cpython/Lib/email/Header.py

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# Copyright (C) 2002 Python Software Foundation
# Author: che@debian.org (Ben Gertzfield)
"""Header encoding and decoding functionality."""
import re
import email.quopriMIME
import email.base64MIME
from email.Charset import Charset
try:
from email._compat22 import _floordiv
except SyntaxError:
# Python 2.1 spells integer division differently
from email._compat21 import _floordiv
CRLFSPACE = '\r\n '
CRLF = '\r\n'
NL = '\n'
SPACE8 = ' ' * 8
EMPTYSTRING = ''
MAXLINELEN = 76
ENCODE = 1
DECODE = 2
# Match encoded-word strings in the form =?charset?q?Hello_World?=
ecre = re.compile(r'''
=\? # literal =?
(?P<charset>[^?]*?) # non-greedy up to the next ? is the charset
\? # literal ?
(?P<encoding>[qb]) # either a "q" or a "b", case insensitive
\? # literal ?
(?P<encoded>.*?) # non-greedy up to the next ?= is the encoded string
\?= # literal ?=
''', re.VERBOSE | re.IGNORECASE)
# Helpers
_max_append = email.quopriMIME._max_append
def decode_header(header):
"""Decode a message header value without converting charset.
Returns a list of (decoded_string, charset) pairs containing each of the
decoded parts of the header. Charset is None for non-encoded parts of the
header, otherwise a lower-case string containing the name of the character
set specified in the encoded string.
"""
# If no encoding, just return the header
header = str(header)
if not ecre.search(header):
return [(header, None)]
decoded = []
dec = ''
for line in header.splitlines():
# This line might not have an encoding in it
if not ecre.search(line):
decoded.append((line, None))
continue
parts = ecre.split(line)
while parts:
unenc = parts.pop(0).strip()
if unenc:
# Should we continue a long line?
if decoded and decoded[-1][1] is None:
decoded[-1] = (decoded[-1][0] + dec, None)
else:
decoded.append((unenc, None))
if parts:
charset, encoding = [s.lower() for s in parts[0:2]]
encoded = parts[2]
dec = ''
if encoding == 'q':
dec = email.quopriMIME.header_decode(encoded)
elif encoding == 'b':
dec = email.base64MIME.decode(encoded)
else:
dec = encoded
if decoded and decoded[-1][1] == charset:
decoded[-1] = (decoded[-1][0] + dec, decoded[-1][1])
else:
decoded.append((dec, charset))
del parts[0:3]
return decoded
def make_header(decoded_seq, maxlinelen=None, header_name=None,
continuation_ws=' '):
"""Create a Header from a sequence of pairs as returned by decode_header()
decode_header() takes a header value string and returns a sequence of
pairs of the format (decoded_string, charset) where charset is the string
name of the character set.
This function takes one of those sequence of pairs and returns a Header
instance. Optional maxlinelen, header_name, and continuation_ws are as in
the Header constructor.
"""
h = Header(maxlinelen=maxlinelen, header_name=header_name,
continuation_ws=continuation_ws)
for s, charset in decoded_seq:
# None means us-ascii but we can simply pass it on to h.append()
if charset is not None and not isinstance(charset, Charset):
charset = Charset(charset)
h.append(s, charset)
return h
class Header:
def __init__(self, s=None, charset=None, maxlinelen=None, header_name=None,
continuation_ws=' '):
"""Create a MIME-compliant header that can contain many languages.
Specify the initial header value in s. If None, the initial header
value is not set.
Specify both s's character set, and the default character set by
setting the charset argument to a Charset object (not a character set
name string!). If None, a us-ascii Charset is used as both s's
initial charset and as the default character set for subsequent
.append() calls.
You can later append to the header with append(s, charset) below;
charset does not have to be the same as the one initially specified
here. In fact, it's optional, and if not given, defaults to the
charset specified in the constructor.
The maximum line length can be specified explicit via maxlinelen. For
splitting the first line to a shorter value (to account for the field
header which isn't included in s, e.g. `Subject') pass in the name of
the field in header_name. The default maxlinelen is 76.
continuation_ws must be RFC 2822 compliant folding whitespace (usually
either a space or a hard tab) which will be prepended to continuation
lines.
"""
if charset is None:
charset = Charset()
self._charset = charset
self._continuation_ws = continuation_ws
cws_expanded_len = len(continuation_ws.replace('\t', SPACE8))
# BAW: I believe `chunks' and `maxlinelen' should be non-public.
self._chunks = []
if s is not None:
self.append(s, charset)
if maxlinelen is None:
maxlinelen = MAXLINELEN
if header_name is None:
# We don't know anything about the field header so the first line
# is the same length as subsequent lines.
self._firstlinelen = maxlinelen
else:
# The first line should be shorter to take into account the field
# header. Also subtract off 2 extra for the colon and space.
self._firstlinelen = maxlinelen - len(header_name) - 2
# Second and subsequent lines should subtract off the length in
# columns of the continuation whitespace prefix.
self._maxlinelen = maxlinelen - cws_expanded_len
def __str__(self):
"""A synonym for self.encode()."""
return self.encode()
def __unicode__(self):
"""Helper for the built-in unicode function."""
# charset item is a Charset instance so we need to stringify it.
uchunks = [unicode(s, str(charset)) for s, charset in self._chunks]
return u''.join(uchunks)
# Rich comparison operators for equality only. BAW: does it make sense to
# have or explicitly disable <, <=, >, >= operators?
def __eq__(self, other):
# other may be a Header or a string. Both are fine so coerce
# ourselves to a string, swap the args and do another comparison.
return other == self.encode()
def __ne__(self, other):
return not self == other
def append(self, s, charset=None):
"""Append string s with Charset charset to the MIME header.
If charset is given, it should be a Charset instance, or the name of a
character set (which will be converted to a Charset instance). A
value of None (the default) means charset is the one given in the
class constructor.
"""
if charset is None:
charset = self._charset
elif not isinstance(charset, Charset):
charset = Charset(charset)
self._chunks.append((s, charset))
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def _split(self, s, charset, firstline=0):
# Split up a header safely for use with encode_chunks. BAW: this
# appears to be a private convenience method.
splittable = charset.to_splittable(s)
encoded = charset.from_splittable(splittable)
elen = charset.encoded_header_len(encoded)
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if elen <= self._maxlinelen:
return [(encoded, charset)]
# BAW: I'm not sure what the right test here is. What we're trying to
# do is be faithful to RFC 2822's recommendation that ($2.2.3):
#
# "Note: Though structured field bodies are defined in such a way that
# folding can take place between many of the lexical tokens (and even
# within some of the lexical tokens), folding SHOULD be limited to
# placing the CRLF at higher-level syntactic breaks."
#
# For now, I can only imagine doing this when the charset is us-ascii,
# although it's possible that other charsets may also benefit from the
# higher-level syntactic breaks.
#
elif charset == 'us-ascii':
return self._ascii_split(s, charset, firstline)
# BAW: should we use encoded?
elif elen == len(s):
# We can split on _maxlinelen boundaries because we know that the
# encoding won't change the size of the string
splitpnt = self._maxlinelen
first = charset.from_splittable(splittable[:splitpnt], 0)
last = charset.from_splittable(splittable[splitpnt:], 0)
else:
# Divide and conquer.
halfway = _floordiv(len(splittable), 2)
first = charset.from_splittable(splittable[:halfway], 0)
last = charset.from_splittable(splittable[halfway:], 0)
# Do the split
return self._split(first, charset, firstline) + \
self._split(last, charset)
def _ascii_split(self, s, charset, firstline):
# Attempt to split the line at the highest-level syntactic break
# possible. Note that we don't have a lot of smarts about field
# syntax; we just try to break on semi-colons, then whitespace.
rtn = []
lines = s.splitlines()
while lines:
line = lines.pop(0)
if firstline:
maxlinelen = self._firstlinelen
firstline = 0
else:
line = line.lstrip()
maxlinelen = self._maxlinelen
# Short lines can remain unchanged
if len(line.replace('\t', SPACE8)) <= maxlinelen:
rtn.append(line)
else:
oldlen = len(line)
# Try to break the line on semicolons, but if that doesn't
# work, try to split on folding whitespace.
while len(line) > maxlinelen:
i = line.rfind(';', 0, maxlinelen)
if i < 0:
break
rtn.append(line[:i] + ';')
line = line[i+1:]
# Is the remaining stuff still longer than maxlinelen?
if len(line) <= maxlinelen:
# Splitting on semis worked
rtn.append(line)
continue
# Splitting on semis didn't finish the job. If it did any
# work at all, stick the remaining junk on the front of the
# `lines' sequence and let the next pass do its thing.
if len(line) <> oldlen:
lines.insert(0, line)
continue
# Otherwise, splitting on semis didn't help at all.
parts = re.split(r'(\s+)', line)
if len(parts) == 1 or (len(parts) == 3 and
parts[0].endswith(':')):
# This line can't be split on whitespace. There's now
# little we can do to get this into maxlinelen. BAW:
# We're still potentially breaking the RFC by possibly
# allowing lines longer than the absolute maximum of 998
# characters. For now, let it slide.
#
# len(parts) will be 1 if this line has no `Field: '
# prefix, otherwise it will be len(3).
rtn.append(line)
continue
# There is whitespace we can split on.
first = parts.pop(0)
sublines = [first]
acc = len(first)
while parts:
len0 = len(parts[0])
len1 = len(parts[1])
if acc + len0 + len1 <= maxlinelen:
sublines.append(parts.pop(0))
sublines.append(parts.pop(0))
acc += len0 + len1
else:
# Split it here, but don't forget to ignore the
# next whitespace-only part
if first <> '':
rtn.append(EMPTYSTRING.join(sublines))
del parts[0]
first = parts.pop(0)
sublines = [first]
acc = len(first)
rtn.append(EMPTYSTRING.join(sublines))
return [(chunk, charset) for chunk in rtn]
def _encode_chunks(self):
"""MIME-encode a header with many different charsets and/or encodings.
Given a list of pairs (string, charset), return a MIME-encoded string
suitable for use in a header field. Each pair may have different
charsets and/or encodings, and the resulting header will accurately
reflect each setting.
Each encoding can be email.Utils.QP (quoted-printable, for ASCII-like
character sets like iso-8859-1), email.Utils.BASE64 (Base64, for
non-ASCII like character sets like KOI8-R and iso-2022-jp), or None
(no encoding).
Each pair will be represented on a separate line; the resulting string
will be in the format:
"=?charset1?q?Mar=EDa_Gonz=E1lez_Alonso?=\n
=?charset2?b?SvxyZ2VuIEL2aW5n?="
"""
chunks = []
for header, charset in self._chunks:
if charset is None or charset.header_encoding is None:
# There's no encoding for this chunk's charsets
_max_append(chunks, header, self._maxlinelen)
else:
_max_append(chunks, charset.header_encode(header, 0),
self._maxlinelen, ' ')
joiner = NL + self._continuation_ws
return joiner.join(chunks)
def encode(self):
"""Encode a message header, possibly converting charset and encoding.
There are many issues involved in converting a given string for use in
an email header. Only certain character sets are readable in most
email clients, and as header strings can only contain a subset of
7-bit ASCII, care must be taken to properly convert and encode (with
Base64 or quoted-printable) header strings. In addition, there is a
75-character length limit on any given encoded header field, so
line-wrapping must be performed, even with double-byte character sets.
This method will do its best to convert the string to the correct
character set used in email, and encode and line wrap it safely with
the appropriate scheme for that character set.
If the given charset is not known or an error occurs during
conversion, this function will return the header untouched.
"""
newchunks = []
for s, charset in self._chunks:
newchunks += self._split(s, charset, 1)
self._chunks = newchunks
return self._encode_chunks()