1 # Copyright (C) 2002-2007 Python Software Foundation 2 # Author: Ben Gertzfield 3 # Contact: email-sig@python.org 4 5 """Base64 content transfer encoding per RFCs 2045-2047. 6 7 This module handles the content transfer encoding method defined in RFC 2045 8 to encode arbitrary 8-bit data using the three 8-bit bytes in four 7-bit 9 characters encoding known as Base64. 10 11 It is used in the MIME standards for email to attach images, audio, and text 12 using some 8-bit character sets to messages. 13 14 This module provides an interface to encode and decode both headers and bodies 15 with Base64 encoding. 16 17 RFC 2045 defines a method for including character set information in an 18 `encoded-word' in a header. This method is commonly used for 8-bit real names 19 in To:, From:, Cc:, etc. fields, as well as Subject: lines. 20 21 This module does not do the line wrapping or end-of-line character conversion 22 necessary for proper internationalized headers; it only does dumb encoding and 23 decoding. To deal with the various line wrapping issues, use the email.header 24 module. 25 """ 26 27 __all__ = [ 28 'body_decode', 29 'body_encode', 30 'decode', 31 'decodestring', 32 'header_encode', 33 'header_length', 34 ] 35 36 37 from base64 import b64encode 38 from binascii import b2a_base64, a2b_base64 39 40 CRLF = '\r\n' 41 NL = '\n' 42 EMPTYSTRING = '' 43 44 # See also Charset.py 45 MISC_LEN = 7 46 47 48 49 # Helpers 50 def header_length(bytearray): 51 """Return the length of s when it is encoded with base64.""" 52 groups_of_3, leftover = divmod(len(bytearray), 3) 53 # 4 bytes out for each 3 bytes (or nonzero fraction thereof) in. 54 n = groups_of_3 * 4 55 if leftover: 56 n += 4 57 return n 58 59 60 61 def header_encode(header_bytes, charset='iso-8859-1'): 62 """Encode a single header line with Base64 encoding in a given charset. 63 64 charset names the character set to use to encode the header. It defaults 65 to iso-8859-1. Base64 encoding is defined in RFC 2045. 66 """ 67 if not header_bytes: 68 return "" 69 if isinstance(header_bytes, str): 70 header_bytes = header_bytes.encode(charset) 71 encoded = b64encode(header_bytes).decode("ascii") 72 return '=?%s?b?%s?=' % (charset, encoded) 73 74 75 76 def body_encode(s, maxlinelen=76, eol=NL): 77 r"""Encode a string with base64. 78 79 Each line will be wrapped at, at most, maxlinelen characters (defaults to 80 76 characters). 81 82 Each line of encoded text will end with eol, which defaults to "\n". Set 83 this to "\r\n" if you will be using the result of this function directly 84 in an email. 85 """ 86 if not s: 87 return s 88 89 encvec = [] 90 max_unencoded = maxlinelen * 3 // 4 91 for i in range(0, len(s), max_unencoded): 92 # BAW: should encode() inherit b2a_base64()'s dubious behavior in 93 # adding a newline to the encoded string? 94 enc = b2a_base64(s[i:i + max_unencoded]).decode("ascii") 95 if enc.endswith(NL) and eol != NL: 96 enc = enc[:-1] + eol 97 encvec.append(enc) 98 return EMPTYSTRING.join(encvec) 99 100 101 102 def decode(string): 103 """Decode a raw base64 string, returning a bytes object. 104 105 This function does not parse a full MIME header value encoded with 106 base64 (like =?iso-8895-1?b?bmloISBuaWgh?=) -- please use the high 107 level email.header class for that functionality. 108 """ 109 if not string: 110 return bytes() 111 elif isinstance(string, str): 112 return a2b_base64(string.encode('raw-unicode-escape')) 113 else: 114 return a2b_base64(string) 115 116 117 # For convenience and backwards compatibility w/ standard base64 module 118 body_decode = decode 119 decodestring = decode |