120 lines
3.5 KiB
Python
120 lines
3.5 KiB
Python
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# Copyright (C) 2002-2007 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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'body_decode',
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'body_encode',
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'decode',
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'decodestring',
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'header_encode',
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'header_length',
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]
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from base64 import b64encode
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from binascii import b2a_base64, a2b_base64
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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 header_length(bytearray):
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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(bytearray), 3)
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# 4 bytes out for each 3 bytes (or nonzero fraction thereof) in.
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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_bytes, charset='iso-8859-1'):
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"""Encode a single header line with Base64 encoding in a given charset.
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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. Base64 encoding is defined in RFC 2045.
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"""
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if not header_bytes:
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return ""
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if isinstance(header_bytes, str):
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header_bytes = header_bytes.encode(charset)
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encoded = b64encode(header_bytes).decode("ascii")
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return '=?%s?b?%s?=' % (charset, encoded)
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def body_encode(s, maxlinelen=76, eol=NL):
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r"""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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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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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]).decode("ascii")
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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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def decode(string):
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"""Decode a raw base64 string, returning a bytes object.
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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 string:
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return bytes()
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elif isinstance(string, str):
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return a2b_base64(string.encode('raw-unicode-escape'))
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else:
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return a2b_base64(string)
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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
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