django-compressor - abstract static URL

compressor_filters.py

"""
Django 'base' app - compressor filters.
"""
from compressor.filters.css_default import CssAbsoluteFilter


class CssRelativeFilter(CssAbsoluteFilter):
    """
    ``compressor.filters.css_default.CssAbsoluteFilter`` converts relative URLs to images, fonts, etc
    in CSS code to absolute URLs like '/static/base/images/logo.svg'.

    But STATIC_URL may change in different environments - 
    this is important for offline compression.

    All compressed CSS files are served on URLs like '/static/CACHE/css/25b44215c797.css'.

    So we can convert relative URLs inside '/static/CACHE/css/25b44215c797.css'
    to '../../base/images/logo.svg' which works with _any_ STATIC_URL.
    """
    def __init__(self, *args, **kwargs):
        super(CssRelativeFilter, self).__init__(*args, **kwargs)
        self.url = '../..'

conf.py

"""
Django 'base' app - config.
"""
from functools import wraps
 
from compressor.management.commands.compress import Command
from compressor.templatetags.compress import CompressorNode
from django.apps.config import AppConfig
from django.conf import settings
 
 
class BaseConfig(AppConfig):
    name = 'base'
    STATIC_URL_PLACEHOLDER = '$STATIC_URL/'
 
    def ready(self):
        self._patch_compressor()
 
    def _patch_compressor(self):
        """
        Patch ``django-compressor`` to read/write offline manifest with STATIC_URL replaced 
        by special placeholder, because STATIC_URL may change in different environments.
        """
        # Patch django-compressor offline manifest generator command
        self._patch_compressor_method(Command, 'compress')
 
        # Patch django-compressor offline manifest check
        self._patch_compressor_method(
            CompressorNode, 'render_offline', lambda r, u: r.replace(self.STATIC_URL_PLACEHOLDER, u)
        )
 
    def _patch_compressor_method(self, cls, name, post_process=None):
        """
        Replace class method with patched one:
 
        - substitute ``settings.STATIC_URL`` with special placeholder
        - execute original method
        - optionally, post-process method return value
        - restore original ``settings.STATIC_URL`` value
 
        :param type cls: Class object to patch
        :param str name: Class method name
        :param function post_process: Takes 2 arguments: method return value and static URL
        """
        method = getattr(cls, name)
        placeholder = self.STATIC_URL_PLACEHOLDER
 
        if hasattr(method, '_original'):
            return
 
        @wraps(method)
        def patched_method(self, *args, **kwargs):
            static_url = settings.STATIC_URL
            # TODO: some processing for settings.COMPRESS_URL needed
            settings.STATIC_URL = settings.COMPRESS_URL = placeholder
            try:
                result = method(self, *args, **kwargs)
                if post_process is not None:
                    result = post_process(result, static_url)
                return result
            finally:
                # TODO: some processing for settings.COMPRESS_URL needed
                settings.STATIC_URL = settings.COMPRESS_URL = static_url
 
        patched_method._original = method
        setattr(cls, name, patched_method)

settings.py

INSTALLED_APPS = [
    'base.conf.BaseConfig'
]

COMPRESS_CSS_FILTERS = [
    'base.compressor_filters.CssRelativeFilter'
]