1"""Policy framework for the email package. 2 3Allows fine grained feature control of how the package parses and emits data. 4""" 5 6import abc 7from email import header 8from email import charset as _charset 9from email.utils import _has_surrogates 10 11__all__ = [ 12 'Policy', 13 'Compat32', 14 'compat32', 15 ] 16 17 18class _PolicyBase: 19 20 """Policy Object basic framework. 21 22 This class is useless unless subclassed. A subclass should define 23 class attributes with defaults for any values that are to be 24 managed by the Policy object. The constructor will then allow 25 non-default values to be set for these attributes at instance 26 creation time. The instance will be callable, taking these same 27 attributes keyword arguments, and returning a new instance 28 identical to the called instance except for those values changed 29 by the keyword arguments. Instances may be added, yielding new 30 instances with any non-default values from the right hand 31 operand overriding those in the left hand operand. That is, 32 33 A + B == A(<non-default values of B>) 34 35 The repr of an instance can be used to reconstruct the object 36 if and only if the repr of the values can be used to reconstruct 37 those values. 38 39 """ 40 41 def __init__(self, **kw): 42 """Create new Policy, possibly overriding some defaults. 43 44 See class docstring for a list of overridable attributes. 45 46 """ 47 for name, value in kw.items(): 48 if hasattr(self, name): 49 super(_PolicyBase,self).__setattr__(name, value) 50 else: 51 raise TypeError( 52 "{!r} is an invalid keyword argument for {}".format( 53 name, self.__class__.__name__)) 54 55 def __repr__(self): 56 args = [ "{}={!r}".format(name, value) 57 for name, value in self.__dict__.items() ] 58 return "{}({})".format(self.__class__.__name__, ', '.join(args)) 59 60 def clone(self, **kw): 61 """Return a new instance with specified attributes changed. 62 63 The new instance has the same attribute values as the current object, 64 except for the changes passed in as keyword arguments. 65 66 """ 67 newpolicy = self.__class__.__new__(self.__class__) 68 for attr, value in self.__dict__.items(): 69 object.__setattr__(newpolicy, attr, value) 70 for attr, value in kw.items(): 71 if not hasattr(self, attr): 72 raise TypeError( 73 "{!r} is an invalid keyword argument for {}".format( 74 attr, self.__class__.__name__)) 75 object.__setattr__(newpolicy, attr, value) 76 return newpolicy 77 78 def __setattr__(self, name, value): 79 if hasattr(self, name): 80 msg = "{!r} object attribute {!r} is read-only" 81 else: 82 msg = "{!r} object has no attribute {!r}" 83 raise AttributeError(msg.format(self.__class__.__name__, name)) 84 85 def __add__(self, other): 86 """Non-default values from right operand override those from left. 87 88 The object returned is a new instance of the subclass. 89 90 """ 91 return self.clone(**other.__dict__) 92 93 94def _append_doc(doc, added_doc): 95 doc = doc.rsplit('\n', 1)[0] 96 added_doc = added_doc.split('\n', 1)[1] 97 return doc + '\n' + added_doc 98 99def _extend_docstrings(cls): 100 if cls.__doc__ and cls.__doc__.startswith('+'): 101 cls.__doc__ = _append_doc(cls.__bases__[0].__doc__, cls.__doc__) 102 for name, attr in cls.__dict__.items(): 103 if attr.__doc__ and attr.__doc__.startswith('+'): 104 for c in (c for base in cls.__bases__ for c in base.mro()): 105 doc = getattr(getattr(c, name), '__doc__') 106 if doc: 107 attr.__doc__ = _append_doc(doc, attr.__doc__) 108 break 109 return cls 110 111 112class Policy(_PolicyBase, metaclass=abc.ABCMeta): 113 114 r"""Controls for how messages are interpreted and formatted. 115 116 Most of the classes and many of the methods in the email package accept 117 Policy objects as parameters. A Policy object contains a set of values and 118 functions that control how input is interpreted and how output is rendered. 119 For example, the parameter 'raise_on_defect' controls whether or not an RFC 120 violation results in an error being raised or not, while 'max_line_length' 121 controls the maximum length of output lines when a Message is serialized. 122 123 Any valid attribute may be overridden when a Policy is created by passing 124 it as a keyword argument to the constructor. Policy objects are immutable, 125 but a new Policy object can be created with only certain values changed by 126 calling the Policy instance with keyword arguments. Policy objects can 127 also be added, producing a new Policy object in which the non-default 128 attributes set in the right hand operand overwrite those specified in the 129 left operand. 130 131 Settable attributes: 132 133 raise_on_defect -- If true, then defects should be raised as errors. 134 Default: False. 135 136 linesep -- string containing the value to use as separation 137 between output lines. Default '\n'. 138 139 cte_type -- Type of allowed content transfer encodings 140 141 7bit -- ASCII only 142 8bit -- Content-Transfer-Encoding: 8bit is allowed 143 144 Default: 8bit. Also controls the disposition of 145 (RFC invalid) binary data in headers; see the 146 documentation of the binary_fold method. 147 148 max_line_length -- maximum length of lines, excluding 'linesep', 149 during serialization. None or 0 means no line 150 wrapping is done. Default is 78. 151 152 mangle_from_ -- a flag that, when True escapes From_ lines in the 153 body of the message by putting a `>' in front of 154 them. This is used when the message is being 155 serialized by a generator. Default: False. 156 157 message_factory -- the class to use to create new message objects. 158 If the value is None, the default is Message. 159 160 verify_generated_headers 161 -- if true, the generator verifies that each header 162 they are properly folded, so that a parser won't 163 treat it as multiple headers, start-of-body, or 164 part of another header. 165 This is a check against custom Header & fold() 166 implementations. 167 """ 168 169 raise_on_defect = False 170 linesep = '\n' 171 cte_type = '8bit' 172 max_line_length = 78 173 mangle_from_ = False 174 message_factory = None 175 verify_generated_headers = True 176 177 def handle_defect(self, obj, defect): 178 """Based on policy, either raise defect or call register_defect. 179 180 handle_defect(obj, defect) 181 182 defect should be a Defect subclass, but in any case must be an 183 Exception subclass. obj is the object on which the defect should be 184 registered if it is not raised. If the raise_on_defect is True, the 185 defect is raised as an error, otherwise the object and the defect are 186 passed to register_defect. 187 188 This method is intended to be called by parsers that discover defects. 189 The email package parsers always call it with Defect instances. 190 191 """ 192 if self.raise_on_defect: 193 raise defect 194 self.register_defect(obj, defect) 195 196 def register_defect(self, obj, defect): 197 """Record 'defect' on 'obj'. 198 199 Called by handle_defect if raise_on_defect is False. This method is 200 part of the Policy API so that Policy subclasses can implement custom 201 defect handling. The default implementation calls the append method of 202 the defects attribute of obj. The objects used by the email package by 203 default that get passed to this method will always have a defects 204 attribute with an append method. 205 206 """ 207 obj.defects.append(defect) 208 209 def header_max_count(self, name): 210 """Return the maximum allowed number of headers named 'name'. 211 212 Called when a header is added to a Message object. If the returned 213 value is not 0 or None, and there are already a number of headers with 214 the name 'name' equal to the value returned, a ValueError is raised. 215 216 Because the default behavior of Message's __setitem__ is to append the 217 value to the list of headers, it is easy to create duplicate headers 218 without realizing it. This method allows certain headers to be limited 219 in the number of instances of that header that may be added to a 220 Message programmatically. (The limit is not observed by the parser, 221 which will faithfully produce as many headers as exist in the message 222 being parsed.) 223 224 The default implementation returns None for all header names. 225 """ 226 return None 227 228 @abc.abstractmethod 229 def header_source_parse(self, sourcelines): 230 """Given a list of linesep terminated strings constituting the lines of 231 a single header, return the (name, value) tuple that should be stored 232 in the model. The input lines should retain their terminating linesep 233 characters. The lines passed in by the email package may contain 234 surrogateescaped binary data. 235 """ 236 raise NotImplementedError 237 238 @abc.abstractmethod 239 def header_store_parse(self, name, value): 240 """Given the header name and the value provided by the application 241 program, return the (name, value) that should be stored in the model. 242 """ 243 raise NotImplementedError 244 245 @abc.abstractmethod 246 def header_fetch_parse(self, name, value): 247 """Given the header name and the value from the model, return the value 248 to be returned to the application program that is requesting that 249 header. The value passed in by the email package may contain 250 surrogateescaped binary data if the lines were parsed by a BytesParser. 251 The returned value should not contain any surrogateescaped data. 252 253 """ 254 raise NotImplementedError 255 256 @abc.abstractmethod 257 def fold(self, name, value): 258 """Given the header name and the value from the model, return a string 259 containing linesep characters that implement the folding of the header 260 according to the policy controls. The value passed in by the email 261 package may contain surrogateescaped binary data if the lines were 262 parsed by a BytesParser. The returned value should not contain any 263 surrogateescaped data. 264 265 """ 266 raise NotImplementedError 267 268 @abc.abstractmethod 269 def fold_binary(self, name, value): 270 """Given the header name and the value from the model, return binary 271 data containing linesep characters that implement the folding of the 272 header according to the policy controls. The value passed in by the 273 email package may contain surrogateescaped binary data. 274 275 """ 276 raise NotImplementedError 277 278 279@_extend_docstrings 280class Compat32(Policy): 281 282 """+ 283 This particular policy is the backward compatibility Policy. It 284 replicates the behavior of the email package version 5.1. 285 """ 286 287 mangle_from_ = True 288 289 def _sanitize_header(self, name, value): 290 # If the header value contains surrogates, return a Header using 291 # the unknown-8bit charset to encode the bytes as encoded words. 292 if not isinstance(value, str): 293 # Assume it is already a header object 294 return value 295 if _has_surrogates(value): 296 return header.Header(value, charset=_charset.UNKNOWN8BIT, 297 header_name=name) 298 else: 299 return value 300 301 def header_source_parse(self, sourcelines): 302 """+ 303 The name is parsed as everything up to the ':' and returned unmodified. 304 The value is determined by stripping leading whitespace off the 305 remainder of the first line joined with all subsequent lines, and 306 stripping any trailing carriage return or linefeed characters. 307 308 """ 309 name, value = sourcelines[0].split(':', 1) 310 value = ''.join((value, *sourcelines[1:])).lstrip(' \t\r\n') 311 return (name, value.rstrip('\r\n')) 312 313 def header_store_parse(self, name, value): 314 """+ 315 The name and value are returned unmodified. 316 """ 317 return (name, value) 318 319 def header_fetch_parse(self, name, value): 320 """+ 321 If the value contains binary data, it is converted into a Header object 322 using the unknown-8bit charset. Otherwise it is returned unmodified. 323 """ 324 return self._sanitize_header(name, value) 325 326 def fold(self, name, value): 327 """+ 328 Headers are folded using the Header folding algorithm, which preserves 329 existing line breaks in the value, and wraps each resulting line to the 330 max_line_length. Non-ASCII binary data are CTE encoded using the 331 unknown-8bit charset. 332 333 """ 334 return self._fold(name, value, sanitize=True) 335 336 def fold_binary(self, name, value): 337 """+ 338 Headers are folded using the Header folding algorithm, which preserves 339 existing line breaks in the value, and wraps each resulting line to the 340 max_line_length. If cte_type is 7bit, non-ascii binary data is CTE 341 encoded using the unknown-8bit charset. Otherwise the original source 342 header is used, with its existing line breaks and/or binary data. 343 344 """ 345 folded = self._fold(name, value, sanitize=self.cte_type=='7bit') 346 return folded.encode('ascii', 'surrogateescape') 347 348 def _fold(self, name, value, sanitize): 349 parts = [] 350 parts.append('%s: ' % name) 351 if isinstance(value, str): 352 if _has_surrogates(value): 353 if sanitize: 354 h = header.Header(value, 355 charset=_charset.UNKNOWN8BIT, 356 header_name=name) 357 else: 358 # If we have raw 8bit data in a byte string, we have no idea 359 # what the encoding is. There is no safe way to split this 360 # string. If it's ascii-subset, then we could do a normal 361 # ascii split, but if it's multibyte then we could break the 362 # string. There's no way to know so the least harm seems to 363 # be to not split the string and risk it being too long. 364 parts.append(value) 365 h = None 366 else: 367 h = header.Header(value, header_name=name) 368 else: 369 # Assume it is a Header-like object. 370 h = value 371 if h is not None: 372 # The Header class interprets a value of None for maxlinelen as the 373 # default value of 78, as recommended by RFC 2822. 374 maxlinelen = 0 375 if self.max_line_length is not None: 376 maxlinelen = self.max_line_length 377 parts.append(h.encode(linesep=self.linesep, maxlinelen=maxlinelen)) 378 parts.append(self.linesep) 379 return ''.join(parts) 380 381 382compat32 = Compat32() 383