~launchpad-pqm/launchpad/devel

# Copyright 2009 Canonical Ltd.  This software is licensed under the

# GNU Affero General Public License version 3 (see the file LICENSE).

"""Validate XML documents against a schema."""

__all__ = [

    'XMLValidator',

    'RelaxNGValidator',

    ]

import os

from tempfile import NamedTemporaryFile

from lp.services.helpers import simple_popen2

class XMLValidator:

    """A validator for XML files against a schema."""

    SCHEMA_ARGUMENT = 'schema'

    def __init__(self, schema_filename):

        """Create a validator instance.

        :param schema_filename: The name of a file containing the schema.

        """

        self.schema_filename = schema_filename

        self._errors = ''

    def validate(self, xml):

        """Validate the string xml

        :return: True, if xml is valid, else False.

        """

        # XXX Abel Deuring, 2008-03-20

        # The original implementation of the validation used the lxml

        # package. Unfortunately, running lxml's Relax NG validator

        # caused segfaults during PQM test runs, hence this class uses

        # an external validator.

        # Performance penalty of the external validator:

        # Using the lxml validator, the tests in this module need ca.

        # 3 seconds on a 2GHz Core2Duo laptop.

        # If the xml data to be validated is passed to xmllint via

        # lp.services.helpers.simple_popen2, the run time

        # of the tests is 38..40 seconds; if the validation input

        # is not passed via stdin but saved in a temporary file,

        # the tests need 28..30 seconds.

        xml_file = NamedTemporaryFile()

        xml_file.write(xml)

        xml_file.flush()

        command = ['xmllint', '--noout', '--nonet',

                   '--%s' % self.SCHEMA_ARGUMENT,

                   self.schema_filename, xml_file.name]

        local_catalog_path = os.path.abspath(

            os.path.join(os.path.dirname(__file__), "tests", "testfiles",

                         "catalog", "catalog"))

        catalogs = " ".join(

            [local_catalog_path, "/etc/xml/catalog"])

        env = {"XML_CATALOG_FILES": catalogs}

        result = simple_popen2(command, '', env=env).strip()

        # The output consists of lines describing possible errors; the

        # last line is either "(file) fails to validate" or

        # "(file) validates".

        parts = result.rsplit('\n', 1)

        if len(parts) > 1:

            self._errors = parts[0]

            status = parts[1]

        else:

            self._errors = ''

            status = parts[0]

        if status == xml_file.name + ' fails to validate':

            return False

        elif status == xml_file.name + ' validates':

            return True

        else:

            raise AssertionError(

                'Unexpected result of running xmllint: %s' % result)

    @property

    def error_log(self):

        """A string with the errors detected by the validator.

        Each line contains one error; if the validation was successful,

        error_log is the empty string.

        """

        return self._errors

class RelaxNGValidator(XMLValidator):

    """A validator for Relax NG schemas."""

    SCHEMA_ARGUMENT = 'relaxng'