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