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Diffstat (limited to 'Lib/email/policy.py')
| -rw-r--r-- | Lib/email/policy.py | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/Lib/email/policy.py b/Lib/email/policy.py new file mode 100644 index 0000000000..38e88afe1d --- /dev/null +++ b/Lib/email/policy.py @@ -0,0 +1,188 @@ +"""This will be the home for the policy that hooks in the new +code that adds all the email6 features. +""" + +from email._policybase import Policy, Compat32, compat32, _extend_docstrings +from email.utils import _has_surrogates +from email.headerregistry import HeaderRegistry as HeaderRegistry + +__all__ = [ + 'Compat32', + 'compat32', + 'Policy', + 'EmailPolicy', + 'default', + 'strict', + 'SMTP', + 'HTTP', + ] + +@_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: + + 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.) + """ + + refold_source = 'long' + header_factory = HeaderRegistry() + + 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, joining all subsequent lines together, and + stripping any trailing carriage return or linefeed characters. (This + is the same as Compat32). + + """ + 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 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: + 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 + return self.header_factory(name, ''.join(value.splitlines())) + + 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. + + """ + folded = self._fold(name, value, refold_binary=self.cte_type=='7bit') + return folded.encode('ascii', '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 float('inf') + lines = value.splitlines() + 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 refold or refold_binary and _has_surrogates(value): + 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) |