1 # Copyright (C) 2001-2006 Python Software Foundation

     2 # Author: Barry Warsaw

     3 # Contact: email-sig@python.org

     4 

     5 """Basic message object for the email package object model."""

     6 

     7 __all__ = ['Message']

     8 

     9 import re

    10 import uu

    11 import binascii

    12 import warnings

    13 from cStringIO import StringIO

    14 

    15 # Intrapackage imports

    16 import email.charset

    17 from email import utils

    18 from email import errors

    19 

    20 SEMISPACE = '; '

    21 

    22 # Regular expression that matches `special' characters in parameters, the

    23 # existance of which force quoting of the parameter value.

    24 tspecials = re.compile(r'[ \(\)<>@,;:\\"/\[\]\?=]')

    25 

    26 

    27 # Helper functions

    28 def _splitparam(param):

    29     # Split header parameters.  BAW: this may be too simple.  It isn't

    30     # strictly RFC 2045 (section 5.1) compliant, but it catches most headers

    31     # found in the wild.  We may eventually need a full fledged parser

    32     # eventually.

    33     a, sep, b = param.partition(';')

    34     if not sep:

    35         return a.strip(), None

    36     return a.strip(), b.strip()

    37 

    38 def _formatparam(param, value=None, quote=True):

    39     """Convenience function to format and return a key=value pair.

    40 

    41     This will quote the value if needed or if quote is true.

    42     """

    43     if value is not None and len(value) > 0:

    44         # A tuple is used for RFC 2231 encoded parameter values where items

    45         # are (charset, language, value).  charset is a string, not a Charset

    46         # instance.

    47         if isinstance(value, tuple):

    48             # Encode as per RFC 2231

    49             param += '*'

    50             value = utils.encode_rfc2231(value[2], value[0], value[1])

    51         # BAW: Please check this.  I think that if quote is set it should

    52         # force quoting even if not necessary.

    53         if quote or tspecials.search(value):

    54             return '%s="%s"' % (param, utils.quote(value))

    55         else:

    56             return '%s=%s' % (param, value)

    57     else:

    58         return param

    59 

    60 def _parseparam(s):

    61     plist = []

    62     while s[:1] == ';':

    63         s = s[1:]

    64         end = s.find(';')

    65         while end > 0 and s.count('"', 0, end) % 2:

    66             end = s.find(';', end + 1)

    67         if end < 0:

    68             end = len(s)

    69         f = s[:end]

    70         if '=' in f:

    71             i = f.index('=')

    72             f = f[:i].strip().lower() + '=' + f[i+1:].strip()

    73         plist.append(f.strip())

    74         s = s[end:]

    75     return plist

    76 

    77 

    78 def _unquotevalue(value):

    79     # This is different than utils.collapse_rfc2231_value() because it doesn't

    80     # try to convert the value to a unicode.  Message.get_param() and

    81     # Message.get_params() are both currently defined to return the tuple in

    82     # the face of RFC 2231 parameters.

    83     if isinstance(value, tuple):

    84         return value[0], value[1], utils.unquote(value[2])

    85     else:

    86         return utils.unquote(value)

    87 

    88 

    89 

    90 class Message:

    91     """Basic message object.

    92 

    93     A message object is defined as something that has a bunch of RFC 2822

    94     headers and a payload.  It may optionally have an envelope header

    95     (a.k.a. Unix-From or From_ header).  If the message is a container (i.e. a

    96     multipart or a message/rfc822), then the payload is a list of Message

    97     objects, otherwise it is a string.

    98 

    99     Message objects implement part of the `mapping' interface, which assumes

   100     there is exactly one occurrance of the header per message.  Some headers

   101     do in fact appear multiple times (e.g. Received) and for those headers,

   102     you must use the explicit API to set or get all the headers.  Not all of

   103     the mapping methods are implemented.

   104     """

   105     def __init__(self):

   106         self._headers = []

   107         self._unixfrom = None

   108         self._payload = None

   109         self._charset = None

   110         # Defaults for multipart messages

   111         self.preamble = self.epilogue = None

   112         self.defects = []

   113         # Default content type

   114         self._default_type = 'text/plain'

   115 

   116     def __str__(self):

   117         """Return the entire formatted message as a string.

   118         This includes the headers, body, and envelope header.

   119         """

   120         return self.as_string(unixfrom=True)

   121 

   122     def as_string(self, unixfrom=False):

   123         """Return the entire formatted message as a string.

   124         Optional `unixfrom' when True, means include the Unix From_ envelope

   125         header.

   126 

   127         This is a convenience method and may not generate the message exactly

   128         as you intend because by default it mangles lines that begin with

   129         "From ".  For more flexibility, use the flatten() method of a

   130         Generator instance.

   131         """

   132         from email.Generator import Generator

   133         fp = StringIO()

   134         g = Generator(fp)

   135         g.flatten(self, unixfrom=unixfrom)

   136         return fp.getvalue()

   137 

   138     def is_multipart(self):

   139         """Return True if the message consists of multiple parts."""

   140         return isinstance(self._payload, list)

   141 

   142     #

   143     # Unix From_ line

   144     #

   145     def set_unixfrom(self, unixfrom):

   146         self._unixfrom = unixfrom

   147 

   148     def get_unixfrom(self):

   149         return self._unixfrom

   150 

   151     #

   152     # Payload manipulation.

   153     #

   154     def attach(self, payload):

   155         """Add the given payload to the current payload.

   156 

   157         The current payload will always be a list of objects after this method

   158         is called.  If you want to set the payload to a scalar object, use

   159         set_payload() instead.

   160         """

   161         if self._payload is None:

   162             self._payload = [payload]

   163         else:

   164             self._payload.append(payload)

   165 

   166     def get_payload(self, i=None, decode=False):

   167         """Return a reference to the payload.

   168 

   169         The payload will either be a list object or a string.  If you mutate

   170         the list object, you modify the message's payload in place.  Optional

   171         i returns that index into the payload.

   172 

   173         Optional decode is a flag indicating whether the payload should be

   174         decoded or not, according to the Content-Transfer-Encoding header

   175         (default is False).

   176 

   177         When True and the message is not a multipart, the payload will be

   178         decoded if this header's value is `quoted-printable' or `base64'.  If

   179         some other encoding is used, or the header is missing, or if the

   180         payload has bogus data (i.e. bogus base64 or uuencoded data), the

   181         payload is returned as-is.

   182 

   183         If the message is a multipart and the decode flag is True, then None

   184         is returned.

   185         """

   186         if i is None:

   187             payload = self._payload

   188         elif not isinstance(self._payload, list):

   189             raise TypeError('Expected list, got %s' % type(self._payload))

   190         else:

   191             payload = self._payload[i]

   192         if decode:

   193             if self.is_multipart():

   194                 return None

   195             cte = self.get('content-transfer-encoding', '').lower()

   196             if cte == 'quoted-printable':

   197                 return utils._qdecode(payload)

   198             elif cte == 'base64':

   199                 try:

   200                     return utils._bdecode(payload)

   201                 except binascii.Error:

   202                     # Incorrect padding

   203                     return payload

   204             elif cte in ('x-uuencode', 'uuencode', 'uue', 'x-uue'):

   205                 sfp = StringIO()

   206                 try:

   207                     uu.decode(StringIO(payload+'\n'), sfp, quiet=True)

   208                     payload = sfp.getvalue()

   209                 except uu.Error:

   210                     # Some decoding problem

   211                     return payload

   212         # Everything else, including encodings with 8bit or 7bit are returned

   213         # unchanged.

   214         return payload

   215 

   216     def set_payload(self, payload, charset=None):

   217         """Set the payload to the given value.

   218 

   219         Optional charset sets the message's default character set.  See

   220         set_charset() for details.

   221         """

   222         self._payload = payload

   223         if charset is not None:

   224             self.set_charset(charset)

   225 

   226     def set_charset(self, charset):

   227         """Set the charset of the payload to a given character set.

   228 

   229         charset can be a Charset instance, a string naming a character set, or

   230         None.  If it is a string it will be converted to a Charset instance.

   231         If charset is None, the charset parameter will be removed from the

   232         Content-Type field.  Anything else will generate a TypeError.

   233 

   234         The message will be assumed to be of type text/* encoded with

   235         charset.input_charset.  It will be converted to charset.output_charset

   236         and encoded properly, if needed, when generating the plain text

   237         representation of the message.  MIME headers (MIME-Version,

   238         Content-Type, Content-Transfer-Encoding) will be added as needed.

   239 

   240         """

   241         if charset is None:

   242             self.del_param('charset')

   243             self._charset = None

   244             return

   245         if isinstance(charset, basestring):

   246             charset = email.charset.Charset(charset)

   247         if not isinstance(charset, email.charset.Charset):

   248             raise TypeError(charset)

   249         # BAW: should we accept strings that can serve as arguments to the

   250         # Charset constructor?

   251         self._charset = charset

   252         if not self.has_key('MIME-Version'):

   253             self.add_header('MIME-Version', '1.0')

   254         if not self.has_key('Content-Type'):

   255             self.add_header('Content-Type', 'text/plain',

   256                             charset=charset.get_output_charset())

   257         else:

   258             self.set_param('charset', charset.get_output_charset())

   259         if str(charset) != charset.get_output_charset():

   260             self._payload = charset.body_encode(self._payload)

   261         if not self.has_key('Content-Transfer-Encoding'):

   262             cte = charset.get_body_encoding()

   263             try:

   264                 cte(self)

   265             except TypeError:

   266                 self._payload = charset.body_encode(self._payload)

   267                 self.add_header('Content-Transfer-Encoding', cte)

   268 

   269     def get_charset(self):

   270         """Return the Charset instance associated with the message's payload.

   271         """

   272         return self._charset

   273 

   274     #

   275     # MAPPING INTERFACE (partial)

   276     #

   277     def __len__(self):

   278         """Return the total number of headers, including duplicates."""

   279         return len(self._headers)

   280 

   281     def __getitem__(self, name):

   282         """Get a header value.

   283 

   284         Return None if the header is missing instead of raising an exception.

   285 

   286         Note that if the header appeared multiple times, exactly which

   287         occurrance gets returned is undefined.  Use get_all() to get all

   288         the values matching a header field name.

   289         """

   290         return self.get(name)

   291 

   292     def __setitem__(self, name, val):

   293         """Set the value of a header.

   294 

   295         Note: this does not overwrite an existing header with the same field

   296         name.  Use __delitem__() first to delete any existing headers.

   297         """

   298         self._headers.append((name, val))

   299 

   300     def __delitem__(self, name):

   301         """Delete all occurrences of a header, if present.

   302 

   303         Does not raise an exception if the header is missing.

   304         """

   305         name = name.lower()

   306         newheaders = []

   307         for k, v in self._headers:

   308             if k.lower() != name:

   309                 newheaders.append((k, v))

   310         self._headers = newheaders

   311 

   312     def __contains__(self, name):

   313         return name.lower() in [k.lower() for k, v in self._headers]

   314 

   315     def has_key(self, name):

   316         """Return true if the message contains the header."""

   317         missing = object()

   318         return self.get(name, missing) is not missing

   319 

   320     def keys(self):

   321         """Return a list of all the message's header field names.

   322 

   323         These will be sorted in the order they appeared in the original

   324         message, or were added to the message, and may contain duplicates.

   325         Any fields deleted and re-inserted are always appended to the header

   326         list.

   327         """

   328         return [k for k, v in self._headers]

   329 

   330     def values(self):

   331         """Return a list of all the message's header values.

   332 

   333         These will be sorted in the order they appeared in the original

   334         message, or were added to the message, and may contain duplicates.

   335         Any fields deleted and re-inserted are always appended to the header

   336         list.

   337         """

   338         return [v for k, v in self._headers]

   339 

   340     def items(self):

   341         """Get all the message's header fields and values.

   342 

   343         These will be sorted in the order they appeared in the original

   344         message, or were added to the message, and may contain duplicates.

   345         Any fields deleted and re-inserted are always appended to the header

   346         list.

   347         """

   348         return self._headers[:]

   349 

   350     def get(self, name, failobj=None):

   351         """Get a header value.

   352 

   353         Like __getitem__() but return failobj instead of None when the field

   354         is missing.

   355         """

   356         name = name.lower()

   357         for k, v in self._headers:

   358             if k.lower() == name:

   359                 return v

   360         return failobj

   361 

   362     #

   363     # Additional useful stuff

   364     #

   365 

   366     def get_all(self, name, failobj=None):

   367         """Return a list of all the values for the named field.

   368 

   369         These will be sorted in the order they appeared in the original

   370         message, and may contain duplicates.  Any fields deleted and

   371         re-inserted are always appended to the header list.

   372 

   373         If no such fields exist, failobj is returned (defaults to None).

   374         """

   375         values = []

   376         name = name.lower()

   377         for k, v in self._headers:

   378             if k.lower() == name:

   379                 values.append(v)

   380         if not values:

   381             return failobj

   382         return values

   383 

   384     def add_header(self, _name, _value, **_params):

   385         """Extended header setting.

   386 

   387         name is the header field to add.  keyword arguments can be used to set

   388         additional parameters for the header field, with underscores converted

   389         to dashes.  Normally the parameter will be added as key="value" unless

   390         value is None, in which case only the key will be added.

   391 

   392         Example:

   393 

   394         msg.add_header('content-disposition', 'attachment', filename='bud.gif')

   395         """

   396         parts = []

   397         for k, v in _params.items():

   398             if v is None:

   399                 parts.append(k.replace('_', '-'))

   400             else:

   401                 parts.append(_formatparam(k.replace('_', '-'), v))

   402         if _value is not None:

   403             parts.insert(0, _value)

   404         self._headers.append((_name, SEMISPACE.join(parts)))

   405 

   406     def replace_header(self, _name, _value):

   407         """Replace a header.

   408 

   409         Replace the first matching header found in the message, retaining

   410         header order and case.  If no matching header was found, a KeyError is

   411         raised.

   412         """

   413         _name = _name.lower()

   414         for i, (k, v) in zip(range(len(self._headers)), self._headers):

   415             if k.lower() == _name:

   416                 self._headers[i] = (k, _value)

   417                 break

   418         else:

   419             raise KeyError(_name)

   420 

   421     #

   422     # Use these three methods instead of the three above.

   423     #

   424 

   425     def get_content_type(self):

   426         """Return the message's content type.

   427 

   428         The returned string is coerced to lower case of the form

   429         `maintype/subtype'.  If there was no Content-Type header in the

   430         message, the default type as given by get_default_type() will be

   431         returned.  Since according to RFC 2045, messages always have a default

   432         type this will always return a value.

   433 

   434         RFC 2045 defines a message's default type to be text/plain unless it

   435         appears inside a multipart/digest container, in which case it would be

   436         message/rfc822.

   437         """

   438         missing = object()

   439         value = self.get('content-type', missing)

   440         if value is missing:

   441             # This should have no parameters

   442             return self.get_default_type()

   443         ctype = _splitparam(value)[0].lower()

   444         # RFC 2045, section 5.2 says if its invalid, use text/plain

   445         if ctype.count('/') != 1:

   446             return 'text/plain'

   447         return ctype

   448 

   449     def get_content_maintype(self):

   450         """Return the message's main content type.

   451 

   452         This is the `maintype' part of the string returned by

   453         get_content_type().

   454         """

   455         ctype = self.get_content_type()

   456         return ctype.split('/')[0]

   457 

   458     def get_content_subtype(self):

   459         """Returns the message's sub-content type.

   460 

   461         This is the `subtype' part of the string returned by

   462         get_content_type().

   463         """

   464         ctype = self.get_content_type()

   465         return ctype.split('/')[1]

   466 

   467     def get_default_type(self):

   468         """Return the `default' content type.

   469 

   470         Most messages have a default content type of text/plain, except for

   471         messages that are subparts of multipart/digest containers.  Such

   472         subparts have a default content type of message/rfc822.

   473         """

   474         return self._default_type

   475 

   476     def set_default_type(self, ctype):

   477         """Set the `default' content type.

   478 

   479         ctype should be either "text/plain" or "message/rfc822", although this

   480         is not enforced.  The default content type is not stored in the

   481         Content-Type header.

   482         """

   483         self._default_type = ctype

   484 

   485     def _get_params_preserve(self, failobj, header):

   486         # Like get_params() but preserves the quoting of values.  BAW:

   487         # should this be part of the public interface?

   488         missing = object()

   489         value = self.get(header, missing)

   490         if value is missing:

   491             return failobj

   492         params = []

   493         for p in _parseparam(';' + value):

   494             try:

   495                 name, val = p.split('=', 1)

   496                 name = name.strip()

   497                 val = val.strip()

   498             except ValueError:

   499                 # Must have been a bare attribute

   500                 name = p.strip()

   501                 val = ''

   502             params.append((name, val))

   503         params = utils.decode_params(params)

   504         return params

   505 

   506     def get_params(self, failobj=None, header='content-type', unquote=True):

   507         """Return the message's Content-Type parameters, as a list.

   508 

   509         The elements of the returned list are 2-tuples of key/value pairs, as

   510         split on the `=' sign.  The left hand side of the `=' is the key,

   511         while the right hand side is the value.  If there is no `=' sign in

   512         the parameter the value is the empty string.  The value is as

   513         described in the get_param() method.

   514 

   515         Optional failobj is the object to return if there is no Content-Type

   516         header.  Optional header is the header to search instead of

   517         Content-Type.  If unquote is True, the value is unquoted.

   518         """

   519         missing = object()

   520         params = self._get_params_preserve(missing, header)

   521         if params is missing:

   522             return failobj

   523         if unquote:

   524             return [(k, _unquotevalue(v)) for k, v in params]

   525         else:

   526             return params

   527 

   528     def get_param(self, param, failobj=None, header='content-type',

   529                   unquote=True):

   530         """Return the parameter value if found in the Content-Type header.

   531 

   532         Optional failobj is the object to return if there is no Content-Type

   533         header, or the Content-Type header has no such parameter.  Optional

   534         header is the header to search instead of Content-Type.

   535 

   536         Parameter keys are always compared case insensitively.  The return

   537         value can either be a string, or a 3-tuple if the parameter was RFC

   538         2231 encoded.  When it's a 3-tuple, the elements of the value are of

   539         the form (CHARSET, LANGUAGE, VALUE).  Note that both CHARSET and

   540         LANGUAGE can be None, in which case you should consider VALUE to be

   541         encoded in the us-ascii charset.  You can usually ignore LANGUAGE.

   542 

   543         Your application should be prepared to deal with 3-tuple return

   544         values, and can convert the parameter to a Unicode string like so:

   545 

   546             param = msg.get_param('foo')

   547             if isinstance(param, tuple):

   548                 param = unicode(param[2], param[0] or 'us-ascii')

   549 

   550         In any case, the parameter value (either the returned string, or the

   551         VALUE item in the 3-tuple) is always unquoted, unless unquote is set

   552         to False.

   553         """

   554         if not self.has_key(header):

   555             return failobj

   556         for k, v in self._get_params_preserve(failobj, header):

   557             if k.lower() == param.lower():

   558                 if unquote:

   559                     return _unquotevalue(v)

   560                 else:

   561                     return v

   562         return failobj

   563 

   564     def set_param(self, param, value, header='Content-Type', requote=True,

   565                   charset=None, language=''):

   566         """Set a parameter in the Content-Type header.

   567 

   568         If the parameter already exists in the header, its value will be

   569         replaced with the new value.

   570 

   571         If header is Content-Type and has not yet been defined for this

   572         message, it will be set to "text/plain" and the new parameter and

   573         value will be appended as per RFC 2045.

   574 

   575         An alternate header can specified in the header argument, and all

   576         parameters will be quoted as necessary unless requote is False.

   577 

   578         If charset is specified, the parameter will be encoded according to RFC

   579         2231.  Optional language specifies the RFC 2231 language, defaulting

   580         to the empty string.  Both charset and language should be strings.

   581         """

   582         if not isinstance(value, tuple) and charset:

   583             value = (charset, language, value)

   584 

   585         if not self.has_key(header) and header.lower() == 'content-type':

   586             ctype = 'text/plain'

   587         else:

   588             ctype = self.get(header)

   589         if not self.get_param(param, header=header):

   590             if not ctype:

   591                 ctype = _formatparam(param, value, requote)

   592             else:

   593                 ctype = SEMISPACE.join(

   594                     [ctype, _formatparam(param, value, requote)])

   595         else:

   596             ctype = ''

   597             for old_param, old_value in self.get_params(header=header,

   598                                                         unquote=requote):

   599                 append_param = ''

   600                 if old_param.lower() == param.lower():

   601                     append_param = _formatparam(param, value, requote)

   602                 else:

   603                     append_param = _formatparam(old_param, old_value, requote)

   604                 if not ctype:

   605                     ctype = append_param

   606                 else:

   607                     ctype = SEMISPACE.join([ctype, append_param])

   608         if ctype != self.get(header):

   609             del self[header]

   610             self[header] = ctype

   611 

   612     def del_param(self, param, header='content-type', requote=True):

   613         """Remove the given parameter completely from the Content-Type header.

   614 

   615         The header will be re-written in place without the parameter or its

   616         value. All values will be quoted as necessary unless requote is

   617         False.  Optional header specifies an alternative to the Content-Type

   618         header.

   619         """

   620         if not self.has_key(header):

   621             return

   622         new_ctype = ''

   623         for p, v in self.get_params(header=header, unquote=requote):

   624             if p.lower() != param.lower():

   625                 if not new_ctype:

   626                     new_ctype = _formatparam(p, v, requote)

   627                 else:

   628                     new_ctype = SEMISPACE.join([new_ctype,

   629                                                 _formatparam(p, v, requote)])

   630         if new_ctype != self.get(header):

   631             del self[header]

   632             self[header] = new_ctype

   633 

   634     def set_type(self, type, header='Content-Type', requote=True):

   635         """Set the main type and subtype for the Content-Type header.

   636 

   637         type must be a string in the form "maintype/subtype", otherwise a

   638         ValueError is raised.

   639 

   640         This method replaces the Content-Type header, keeping all the

   641         parameters in place.  If requote is False, this leaves the existing

   642         header's quoting as is.  Otherwise, the parameters will be quoted (the

   643         default).

   644 

   645         An alternative header can be specified in the header argument.  When

   646         the Content-Type header is set, we'll always also add a MIME-Version

   647         header.

   648         """

   649         # BAW: should we be strict?

   650         if not type.count('/') == 1:

   651             raise ValueError

   652         # Set the Content-Type, you get a MIME-Version

   653         if header.lower() == 'content-type':

   654             del self['mime-version']

   655             self['MIME-Version'] = '1.0'

   656         if not self.has_key(header):

   657             self[header] = type

   658             return

   659         params = self.get_params(header=header, unquote=requote)

   660         del self[header]

   661         self[header] = type

   662         # Skip the first param; it's the old type.

   663         for p, v in params[1:]:

   664             self.set_param(p, v, header, requote)

   665 

   666     def get_filename(self, failobj=None):

   667         """Return the filename associated with the payload if present.

   668 

   669         The filename is extracted from the Content-Disposition header's

   670         `filename' parameter, and it is unquoted.  If that header is missing

   671         the `filename' parameter, this method falls back to looking for the

   672         `name' parameter.

   673         """

   674         missing = object()

   675         filename = self.get_param('filename', missing, 'content-disposition')

   676         if filename is missing:

   677             filename = self.get_param('name', missing, 'content-disposition')

   678         if filename is missing:

   679             return failobj

   680         return utils.collapse_rfc2231_value(filename).strip()

   681 

   682     def get_boundary(self, failobj=None):

   683         """Return the boundary associated with the payload if present.

   684 

   685         The boundary is extracted from the Content-Type header's `boundary'

   686         parameter, and it is unquoted.

   687         """

   688         missing = object()

   689         boundary = self.get_param('boundary', missing)

   690         if boundary is missing:

   691             return failobj

   692         # RFC 2046 says that boundaries may begin but not end in w/s

   693         return utils.collapse_rfc2231_value(boundary).rstrip()

   694 

   695     def set_boundary(self, boundary):

   696         """Set the boundary parameter in Content-Type to 'boundary'.

   697 

   698         This is subtly different than deleting the Content-Type header and

   699         adding a new one with a new boundary parameter via add_header().  The

   700         main difference is that using the set_boundary() method preserves the

   701         order of the Content-Type header in the original message.

   702 

   703         HeaderParseError is raised if the message has no Content-Type header.

   704         """

   705         missing = object()

   706         params = self._get_params_preserve(missing, 'content-type')

   707         if params is missing:

   708             # There was no Content-Type header, and we don't know what type

   709             # to set it to, so raise an exception.

   710             raise errors.HeaderParseError('No Content-Type header found')

   711         newparams = []

   712         foundp = False

   713         for pk, pv in params:

   714             if pk.lower() == 'boundary':

   715                 newparams.append(('boundary', '"%s"' % boundary))

   716                 foundp = True

   717             else:

   718                 newparams.append((pk, pv))

   719         if not foundp:

   720             # The original Content-Type header had no boundary attribute.

   721             # Tack one on the end.  BAW: should we raise an exception

   722             # instead???

   723             newparams.append(('boundary', '"%s"' % boundary))

   724         # Replace the existing Content-Type header with the new value

   725         newheaders = []

   726         for h, v in self._headers:

   727             if h.lower() == 'content-type':

   728                 parts = []

   729                 for k, v in newparams:

   730                     if v == '':

   731                         parts.append(k)

   732                     else:

   733                         parts.append('%s=%s' % (k, v))

   734                 newheaders.append((h, SEMISPACE.join(parts)))

   735 

   736             else:

   737                 newheaders.append((h, v))

   738         self._headers = newheaders

   739 

   740     def get_content_charset(self, failobj=None):

   741         """Return the charset parameter of the Content-Type header.

   742 

   743         The returned string is always coerced to lower case.  If there is no

   744         Content-Type header, or if that header has no charset parameter,

   745         failobj is returned.

   746         """

   747         missing = object()

   748         charset = self.get_param('charset', missing)

   749         if charset is missing:

   750             return failobj

   751         if isinstance(charset, tuple):

   752             # RFC 2231 encoded, so decode it, and it better end up as ascii.

   753             pcharset = charset[0] or 'us-ascii'

   754             try:

   755                 # LookupError will be raised if the charset isn't known to

   756                 # Python.  UnicodeError will be raised if the encoded text

   757                 # contains a character not in the charset.

   758                 charset = unicode(charset[2], pcharset).encode('us-ascii')

   759             except (LookupError, UnicodeError):

   760                 charset = charset[2]

   761         # charset character must be in us-ascii range

   762         try:

   763             if isinstance(charset, str):

   764                 charset = unicode(charset, 'us-ascii')

   765             charset = charset.encode('us-ascii')

   766         except UnicodeError:

   767             return failobj

   768         # RFC 2046, $4.1.2 says charsets are not case sensitive

   769         return charset.lower()

   770 

   771     def get_charsets(self, failobj=None):

   772         """Return a list containing the charset(s) used in this message.

   773 

   774         The returned list of items describes the Content-Type headers'

   775         charset parameter for this message and all the subparts in its

   776         payload.

   777 

   778         Each item will either be a string (the value of the charset parameter

   779         in the Content-Type header of that part) or the value of the

   780         'failobj' parameter (defaults to None), if the part does not have a

   781         main MIME type of "text", or the charset is not defined.

   782 

   783         The list will contain one string for each part of the message, plus

   784         one for the container message (i.e. self), so that a non-multipart

   785         message will still return a list of length 1.

   786         """

   787         return [part.get_content_charset(failobj) for part in self.walk()]

   788 

   789     # I.e. def walk(self): ...

   790     from email.Iterators import walk