1 # Copyright (C) 2001-2006 Python Software Foundation 2 # Author: Ben Gertzfield 3 # Contact: email-sig (at] python.org 4 5 """Quoted-printable content transfer encoding per RFCs 2045-2047. 6 7 This module handles the content transfer encoding method defined in RFC 2045 8 to encode US ASCII-like 8-bit data called `quoted-printable'. It is used to 9 safely encode text that is in a character set similar to the 7-bit US ASCII 10 character set, but that includes some 8-bit characters that are normally not 11 allowed in email bodies or headers. 12 13 Quoted-printable is very space-inefficient for encoding binary files; use the 14 email.base64mime module for that instead. 15 16 This module provides an interface to encode and decode both headers and bodies 17 with quoted-printable encoding. 18 19 RFC 2045 defines a method for including character set information in an 20 `encoded-word' in a header. This method is commonly used for 8-bit real names 21 in To:/From:/Cc: etc. fields, as well as Subject: lines. 22 23 This module does not do the line wrapping or end-of-line character 24 conversion necessary for proper internationalized headers; it only 25 does dumb encoding and decoding. To deal with the various line 26 wrapping issues, use the email.header module. 27 """ 28 29 __all__ = [ 30 'body_decode', 31 'body_encode', 32 'body_length', 33 'decode', 34 'decodestring', 35 'header_decode', 36 'header_encode', 37 'header_length', 38 'quote', 39 'unquote', 40 ] 41 42 import re 43 44 from string import ascii_letters, digits, hexdigits 45 46 CRLF = '\r\n' 47 NL = '\n' 48 EMPTYSTRING = '' 49 50 # Build a mapping of octets to the expansion of that octet. Since we're only 51 # going to have 256 of these things, this isn't terribly inefficient 52 # space-wise. Remember that headers and bodies have different sets of safe 53 # characters. Initialize both maps with the full expansion, and then override 54 # the safe bytes with the more compact form. 55 _QUOPRI_MAP = ['=%02X' % c for c in range(256)] 56 _QUOPRI_HEADER_MAP = _QUOPRI_MAP[:] 57 _QUOPRI_BODY_MAP = _QUOPRI_MAP[:] 58 59 # Safe header bytes which need no encoding. 60 for c in b'-!*+/' + ascii_letters.encode('ascii') + digits.encode('ascii'): 61 _QUOPRI_HEADER_MAP[c] = chr(c) 62 # Headers have one other special encoding; spaces become underscores. 63 _QUOPRI_HEADER_MAP[ord(' ')] = '_' 64 65 # Safe body bytes which need no encoding. 66 for c in (b' !"#$%&\'()*+,-./0123456789:;<>' 67 b'?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`' 68 b'abcdefghijklmnopqrstuvwxyz{|}~\t'): 69 _QUOPRI_BODY_MAP[c] = chr(c) 70 71 72 73 # Helpers 74 def header_check(octet): 75 """Return True if the octet should be escaped with header quopri.""" 76 return chr(octet) != _QUOPRI_HEADER_MAP[octet] 77 78 79 def body_check(octet): 80 """Return True if the octet should be escaped with body quopri.""" 81 return chr(octet) != _QUOPRI_BODY_MAP[octet] 82 83 84 def header_length(bytearray): 85 """Return a header quoted-printable encoding length. 86 87 Note that this does not include any RFC 2047 chrome added by 88 `header_encode()`. 89 90 :param bytearray: An array of bytes (a.k.a. octets). 91 :return: The length in bytes of the byte array when it is encoded with 92 quoted-printable for headers. 93 """ 94 return sum(len(_QUOPRI_HEADER_MAP[octet]) for octet in bytearray) 95 96 97 def body_length(bytearray): 98 """Return a body quoted-printable encoding length. 99 100 :param bytearray: An array of bytes (a.k.a. octets). 101 :return: The length in bytes of the byte array when it is encoded with 102 quoted-printable for bodies. 103 """ 104 return sum(len(_QUOPRI_BODY_MAP[octet]) for octet in bytearray) 105 106 107 def _max_append(L, s, maxlen, extra=''): 108 if not isinstance(s, str): 109 s = chr(s) 110 if not L: 111 L.append(s.lstrip()) 112 elif len(L[-1]) + len(s) <= maxlen: 113 L[-1] += extra + s 114 else: 115 L.append(s.lstrip()) 116 117 118 def unquote(s): 119 """Turn a string in the form =AB to the ASCII character with value 0xab""" 120 return chr(int(s[1:3], 16)) 121 122 123 def quote(c): 124 return _QUOPRI_MAP[ord(c)] 125 126 127 def header_encode(header_bytes, charset='iso-8859-1'): 128 """Encode a single header line with quoted-printable (like) encoding. 129 130 Defined in RFC 2045, this `Q' encoding is similar to quoted-printable, but 131 used specifically for email header fields to allow charsets with mostly 7 132 bit characters (and some 8 bit) to remain more or less readable in non-RFC 133 2045 aware mail clients. 134 135 charset names the character set to use in the RFC 2046 header. It 136 defaults to iso-8859-1. 137 """ 138 # Return empty headers as an empty string. 139 if not header_bytes: 140 return '' 141 # Iterate over every byte, encoding if necessary. 142 encoded = header_bytes.decode('latin1').translate(_QUOPRI_HEADER_MAP) 143 # Now add the RFC chrome to each encoded chunk and glue the chunks 144 # together. 145 return '=?%s?q?%s?=' % (charset, encoded) 146 147 148 _QUOPRI_BODY_ENCODE_MAP = _QUOPRI_BODY_MAP[:] 149 for c in b'\r\n': 150 _QUOPRI_BODY_ENCODE_MAP[c] = chr(c) 151 152 def body_encode(body, maxlinelen=76, eol=NL): 153 """Encode with quoted-printable, wrapping at maxlinelen characters. 154 155 Each line of encoded text will end with eol, which defaults to "\\n". Set 156 this to "\\r\\n" if you will be using the result of this function directly 157 in an email. 158 159 Each line will be wrapped at, at most, maxlinelen characters before the 160 eol string (maxlinelen defaults to 76 characters, the maximum value 161 permitted by RFC 2045). Long lines will have the 'soft line break' 162 quoted-printable character "=" appended to them, so the decoded text will 163 be identical to the original text. 164 165 The minimum maxlinelen is 4 to have room for a quoted character ("=XX") 166 followed by a soft line break. Smaller values will generate a 167 ValueError. 168 169 """ 170 171 if maxlinelen < 4: 172 raise ValueError("maxlinelen must be at least 4") 173 if not body: 174 return body 175 176 # quote special characters 177 body = body.translate(_QUOPRI_BODY_ENCODE_MAP) 178 179 soft_break = '=' + eol 180 # leave space for the '=' at the end of a line 181 maxlinelen1 = maxlinelen - 1 182 183 encoded_body = [] 184 append = encoded_body.append 185 186 for line in body.splitlines(): 187 # break up the line into pieces no longer than maxlinelen - 1 188 start = 0 189 laststart = len(line) - 1 - maxlinelen 190 while start <= laststart: 191 stop = start + maxlinelen1 192 # make sure we don't break up an escape sequence 193 if line[stop - 2] == '=': 194 append(line[start:stop - 1]) 195 start = stop - 2 196 elif line[stop - 1] == '=': 197 append(line[start:stop]) 198 start = stop - 1 199 else: 200 append(line[start:stop] + '=') 201 start = stop 202 203 # handle rest of line, special case if line ends in whitespace 204 if line and line[-1] in ' \t': 205 room = start - laststart 206 if room >= 3: 207 # It's a whitespace character at end-of-line, and we have room 208 # for the three-character quoted encoding. 209 q = quote(line[-1]) 210 elif room == 2: 211 # There's room for the whitespace character and a soft break. 212 q = line[-1] + soft_break 213 else: 214 # There's room only for a soft break. The quoted whitespace 215 # will be the only content on the subsequent line. 216 q = soft_break + quote(line[-1]) 217 append(line[start:-1] + q) 218 else: 219 append(line[start:]) 220 221 # add back final newline if present 222 if body[-1] in CRLF: 223 append('') 224 225 return eol.join(encoded_body) 226 227 228 229 # BAW: I'm not sure if the intent was for the signature of this function to be 230 # the same as base64MIME.decode() or not... 231 def decode(encoded, eol=NL): 232 """Decode a quoted-printable string. 233 234 Lines are separated with eol, which defaults to \\n. 235 """ 236 if not encoded: 237 return encoded 238 # BAW: see comment in encode() above. Again, we're building up the 239 # decoded string with string concatenation, which could be done much more 240 # efficiently. 241 decoded = '' 242 243 for line in encoded.splitlines(): 244 line = line.rstrip() 245 if not line: 246 decoded += eol 247 continue 248 249 i = 0 250 n = len(line) 251 while i < n: 252 c = line[i] 253 if c != '=': 254 decoded += c 255 i += 1 256 # Otherwise, c == "=". Are we at the end of the line? If so, add 257 # a soft line break. 258 elif i+1 == n: 259 i += 1 260 continue 261 # Decode if in form =AB 262 elif i+2 < n and line[i+1] in hexdigits and line[i+2] in hexdigits: 263 decoded += unquote(line[i:i+3]) 264 i += 3 265 # Otherwise, not in form =AB, pass literally 266 else: 267 decoded += c 268 i += 1 269 270 if i == n: 271 decoded += eol 272 # Special case if original string did not end with eol 273 if encoded[-1] not in '\r\n' and decoded.endswith(eol): 274 decoded = decoded[:-1] 275 return decoded 276 277 278 # For convenience and backwards compatibility w/ standard base64 module 279 body_decode = decode 280 decodestring = decode 281 282 283 284 def _unquote_match(match): 285 """Turn a match in the form =AB to the ASCII character with value 0xab""" 286 s = match.group(0) 287 return unquote(s) 288 289 290 # Header decoding is done a bit differently 291 def header_decode(s): 292 """Decode a string encoded with RFC 2045 MIME header `Q' encoding. 293 294 This function does not parse a full MIME header value encoded with 295 quoted-printable (like =?iso-8859-1?q?Hello_World?=) -- please use 296 the high level email.header class for that functionality. 297 """ 298 s = s.replace('_', ' ') 299 return re.sub(r'=[a-fA-F0-9]{2}', _unquote_match, s, flags=re.ASCII) 300
