diff options
Diffstat (limited to 'Lib/email/header.py')
| -rw-r--r-- | Lib/email/header.py | 662 |
1 files changed, 347 insertions, 315 deletions
diff --git a/Lib/email/header.py b/Lib/email/header.py index 2cf870fd575..e33324ad38e 100644 --- a/Lib/email/header.py +++ b/Lib/email/header.py @@ -1,4 +1,4 @@ -# Copyright (C) 2002-2006 Python Software Foundation +# Copyright (C) 2002-2007 Python Software Foundation # Author: Ben Gertzfield, Barry Warsaw # Contact: email-sig@python.org @@ -17,15 +17,16 @@ import email.quoprimime import email.base64mime from email.errors import HeaderParseError -from email.charset import Charset +from email import charset as _charset +Charset = _charset.Charset NL = '\n' SPACE = ' ' -USPACE = u' ' +BSPACE = b' ' SPACE8 = ' ' * 8 -UEMPTYSTRING = u'' - -MAXLINELEN = 76 +EMPTYSTRING = '' +MAXLINELEN = 78 +FWS = ' \t' USASCII = Charset('us-ascii') UTF8 = Charset('utf-8') @@ -61,60 +62,82 @@ _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. + Returns a list of (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. + + header may be a string that may or may not contain RFC2047 encoded words, + or it may be a Header object. 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 it is a Header object, we can just return the encoded chunks. + if hasattr(header, '_chunks'): + return [(_charset._encode(string, str(charset)), str(charset)) + for string, charset in header._chunks] + # If no encoding, just return the header with no charset. if not ecre.search(header): return [(header, None)] - decoded = [] - dec = '' + # First step is to parse all the encoded parts into triplets of the form + # (encoded_string, encoding, charset). For unencoded strings, the last + # two parts will be None. + words = [] 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)) + unencoded = parts.pop(0).strip() + if unencoded: + words.append((unencoded, None, 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 + charset = parts.pop(0).lower() + encoding = parts.pop(0).lower() + encoded = parts.pop(0) + words.append((encoded, encoding, charset)) + # The next step is to decode each encoded word by applying the reverse + # base64 or quopri transformation. decoded_words is now a list of the + # form (decoded_word, charset). + decoded_words = [] + for encoded_string, encoding, charset in words: + if encoding is None: + # This is an unencoded word. + decoded_words.append((encoded_string, charset)) + elif encoding == 'q': + word = email.quoprimime.header_decode(encoded_string) + decoded_words.append((word, charset)) + elif encoding == 'b': + paderr = len(encoded_string) % 4 # Postel's law: add missing padding + if paderr: + encoded_string += '==='[:4 - paderr] + try: + word = email.base64mime.decode(encoded_string) + except binascii.Error: + raise HeaderParseError('Base64 decoding error') + else: + decoded_words.append((word, charset)) + else: + raise AssertionError('Unexpected encoding: ' + encoding) + # Now convert all words to bytes and collapse consecutive runs of + # similarly encoded words. + collapsed = [] + last_word = last_charset = None + for word, charset in decoded_words: + if isinstance(word, str): + word = bytes(word, 'raw-unicode-escape') + if last_word is None: + last_word = word + last_charset = charset + elif charset != last_charset: + collapsed.append((last_word, last_charset)) + last_word = word + last_charset = charset + elif last_charset is None: + last_word += BSPACE + word + else: + last_word += word + collapsed.append((last_word, last_charset)) + return collapsed @@ -159,10 +182,11 @@ class Header: 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 + The maximum line length can be specified explicitly 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. + the field in header_name. The default maxlinelen is 78 as recommended + by RFC 2822. continuation_ws must be RFC 2822 compliant folding whitespace (usually either a space or a hard tab) which will be prepended to continuation @@ -172,60 +196,54 @@ class Header: """ if charset is None: charset = USASCII - if not isinstance(charset, Charset): + elif 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 + self._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 + self._headerlen = 0 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 + # Take the separating colon and space into account. + self._headerlen = len(header_name) + 2 def __str__(self): - """A synonym for self.encode().""" - return self.encode() - - def __unicode__(self): - """Helper for the built-in unicode function.""" + """Return the string value of the header.""" + self._normalize() uchunks = [] lastcs = None - for s, charset in self._chunks: + for string, 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 nextcs == _charset.UNKNOWN8BIT: + original_bytes = string.encode('ascii', 'surrogateescape') + string = original_bytes.decode('ascii', 'replace') if uchunks: if lastcs not in (None, 'us-ascii'): if nextcs in (None, 'us-ascii'): - uchunks.append(USPACE) + uchunks.append(SPACE) nextcs = None elif nextcs not in (None, 'us-ascii'): - uchunks.append(USPACE) + uchunks.append(SPACE) lastcs = nextcs - uchunks.append(unicode(s, str(charset))) - return UEMPTYSTRING.join(uchunks) + uchunks.append(string) + return EMPTYSTRING.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() + # ourselves to a unicode (of the unencoded header value), swap the + # args and do another comparison. + return other == str(self) def __ne__(self, other): return not self == other @@ -239,140 +257,42 @@ class Header: 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 + (i.e. isinstance(s, str) is false), 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. + the string. In either case, when producing an RFC 2822 compliant + header using RFC 2047 rules, the string will be encoded using the + output codec of the charset. If the string cannot be encoded to the + output codec, a UnicodeError will be raised. - Optional `errors' is passed as the third argument to any unicode() or - ustr.encode() call. + Optional `errors' is passed as the errors argument to the decode + call if s is a byte string. """ 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 = '' + if not isinstance(s, str): + input_charset = charset.input_codec or 'us-ascii' + if input_charset == _charset.UNKNOWN8BIT: + s = s.decode('us-ascii', 'surrogateescape') else: - extra = ' ' - _max_append(chunks, s, maxlinelen, extra) - joiner = NL + self._continuation_ws - return joiner.join(chunks) + s = s.decode(input_charset, errors) + # Ensure that the bytes we're storing can be decoded to the output + # character set, otherwise an early error is raised. + output_charset = charset.output_codec or 'us-ascii' + if output_charset != _charset.UNKNOWN8BIT: + try: + s.encode(output_charset, errors) + except UnicodeEncodeError: + if output_charset!='us-ascii': + raise + charset = UTF8 + self._chunks.append((s, charset)) - def encode(self, splitchars=';, '): - """Encode a message header into an RFC-compliant format. + def encode(self, splitchars=';, \t', maxlinelen=None, linesep='\n'): + r"""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 @@ -382,133 +302,245 @@ class Header: 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. + Optional maxlinelen specifies the maximum length of each generated + line, exclusive of the linesep string. Individual lines may be longer + than maxlinelen if a folding point cannot be found. The first line + will be shorter by the length of the header name plus ": " if a header + name was specified at Header construction time. The default value for + maxlinelen is determined at header construction time. + + Optional splitchars is a string containing characters which should be + given extra weight by the splitting algorithm during normal header + wrapping. This is in very rough support of RFC 2822's `higher level + syntactic breaks': split points preceded by a splitchar are preferred + during line splitting, with the characters preferred in the order in + which they appear in the string. Space and tab may be included in the + string to indicate whether preference should be given to one over the + other as a split point when other split chars do not appear in the line + being split. Splitchars does not affect RFC 2047 encoded lines. + + Optional linesep is a string to be used to separate the lines of + the value. The default value is the most useful for typical + Python applications, but it can be set to \r\n to produce RFC-compliant + line separators when needed. """ - 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) + self._normalize() + if maxlinelen is None: + maxlinelen = self._maxlinelen + # A maxlinelen of 0 means don't wrap. For all practical purposes, + # choosing a huge number here accomplishes that and makes the + # _ValueFormatter algorithm much simpler. + if maxlinelen == 0: + maxlinelen = 1000000 + formatter = _ValueFormatter(self._headerlen, maxlinelen, + self._continuation_ws, splitchars) + for string, charset in self._chunks: + lines = string.splitlines() + if lines: + formatter.feed('', lines[0], charset) + else: + formatter.feed('', '', charset) + for line in lines[1:]: + formatter.newline() + if charset.header_encoding is not None: + formatter.feed(self._continuation_ws, ' ' + line.lstrip(), + charset) + else: + sline = line.lstrip() + fws = line[:len(line)-len(sline)] + formatter.feed(fws, sline, charset) + if len(lines) > 1: + formatter.newline() + formatter.add_transition() + value = formatter._str(linesep) if _embeded_header.search(value): raise HeaderParseError("header value appears to contain " "an embedded header: {!r}".format(value)) return value + def _normalize(self): + # Step 1: Normalize the chunks so that all runs of identical charsets + # get collapsed into a single unicode string. + chunks = [] + last_charset = None + last_chunk = [] + for string, charset in self._chunks: + if charset == last_charset: + last_chunk.append(string) + else: + if last_charset is not None: + chunks.append((SPACE.join(last_chunk), last_charset)) + last_chunk = [string] + last_charset = charset + if last_chunk: + chunks.append((SPACE.join(last_chunk), last_charset)) + self._chunks = chunks + -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 +class _ValueFormatter: + def __init__(self, headerlen, maxlen, continuation_ws, splitchars): + self._maxlen = maxlen + self._continuation_ws = continuation_ws + self._continuation_ws_len = len(continuation_ws) + self._splitchars = splitchars + self._lines = [] + self._current_line = _Accumulator(headerlen) + + def _str(self, linesep): + self.newline() + return linesep.join(self._lines) + + def __str__(self): + return self._str(NL) + + def newline(self): + end_of_line = self._current_line.pop() + if end_of_line != (' ', ''): + self._current_line.push(*end_of_line) + if len(self._current_line) > 0: + if self._current_line.is_onlyws(): + self._lines[-1] += str(self._current_line) + else: + self._lines.append(str(self._current_line)) + self._current_line.reset() + + def add_transition(self): + self._current_line.push(' ', '') + + def feed(self, fws, string, charset): + # If the charset has no header encoding (i.e. it is an ASCII encoding) + # then we must split the header 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 + # whitespace. Eventually, this should be pluggable. + if charset.header_encoding is None: + self._ascii_split(fws, string, self._splitchars) + return + # Otherwise, we're doing either a Base64 or a quoted-printable + # encoding which means we don't need to split the line on syntactic + # breaks. We can basically just find enough characters to fit on the + # current line, minus the RFC 2047 chrome. What makes this trickier + # though is that we have to split at octet boundaries, not character + # boundaries but it's only safe to split at character boundaries so at + # best we can only get close. + encoded_lines = charset.header_encode_lines(string, self._maxlengths()) + # The first element extends the current line, but if it's None then + # nothing more fit on the current line so start a new line. + try: + first_line = encoded_lines.pop(0) + except IndexError: + # There are no encoded lines, so we're done. + return + if first_line is not None: + self._append_chunk(fws, first_line) + try: + last_line = encoded_lines.pop() + except IndexError: + # There was only one line. + return + self.newline() + self._current_line.push(self._continuation_ws, last_line) + # Everything else are full lines in themselves. + for line in encoded_lines: + self._lines.append(self._continuation_ws + line) + + def _maxlengths(self): + # The first line's length. + yield self._maxlen - len(self._current_line) + while True: + yield self._maxlen - self._continuation_ws_len + + def _ascii_split(self, fws, string, splitchars): + # The RFC 2822 header folding algorithm is simple in principle but + # complex in practice. Lines may be folded any place where "folding + # white space" appears by inserting a linesep character in front of the + # FWS. The complication is that not all spaces or tabs qualify as FWS, + # and we are also supposed to prefer to break at "higher level + # syntactic breaks". We can't do either of these without intimate + # knowledge of the structure of structured headers, which we don't have + # here. So the best we can do here is prefer to break at the specified + # splitchars, and hope that we don't choose any spaces or tabs that + # aren't legal FWS. (This is at least better than the old algorithm, + # where we would sometimes *introduce* FWS after a splitchar, or the + # algorithm before that, where we would turn all white space runs into + # single spaces or tabs.) + parts = re.split("(["+FWS+"]+)", fws+string) + if parts[0]: + parts[:0] = [''] 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]] + parts.pop(0) + for fws, part in zip(*[iter(parts)]*2): + self._append_chunk(fws, part) + + def _append_chunk(self, fws, string): + self._current_line.push(fws, string) + if len(self._current_line) > self._maxlen: + # Find the best split point, working backward from the end. + # There might be none, on a long first line. + for ch in self._splitchars: + for i in range(self._current_line.part_count()-1, 0, -1): + if ch.isspace(): + fws = self._current_line[i][0] + if fws and fws[0]==ch: + break + prevpart = self._current_line[i-1][1] + if prevpart and prevpart[-1]==ch: + break else: - this = [part] - linelen = wslen + len(this[-1]) - maxlen = restlen + continue + break 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 + fws, part = self._current_line.pop() + if self._current_line._initial_size > 0: + # There will be a header, so leave it on a line by itself. + self.newline() + if not fws: + # We don't use continuation_ws here because the whitespace + # after a header should always be a space. + fws = ' ' + self._current_line.push(fws, part) + return + remainder = self._current_line.pop_from(i) + self._lines.append(str(self._current_line)) + self._current_line.reset(remainder) + + +class _Accumulator(list): + + def __init__(self, initial_size=0): + self._initial_size = initial_size + super().__init__() + + def push(self, fws, string): + self.append((fws, string)) + + def pop_from(self, i=0): + popped = self[i:] + self[i:] = [] + return popped + + def pop(self): + if self.part_count()==0: + return ('', '') + return super().pop() + + def __len__(self): + return sum((len(fws)+len(part) for fws, part in self), + self._initial_size) + def __str__(self): + return EMPTYSTRING.join((EMPTYSTRING.join((fws, part)) + for fws, part in self)) - -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 + def reset(self, startval=None): + if startval is None: + startval = [] + self[:] = startval + self._initial_size = 0 + + def is_onlyws(self): + return self._initial_size==0 and (not self or str(self).isspace()) + + def part_count(self): + return super().__len__() |