| # Copyright (C) 2002-2006 Python Software Foundation | |
| # Author: Ben Gertzfield, Barry Warsaw | |
| # Contact: email-sig@python.org | |
| """Header encoding and decoding functionality.""" | |
| __all__ = [ | |
| 'Header', | |
| 'decode_header', | |
| 'make_header', | |
| ] | |
| import re | |
| import binascii | |
| import email.quoprimime | |
| import email.base64mime | |
| from email.errors import HeaderParseError | |
| from email.charset import Charset | |
| NL = '\n' | |
| SPACE = ' ' | |
| USPACE = u' ' | |
| SPACE8 = ' ' * 8 | |
| UEMPTYSTRING = u'' | |
| MAXLINELEN = 76 | |
| USASCII = Charset('us-ascii') | |
| UTF8 = Charset('utf-8') | |
| # 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 ?= | |
| (?=[ \t]|$) # whitespace or the end of the string | |
| ''', re.VERBOSE | re.IGNORECASE | re.MULTILINE) | |
| # Field name regexp, including trailing colon, but not separating whitespace, | |
| # according to RFC 2822. Character range is from tilde to exclamation mark. | |
| # For use with .match() | |
| fcre = re.compile(r'[\041-\176]+:$') | |
| # Find a header embedded in a putative header value. Used to check for | |
| # header injection attack. | |
| _embeded_header = re.compile(r'\n[^ \t]+:') | |
| # 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. | |
| An email.errors.HeaderParseError may be raised when certain decoding error | |
| occurs (e.g. a base64 decoding exception). | |
| """ | |
| # 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] + SPACE + unenc, None) | |
| else: | |
| decoded.append((unenc, None)) | |
| if parts: | |
| charset, encoding = [s.lower() for s in parts[0:2]] | |
| encoded = parts[2] | |
| dec = None | |
| if encoding == 'q': | |
| dec = email.quoprimime.header_decode(encoded) | |
| elif encoding == 'b': | |
| paderr = len(encoded) % 4 # Postel's law: add missing padding | |
| if paderr: | |
| encoded += '==='[:4 - paderr] | |
| try: | |
| dec = email.base64mime.decode(encoded) | |
| except binascii.Error: | |
| # Turn this into a higher level exception. BAW: Right | |
| # now we throw the lower level exception away but | |
| # when/if we get exception chaining, we'll preserve it. | |
| raise HeaderParseError | |
| if dec is None: | |
| 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=' ', errors='strict'): | |
| """Create a MIME-compliant header that can contain many character sets. | |
| Optional s is the initial header value. If None, the initial header | |
| value is not set. You can later append to the header with .append() | |
| method calls. s may be a byte string or a Unicode string, but see the | |
| .append() documentation for semantics. | |
| Optional charset serves two purposes: it has the same meaning as the | |
| charset argument to the .append() method. It also sets the default | |
| character set for all subsequent .append() calls that omit the charset | |
| argument. If charset is not provided in the constructor, the us-ascii | |
| charset is used both as s's initial charset and as the default for | |
| subsequent .append() calls. | |
| 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. | |
| errors is passed through to the .append() call. | |
| """ | |
| if charset is None: | |
| charset = USASCII | |
| if not isinstance(charset, Charset): | |
| charset = 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, errors) | |
| 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.""" | |
| uchunks = [] | |
| lastcs = None | |
| for s, charset in self._chunks: | |
| # We must preserve spaces between encoded and non-encoded word | |
| # boundaries, which means for us we need to add a space when we go | |
| # from a charset to None/us-ascii, or from None/us-ascii to a | |
| # charset. Only do this for the second and subsequent chunks. | |
| nextcs = charset | |
| if uchunks: | |
| if lastcs not in (None, 'us-ascii'): | |
| if nextcs in (None, 'us-ascii'): | |
| uchunks.append(USPACE) | |
| nextcs = None | |
| elif nextcs not in (None, 'us-ascii'): | |
| uchunks.append(USPACE) | |
| lastcs = nextcs | |
| uchunks.append(unicode(s, str(charset))) | |
| return UEMPTYSTRING.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, errors='strict'): | |
| """Append a string to the MIME header. | |
| Optional charset, if given, 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 that the charset given in the | |
| constructor is used. | |
| s may be a byte string or a Unicode string. If it is a byte string | |
| (i.e. isinstance(s, str) is true), then charset is the encoding of | |
| that byte string, and a UnicodeError will be raised if the string | |
| cannot be decoded with that charset. If s is a Unicode string, then | |
| charset is a hint specifying the character set of the characters in | |
| the string. In this case, when producing an RFC 2822 compliant header | |
| using RFC 2047 rules, the Unicode string will be encoded using the | |
| following charsets in order: us-ascii, the charset hint, utf-8. The | |
| first character set not to provoke a UnicodeError is used. | |
| Optional `errors' is passed as the third argument to any unicode() or | |
| ustr.encode() call. | |
| """ | |
| if charset is None: | |
| charset = self._charset | |
| elif not isinstance(charset, Charset): | |
| charset = Charset(charset) | |
| # If the charset is our faux 8bit charset, leave the string unchanged | |
| if charset != '8bit': | |
| # We need to test that the string can be converted to unicode and | |
| # back to a byte string, given the input and output codecs of the | |
| # charset. | |
| if isinstance(s, str): | |
| # Possibly raise UnicodeError if the byte string can't be | |
| # converted to a unicode with the input codec of the charset. | |
| incodec = charset.input_codec or 'us-ascii' | |
| ustr = unicode(s, incodec, errors) | |
| # Now make sure that the unicode could be converted back to a | |
| # byte string with the output codec, which may be different | |
| # than the iput coded. Still, use the original byte string. | |
| outcodec = charset.output_codec or 'us-ascii' | |
| ustr.encode(outcodec, errors) | |
| elif isinstance(s, unicode): | |
| # Now we have to be sure the unicode string can be converted | |
| # to a byte string with a reasonable output codec. We want to | |
| # use the byte string in the chunk. | |
| for charset in USASCII, charset, UTF8: | |
| try: | |
| outcodec = charset.output_codec or 'us-ascii' | |
| s = s.encode(outcodec, errors) | |
| break | |
| except UnicodeError: | |
| pass | |
| else: | |
| assert False, 'utf-8 conversion failed' | |
| self._chunks.append((s, charset)) | |
| def _split(self, s, charset, maxlinelen, splitchars): | |
| # Split up a header safely for use with encode_chunks. | |
| splittable = charset.to_splittable(s) | |
| encoded = charset.from_splittable(splittable, True) | |
| elen = charset.encoded_header_len(encoded) | |
| # If the line's encoded length first, just return it | |
| if elen <= maxlinelen: | |
| return [(encoded, charset)] | |
| # If we have undetermined raw 8bit characters sitting in a byte | |
| # string, we really don't know what the right thing to do is. We | |
| # can't really split it because it might be multibyte data which we | |
| # could break if we split it between pairs. The least harm seems to | |
| # be to not split the header at all, but that means they could go out | |
| # longer than maxlinelen. | |
| if charset == '8bit': | |
| return [(s, 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._split_ascii(s, charset, maxlinelen, splitchars) | |
| # 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 = maxlinelen | |
| first = charset.from_splittable(splittable[:splitpnt], False) | |
| last = charset.from_splittable(splittable[splitpnt:], False) | |
| else: | |
| # Binary search for split point | |
| first, last = _binsplit(splittable, charset, maxlinelen) | |
| # first is of the proper length so just wrap it in the appropriate | |
| # chrome. last must be recursively split. | |
| fsplittable = charset.to_splittable(first) | |
| fencoded = charset.from_splittable(fsplittable, True) | |
| chunk = [(fencoded, charset)] | |
| return chunk + self._split(last, charset, self._maxlinelen, splitchars) | |
| def _split_ascii(self, s, charset, firstlen, splitchars): | |
| chunks = _split_ascii(s, firstlen, self._maxlinelen, | |
| self._continuation_ws, splitchars) | |
| return zip(chunks, [charset]*len(chunks)) | |
| def _encode_chunks(self, newchunks, maxlinelen): | |
| # 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 newchunks: | |
| if not header: | |
| continue | |
| if charset is None or charset.header_encoding is None: | |
| s = header | |
| else: | |
| s = charset.header_encode(header) | |
| # Don't add more folding whitespace than necessary | |
| if chunks and chunks[-1].endswith(' '): | |
| extra = '' | |
| else: | |
| extra = ' ' | |
| _max_append(chunks, s, maxlinelen, extra) | |
| joiner = NL + self._continuation_ws | |
| return joiner.join(chunks) | |
| def encode(self, splitchars=';, '): | |
| """Encode a message header into an RFC-compliant format. | |
| 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. | |
| Optional splitchars is a string containing characters to split long | |
| ASCII lines on, in rough support of RFC 2822's `highest level | |
| syntactic breaks'. This doesn't affect RFC 2047 encoded lines. | |
| """ | |
| newchunks = [] | |
| maxlinelen = self._firstlinelen | |
| lastlen = 0 | |
| for s, charset in self._chunks: | |
| # The first bit of the next chunk should be just long enough to | |
| # fill the next line. Don't forget the space separating the | |
| # encoded words. | |
| targetlen = maxlinelen - lastlen - 1 | |
| if targetlen < charset.encoded_header_len(''): | |
| # Stick it on the next line | |
| targetlen = maxlinelen | |
| newchunks += self._split(s, charset, targetlen, splitchars) | |
| lastchunk, lastcharset = newchunks[-1] | |
| lastlen = lastcharset.encoded_header_len(lastchunk) | |
| value = self._encode_chunks(newchunks, maxlinelen) | |
| if _embeded_header.search(value): | |
| raise HeaderParseError("header value appears to contain " | |
| "an embedded header: {!r}".format(value)) | |
| return value | |
| def _split_ascii(s, firstlen, restlen, continuation_ws, splitchars): | |
| lines = [] | |
| maxlen = firstlen | |
| for line in s.splitlines(): | |
| # Ignore any leading whitespace (i.e. continuation whitespace) already | |
| # on the line, since we'll be adding our own. | |
| line = line.lstrip() | |
| if len(line) < maxlen: | |
| lines.append(line) | |
| maxlen = restlen | |
| continue | |
| # 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 commas, then | |
| # whitespace. | |
| for ch in splitchars: | |
| if ch in line: | |
| break | |
| else: | |
| # There's nothing useful to split the line on, not even spaces, so | |
| # just append this line unchanged | |
| lines.append(line) | |
| maxlen = restlen | |
| continue | |
| # Now split the line on the character plus trailing whitespace | |
| cre = re.compile(r'%s\s*' % ch) | |
| if ch in ';,': | |
| eol = ch | |
| else: | |
| eol = '' | |
| joiner = eol + ' ' | |
| joinlen = len(joiner) | |
| wslen = len(continuation_ws.replace('\t', SPACE8)) | |
| this = [] | |
| linelen = 0 | |
| for part in cre.split(line): | |
| curlen = linelen + max(0, len(this)-1) * joinlen | |
| partlen = len(part) | |
| onfirstline = not lines | |
| # We don't want to split after the field name, if we're on the | |
| # first line and the field name is present in the header string. | |
| if ch == ' ' and onfirstline and \ | |
| len(this) == 1 and fcre.match(this[0]): | |
| this.append(part) | |
| linelen += partlen | |
| elif curlen + partlen > maxlen: | |
| if this: | |
| lines.append(joiner.join(this) + eol) | |
| # If this part is longer than maxlen and we aren't already | |
| # splitting on whitespace, try to recursively split this line | |
| # on whitespace. | |
| if partlen > maxlen and ch != ' ': | |
| subl = _split_ascii(part, maxlen, restlen, | |
| continuation_ws, ' ') | |
| lines.extend(subl[:-1]) | |
| this = [subl[-1]] | |
| else: | |
| this = [part] | |
| linelen = wslen + len(this[-1]) | |
| maxlen = restlen | |
| else: | |
| this.append(part) | |
| linelen += partlen | |
| # Put any left over parts on a line by themselves | |
| if this: | |
| lines.append(joiner.join(this)) | |
| return lines | |
| def _binsplit(splittable, charset, maxlinelen): | |
| i = 0 | |
| j = len(splittable) | |
| while i < j: | |
| # Invariants: | |
| # 1. splittable[:k] fits for all k <= i (note that we *assume*, | |
| # at the start, that splittable[:0] fits). | |
| # 2. splittable[:k] does not fit for any k > j (at the start, | |
| # this means we shouldn't look at any k > len(splittable)). | |
| # 3. We don't know about splittable[:k] for k in i+1..j. | |
| # 4. We want to set i to the largest k that fits, with i <= k <= j. | |
| # | |
| m = (i+j+1) >> 1 # ceiling((i+j)/2); i < m <= j | |
| chunk = charset.from_splittable(splittable[:m], True) | |
| chunklen = charset.encoded_header_len(chunk) | |
| if chunklen <= maxlinelen: | |
| # m is acceptable, so is a new lower bound. | |
| i = m | |
| else: | |
| # m is not acceptable, so final i must be < m. | |
| j = m - 1 | |
| # i == j. Invariant #1 implies that splittable[:i] fits, and | |
| # invariant #2 implies that splittable[:i+1] does not fit, so i | |
| # is what we're looking for. | |
| first = charset.from_splittable(splittable[:i], False) | |
| last = charset.from_splittable(splittable[i:], False) | |
| return first, last |