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515 lines
22 KiB
515 lines
22 KiB
5 years ago
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# Copyright (C) 2002-2006 Python Software Foundation
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# Author: Ben Gertzfield, Barry Warsaw
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# Contact: email-sig@python.org
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"""Header encoding and decoding functionality."""
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__all__ = [
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'Header',
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'decode_header',
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'make_header',
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]
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import re
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import binascii
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import email.quoprimime
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import email.base64mime
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from email.errors import HeaderParseError
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from email.charset import Charset
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NL = '\n'
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SPACE = ' '
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USPACE = u' '
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SPACE8 = ' ' * 8
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UEMPTYSTRING = u''
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MAXLINELEN = 76
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USASCII = Charset('us-ascii')
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UTF8 = Charset('utf-8')
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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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(?=[ \t]|$) # whitespace or the end of the string
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''', re.VERBOSE | re.IGNORECASE | re.MULTILINE)
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# Field name regexp, including trailing colon, but not separating whitespace,
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# according to RFC 2822. Character range is from tilde to exclamation mark.
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# For use with .match()
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fcre = re.compile(r'[\041-\176]+:$')
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# Find a header embedded in a putative header value. Used to check for
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# header injection attack.
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_embeded_header = re.compile(r'\n[^ \t]+:')
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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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An email.errors.HeaderParseError may be raised when certain decoding error
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occurs (e.g. a base64 decoding exception).
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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] + SPACE + unenc, 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 = None
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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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paderr = len(encoded) % 4 # Postel's law: add missing padding
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if paderr:
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encoded += '==='[:4 - paderr]
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try:
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dec = email.base64mime.decode(encoded)
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except binascii.Error:
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# Turn this into a higher level exception. BAW: Right
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# now we throw the lower level exception away but
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# when/if we get exception chaining, we'll preserve it.
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raise HeaderParseError
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if dec is None:
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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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def make_header(decoded_seq, maxlinelen=None, header_name=None,
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continuation_ws=' '):
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"""Create a Header from a sequence of pairs as returned by decode_header()
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decode_header() takes a header value string and returns a sequence of
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pairs of the format (decoded_string, charset) where charset is the string
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name of the character set.
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This function takes one of those sequence of pairs and returns a Header
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instance. Optional maxlinelen, header_name, and continuation_ws are as in
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the Header constructor.
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"""
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h = Header(maxlinelen=maxlinelen, header_name=header_name,
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continuation_ws=continuation_ws)
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for s, charset in decoded_seq:
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# None means us-ascii but we can simply pass it on to h.append()
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if charset is not None and not isinstance(charset, Charset):
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charset = Charset(charset)
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h.append(s, charset)
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return h
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class Header:
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def __init__(self, s=None, charset=None,
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maxlinelen=None, header_name=None,
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continuation_ws=' ', errors='strict'):
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"""Create a MIME-compliant header that can contain many character sets.
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Optional s is the initial header value. If None, the initial header
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value is not set. You can later append to the header with .append()
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method calls. s may be a byte string or a Unicode string, but see the
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.append() documentation for semantics.
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Optional charset serves two purposes: it has the same meaning as the
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charset argument to the .append() method. It also sets the default
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character set for all subsequent .append() calls that omit the charset
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argument. If charset is not provided in the constructor, the us-ascii
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charset is used both as s's initial charset and as the default for
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subsequent .append() calls.
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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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errors is passed through to the .append() call.
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"""
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if charset is None:
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charset = USASCII
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if not isinstance(charset, Charset):
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charset = 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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if s is not None:
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self.append(s, charset, errors)
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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 __unicode__(self):
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"""Helper for the built-in unicode function."""
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uchunks = []
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lastcs = None
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for s, charset in self._chunks:
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# We must preserve spaces between encoded and non-encoded word
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# boundaries, which means for us we need to add a space when we go
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# from a charset to None/us-ascii, or from None/us-ascii to a
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# charset. Only do this for the second and subsequent chunks.
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nextcs = charset
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if uchunks:
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if lastcs not in (None, 'us-ascii'):
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if nextcs in (None, 'us-ascii'):
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uchunks.append(USPACE)
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nextcs = None
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elif nextcs not in (None, 'us-ascii'):
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uchunks.append(USPACE)
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lastcs = nextcs
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uchunks.append(unicode(s, str(charset)))
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return UEMPTYSTRING.join(uchunks)
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# Rich comparison operators for equality only. BAW: does it make sense to
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# have or explicitly disable <, <=, >, >= operators?
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def __eq__(self, other):
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# other may be a Header or a string. Both are fine so coerce
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# ourselves to a string, swap the args and do another comparison.
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return other == self.encode()
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def __ne__(self, other):
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return not self == other
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def append(self, s, charset=None, errors='strict'):
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"""Append a string to the MIME header.
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Optional charset, if given, should be a Charset instance or the name
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of a character set (which will be converted to a Charset instance). A
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value of None (the default) means that the charset given in the
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constructor is used.
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s may be a byte string or a Unicode string. If it is a byte string
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(i.e. isinstance(s, str) is true), then charset is the encoding of
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that byte string, and a UnicodeError will be raised if the string
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cannot be decoded with that charset. If s is a Unicode string, then
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charset is a hint specifying the character set of the characters in
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the string. In this case, when producing an RFC 2822 compliant header
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using RFC 2047 rules, the Unicode string will be encoded using the
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following charsets in order: us-ascii, the charset hint, utf-8. The
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first character set not to provoke a UnicodeError is used.
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Optional `errors' is passed as the third argument to any unicode() or
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ustr.encode() call.
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"""
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if charset is None:
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charset = self._charset
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elif not isinstance(charset, Charset):
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charset = Charset(charset)
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# If the charset is our faux 8bit charset, leave the string unchanged
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if charset != '8bit':
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# We need to test that the string can be converted to unicode and
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# back to a byte string, given the input and output codecs of the
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# charset.
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if isinstance(s, str):
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# Possibly raise UnicodeError if the byte string can't be
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# converted to a unicode with the input codec of the charset.
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incodec = charset.input_codec or 'us-ascii'
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ustr = unicode(s, incodec, errors)
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# Now make sure that the unicode could be converted back to a
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# byte string with the output codec, which may be different
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# than the iput coded. Still, use the original byte string.
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outcodec = charset.output_codec or 'us-ascii'
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ustr.encode(outcodec, errors)
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elif isinstance(s, unicode):
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# Now we have to be sure the unicode string can be converted
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# to a byte string with a reasonable output codec. We want to
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# use the byte string in the chunk.
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for charset in USASCII, charset, UTF8:
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try:
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outcodec = charset.output_codec or 'us-ascii'
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s = s.encode(outcodec, errors)
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break
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except UnicodeError:
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pass
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else:
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assert False, 'utf-8 conversion failed'
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self._chunks.append((s, charset))
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def _split(self, s, charset, maxlinelen, splitchars):
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# Split up a header safely for use with encode_chunks.
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splittable = charset.to_splittable(s)
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encoded = charset.from_splittable(splittable, True)
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elen = charset.encoded_header_len(encoded)
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# If the line's encoded length first, just return it
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if elen <= maxlinelen:
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return [(encoded, charset)]
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# If we have undetermined raw 8bit characters sitting in a byte
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# string, we really don't know what the right thing to do is. We
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# can't really split it because it might be multibyte data which we
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# could break if we split it between pairs. The least harm seems to
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# be to not split the header at all, but that means they could go out
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# longer than maxlinelen.
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if charset == '8bit':
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return [(s, 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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elif charset == 'us-ascii':
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return self._split_ascii(s, charset, maxlinelen, splitchars)
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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 = maxlinelen
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first = charset.from_splittable(splittable[:splitpnt], False)
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last = charset.from_splittable(splittable[splitpnt:], False)
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else:
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# Binary search for split point
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first, last = _binsplit(splittable, charset, maxlinelen)
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# first is of the proper length so just wrap it in the appropriate
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# chrome. last must be recursively split.
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fsplittable = charset.to_splittable(first)
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fencoded = charset.from_splittable(fsplittable, True)
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chunk = [(fencoded, charset)]
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return chunk + self._split(last, charset, self._maxlinelen, splitchars)
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def _split_ascii(self, s, charset, firstlen, splitchars):
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chunks = _split_ascii(s, firstlen, self._maxlinelen,
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self._continuation_ws, splitchars)
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return zip(chunks, [charset]*len(chunks))
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def _encode_chunks(self, newchunks, maxlinelen):
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# MIME-encode a header with many different charsets and/or encodings.
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#
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# Given a list of pairs (string, charset), return a MIME-encoded
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# string suitable for use in a header field. Each pair may have
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# different charsets and/or encodings, and the resulting header will
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# accurately reflect each setting.
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#
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# Each encoding can be email.utils.QP (quoted-printable, for
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# ASCII-like character sets like iso-8859-1), email.utils.BASE64
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# (Base64, for non-ASCII like character sets like KOI8-R and
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# iso-2022-jp), or None (no encoding).
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#
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|
|
# 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
|