python-2.5.2/win32/Lib/email/base64mime.py
author jjkang
Fri, 11 Jun 2010 15:22:40 +0800
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parent 0 ae805ac0140d
permissions -rw-r--r--
Change SFL to EPL
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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# Copyright (C) 2002-2006 Python Software Foundation
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# Author: Ben Gertzfield
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# Contact: email-sig@python.org
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"""Base64 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 arbitrary 8-bit data using the three 8-bit bytes in four 7-bit
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characters encoding known as Base64.
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It is used in the MIME standards for email to attach images, audio, and text
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using some 8-bit character sets to messages.
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This module provides an interface to encode and decode both headers and bodies
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with Base64 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 conversion
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necessary for proper internationalized headers; it only does dumb encoding and
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decoding.  To deal with the various line wrapping issues, use the email.Header
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module.
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"""
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__all__ = [
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    'base64_len',
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    'body_decode',
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    'body_encode',
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    'decode',
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    'decodestring',
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    'encode',
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    'encodestring',
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    'header_encode',
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    ]
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import re
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from binascii import b2a_base64, a2b_base64
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from email.utils import fix_eols
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CRLF = '\r\n'
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NL = '\n'
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EMPTYSTRING = ''
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# See also Charset.py
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MISC_LEN = 7
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# Helpers
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def base64_len(s):
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    """Return the length of s when it is encoded with base64."""
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    groups_of_3, leftover = divmod(len(s), 3)
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    # 4 bytes out for each 3 bytes (or nonzero fraction thereof) in.
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    # Thanks, Tim!
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    n = groups_of_3 * 4
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    if leftover:
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        n += 4
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    return n
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def header_encode(header, charset='iso-8859-1', keep_eols=False,
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                  maxlinelen=76, eol=NL):
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    """Encode a single header line with Base64 encoding in a given charset.
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    Defined in RFC 2045, this Base64 encoding is identical to normal Base64
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    encoding, except that each line must be intelligently wrapped (respecting
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    the Base64 encoding), and subsequent lines must start with a space.
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    charset names the character set to use to encode the header.  It defaults
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    to iso-8859-1.
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    End-of-line characters (\\r, \\n, \\r\\n) will be automatically converted
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    to the canonical email line separator \\r\\n unless the keep_eols
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    parameter is True (the default is False).
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    Each line of the header will be terminated in the value of eol, which
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    defaults to "\\n".  Set this to "\\r\\n" if you are using the result of
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    this function directly in email.
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    The resulting string will be in the form:
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    "=?charset?b?WW/5ciBtYXp66XLrIHf8eiBhIGhhbXBzdGHuciBBIFlv+XIgbWF6euly?=\\n
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      =?charset?b?6yB3/HogYSBoYW1wc3Rh7nIgQkMgWW/5ciBtYXp66XLrIHf8eiBhIGhh?="
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    with each line wrapped at, at most, maxlinelen characters (defaults to 76
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    characters).
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    """
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    # Return empty headers unchanged
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    if not header:
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        return header
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    if not keep_eols:
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        header = fix_eols(header)
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    # Base64 encode each line, in encoded chunks no greater than maxlinelen in
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    # length, after the RFC chrome is added in.
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    base64ed = []
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    max_encoded = maxlinelen - len(charset) - MISC_LEN
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    max_unencoded = max_encoded * 3 // 4
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    for i in range(0, len(header), max_unencoded):
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        base64ed.append(b2a_base64(header[i:i+max_unencoded]))
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    # Now add the RFC chrome to each encoded chunk
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    lines = []
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    for line in base64ed:
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        # Ignore the last character of each line if it is a newline
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        if line.endswith(NL):
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            line = line[:-1]
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        # Add the chrome
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        lines.append('=?%s?b?%s?=' % (charset, line))
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    # Glue the lines together and return it.  BAW: should we be able to
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    # specify the leading whitespace in the joiner?
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    joiner = eol + ' '
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    return joiner.join(lines)
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def encode(s, binary=True, maxlinelen=76, eol=NL):
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    """Encode a string with base64.
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    Each line will be wrapped at, at most, maxlinelen characters (defaults to
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    76 characters).
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    If binary is False, end-of-line characters will be converted to the
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    canonical email end-of-line sequence \\r\\n.  Otherwise they will be left
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    verbatim (this is the default).
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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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    """
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    if not s:
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        return s
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    if not binary:
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        s = fix_eols(s)
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    encvec = []
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    max_unencoded = maxlinelen * 3 // 4
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    for i in range(0, len(s), max_unencoded):
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        # BAW: should encode() inherit b2a_base64()'s dubious behavior in
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        # adding a newline to the encoded string?
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        enc = b2a_base64(s[i:i + max_unencoded])
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        if enc.endswith(NL) and eol <> NL:
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            enc = enc[:-1] + eol
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        encvec.append(enc)
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    return EMPTYSTRING.join(encvec)
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# For convenience and backwards compatibility w/ standard base64 module
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body_encode = encode
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encodestring = encode
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def decode(s, convert_eols=None):
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    """Decode a raw base64 string.
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    If convert_eols is set to a string value, all canonical email linefeeds,
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    e.g. "\\r\\n", in the decoded text will be converted to the value of
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    convert_eols.  os.linesep is a good choice for convert_eols if you are
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    decoding a text attachment.
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    This function does not parse a full MIME header value encoded with
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    base64 (like =?iso-8895-1?b?bmloISBuaWgh?=) -- please use the high
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    level email.Header class for that functionality.
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    """
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    if not s:
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        return s
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    dec = a2b_base64(s)
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    if convert_eols:
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        return dec.replace(CRLF, convert_eols)
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    return dec
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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