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