Source code for revproxy.transformer

import re

from io import StringIO

import logging

from django.utils.six import string_types
from django.template import loader

try:
    from diazo.compiler import compile_theme
except ImportError:
    #: Variable used to identify if diazo is available
    HAS_DIAZO = False
else:
    HAS_DIAZO = True
    from lxml import etree

from .utils import get_charset, is_html_content_type

#: Regex used to find the doctype-header in a html content
doctype_re = re.compile(br"^<!DOCTYPE\s[^>]+>\s*", re.MULTILINE)
#: String used to verify if request has a 'HTTP_X_DIAZO_OFF' header
DIAZO_OFF_REQUEST_HEADER = 'HTTP_X_DIAZO_OFF'
#: String used to verify if request has a 'X-Diazo-Off' header
DIAZO_OFF_RESPONSE_HEADER = 'X-Diazo-Off'


def asbool(value):
    """Function used to convert certain string values into an appropriated
    boolean value.If value is not a string the built-in python
    bool function will be used to convert the passed parameter

    :param      value: an object to be converted to a boolean value
    :returns:   A boolean value
    """

    is_string = isinstance(value, string_types)

    if is_string:
        value = value.strip().lower()
        if value in ('true', 'yes', 'on', 'y', 't', '1',):
            return True
        elif value in ('false', 'no', 'off', 'n', 'f', '0'):
            return False
        else:
            raise ValueError("String is not true/false: %r" % value)
    else:
        return bool(value)


class DiazoTransformer(object):
    """Class used to make a diazo transformation on a request or a response"""

    def __init__(self, request, response):
        self.request = request
        self.response = response
        self.log = logging.getLogger('revproxy.transformer')
        self.log.info("DiazoTransformer created")

    def should_transform(self):
        """Determine if we should transform the response

        :returns:  A boolean value
        """

        if not HAS_DIAZO:
            self.log.info("HAS_DIAZO: false")
            return False

        if asbool(self.request.META.get(DIAZO_OFF_REQUEST_HEADER)):
            self.log.info("DIAZO_OFF_REQUEST_HEADER in request.META: off")
            return False

        if asbool(self.response.get(DIAZO_OFF_RESPONSE_HEADER)):
            self.log.info("DIAZO_OFF_RESPONSE_HEADER in response.get: off")
            return False

        if self.request.is_ajax():
            self.log.info("Request is AJAX")
            return False

        if self.response.streaming:
            self.log.info("Response has streaming")
            return False

        content_type = self.response.get('Content-Type')
        if not is_html_content_type(content_type):
            self.log.info("Content-type: false")
            return False

        content_encoding = self.response.get('Content-Encoding')
        if content_encoding in ('zip', 'compress'):
            self.log.info("Content encode is %s", content_encoding)
            return False

        status_code = str(self.response.status_code)
        if status_code.startswith('3') or \
                status_code == '204' or \
                status_code == '401':
            self.log.info("Status code: %s", status_code)
            return False

        if len(self.response.content) == 0:
            self.log.info("Response Content is EMPTY")
            return False

        self.log.info("Transform")
        return True

    def transform(self, rules, theme_template, is_html5, context_data=None):
        """Method used to make a transformation on the content of
        the http response based on the rules and theme_templates
        passed as paremters

        :param  rules: A file with a set of diazo rules to make a
                       transformation over the original response content
        :param  theme_template: A file containing the template used to format
                                the the original response content
        :param    is_html5: A boolean parameter to identify a html5 doctype
        :returns: A response with a content transformed based on the rules and
                  theme_template
        """

        if not self.should_transform():
            self.log.info("Don't need to be transformed")
            return self.response

        theme = loader.render_to_string(theme_template, context=context_data,
                                        request=self.request)
        output_xslt = compile_theme(
            rules=rules,
            theme=StringIO(theme),
        )

        transform = etree.XSLT(output_xslt)
        self.log.debug("Transform: %s", transform)

        charset = get_charset(self.response.get('Content-Type'))

        try:
            decoded_response = self.response.content.decode(charset)
        except UnicodeDecodeError:
            decoded_response = self.response.content.decode(charset, 'ignore')
            self.log.warning("Charset is {} and type of encode used in file is\
                              different. Some unknown characteres might be\
                              ignored.".format(charset))

        content_doc = etree.fromstring(decoded_response,
                                       parser=etree.HTMLParser())

        self.response.content = transform(content_doc)

        if is_html5:
            self.set_html5_doctype()

        self.reset_headers()

        self.log.debug("Response transformer: %s", self.response)
        return self.response

    def reset_headers(self):
        """This method remove the header Content-Length entry
        from the response
        """
        self.log.info("Reset header")
        del self.response['Content-Length']

    def set_html5_doctype(self):
        """Method used to transform a doctype in to a properly html5 doctype
        """
        doctype = b'<!DOCTYPE html>\n'
        content = doctype_re.subn(doctype, self.response.content, 1)[0]
        self.response.content = content