deb-python-falcon/falcon/http_error.py

# Copyright 2013 by Rackspace Hosting, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import json
import sys
import xml.etree.ElementTree as et

if sys.version_info < (2, 7):  # pragma: no cover
    # NOTE(kgriffs): We could use the module from PyPI, but ordering isn't
    # critical in JSON, and Falcon eschews dependencies.
    OrderedDict = dict
else:  # pragma: no cover
    from collections import OrderedDict

from falcon.util import uri


class HTTPError(Exception):
    """Represents a generic HTTP error.

    Raise this or a child class to have Falcon automagically return pretty
    error responses (with an appropriate HTTP status code) to the client
    when something goes wrong.

    Attributes:
        status (str): HTTP status line, such as "748 Confounded by Ponies".
        has_representation (bool): Read-only property that determines
            whether error details will be serialized when composing
            the HTTP response. In ``HTTPError`` this property always
            returns ``True``, but child classes may override this property
            in order to return ``False`` when an empty HTTP body is desired.
        title (str): Error title to send to the client. Will be ``None`` if
            the error should result in an HTTP response with an empty body.
        description (str): Description of the error to send to the client.
        headers (dict): Extra headers to add to the response.
        link (str): An href that the client can provide to the user for
            getting help.
        code (int): An internal application code that a user can reference when
            requesting support for the error.

    Args:
        status (str): HTTP status code and text, such as "400 Bad Request"

    Keyword Args:
        title (str): Human-friendly error title (default ``None``).
        description (str): Human-friendly description of the error, along with
            a helpful suggestion or two (default ``None``).
        headers (dict or list): A dictionary of header names and values
            to set, or list of (name, value) tuples. Both names and
            values must be of type str or StringType, and only character
            values 0x00 through 0xFF may be used on platforms that use
            wide characters.

            Note:
                The Content-Type header, if present, will be overriden. If
                you wish to return custom error messages, you can create
                your own HTTP error class, and install an error handler
                to convert it into an appropriate HTTP response for the
                client

            Note:
                Falcon can process a list of tuples slightly faster
                than a dict.

        headers (dict): Extra headers to return in the
            response to the client (default ``None``).
        href (str): A URL someone can visit to find out more information
            (default ``None``). Unicode characters are percent-encoded.
        href_text (str): If href is given, use this as the friendly
            title/description for the link (defaults to "API documentation
            for this error").
        code (int): An internal code that customers can reference in their
            support request or to help them when searching for knowledge
            base articles related to this error (default ``None``).
    """

    __slots__ = (
        'status',
        'title',
        'description',
        'headers',
        'link',
        'code',
    )

    def __init__(self, status, title=None, description=None, headers=None,
                 href=None, href_text=None, code=None):
        self.status = status
        self.title = title
        self.description = description
        self.headers = headers
        self.code = code

        if href:
            link = self.link = OrderedDict()
            link['text'] = (href_text or 'API documention for this error')
            link['href'] = uri.encode(href)
            link['rel'] = 'help'
        else:
            self.link = None

    @property
    def has_representation(self):
        return True

    def raw(self, obj_type=dict):
        """Returns a raw dictionary representing the error.

        This method can be useful when serializing the error to hash-like
        media types, such as YAML, JSON, and MessagePack.

        Args:
            obj_type: A dict-like type that will be used to store the
                error information (default *dict*).

        Returns:
            A dictionary populated with the error's title, description, etc.

        """

        assert self.has_representation

        obj = obj_type()

        if self.title is not None:
            obj['title'] = self.title

        if self.description is not None:
            obj['description'] = self.description

        if self.code is not None:
            obj['code'] = self.code

        if self.link is not None:
            obj['link'] = self.link

        return obj

    def json(self):
        """Returns a pretty-printed JSON representation of the error.

        Returns:
            A JSON document for the error.

        """

        obj = self.raw(OrderedDict)
        return json.dumps(obj, indent=4, separators=(',', ': '),
                          ensure_ascii=False)

    def xml(self):
        """Returns an XML-encoded representation of the error.

        Returns:
            An XML document for the error.

        """

        assert self.has_representation

        error_element = et.Element('error')

        if self.title is not None:
            et.SubElement(error_element, 'title').text = self.title

        if self.description is not None:
            et.SubElement(error_element, 'description').text = self.description

        if self.code is not None:
            et.SubElement(error_element, 'code').text = str(self.code)

        if self.link is not None:
            link_element = et.SubElement(error_element, 'link')

            for key in ('text', 'href', 'rel'):
                et.SubElement(link_element, key).text = self.link[key]

        return (b'<?xml version="1.0" encoding="UTF-8"?>' +
                et.tostring(error_element, encoding='utf-8'))