107 lines
3.6 KiB
Python
107 lines
3.6 KiB
Python
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# This file contains two main methods used to encode and decode UTF-7
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# string, described in the RFC 3501. There are some variations specific
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# to IMAP4rev1, so the built-in Python UTF-7 codec can't be used instead.
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#
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# The main difference is the shift character (used to switch from ASCII to
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# base64 encoding context), which is & in this modified UTF-7 convention,
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# since + is considered as mainly used in mailbox names.
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# Other variations and examples can be found in the RFC 3501, section 5.1.3.
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from __future__ import unicode_literals
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import binascii
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from six import binary_type, text_type, byte2int, iterbytes, unichr
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def encode(s):
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"""Encode a folder name using IMAP modified UTF-7 encoding.
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Input is unicode; output is bytes (Python 3) or str (Python 2). If
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non-unicode input is provided, the input is returned unchanged.
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"""
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if not isinstance(s, text_type):
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return s
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res = []
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b64_buffer = []
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def consume_b64_buffer(buf):
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"""
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Consume the buffer by encoding it into a modified base 64 representation
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and surround it with shift characters & and -
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"""
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if b64_buffer:
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res.extend([b'&', base64_utf7_encode(buf), b'-'])
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del buf[:]
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for c in s:
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# printable ascii case should not be modified
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if 0x20 <= ord(c) <= 0x7e:
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consume_b64_buffer(b64_buffer)
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# Special case: & is used as shift character so we need to escape it in ASCII
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if c == '&':
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res.append(b'&-')
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else:
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res.append(c.encode('ascii'))
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# Bufferize characters that will be encoded in base64 and append them later
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# in the result, when iterating over ASCII character or the end of string
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else:
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b64_buffer.append(c)
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# Consume the remaining buffer if the string finish with non-ASCII characters
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consume_b64_buffer(b64_buffer)
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return b''.join(res)
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AMPERSAND_ORD = byte2int(b'&')
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DASH_ORD = byte2int(b'-')
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def decode(s):
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"""Decode a folder name from IMAP modified UTF-7 encoding to unicode.
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Input is bytes (Python 3) or str (Python 2); output is always
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unicode. If non-bytes/str input is provided, the input is returned
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unchanged.
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"""
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if not isinstance(s, binary_type):
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return s
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res = []
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# Store base64 substring that will be decoded once stepping on end shift character
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b64_buffer = bytearray()
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for c in iterbytes(s):
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# Shift character without anything in buffer -> starts storing base64 substring
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if c == AMPERSAND_ORD and not b64_buffer:
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b64_buffer.append(c)
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# End shift char. -> append the decoded buffer to the result and reset it
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elif c == DASH_ORD and b64_buffer:
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# Special case &-, representing "&" escaped
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if len(b64_buffer) == 1:
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res.append('&')
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else:
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res.append(base64_utf7_decode(b64_buffer[1:]))
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b64_buffer = bytearray()
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# Still buffering between the shift character and the shift back to ASCII
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elif b64_buffer:
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b64_buffer.append(c)
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# No buffer initialized yet, should be an ASCII printable char
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else:
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res.append(unichr(c))
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# Decode the remaining buffer if any
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if b64_buffer:
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res.append(base64_utf7_decode(b64_buffer[1:]))
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return ''.join(res)
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def base64_utf7_encode(buffer):
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s = ''.join(buffer).encode('utf-16be')
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return binascii.b2a_base64(s).rstrip(b'\n=').replace(b'/', b',')
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def base64_utf7_decode(s):
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s_utf7 = b'+' + s.replace(b',', b'/') + b'-'
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return s_utf7.decode('utf-7')
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