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129 lines
4.6 KiB
ReStructuredText
129 lines
4.6 KiB
ReStructuredText
Common Use Cases
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================
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Include in Web Applications
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---------------------------
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Using WeasyPrint in web applications sometimes requires attention on some
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details.
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Security Problems
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.................
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First of all, rendering untrusted HTML and CSS files can lead to :ref:`security
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problems <Security>`. Please be sure to carefully follow the different proposed
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solutions if you allow your users to modify the source of the rendered
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documents in any way.
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Rights Management
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.................
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Another problem is rights management: you often need to render templates that
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can only be accessed by authenticated users, and WeasyPrint installed on the
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server doesn’t send the same cookies as the ones sent by the users. Extensions
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such as Flask-WeasyPrint_ (for Flask_) or Django-WeasyPrint_ (for Django_)
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solve this issue with a small amount of code. If you use another framework, you
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can read these extensions and probably find an equivalent workaround.
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.. _Flask-Weasyprint: https://github.com/Kozea/Flask-WeasyPrint
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.. _Flask: https://flask.palletsprojects.com/
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.. _Django-WeasyPrint: https://github.com/fdemmer/django-weasyprint
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.. _Django: https://www.djangoproject.com/
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Server Side Requests & Self-Signed SSL Certificates
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...................................................
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If your server is requesting data from itself, you may encounter a self-signed
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certificate error, even if you have a valid certificate.
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You need to add yourself as a Certificate Authority, so that your self-signed
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SSL certificates can be requested.
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.. code-block:: bash
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# If you have not yet created a certificate.
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sudo openssl req -x509 \
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-sha256 \
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-nodes \
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-newkey rsa:4096 \
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-days 365 \
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-keyout localhost.key \
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-out localhost.crt
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# Follow the prompts about your certificate and the domain name.
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openssl x509 -text -noout -in localhost.crt
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Add your new self-signed SSL certificate to your nginx.conf, below the line
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``server_name 123.123.123.123;``:
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.. code-block:: bash
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ssl_certificate /etc/ssl/certs/localhost.crt;
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ssl_certificate_key /etc/ssl/private/localhost.key;
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The SSL certificate will be valid when accessing your website from the
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internet. However, images will not render when requesting files from the same
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server.
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You will need to add your new self-signed certificates as trusted:
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.. code-block:: bash
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sudo cp /etc/ssl/certs/localhost.crt /usr/local/share/ca-certificates/localhost.crt
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sudo cp /etc/ssl/private/localhost.key /usr/local/share/ca-certificates/localhost.key
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# Update the certificate authority trusted certificates.
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sudo update-ca-certificates
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# Export your newly updated Certificate Authority Bundle file.
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# If using Django, it will use the newly signed certificate authority as
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# valid and images will load properly.
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sudo tee -a /etc/environment <<< 'export REQUESTS_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt'
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Adjust Document Dimensions
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--------------------------
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WeasyPrint does not provide support for adjusting page size or document margins
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via command-line flags. This is best accomplished with the CSS ``@page``
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at-rule. Consider the following example:
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.. code-block:: css
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@page {
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size: Letter; /* Change from the default size of A4 */
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margin: 3cm; /* Set margin on each page */
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}
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There is much more which can be achieved with the ``@page`` at-rule,
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such as page numbers, headers, etc. Read more about the page_ at-rule.
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.. _page: https://developer.mozilla.org/en-US/docs/Web/CSS/@page
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Improve Rendering Speed and Memory Use
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--------------------------------------
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WeasyPrint is often slower than other web engines. Python is the usual suspect,
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but it’s not the main culprit here. :ref:`Optimization is not the main goal of
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WeasyPrint <Why Python?>` and it may lead to unbearable long rendering times.
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First of all: WeasyPrint’s performance gets generally better with time. You can
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check WeasyPerf_ to compare time and memory needed across versions.
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Some tips may help you to get better results.
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- A high number of CSS properties with a high number of HTML tags can lead to a
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huge amount of time spent for the cascade. Avoiding large CSS frameworks can
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drastically reduce the rendering time.
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- Tables are known to be slow, especially when they are rendered on multiple
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pages. When possible, using a common block layout instead gives much faster
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layouts.
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- Optimizing images and fonts can reduce the PDF size, but increase the
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rendering time. Moreover, caching images gives the possibility to read and
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optimize images only once, and thus to save time when the same image is used
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multiple times. See :ref:`Image Cache and Optimization`.
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.. _WeasyPerf: https://kozea.github.io/WeasyPerf/
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