300 lines
9.6 KiB
Python
300 lines
9.6 KiB
Python
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# Copyright (C) 2001-2006 Python Software Foundation
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# Author: Ben Gertzfield
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# Contact: email-sig@python.org
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"""Quoted-printable content transfer encoding per RFCs 2045-2047.
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This module handles the content transfer encoding method defined in RFC 2045
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to encode US ASCII-like 8-bit data called `quoted-printable'. It is used to
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safely encode text that is in a character set similar to the 7-bit US ASCII
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character set, but that includes some 8-bit characters that are normally not
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allowed in email bodies or headers.
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Quoted-printable is very space-inefficient for encoding binary files; use the
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email.base64mime module for that instead.
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This module provides an interface to encode and decode both headers and bodies
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with quoted-printable encoding.
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RFC 2045 defines a method for including character set information in an
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`encoded-word' in a header. This method is commonly used for 8-bit real names
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in To:/From:/Cc: etc. fields, as well as Subject: lines.
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This module does not do the line wrapping or end-of-line character
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conversion necessary for proper internationalized headers; it only
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does dumb encoding and decoding. To deal with the various line
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wrapping issues, use the email.header module.
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"""
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__all__ = [
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'body_decode',
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'body_encode',
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'body_length',
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'decode',
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'decodestring',
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'header_decode',
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'header_encode',
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'header_length',
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'quote',
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'unquote',
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]
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import re
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from string import ascii_letters, digits, hexdigits
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CRLF = '\r\n'
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NL = '\n'
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EMPTYSTRING = ''
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# Build a mapping of octets to the expansion of that octet. Since we're only
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# going to have 256 of these things, this isn't terribly inefficient
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# space-wise. Remember that headers and bodies have different sets of safe
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# characters. Initialize both maps with the full expansion, and then override
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# the safe bytes with the more compact form.
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_QUOPRI_MAP = ['=%02X' % c for c in range(256)]
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_QUOPRI_HEADER_MAP = _QUOPRI_MAP[:]
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_QUOPRI_BODY_MAP = _QUOPRI_MAP[:]
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# Safe header bytes which need no encoding.
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for c in b'-!*+/' + ascii_letters.encode('ascii') + digits.encode('ascii'):
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_QUOPRI_HEADER_MAP[c] = chr(c)
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# Headers have one other special encoding; spaces become underscores.
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_QUOPRI_HEADER_MAP[ord(' ')] = '_'
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# Safe body bytes which need no encoding.
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for c in (b' !"#$%&\'()*+,-./0123456789:;<>'
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b'?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`'
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b'abcdefghijklmnopqrstuvwxyz{|}~\t'):
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_QUOPRI_BODY_MAP[c] = chr(c)
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# Helpers
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def header_check(octet):
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"""Return True if the octet should be escaped with header quopri."""
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return chr(octet) != _QUOPRI_HEADER_MAP[octet]
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def body_check(octet):
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"""Return True if the octet should be escaped with body quopri."""
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return chr(octet) != _QUOPRI_BODY_MAP[octet]
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def header_length(bytearray):
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"""Return a header quoted-printable encoding length.
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Note that this does not include any RFC 2047 chrome added by
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`header_encode()`.
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:param bytearray: An array of bytes (a.k.a. octets).
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:return: The length in bytes of the byte array when it is encoded with
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quoted-printable for headers.
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"""
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return sum(len(_QUOPRI_HEADER_MAP[octet]) for octet in bytearray)
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def body_length(bytearray):
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"""Return a body quoted-printable encoding length.
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:param bytearray: An array of bytes (a.k.a. octets).
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:return: The length in bytes of the byte array when it is encoded with
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quoted-printable for bodies.
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"""
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return sum(len(_QUOPRI_BODY_MAP[octet]) for octet in bytearray)
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def _max_append(L, s, maxlen, extra=''):
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if not isinstance(s, str):
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s = chr(s)
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if not L:
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L.append(s.lstrip())
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elif len(L[-1]) + len(s) <= maxlen:
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L[-1] += extra + s
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else:
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L.append(s.lstrip())
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def unquote(s):
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"""Turn a string in the form =AB to the ASCII character with value 0xab"""
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return chr(int(s[1:3], 16))
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def quote(c):
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return _QUOPRI_MAP[ord(c)]
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def header_encode(header_bytes, charset='iso-8859-1'):
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"""Encode a single header line with quoted-printable (like) encoding.
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Defined in RFC 2045, this `Q' encoding is similar to quoted-printable, but
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used specifically for email header fields to allow charsets with mostly 7
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bit characters (and some 8 bit) to remain more or less readable in non-RFC
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2045 aware mail clients.
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charset names the character set to use in the RFC 2046 header. It
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defaults to iso-8859-1.
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"""
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# Return empty headers as an empty string.
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if not header_bytes:
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return ''
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# Iterate over every byte, encoding if necessary.
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encoded = header_bytes.decode('latin1').translate(_QUOPRI_HEADER_MAP)
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# Now add the RFC chrome to each encoded chunk and glue the chunks
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# together.
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return '=?%s?q?%s?=' % (charset, encoded)
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_QUOPRI_BODY_ENCODE_MAP = _QUOPRI_BODY_MAP[:]
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for c in b'\r\n':
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_QUOPRI_BODY_ENCODE_MAP[c] = chr(c)
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def body_encode(body, maxlinelen=76, eol=NL):
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"""Encode with quoted-printable, wrapping at maxlinelen characters.
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Each line of encoded text will end with eol, which defaults to "\\n". Set
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this to "\\r\\n" if you will be using the result of this function directly
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in an email.
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Each line will be wrapped at, at most, maxlinelen characters before the
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eol string (maxlinelen defaults to 76 characters, the maximum value
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permitted by RFC 2045). Long lines will have the 'soft line break'
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quoted-printable character "=" appended to them, so the decoded text will
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be identical to the original text.
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The minimum maxlinelen is 4 to have room for a quoted character ("=XX")
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followed by a soft line break. Smaller values will generate a
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ValueError.
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"""
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if maxlinelen < 4:
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raise ValueError("maxlinelen must be at least 4")
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if not body:
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return body
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# quote speacial characters
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body = body.translate(_QUOPRI_BODY_ENCODE_MAP)
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soft_break = '=' + eol
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# leave space for the '=' at the end of a line
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maxlinelen1 = maxlinelen - 1
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encoded_body = []
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append = encoded_body.append
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for line in body.splitlines():
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# break up the line into pieces no longer than maxlinelen - 1
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start = 0
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laststart = len(line) - 1 - maxlinelen
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while start <= laststart:
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stop = start + maxlinelen1
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# make sure we don't break up an escape sequence
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if line[stop - 2] == '=':
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append(line[start:stop - 1])
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start = stop - 2
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elif line[stop - 1] == '=':
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append(line[start:stop])
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start = stop - 1
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else:
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append(line[start:stop] + '=')
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start = stop
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# handle rest of line, special case if line ends in whitespace
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if line and line[-1] in ' \t':
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room = start - laststart
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if room >= 3:
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# It's a whitespace character at end-of-line, and we have room
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# for the three-character quoted encoding.
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q = quote(line[-1])
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elif room == 2:
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# There's room for the whitespace character and a soft break.
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q = line[-1] + soft_break
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else:
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# There's room only for a soft break. The quoted whitespace
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# will be the only content on the subsequent line.
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q = soft_break + quote(line[-1])
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append(line[start:-1] + q)
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else:
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append(line[start:])
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# add back final newline if present
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if body[-1] in CRLF:
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append('')
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return eol.join(encoded_body)
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# BAW: I'm not sure if the intent was for the signature of this function to be
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# the same as base64MIME.decode() or not...
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def decode(encoded, eol=NL):
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"""Decode a quoted-printable string.
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Lines are separated with eol, which defaults to \\n.
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"""
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if not encoded:
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return encoded
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# BAW: see comment in encode() above. Again, we're building up the
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# decoded string with string concatenation, which could be done much more
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# efficiently.
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decoded = ''
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for line in encoded.splitlines():
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line = line.rstrip()
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if not line:
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decoded += eol
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continue
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i = 0
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n = len(line)
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while i < n:
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c = line[i]
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if c != '=':
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decoded += c
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i += 1
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# Otherwise, c == "=". Are we at the end of the line? If so, add
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# a soft line break.
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elif i+1 == n:
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i += 1
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continue
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# Decode if in form =AB
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elif i+2 < n and line[i+1] in hexdigits and line[i+2] in hexdigits:
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decoded += unquote(line[i:i+3])
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i += 3
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# Otherwise, not in form =AB, pass literally
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else:
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decoded += c
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i += 1
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if i == n:
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decoded += eol
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# Special case if original string did not end with eol
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if encoded[-1] not in '\r\n' and decoded.endswith(eol):
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decoded = decoded[:-1]
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return decoded
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# For convenience and backwards compatibility w/ standard base64 module
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body_decode = decode
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decodestring = decode
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def _unquote_match(match):
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"""Turn a match in the form =AB to the ASCII character with value 0xab"""
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s = match.group(0)
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return unquote(s)
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# Header decoding is done a bit differently
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def header_decode(s):
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"""Decode a string encoded with RFC 2045 MIME header `Q' encoding.
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This function does not parse a full MIME header value encoded with
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quoted-printable (like =?iso-8895-1?q?Hello_World?=) -- please use
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the high level email.header class for that functionality.
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"""
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s = s.replace('_', ' ')
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return re.sub(r'=[a-fA-F0-9]{2}', _unquote_match, s, flags=re.ASCII)
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