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policy.py
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"""This will be the home for the policy that hooks in the new code that adds all the email6 features. """ import re import sys from email._policybase import Policy, Compat32, compat32, _extend_docstrings from email.utils import _has_surrogates from email.headerregistry import HeaderRegistry as HeaderRegistry from email.contentmanager import raw_data_manager from email.message import EmailMessage __all__ = [ 'Compat32', 'compat32', 'Policy', 'EmailPolicy', 'default', 'strict', 'SMTP', 'HTTP', ] linesep_splitter = re.compile(r'\n|\r\n?') @_extend_docstrings class EmailPolicy(Policy): """+ PROVISIONAL The API extensions enabled by this policy are currently provisional. Refer to the documentation for details. This policy adds new header parsing and folding algorithms. Instead of simple strings, headers are custom objects with custom attributes depending on the type of the field. The folding algorithm fully implements RFCs 2047 and 5322. In addition to the settable attributes listed above that apply to all Policies, this policy adds the following additional attributes: utf8 -- if False (the default) message headers will be serialized as ASCII, using encoded words to encode any non-ASCII characters in the source strings. If True, the message headers will be serialized using utf8 and will not contain encoded words (see RFC 6532 for more on this serialization format). refold_source -- if the value for a header in the Message object came from the parsing of some source, this attribute indicates whether or not a generator should refold that value when transforming the message back into stream form. The possible values are: none -- all source values use original folding long -- source values that have any line that is longer than max_line_length will be refolded all -- all values are refolded. The default is 'long'. header_factory -- a callable that takes two arguments, 'name' and 'value', where 'name' is a header field name and 'value' is an unfolded header field value, and returns a string-like object that represents that header. A default header_factory is provided that understands some of the RFC5322 header field types. (Currently address fields and date fields have special treatment, while all other fields are treated as unstructured. This list will be completed before the extension is marked stable.) content_manager -- an object with at least two methods: get_content and set_content. When the get_content or set_content method of a Message object is called, it calls the corresponding method of this object, passing it the message object as its first argument, and any arguments or keywords that were passed to it as additional arguments. The default content_manager is :data:`~email.contentmanager.raw_data_manager`. """ message_factory = EmailMessage utf8 = False refold_source = 'long' header_factory = HeaderRegistry() content_manager = raw_data_manager def __init__(self, **kw): # Ensure that each new instance gets a unique header factory # (as opposed to clones, which share the factory). if 'header_factory' not in kw: object.__setattr__(self, 'header_factory', HeaderRegistry()) super().__init__(**kw) def header_max_count(self, name): """+ The implementation for this class returns the max_count attribute from the specialized header class that would be used to construct a header of type 'name'. """ return self.header_factory[name].max_count # The logic of the next three methods is chosen such that it is possible to # switch a Message object between a Compat32 policy and a policy derived # from this class and have the results stay consistent. This allows a # Message object constructed with this policy to be passed to a library # that only handles Compat32 objects, or to receive such an object and # convert it to use the newer style by just changing its policy. It is # also chosen because it postpones the relatively expensive full rfc5322 # parse until as late as possible when parsing from source, since in many # applications only a few headers will actually be inspected. 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 joined with all subsequent lines, and stripping any trailing carriage return or linefeed characters. (This is the same as Compat32). """ name, value = sourcelines[0].split(':', 1) value = ''.join((value, *sourcelines[1:])).lstrip(' \t\r\n') return (name, value.rstrip('\r\n')) def header_store_parse(self, name, value): """+ The name is returned unchanged. If the input value has a 'name' attribute and it matches the name ignoring case, the value is returned unchanged. Otherwise the name and value are passed to header_factory method, and the resulting custom header object is returned as the value. In this case a ValueError is raised if the input value contains CR or LF characters. """ if hasattr(value, 'name') and value.name.lower() == name.lower(): return (name, value) if isinstance(value, str) and len(value.splitlines())>1: # XXX this error message isn't quite right when we use splitlines # (see issue 22233), but I'm not sure what should happen here. raise ValueError("Header values may not contain linefeed " "or carriage return characters") return (name, self.header_factory(name, value)) def header_fetch_parse(self, name, value): """+ If the value has a 'name' attribute, it is returned to unmodified. Otherwise the name and the value with any linesep characters removed are passed to the header_factory method, and the resulting custom header object is returned. Any surrogateescaped bytes get turned into the unicode unknown-character glyph. """ if hasattr(value, 'name'): return value # We can't use splitlines here because it splits on more than \r and \n. value = ''.join(linesep_splitter.split(value)) return self.header_factory(name, value) def fold(self, name, value): """+ Header folding is controlled by the refold_source policy setting. A value is considered to be a 'source value' if and only if it does not have a 'name' attribute (having a 'name' attribute means it is a header object of some sort). If a source value needs to be refolded according to the policy, it is converted into a custom header object by passing the name and the value with any linesep characters removed to the header_factory method. Folding of a custom header object is done by calling its fold method with the current policy. Source values are split into lines using splitlines. If the value is not to be refolded, the lines are rejoined using the linesep from the policy and returned. The exception is lines containing non-ascii binary data. In that case the value is refolded regardless of the refold_source setting, which causes the binary data to be CTE encoded using the unknown-8bit charset. """ return self._fold(name, value, refold_binary=True) def fold_binary(self, name, value): """+ The same as fold if cte_type is 7bit, except that the returned value is bytes. If cte_type is 8bit, non-ASCII binary data is converted back into bytes. Headers with binary data are not refolded, regardless of the refold_header setting, since there is no way to know whether the binary data consists of single byte characters or multibyte characters. If utf8 is true, headers are encoded to utf8, otherwise to ascii with non-ASCII unicode rendered as encoded words. """ folded = self._fold(name, value, refold_binary=self.cte_type=='7bit') charset = 'utf8' if self.utf8 else 'ascii' return folded.encode(charset, 'surrogateescape') def _fold(self, name, value, refold_binary=False): if hasattr(value, 'name'): return value.fold(policy=self) maxlen = self.max_line_length if self.max_line_length else sys.maxsize # We can't use splitlines here because it splits on more than \r and \n. lines = linesep_splitter.split(value) refold = (self.refold_source == 'all' or self.refold_source == 'long' and (lines and len(lines[0])+len(name)+2 > maxlen or any(len(x) > maxlen for x in lines[1:]))) if not refold: if not self.utf8: refold = not value.isascii() elif refold_binary: refold = _has_surrogates(value) if refold: return self.header_factory(name, ''.join(lines)).fold(policy=self) return name + ': ' + self.linesep.join(lines) + self.linesep default = EmailPolicy() # Make the default policy use the class default header_factory del default.header_factory strict = default.clone(raise_on_defect=True) SMTP = default.clone(linesep='\r\n') HTTP = default.clone(linesep='\r\n', max_line_length=None) SMTPUTF8 = SMTP.clone(utf8=True)