Weasyprint: Get rid of external dependencies

[mojimi]

I'm just opening this issue to have a discussion on it. And because it doesn't exist 😏

WeasyPrint is amazing and heavily differentiates from any other pdf creating library since it implemented its own css engine, but at the moment all the dependencies are the biggest downside in my view.

All the libraries it requires can be a hassle when building cross-platform, I've had several issues deploying to AWS services and testing on Windows.

Discussions to consider :

1) Is it feasible to think about removing the dependencies in some near feature?
2) Do you guys plan on ever doing it or there would need to be some type of investment/external incentive?
3) Which of the dependencies would be the harder to redo in python?
4) What are the biggest challenges here?

*Btw I'm only talking about external libs like Pango/Cairo/GDK

[MindFluid]

You could set up a docker container that can be easily deployed to other instances.

[liZe]

Hello,

I love removing external dependencies. Using something different from cairo has already been discussed in #342 for example. Really, I'd love to.

I can imagine rewriting cairo, or at least imagine generating PDF files out of simple drawing operations. I would love to, and maybe one day will. But there's one big problem: text.

Drawing text is not difficult. It's not really difficult. It's a nightmare. Well, it's actually never-ending nightmares in a never-ending night. You can even call that "hell" if you want.

So… Maybe one day I'll drop Pango and use HarfBuzz instead (it means rewriting the whole line-breaking algorithm in WeasyPrint, that's already frightening). But I can't even imagine not relying on HarfBuzz. And I'm not the only one:

HarfBuzz is used in Android, Chrome, ChromeOS, Firefox, GNOME, GTK+, KDE, LibreOffice, OpenJDK, PlayStation, Qt, XeTeX, and other places.

Bad news: Pango is not the only library WeasyPrint relies on to render text. It also relies on Fontconfig to find and configure fonts, and FreeType to render TrueType fonts. In case you're wondering: it's really painful too.

TL;DR: Replacing cairo and Pango can be done with a lot of work. Getting rid of all the non-Python external dependencies is nothing more than an illusion.

You could set up a docker container that can be easily deployed to other instances.

Yes. Providing Snap or Flatpak packages could be another solution.

[mojimi]

I guess more a more batteries-ready documentation could also be a decent solution.

As mentioned, ready docker packages, but also AWS Lambda packages (and other PaaS) could be included in the docs as well as deployment steps for each platform. But I understand that's mostly up to the community.

[pperona]

Here is an example of what can go wrong:

In [2]: import jinja2                                                           

In [3]: import weasyprint                                                       
---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-3-4d0739b75804> in <module>
----> 1 import weasyprint

~/anaconda3/lib/python3.6/site-packages/weasyprint/__init__.py in <module>
    439 
    440 # Work around circular imports.
--> 441 from .css import preprocess_stylesheet  # noqa isort:skip
    442 from .html import (  # noqa isort:skip
    443     HTML5_UA_STYLESHEET, HTML5_PH_STYLESHEET, find_base_url, get_html_metadata)

~/anaconda3/lib/python3.6/site-packages/weasyprint/css/__init__.py in <module>
     28 from ..logger import LOGGER, PROGRESS_LOGGER
     29 from ..urls import URLFetchingError, get_url_attribute, url_join
---> 30 from . import computed_values, media_queries
     31 from .properties import INHERITED, INITIAL_NOT_COMPUTED, INITIAL_VALUES
     32 from .utils import remove_whitespace

~/anaconda3/lib/python3.6/site-packages/weasyprint/css/computed_values.py in <module>
     15 from tinycss2.color3 import parse_color
     16 
---> 17 from .. import text
     18 from ..logger import LOGGER
     19 from ..urls import get_link_attribute

~/anaconda3/lib/python3.6/site-packages/weasyprint/text.py in <module>
     12 import re
     13 
---> 14 import cairocffi as cairo
     15 import cffi
     16 import pyphen

~/anaconda3/lib/python3.6/site-packages/cairocffi/__init__.py in <module>
     37 
     38 
---> 39 cairo = dlopen(ffi, 'cairo', 'cairo-2', 'cairo-gobject-2', 'cairo.so.2')
     40 
     41 

~/anaconda3/lib/python3.6/site-packages/cairocffi/__init__.py in dlopen(ffi, *names)
     34             except OSError:
     35                 pass
---> 36     raise OSError("dlopen() failed to load a library: %s" % ' / '.join(names))
     37 
     38 

OSError: dlopen() failed to load a library: cairo / cairo-2 / cairo-gobject-2 / cairo.so.2

In [4]: quit 

[liZe]

Here is an example of what can go wrong:

There's no need to convince anyone that things may go wrong when you have external dependencies (moreover when you don't follow the installation guide and try to use Anaconda, but that's another story :wink:). We'd really like to find a solution about this, but without a port of Pango and Cairo (and Fontconfig and Freetype and GDK-Pixbuf and …) in Python, the only solutions we have are a better documentation or packaged distributions of WeasyPrint.

As mentioned, ready docker packages, but also AWS Lambda packages (and other PaaS) could be included in the docs as well as deployment steps for each platform. But I understand that's mostly up to the community.

Yes, I've done my best to have a pretty good documentation for many Linux distributions, @Tontyna has really improved both the code and the documentation about installation on Windows, but we can't cover all the cases needed by users, and we have to rely on everybody's work for that. I'd be really happy to merge pull requests adding more documentation about Docker images, AWS and Anaconda :heart:.

[pperona]

Thank you!

On Sat, Apr 13, 2019 at 12:44 PM Guillaume Ayoub [e-mail]
wrote:

Here is an example of what can go wrong:

There's no need to convince anyone that things may go wrong when you have
external dependencies (moreover when you don't follow the installation
guide https://weasyprint.readthedocs.io/en/latest/install.html and try
to use Anaconda, but that's another story 😉). We'd really like to find a
solution about this, but without a port of Pango and Cairo (and Fontconfig
and Freetype and GDK-Pixbuf and …) in Python, the only solutions we have
are a better documentation or packaged distributions of WeasyPrint.

As mentioned, ready docker packages, but also AWS Lambda packages (and
other PaaS) could be included in the docs as well as deployment steps for
each platform. But I understand that's mostly up to the community.

Yes, I've done my best to have a pretty good documentation for many Linux
distributions, @Tontyna https://github.com/Tontyna has really improved
both the code and the documentation about installation on Windows, but we
can't cover all the cases needed by users, and we have to rely on
everybody's work for that. I'd be really happy to merge pull requests
adding more documentation about Docker images, AWS and Anaconda ❤️.

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[stuaxo]

A manylinux build of CairoCFFI could help a lot here, that's tricky in it's own right - but not impossible.

[liZe]

A manylinux build of CairoCFFI could help a lot here, that's tricky in it's own right - but not impossible.

CairoCFFI requires a file generation step during its installation, and I think that the generated file depends on the version of Cairo installed on the system. I'd be happy to discuss this on a separate issue for CairoCFFI.

[liZe]

Cairo is now gone :).