Source code for falcon.http_error

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"""HTTPError exception class."""

from collections import OrderedDict
import xml.etree.ElementTree as et

from falcon.constants import MEDIA_JSON
from falcon.util import uri
from falcon.util.deprecation import deprecated
from falcon.util.deprecation import deprecated_args


[docs]class HTTPError(Exception): """Represents a generic HTTP error. Raise an instance or subclass of ``HTTPError`` to have Falcon return a formatted error response and an appropriate HTTP status code to the client when something goes wrong. JSON and XML media types are supported by default. To customize the error presentation, implement a custom error serializer and set it on the :class:`~.App` instance via :meth:`~.App.set_error_serializer`. To customize what data is passed to the serializer, subclass ``HTTPError`` and override the ``to_dict()`` method (``to_json()`` is implemented via ``to_dict()``). To also support XML, override the ``to_xml()`` method. Note: ``status`` is the only positional argument allowed, the other arguments should be used as keyword only. Using them as positional arguments will raise a deprecation warning and will result in an error in a future version of falcon. Args: status (str): HTTP status code and text, such as "400 Bad Request" Keyword Args: title (str): Human-friendly error title. If not provided, defaults to the HTTP status line as determined by the ``status`` argument. description (str): Human-friendly description of the error, along with a helpful suggestion or two (default ``None``). headers (dict or list): A ``dict`` of header names and values to set, or a ``list`` of (*name*, *value*) tuples. Both *name* and *value* 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 overridden. 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 ``tuple`` slightly faster than a ``dict``. 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 (default 'App 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``). Attributes: status (str): HTTP status line, e.g. '748 Confounded by Ponies'. title (str): Error title to send to the client. 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. """ __slots__ = ( 'status', 'title', 'description', 'headers', 'link', 'code', ) @deprecated_args(allowed_positional=1) def __init__( self, status, title=None, description=None, headers=None, href=None, href_text=None, code=None, ): self.status = status # TODO(kgriffs): HTTP/2 does away with the "reason phrase". Eventually # we'll probably switch over to making everything code-based to more # easily support HTTP/2. When that happens, should we continue to # include the reason phrase in the title? self.title = title or status self.description = description self.headers = headers self.code = code if href: link = self.link = OrderedDict() link['text'] = href_text or 'Documentation related to this error' link['href'] = uri.encode(href) link['rel'] = 'help' else: self.link = None def __repr__(self): return '<%s: %s>' % (self.__class__.__name__, self.status) __str__ = __repr__ @property # type: ignore @deprecated( 'has_representation is deprecated and is currently unused by falcon', is_property=True, ) def has_representation(self): return True
[docs] def to_dict(self, obj_type=dict): """Return a basic 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: dict: A dictionary populated with the error's title, description, etc. """ obj = obj_type() 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
[docs] def to_json(self, handler=None): """Return a JSON representation of the error. Args: handler: Handler object that will be used to serialize the representation of this error to JSON. When not provided, a default handler using the builtin JSON library will be used (default ``None``). Returns: bytes: A JSON document for the error. """ obj = self.to_dict(OrderedDict) if handler is None: handler = _DEFAULT_JSON_HANDLER return handler.serialize(obj, MEDIA_JSON)
[docs] def to_xml(self): """Return an XML-encoded representation of the error. Returns: bytes: An XML document for the error. """ error_element = et.Element('error') 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' )
# NOTE: initialized in falcon.media.json, that is always imported since Request/Respose # are imported by falcon init. _DEFAULT_JSON_HANDLER = None class NoRepresentation: """Mixin for ``HTTPError`` child classes that have no representation. This class can be mixed in when inheriting from ``HTTPError``, in order to override the `has_representation` property such that it always returns ``False``. This, in turn, will cause Falcon to return an empty response body to the client. You can use this mixin when defining errors that either should not have a body (as dictated by HTTP standards or common practice), or in the case that a detailed error response may leak information to an attacker. Note: This mixin class must appear before ``HTTPError`` in the base class list when defining the child; otherwise, it will not override the `has_representation` property as expected. Warning: As of Falcon 3.0, this mixin class is no longer used since all Falcon errors have a representation. This class is considered deprecated and will be removed in a future release. """ @property # type: ignore @deprecated( 'has_representation is deprecated and is currently unused by falcon. ' 'The class NoRepresentation is deprecated and will be removed in a ' 'future release', is_property=True, ) def has_representation(self): return False class OptionalRepresentation: """Mixin for ``HTTPError`` child classes that may have a representation. This class can be mixed in when inheriting from ``HTTPError`` in order to override the `has_representation` property, such that it will return ``False`` when the error instance has no description (i.e., the `description` kwarg was not set). You can use this mixin when defining errors that do not include a body in the HTTP response by default, serializing details only when the web developer provides a description of the error. Note: This mixin class must appear before ``HTTPError`` in the base class list when defining the child; otherwise, it will not override the `has_representation` property as expected. Warning: As of Falcon 3.0, this mixin class is no longer used since all Falcon errors have a representation. This class is considered deprecated and will be removed in a future release. """ @property # type: ignore @deprecated( 'has_representation is deprecated and is currently unused by falcon. ' 'The class OptionalRepresentation is deprecated and will be removed ' 'in a future release', is_property=True, ) def has_representation(self): return self.description is not None