libsass-python/sassutils/wsgi.py

""":mod:`sassutils.wsgi` --- WSGI middleware for development purpose
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"""
from __future__ import absolute_import

import logging
import os
import os.path

from pkg_resources import resource_filename

from sass import CompileError
from sassutils._compat import collections_abc
from .builder import Manifest

__all__ = 'SassMiddleware',


class SassMiddleware(object):
    r"""WSGI middleware for development purpose.  Every time a CSS file has
    requested it finds a matched Sass/SCSS source file and then compiled
    it into CSS.

    It shows syntax errors in three ways:

    Heading comment
        The result CSS includes detailed error message in the heading
        CSS comment e.g.:

        .. code-block:: css

            /*
            Error: invalid property name
            */

    Red text in ``body:before``
        The result CSS draws detailed error message in ``:before``
        pseudo-class of ``body`` element e.g.:

        .. code-block:: css

            body:before {
                content: 'Error: invalid property name';
                color: maroon;
                background-color: white;
            }

        In most cases you could be aware of syntax error by refreshing your
        working document because it will removes all other styles and leaves
        only a red text.

    :mod:`logging`
        It logs syntax errors if exist during compilation to
        ``sassutils.wsgi.SassMiddleware`` logger with level ``ERROR``.

        To enable this::

            from logging import Formatter, StreamHandler, getLogger
            logger = getLogger('sassutils.wsgi.SassMiddleware')
            handler = StreamHandler(level=logging.ERROR)
            formatter = Formatter(fmt='*' * 80 + '\n%(message)s\n' + '*' * 80)
            handler.setFormatter(formatter)
            logger.addHandler(handler)

        Or simply::

            import logging
            logging.basicConfig()

    :param app: the WSGI application to wrap
    :type app: :class:`collections.abc.Callable`
    :param manifests: build settings.  the same format to
                      :file:`setup.py` script's ``sass_manifests``
                      option
    :type manifests: :class:`collections.abc.Mapping`
    :param package_dir: optional mapping of package names to directories.
                        the same format to :file:`setup.py` script's
                        ``package_dir`` option
    :type package_dir: :class:`collections.abc.Mapping`

    .. versionchanged:: 0.4.0
       It creates also source map files with filenames followed by
       :file:`.map` suffix.

    .. versionadded:: 0.8.0
       It logs syntax errors if exist during compilation to
       ``sassutils.wsgi.SassMiddleware`` logger with level ``ERROR``.

    """

    def __init__(
        self, app, manifests, package_dir={},
        error_status='200 OK',
    ):
        if not callable(app):
            raise TypeError(
                'app must be a WSGI-compliant callable object, '
                'not ' + repr(app),
            )
        self.app = app
        self.manifests = Manifest.normalize_manifests(manifests)
        if not isinstance(package_dir, collections_abc.Mapping):
            raise TypeError(
                'package_dir must be a mapping object, not ' +
                repr(package_dir),
            )
        self.error_status = error_status
        self.package_dir = dict(package_dir)
        for package_name in self.manifests:
            if package_name in self.package_dir:
                continue
            path = resource_filename(package_name, '')
            self.package_dir[package_name] = path
        self.paths = []
        for package_name, manifest in self.manifests.items():
            wsgi_path = manifest.wsgi_path
            if not wsgi_path.startswith('/'):
                wsgi_path = '/' + wsgi_path
            if not wsgi_path.endswith('/'):
                wsgi_path += '/'
            package_dir = self.package_dir[package_name]
            self.paths.append((wsgi_path, package_dir, manifest))

    def __call__(self, environ, start_response):
        path = environ.get('PATH_INFO', '/')
        if path.endswith('.css'):
            for prefix, package_dir, manifest in self.paths:
                if not path.startswith(prefix):
                    continue
                css_filename = path[len(prefix):]
                sass_filename = manifest.unresolve_filename(
                    package_dir, css_filename,
                )
                try:
                    result = manifest.build_one(
                        package_dir,
                        sass_filename,
                        source_map=True,
                    )
                except (IOError, OSError):
                    break
                except CompileError as e:
                    logger = logging.getLogger(__name__ + '.SassMiddleware')
                    logger.error(str(e))
                    start_response(
                        self.error_status,
                        [('Content-Type', 'text/css; charset=utf-8')],
                    )
                    return [
                        b'/*\n', str(e).encode('utf-8'), b'\n*/\n\n',
                        b'body:before { content: ',
                        self.quote_css_string(str(e)).encode('utf-8'),
                        b'; color: maroon; background-color: white',
                        b'; white-space: pre-wrap; display: block',
                        b'; font-family: "Courier New", monospace'
                        b'; user-select: text; }',
                    ]

                def read_file(path):
                    with open(path, 'rb') as in_:
                        while 1:
                            chunk = in_.read(4096)
                            if chunk:
                                yield chunk
                            else:
                                break
                start_response('200 OK', [('Content-Type', 'text/css')])
                return read_file(os.path.join(package_dir, result))
        return self.app(environ, start_response)

    @staticmethod
    def quote_css_string(s):
        """Quotes a string as CSS string literal."""
        return "'" + ''.join('\\%06x' % ord(c) for c in s) + "'"