# Copyright (C) 2002-2006 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__ = [

    'base64_len',

    'body_decode',

    'body_encode',

    'decode',

    'decodestring',

    'encode',

    'encodestring',

    'header_encode',

    ]

from binascii import b2a_base64, a2b_base64

from email.utils import fix_eols

CRLF = '\r\n'

NL = '\n'

EMPTYSTRING = ''

# See also Charset.py

MISC_LEN = 7

# Helpers

def base64_len(s):

    """Return the length of s when it is encoded with base64."""

    groups_of_3, leftover = divmod(len(s), 3)

    # 4 bytes out for each 3 bytes (or nonzero fraction thereof) in.

    # Thanks, Tim!

    n = groups_of_3 * 4

    if leftover:

        n += 4

    return n

def header_encode(header, charset='iso-8859-1', keep_eols=False,

                  maxlinelen=76, eol=NL):

    """Encode a single header line with Base64 encoding in a given charset.

    Defined in RFC 2045, this Base64 encoding is identical to normal Base64

    encoding, except that each line must be intelligently wrapped (respecting

    the Base64 encoding), and subsequent lines must start with a space.

    charset names the character set to use to encode the header.  It defaults

    to iso-8859-1.

    End-of-line characters (\\r, \\n, \\r\\n) will be automatically converted

    to the canonical email line separator \\r\\n unless the keep_eols

    parameter is True (the default is False).

    Each line of the header will be terminated in the value of eol, which

    defaults to "\\n".  Set this to "\\r\\n" if you are using the result of

    this function directly in email.

    The resulting string will be in the form:

    "=?charset?b?WW/5ciBtYXp66XLrIHf8eiBhIGhhbXBzdGHuciBBIFlv+XIgbWF6euly?=\\n

      =?charset?b?6yB3/HogYSBoYW1wc3Rh7nIgQkMgWW/5ciBtYXp66XLrIHf8eiBhIGhh?="

    with each line wrapped at, at most, maxlinelen characters (defaults to 76

    characters).

    """

    # Return empty headers unchanged

    if not header:

        return header

    if not keep_eols:

        header = fix_eols(header)

    # Base64 encode each line, in encoded chunks no greater than maxlinelen in

    # length, after the RFC chrome is added in.

    base64ed = []

    max_encoded = maxlinelen - len(charset) - MISC_LEN

    max_unencoded = max_encoded * 3 // 4

    for i in range(0, len(header), max_unencoded):

        base64ed.append(b2a_base64(header[i:i+max_unencoded]))

    # Now add the RFC chrome to each encoded chunk

    lines = []

    for line in base64ed:

        # Ignore the last character of each line if it is a newline

        if line.endswith(NL):

            line = line[:-1]

        # Add the chrome

        lines.append('=?%s?b?%s?=' % (charset, line))

    # Glue the lines together and return it.  BAW: should we be able to

    # specify the leading whitespace in the joiner?

    joiner = eol + ' '

    return joiner.join(lines)

def encode(s, binary=True, maxlinelen=76, eol=NL):

    """Encode a string with base64.

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

    76 characters).

    If binary is False, end-of-line characters will be converted to the

    canonical email end-of-line sequence \\r\\n.  Otherwise they will be left

    verbatim (this is the default).

    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

    if not binary:

        s = fix_eols(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])

        if enc.endswith(NL) and eol != NL:

            enc = enc[:-1] + eol

        encvec.append(enc)

    return EMPTYSTRING.join(encvec)

# For convenience and backwards compatibility w/ standard base64 module

body_encode = encode

encodestring = encode

def decode(s, convert_eols=None):

    """Decode a raw base64 string.

    If convert_eols is set to a string value, all canonical email linefeeds,

    e.g. "\\r\\n", in the decoded text will be converted to the value of

    convert_eols.  os.linesep is a good choice for convert_eols if you are

    decoding a text attachment.

    This function does not parse a full MIME header value encoded with

    base64 (like =?iso-8895-1?b?bmloISBuaWgh?=) -- please use the high

    level email.Header class for that functionality.

    """

    if not s:

        return s

    dec = a2b_base64(s)

    if convert_eols:

        return dec.replace(CRLF, convert_eols)

    return dec

# For convenience and backwards compatibility w/ standard base64 module

body_decode = decode

decodestring = decode