python-3.6.zip added from Github

README.cosmo contains the necessary links.

third_party/python/Lib/email/base64mime.py

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+# Copyright (C) 2002-2007 Python Software Foundation
+# Author: Ben Gertzfield
+# Contact: email-sig@python.org
+
+"""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.
+"""
+
+__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):
+    """Return the length of s when it is encoded with base64."""
+    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'):
+    """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.
+    """
+    if not header_bytes:
+        return ""
+    if isinstance(header_bytes, str):
+        header_bytes = header_bytes.encode(charset)
+    encoded = b64encode(header_bytes).decode("ascii")
+    return '=?%s?b?%s?=' % (charset, encoded)
+
+
+
+def body_encode(s, maxlinelen=76, eol=NL):
+    r"""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 "\n".  Set
+    this to "\r\n" if you will be using the result of this function directly
+    in an email.
+    """
+    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("ascii")
+        if enc.endswith(NL) and eol != NL:
+            enc = enc[:-1] + eol
+        encvec.append(enc)
+    return EMPTYSTRING.join(encvec)
+
+
+
+def decode(string):
+    """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.
+    """
+    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