<h2>Editing File: /lib64/python3.8/email/base64mime.py</h2><form method='post'><textarea name='content' class='file-edit'># Copyright (C) 2002-2007 Python Software Foundation
# Author: Ben Gertzfield
# Contact: email-sig@python.org

&quot;&quot;&quot;Base64 content transfer encoding per RFCs 2045-2047.

This module handles the content transfer encoding method defined in RFC 2045
to encode arbitrary 8-bit data using the three 8-bit bytes in four 7-bit
characters encoding known as Base64.

It is used in the MIME standards for email to attach images, audio, and text
using some 8-bit character sets to messages.

This module provides an interface to encode and decode both headers and bodies
with Base64 encoding.

RFC 2045 defines a method for including character set information in an
`encoded-word' in a header.  This method is commonly used for 8-bit real names
in To:, From:, Cc:, etc. fields, as well as Subject: lines.

This module does not do the line wrapping or end-of-line character conversion
necessary for proper internationalized headers; it only does dumb encoding and
decoding.  To deal with the various line wrapping issues, use the email.header
module.
&quot;&quot;&quot;

__all__ = [
    'body_decode',
    'body_encode',
    'decode',
    'decodestring',
    'header_encode',
    'header_length',
    ]


from base64 import b64encode
from binascii import b2a_base64, a2b_base64

CRLF = '\r\n'
NL = '\n'
EMPTYSTRING = ''

# See also Charset.py
MISC_LEN = 7


# Helpers
def header_length(bytearray):
    &quot;&quot;&quot;Return the length of s when it is encoded with base64.&quot;&quot;&quot;
    groups_of_3, leftover = divmod(len(bytearray), 3)
    # 4 bytes out for each 3 bytes (or nonzero fraction thereof) in.
    n = groups_of_3 * 4
    if leftover:
        n += 4
    return n


def header_encode(header_bytes, charset='iso-8859-1'):
    &quot;&quot;&quot;Encode a single header line with Base64 encoding in a given charset.

    charset names the character set to use to encode the header.  It defaults
    to iso-8859-1.  Base64 encoding is defined in RFC 2045.
    &quot;&quot;&quot;
    if not header_bytes:
        return &quot;&quot;
    if isinstance(header_bytes, str):
        header_bytes = header_bytes.encode(charset)
    encoded = b64encode(header_bytes).decode(&quot;ascii&quot;)
    return '=?%s?b?%s?=' % (charset, encoded)


def body_encode(s, maxlinelen=76, eol=NL):
    r&quot;&quot;&quot;Encode a string with base64.

    Each line will be wrapped at, at most, maxlinelen characters (defaults to
    76 characters).

    Each line of encoded text will end with eol, which defaults to &quot;\n&quot;.  Set
    this to &quot;\r\n&quot; if you will be using the result of this function directly
    in an email.
    &quot;&quot;&quot;
    if not s:
        return s

    encvec = []
    max_unencoded = maxlinelen * 3 // 4
    for i in range(0, len(s), max_unencoded):
        # BAW: should encode() inherit b2a_base64()'s dubious behavior in
        # adding a newline to the encoded string?
        enc = b2a_base64(s[i:i + max_unencoded]).decode(&quot;ascii&quot;)
        if enc.endswith(NL) and eol != NL:
            enc = enc[:-1] + eol
        encvec.append(enc)
    return EMPTYSTRING.join(encvec)


def decode(string):
    &quot;&quot;&quot;Decode a raw base64 string, returning a bytes object.

    This function does not parse a full MIME header value encoded with
    base64 (like =?iso-8859-1?b?bmloISBuaWgh?=) -- please use the high
    level email.header class for that functionality.
    &quot;&quot;&quot;
    if not string:
        return bytes()
    elif isinstance(string, str):
        return a2b_base64(string.encode('raw-unicode-escape'))
    else:
        return a2b_base64(string)


# For convenience and backwards compatibility w/ standard base64 module
body_decode = decode
decodestring = decode
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