BASE setting contains the default mapping of
handlers. You can use the :setting:DOWNLOAD_HANDLERS setting to add handlers
for additional schemes and to replace or disable default ones:
.. code-block:: python
DOWNLOAD_HANDLERS = {
# disable support for ftp:// requests
"ftp": None,
# replace the default one for http://
"http": "my.download_handlers.HttpHandler",
# http:// and https:// are different schemes,
# even though they may use the same handler
"https": "my.download_handlers.HttpHandler",
# support for any custom scheme can be added
"sftp": "my.download_handlers.SftpHandler",
}
While Scrapy provides a default handler for http and https schemes,
users may want to use a different handler, provided by Scrapy or by some
3rd-party package. There are several considerations to keep in mind related to
this.
First of all, as http and https are separate schemes, they need
separate entries in the :setting:DOWNLOAD_HANDLERS setting, even though it's
likely that the same handler class will be used for both schemes.
Additionally, some of the Scrapy settings, like :setting:DOWNLOAD_MAXSIZE,
are honored by the default HTTP(S) handler but not necessarily by alternative
ones. The same may apply to other Scrapy features, e.g. the
:signal:bytes_received and :signal:headers_received signals.
.. _lazy-download-handlers:
A download handler can be marked as "lazy" by setting its lazy class
attribute to True. Such handlers are only instantiated when they need to
download their first request. This may be useful when the instantiation is slow
or requires dependencies that are not always available, and the handler is not
needed on every spider run. For example, :class:the built-in S3 handler <.S3DownloadHandler> is lazy.
A download handler is a :ref:component <topics-components> that defines
the following API:
.. class:: SampleDownloadHandler
.. attribute:: lazy
:type: bool
If ``False``, the handler will be instantiated when Scrapy is
initialized.
If ``True``, the handler will only be instantiated when the first
request handled by it needs to be downloaded.
.. method:: download_request(request: Request) -> Response:
:async:
Download the given request and return a response.
.. method:: close() -> None
:async:
Clean up any resources used by the handler.
An optional base class for custom handlers is provided:
.. autoclass:: scrapy.core.downloader.handlers.base.BaseDownloadHandler :members: :undoc-members: :member-order: bysource
.. _download-handlers-exceptions:
.. versionadded:: 2.15.0
The built-in download handlers raise Scrapy-specific exceptions instead of implementation-specific ones, so that code that handles these exceptions can be written in a generic way. We recommend custom download handlers to also use these exceptions.
.. autoexception:: scrapy.exceptions.CannotResolveHostError
.. autoexception:: scrapy.exceptions.DownloadCancelledError
.. autoexception:: scrapy.exceptions.DownloadConnectionRefusedError
.. autoexception:: scrapy.exceptions.DownloadFailedError
.. autoexception:: scrapy.exceptions.DownloadTimeoutError
.. autoexception:: scrapy.exceptions.ResponseDataLossError
.. autoexception:: scrapy.exceptions.UnsupportedURLSchemeError
.. _download-handlers-ref:
.. autoclass:: scrapy.core.downloader.handlers.datauri.DataURIDownloadHandler
| Supported scheme: data.
| Lazy: no.
This handler supports RFC 2397 data:content/type;base64, data URIs.
.. autoclass:: scrapy.core.downloader.handlers.file.FileDownloadHandler
| Supported scheme: file.
| Lazy: no.
This handler supports file:///path local file URIs. It doesn't
support remote files.
.. autoclass:: scrapy.core.downloader.handlers.ftp.FTPDownloadHandler
| Supported scheme: ftp.
| Lazy: no.
This handler supports ftp://host/path FTP URIs.
It's implemented using :mod:twisted.protocols.ftp.
.. note::
This handler is not supported when :setting:TWISTED_REACTOR_ENABLED is False.
.. _twisted-http2-handler:
.. autoclass:: scrapy.core.downloader.handlers.http2.H2DownloadHandler
| Supported scheme: https.
| Lazy: yes.
This handler supports https://host/path URLs and uses the HTTP/2 protocol
for them.
It's implemented using :mod:twisted.web.client and the h2 library.
For this handler to work you need to install the Twisted[http2] extra
dependency.
If you want to use this handler you need to replace the default one for the
https scheme:
.. code-block:: python
DOWNLOAD_HANDLERS = {
"https": "scrapy.core.downloader.handlers.http2.H2DownloadHandler",
}
.. warning::
This handler is experimental, and not yet recommended for production
environments. Future Scrapy versions may introduce related changes without
a deprecation period or warning.
.. note::
Known limitations of the HTTP/2 implementation in this handler include:
- No support for HTTP/2 Cleartext (h2c), since no major browser supports
HTTP/2 unencrypted (refer `http2 faq`_).
- No setting to specify a maximum `frame size`_ larger than the default
value, 16384. Connections to servers that send a larger frame will
fail.
- No support for `server pushes`_, which are ignored.
- No support for the :signal:`bytes_received` and
:signal:`headers_received` signals.
.. _frame size: https://datatracker.ietf.org/doc/html/rfc7540#section-4.2 .. _http2 faq: https://http2.github.io/faq/#does-http2-require-encryption .. _server pushes: https://datatracker.ietf.org/doc/html/rfc7540#section-8.2
.. note::
This handler is not supported when :setting:TWISTED_REACTOR_ENABLED is False.
.. autoclass:: scrapy.core.downloader.handlers.http11.HTTP11DownloadHandler
| Supported schemes: http, https.
| Lazy: no.
This handler supports http://host/path and https://host/path URLs and
uses the HTTP/1.1 protocol for them.
It's implemented using :mod:twisted.web.client.
.. note::
This handler is not supported when :setting:TWISTED_REACTOR_ENABLED is False.
.. autoclass:: scrapy.core.downloader.handlers._httpx.HttpxDownloadHandler
| Supported schemes: http, https.
| Lazy: no.
This handler supports http://host/path and https://host/path URLs and
uses the HTTP/1.1 protocol for them.
It's implemented using the httpx library and needs it to be installed.
If you want to use this handler you need to replace the default ones for the
http and https schemes:
.. code-block:: python
DOWNLOAD_HANDLERS = {
"http": "scrapy.core.downloader.handlers._httpx.HttpxDownloadHandler",
"https": "scrapy.core.downloader.handlers._httpx.HttpxDownloadHandler",
}
.. warning::
This handler is experimental, and not yet recommended for production
environments. Future Scrapy versions may introduce related changes without
a deprecation period or warning or even remove it altogether.
.. note::
As this handler is based on a different HTTP client implementation compared
to :class:`~.HTTP11DownloadHandler`, it's expected that its behavior on
some websites may be different. Additionally, these are the Scrapy features
that are explicitly not supported when using it:
- Proxy support (the :reqmeta:`proxy` meta key).
- Per-request bind address support (the :reqmeta:`bindaddress` meta key).
The global :setting:`DOWNLOAD_BIND_ADDRESS` setting is supported but the
port number, if specified, will be ignored.
- The :setting:`DOWNLOADER_CLIENT_TLS_CIPHERS` and
:setting:`DOWNLOADER_CLIENT_TLS_METHOD` settings.
- Settings specific to the Twisted networking or HTTP implementation, like
:setting:`DNS_RESOLVER`.
- Using :ref:`non-asyncio reactors <disable-asyncio>` (``httpx`` requires
``asyncio``).
.. autoclass:: scrapy.core.downloader.handlers.s3.S3DownloadHandler
| Supported scheme: s3.
| Lazy: yes.
This handler supports s3://bucket/path S3 URIs.
It's implemented using the botocore library and needs it to be installed.