339 lines
13 KiB
Python
339 lines
13 KiB
Python
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"""Policy framework for the email package.
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Allows fine grained feature control of how the package parses and emits data.
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"""
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import abc
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from email import header
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from email import charset as _charset
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from email.utils import _has_surrogates
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__all__ = [
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'Policy',
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'Compat32',
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'compat32',
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]
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class _PolicyBase:
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"""Policy Object basic framework.
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This class is useless unless subclassed. A subclass should define
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class attributes with defaults for any values that are to be
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managed by the Policy object. The constructor will then allow
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non-default values to be set for these attributes at instance
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creation time. The instance will be callable, taking these same
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attributes keyword arguments, and returning a new instance
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identical to the called instance except for those values changed
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by the keyword arguments. Instances may be added, yielding new
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instances with any non-default values from the right hand
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operand overriding those in the left hand operand. That is,
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A + B == A(<non-default values of B>)
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The repr of an instance can be used to reconstruct the object
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if and only if the repr of the values can be used to reconstruct
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those values.
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"""
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def __init__(self, **kw):
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"""Create new Policy, possibly overriding some defaults.
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See class docstring for a list of overridable attributes.
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"""
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for name, value in kw.items():
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if hasattr(self, name):
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super(_PolicyBase,self).__setattr__(name, value)
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else:
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raise TypeError(
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"{!r} is an invalid keyword argument for {}".format(
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name, self.__class__.__name__))
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def __repr__(self):
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args = [ "{}={!r}".format(name, value)
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for name, value in self.__dict__.items() ]
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return "{}({})".format(self.__class__.__name__, ', '.join(args))
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def clone(self, **kw):
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"""Return a new instance with specified attributes changed.
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The new instance has the same attribute values as the current object,
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except for the changes passed in as keyword arguments.
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"""
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for attr, value in self.__dict__.items():
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if attr not in kw:
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kw[attr] = value
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return self.__class__(**kw)
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def __setattr__(self, name, value):
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if hasattr(self, name):
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msg = "{!r} object attribute {!r} is read-only"
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else:
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msg = "{!r} object has no attribute {!r}"
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raise AttributeError(msg.format(self.__class__.__name__, name))
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def __add__(self, other):
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"""Non-default values from right operand override those from left.
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The object returned is a new instance of the subclass.
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"""
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return self.clone(**other.__dict__)
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# Conceptually this isn't a subclass of ABCMeta, but since we want Policy to
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# use ABCMeta as a metaclass *and* we want it to use this one as well, we have
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# to make this one a subclas of ABCMeta.
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class _DocstringExtenderMetaclass(abc.ABCMeta):
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def __new__(meta, classname, bases, classdict):
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if classdict.get('__doc__') and classdict['__doc__'].startswith('+'):
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classdict['__doc__'] = meta._append_doc(bases[0].__doc__,
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classdict['__doc__'])
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for name, attr in classdict.items():
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if attr.__doc__ and attr.__doc__.startswith('+'):
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for cls in (cls for base in bases for cls in base.mro()):
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doc = getattr(getattr(cls, name), '__doc__')
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if doc:
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attr.__doc__ = meta._append_doc(doc, attr.__doc__)
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break
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return super().__new__(meta, classname, bases, classdict)
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@staticmethod
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def _append_doc(doc, added_doc):
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added_doc = added_doc.split('\n', 1)[1]
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return doc + '\n' + added_doc
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class Policy(_PolicyBase, metaclass=_DocstringExtenderMetaclass):
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r"""Controls for how messages are interpreted and formatted.
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Most of the classes and many of the methods in the email package accept
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Policy objects as parameters. A Policy object contains a set of values and
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functions that control how input is interpreted and how output is rendered.
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For example, the parameter 'raise_on_defect' controls whether or not an RFC
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violation results in an error being raised or not, while 'max_line_length'
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controls the maximum length of output lines when a Message is serialized.
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Any valid attribute may be overridden when a Policy is created by passing
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it as a keyword argument to the constructor. Policy objects are immutable,
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but a new Policy object can be created with only certain values changed by
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calling the Policy instance with keyword arguments. Policy objects can
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also be added, producing a new Policy object in which the non-default
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attributes set in the right hand operand overwrite those specified in the
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left operand.
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Settable attributes:
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raise_on_defect -- If true, then defects should be raised as errors.
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Default: False.
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linesep -- string containing the value to use as separation
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between output lines. Default '\n'.
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cte_type -- Type of allowed content transfer encodings
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7bit -- ASCII only
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8bit -- Content-Transfer-Encoding: 8bit is allowed
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Default: 8bit. Also controls the disposition of
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(RFC invalid) binary data in headers; see the
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documentation of the binary_fold method.
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max_line_length -- maximum length of lines, excluding 'linesep',
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during serialization. None or 0 means no line
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wrapping is done. Default is 78.
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"""
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raise_on_defect = False
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linesep = '\n'
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cte_type = '8bit'
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max_line_length = 78
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def handle_defect(self, obj, defect):
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"""Based on policy, either raise defect or call register_defect.
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handle_defect(obj, defect)
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defect should be a Defect subclass, but in any case must be an
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Exception subclass. obj is the object on which the defect should be
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registered if it is not raised. If the raise_on_defect is True, the
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defect is raised as an error, otherwise the object and the defect are
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passed to register_defect.
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This method is intended to be called by parsers that discover defects.
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The email package parsers always call it with Defect instances.
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"""
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if self.raise_on_defect:
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raise defect
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self.register_defect(obj, defect)
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def register_defect(self, obj, defect):
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"""Record 'defect' on 'obj'.
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Called by handle_defect if raise_on_defect is False. This method is
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part of the Policy API so that Policy subclasses can implement custom
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defect handling. The default implementation calls the append method of
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the defects attribute of obj. The objects used by the email package by
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default that get passed to this method will always have a defects
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attribute with an append method.
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"""
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obj.defects.append(defect)
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@abc.abstractmethod
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def header_source_parse(self, sourcelines):
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"""Given a list of linesep terminated strings constituting the lines of
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a single header, return the (name, value) tuple that should be stored
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in the model. The input lines should retain their terminating linesep
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characters. The lines passed in by the email package may contain
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surrogateescaped binary data.
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"""
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raise NotImplementedError
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@abc.abstractmethod
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def header_store_parse(self, name, value):
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"""Given the header name and the value provided by the application
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program, return the (name, value) that should be stored in the model.
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"""
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raise NotImplementedError
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@abc.abstractmethod
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def header_fetch_parse(self, name, value):
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"""Given the header name and the value from the model, return the value
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to be returned to the application program that is requesting that
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header. The value passed in by the email package may contain
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surrogateescaped binary data if the lines were parsed by a BytesParser.
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The returned value should not contain any surrogateescaped data.
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"""
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raise NotImplementedError
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@abc.abstractmethod
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def fold(self, name, value):
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"""Given the header name and the value from the model, return a string
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containing linesep characters that implement the folding of the header
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according to the policy controls. The value passed in by the email
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package may contain surrogateescaped binary data if the lines were
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parsed by a BytesParser. The returned value should not contain any
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surrogateescaped data.
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"""
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raise NotImplementedError
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@abc.abstractmethod
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def fold_binary(self, name, value):
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"""Given the header name and the value from the model, return binary
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data containing linesep characters that implement the folding of the
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header according to the policy controls. The value passed in by the
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email package may contain surrogateescaped binary data.
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"""
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raise NotImplementedError
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class Compat32(Policy):
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"""+
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This particular policy is the backward compatibility Policy. It
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replicates the behavior of the email package version 5.1.
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"""
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def _sanitize_header(self, name, value):
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# If the header value contains surrogates, return a Header using
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# the unknown-8bit charset to encode the bytes as encoded words.
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if not isinstance(value, str):
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# Assume it is already a header object
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return value
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if _has_surrogates(value):
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return header.Header(value, charset=_charset.UNKNOWN8BIT,
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header_name=name)
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else:
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return value
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def header_source_parse(self, sourcelines):
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"""+
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The name is parsed as everything up to the ':' and returned unmodified.
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The value is determined by stripping leading whitespace off the
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remainder of the first line, joining all subsequent lines together, and
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stripping any trailing carriage return or linefeed characters.
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"""
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name, value = sourcelines[0].split(':', 1)
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value = value.lstrip(' \t') + ''.join(sourcelines[1:])
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return (name, value.rstrip('\r\n'))
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def header_store_parse(self, name, value):
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"""+
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The name and value are returned unmodified.
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"""
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return (name, value)
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def header_fetch_parse(self, name, value):
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"""+
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If the value contains binary data, it is converted into a Header object
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using the unknown-8bit charset. Otherwise it is returned unmodified.
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"""
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return self._sanitize_header(name, value)
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def fold(self, name, value):
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"""+
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Headers are folded using the Header folding algorithm, which preserves
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existing line breaks in the value, and wraps each resulting line to the
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max_line_length. Non-ASCII binary data are CTE encoded using the
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unknown-8bit charset.
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"""
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return self._fold(name, value, sanitize=True)
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def fold_binary(self, name, value):
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"""+
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Headers are folded using the Header folding algorithm, which preserves
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existing line breaks in the value, and wraps each resulting line to the
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max_line_length. If cte_type is 7bit, non-ascii binary data is CTE
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encoded using the unknown-8bit charset. Otherwise the original source
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header is used, with its existing line breaks and/or binary data.
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"""
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folded = self._fold(name, value, sanitize=self.cte_type=='7bit')
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return folded.encode('ascii', 'surrogateescape')
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def _fold(self, name, value, sanitize):
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parts = []
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parts.append('%s: ' % name)
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if isinstance(value, str):
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if _has_surrogates(value):
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if sanitize:
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h = header.Header(value,
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charset=_charset.UNKNOWN8BIT,
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header_name=name)
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else:
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# If we have raw 8bit data in a byte string, we have no idea
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# what the encoding is. There is no safe way to split this
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# string. If it's ascii-subset, then we could do a normal
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# ascii split, but if it's multibyte then we could break the
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# string. There's no way to know so the least harm seems to
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# be to not split the string and risk it being too long.
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parts.append(value)
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h = None
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else:
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h = header.Header(value, header_name=name)
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else:
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# Assume it is a Header-like object.
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h = value
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if h is not None:
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parts.append(h.encode(linesep=self.linesep,
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maxlinelen=self.max_line_length))
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parts.append(self.linesep)
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return ''.join(parts)
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compat32 = Compat32()
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