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cpython/Lib/email/charset.py

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# Copyright (C) 2001-2006 Python Software Foundation
# Author: Ben Gertzfield, Barry Warsaw
# Contact: email-sig@python.org
__all__ = [
'Charset',
'add_alias',
'add_charset',
'add_codec',
]
import email.base64mime
import email.quoprimime
from email import errors
from email.encoders import encode_7or8bit
# Flags for types of header encodings
QP = 1 # Quoted-Printable
BASE64 = 2 # Base64
SHORTEST = 3 # the shorter of QP and base64, but only for headers
# In "=?charset?q?hello_world?=", the =?, ?q?, and ?= add up to 7
MISC_LEN = 7
DEFAULT_CHARSET = 'us-ascii'
# Defaults
CHARSETS = {
# input header enc body enc output conv
'iso-8859-1': (QP, QP, None),
'iso-8859-2': (QP, QP, None),
'iso-8859-3': (QP, QP, None),
'iso-8859-4': (QP, QP, None),
# iso-8859-5 is Cyrillic, and not especially used
# iso-8859-6 is Arabic, also not particularly used
# iso-8859-7 is Greek, QP will not make it readable
# iso-8859-8 is Hebrew, QP will not make it readable
'iso-8859-9': (QP, QP, None),
'iso-8859-10': (QP, QP, None),
# iso-8859-11 is Thai, QP will not make it readable
'iso-8859-13': (QP, QP, None),
'iso-8859-14': (QP, QP, None),
'iso-8859-15': (QP, QP, None),
'windows-1252':(QP, QP, None),
'viscii': (QP, QP, None),
'us-ascii': (None, None, None),
'big5': (BASE64, BASE64, None),
'gb2312': (BASE64, BASE64, None),
'euc-jp': (BASE64, None, 'iso-2022-jp'),
'shift_jis': (BASE64, None, 'iso-2022-jp'),
'iso-2022-jp': (BASE64, None, None),
'koi8-r': (BASE64, BASE64, None),
'utf-8': (SHORTEST, BASE64, 'utf-8'),
# We're making this one up to represent raw unencoded 8-bit
'8bit': (None, BASE64, 'utf-8'),
}
# Aliases for other commonly-used names for character sets. Map
# them to the real ones used in email.
ALIASES = {
'latin_1': 'iso-8859-1',
'latin-1': 'iso-8859-1',
'latin_2': 'iso-8859-2',
'latin-2': 'iso-8859-2',
'latin_3': 'iso-8859-3',
'latin-3': 'iso-8859-3',
'latin_4': 'iso-8859-4',
'latin-4': 'iso-8859-4',
'latin_5': 'iso-8859-9',
'latin-5': 'iso-8859-9',
'latin_6': 'iso-8859-10',
'latin-6': 'iso-8859-10',
'latin_7': 'iso-8859-13',
'latin-7': 'iso-8859-13',
'latin_8': 'iso-8859-14',
'latin-8': 'iso-8859-14',
'latin_9': 'iso-8859-15',
'latin-9': 'iso-8859-15',
'cp949': 'ks_c_5601-1987',
'euc_jp': 'euc-jp',
'euc_kr': 'euc-kr',
'ascii': 'us-ascii',
}
# Map charsets to their Unicode codec strings.
CODEC_MAP = {
'gb2312': 'eucgb2312_cn',
'big5': 'big5_tw',
# Hack: We don't want *any* conversion for stuff marked us-ascii, as all
# sorts of garbage might be sent to us in the guise of 7-bit us-ascii.
# Let that stuff pass through without conversion to/from Unicode.
'us-ascii': None,
}
# Convenience functions for extending the above mappings
def add_charset(charset, header_enc=None, body_enc=None, output_charset=None):
"""Add character set properties to the global registry.
charset is the input character set, and must be the canonical name of a
character set.
Optional header_enc and body_enc is either Charset.QP for
quoted-printable, Charset.BASE64 for base64 encoding, Charset.SHORTEST for
the shortest of qp or base64 encoding, or None for no encoding. SHORTEST
is only valid for header_enc. It describes how message headers and
message bodies in the input charset are to be encoded. Default is no
encoding.
Optional output_charset is the character set that the output should be
in. Conversions will proceed from input charset, to Unicode, to the
output charset when the method Charset.convert() is called. The default
is to output in the same character set as the input.
Both input_charset and output_charset must have Unicode codec entries in
the module's charset-to-codec mapping; use add_codec(charset, codecname)
to add codecs the module does not know about. See the codecs module's
documentation for more information.
"""
if body_enc == SHORTEST:
raise ValueError('SHORTEST not allowed for body_enc')
CHARSETS[charset] = (header_enc, body_enc, output_charset)
def add_alias(alias, canonical):
"""Add a character set alias.
alias is the alias name, e.g. latin-1
canonical is the character set's canonical name, e.g. iso-8859-1
"""
ALIASES[alias] = canonical
def add_codec(charset, codecname):
"""Add a codec that map characters in the given charset to/from Unicode.
charset is the canonical name of a character set. codecname is the name
of a Python codec, as appropriate for the second argument to the unicode()
built-in, or to the encode() method of a Unicode string.
"""
CODEC_MAP[charset] = codecname
class Charset:
"""Map character sets to their email properties.
This class provides information about the requirements imposed on email
for a specific character set. It also provides convenience routines for
converting between character sets, given the availability of the
applicable codecs. Given a character set, it will do its best to provide
information on how to use that character set in an email in an
RFC-compliant way.
Certain character sets must be encoded with quoted-printable or base64
when used in email headers or bodies. Certain character sets must be
converted outright, and are not allowed in email. Instances of this
module expose the following information about a character set:
input_charset: The initial character set specified. Common aliases
are converted to their `official' email names (e.g. latin_1
is converted to iso-8859-1). Defaults to 7-bit us-ascii.
header_encoding: If the character set must be encoded before it can be
used in an email header, this attribute will be set to
Charset.QP (for quoted-printable), Charset.BASE64 (for
base64 encoding), or Charset.SHORTEST for the shortest of
QP or BASE64 encoding. Otherwise, it will be None.
body_encoding: Same as header_encoding, but describes the encoding for the
mail message's body, which indeed may be different than the
header encoding. Charset.SHORTEST is not allowed for
body_encoding.
output_charset: Some character sets must be converted before the can be
used in email headers or bodies. If the input_charset is
one of them, this attribute will contain the name of the
charset output will be converted to. Otherwise, it will
be None.
input_codec: The name of the Python codec used to convert the
input_charset to Unicode. If no conversion codec is
necessary, this attribute will be None.
output_codec: The name of the Python codec used to convert Unicode
to the output_charset. If no conversion codec is necessary,
this attribute will have the same value as the input_codec.
"""
def __init__(self, input_charset=DEFAULT_CHARSET):
# RFC 2046, $4.1.2 says charsets are not case sensitive. We coerce to
# unicode because its .lower() is locale insensitive. If the argument
# is already a unicode, we leave it at that, but ensure that the
# charset is ASCII, as the standard (RFC XXX) requires.
try:
if isinstance(input_charset, unicode):
input_charset.encode('ascii')
else:
input_charset = unicode(input_charset, 'ascii')
except UnicodeError:
raise errors.CharsetError(input_charset)
input_charset = input_charset.lower()
# Set the input charset after filtering through the aliases
self.input_charset = ALIASES.get(input_charset, input_charset)
# We can try to guess which encoding and conversion to use by the
# charset_map dictionary. Try that first, but let the user override
# it.
henc, benc, conv = CHARSETS.get(self.input_charset,
(SHORTEST, BASE64, None))
if not conv:
conv = self.input_charset
# Set the attributes, allowing the arguments to override the default.
self.header_encoding = henc
self.body_encoding = benc
self.output_charset = ALIASES.get(conv, conv)
# Now set the codecs. If one isn't defined for input_charset,
# guess and try a Unicode codec with the same name as input_codec.
self.input_codec = CODEC_MAP.get(self.input_charset,
self.input_charset)
self.output_codec = CODEC_MAP.get(self.output_charset,
self.output_charset)
def __str__(self):
return self.input_charset.lower()
__repr__ = __str__
def __eq__(self, other):
return str(self) == str(other).lower()
def __ne__(self, other):
return not self.__eq__(other)
def get_body_encoding(self):
"""Return the content-transfer-encoding used for body encoding.
This is either the string `quoted-printable' or `base64' depending on
the encoding used, or it is a function in which case you should call
the function with a single argument, the Message object being
encoded. The function should then set the Content-Transfer-Encoding
header itself to whatever is appropriate.
Returns "quoted-printable" if self.body_encoding is QP.
Returns "base64" if self.body_encoding is BASE64.
Returns "7bit" otherwise.
"""
assert self.body_encoding <> SHORTEST
if self.body_encoding == QP:
return 'quoted-printable'
elif self.body_encoding == BASE64:
return 'base64'
else:
return encode_7or8bit
def convert(self, s):
"""Convert a string from the input_codec to the output_codec."""
if self.input_codec <> self.output_codec:
return unicode(s, self.input_codec).encode(self.output_codec)
else:
return s
def to_splittable(self, s):
"""Convert a possibly multibyte string to a safely splittable format.
Uses the input_codec to try and convert the string to Unicode, so it
can be safely split on character boundaries (even for multibyte
characters).
Returns the string as-is if it isn't known how to convert it to
Unicode with the input_charset.
Characters that could not be converted to Unicode will be replaced
with the Unicode replacement character U+FFFD.
"""
if isinstance(s, unicode) or self.input_codec is None:
return s
try:
return unicode(s, self.input_codec, 'replace')
except LookupError:
# Input codec not installed on system, so return the original
# string unchanged.
return s
def from_splittable(self, ustr, to_output=True):
"""Convert a splittable string back into an encoded string.
Uses the proper codec to try and convert the string from Unicode back
into an encoded format. Return the string as-is if it is not Unicode,
or if it could not be converted from Unicode.
Characters that could not be converted from Unicode will be replaced
with an appropriate character (usually '?').
If to_output is True (the default), uses output_codec to convert to an
encoded format. If to_output is False, uses input_codec.
"""
if to_output:
codec = self.output_codec
else:
codec = self.input_codec
if not isinstance(ustr, unicode) or codec is None:
return ustr
try:
return ustr.encode(codec, 'replace')
except LookupError:
# Output codec not installed
return ustr
def get_output_charset(self):
"""Return the output character set.
This is self.output_charset if that is not None, otherwise it is
self.input_charset.
"""
return self.output_charset or self.input_charset
def encoded_header_len(self, s):
"""Return the length of the encoded header string."""
cset = self.get_output_charset()
# The len(s) of a 7bit encoding is len(s)
if self.header_encoding == BASE64:
return email.base64mime.base64_len(s) + len(cset) + MISC_LEN
elif self.header_encoding == QP:
return email.quoprimime.header_quopri_len(s) + len(cset) + MISC_LEN
elif self.header_encoding == SHORTEST:
lenb64 = email.base64mime.base64_len(s)
lenqp = email.quoprimime.header_quopri_len(s)
return min(lenb64, lenqp) + len(cset) + MISC_LEN
else:
return len(s)
def header_encode(self, s, convert=False):
"""Header-encode a string, optionally converting it to output_charset.
If convert is True, the string will be converted from the input
charset to the output charset automatically. This is not useful for
multibyte character sets, which have line length issues (multibyte
characters must be split on a character, not a byte boundary); use the
high-level Header class to deal with these issues. convert defaults
to False.
The type of encoding (base64 or quoted-printable) will be based on
self.header_encoding.
"""
cset = self.get_output_charset()
if convert:
s = self.convert(s)
# 7bit/8bit encodings return the string unchanged (modulo conversions)
if self.header_encoding == BASE64:
return email.base64mime.header_encode(s, cset)
elif self.header_encoding == QP:
return email.quoprimime.header_encode(s, cset, maxlinelen=None)
elif self.header_encoding == SHORTEST:
lenb64 = email.base64mime.base64_len(s)
lenqp = email.quoprimime.header_quopri_len(s)
if lenb64 < lenqp:
return email.base64mime.header_encode(s, cset)
else:
return email.quoprimime.header_encode(s, cset, maxlinelen=None)
else:
return s
def body_encode(self, s, convert=True):
"""Body-encode a string and convert it to output_charset.
If convert is True (the default), the string will be converted from
the input charset to output charset automatically. Unlike
header_encode(), there are no issues with byte boundaries and
multibyte charsets in email bodies, so this is usually pretty safe.
The type of encoding (base64 or quoted-printable) will be based on
self.body_encoding.
"""
if convert:
s = self.convert(s)
# 7bit/8bit encodings return the string unchanged (module conversions)
if self.body_encoding is BASE64:
return email.base64mime.body_encode(s)
elif self.body_encoding is QP:
return email.quoprimime.body_encode(s)
else:
return s
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