1 | # Copyright (C) 2002-2006 Python Software Foundation |
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2 | # Author: Ben Gertzfield, Barry Warsaw |
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3 | # Contact: email-sig@python.org |
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4 | |
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5 | """Header encoding and decoding functionality.""" |
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6 | |
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7 | __all__ = [ |
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8 | 'Header', |
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9 | 'decode_header', |
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10 | 'make_header', |
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11 | ] |
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12 | |
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13 | import re |
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14 | import binascii |
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15 | |
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16 | import email.quoprimime |
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17 | import email.base64mime |
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18 | |
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19 | from email.errors import HeaderParseError |
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20 | from email.charset import Charset |
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21 | |
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22 | NL = '\n' |
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23 | SPACE = ' ' |
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24 | USPACE = u' ' |
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25 | SPACE8 = ' ' * 8 |
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26 | UEMPTYSTRING = u'' |
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27 | |
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28 | MAXLINELEN = 76 |
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29 | |
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30 | USASCII = Charset('us-ascii') |
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31 | UTF8 = Charset('utf-8') |
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32 | |
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33 | # Match encoded-word strings in the form =?charset?q?Hello_World?= |
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34 | ecre = re.compile(r''' |
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35 | =\? # literal =? |
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36 | (?P<charset>[^?]*?) # non-greedy up to the next ? is the charset |
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37 | \? # literal ? |
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38 | (?P<encoding>[qb]) # either a "q" or a "b", case insensitive |
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39 | \? # literal ? |
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40 | (?P<encoded>.*?) # non-greedy up to the next ?= is the encoded string |
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41 | \?= # literal ?= |
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42 | (?=[ \t]|$) # whitespace or the end of the string |
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43 | ''', re.VERBOSE | re.IGNORECASE | re.MULTILINE) |
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44 | |
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45 | # Field name regexp, including trailing colon, but not separating whitespace, |
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46 | # according to RFC 2822. Character range is from tilde to exclamation mark. |
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47 | # For use with .match() |
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48 | fcre = re.compile(r'[\041-\176]+:$') |
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49 | |
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50 | # Find a header embedded in a putative header value. Used to check for |
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51 | # header injection attack. |
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52 | _embeded_header = re.compile(r'\n[^ \t]+:') |
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53 | |
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54 | |
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55 | |
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56 | # Helpers |
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57 | _max_append = email.quoprimime._max_append |
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58 | |
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59 | |
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60 | |
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61 | def decode_header(header): |
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62 | """Decode a message header value without converting charset. |
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63 | |
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64 | Returns a list of (decoded_string, charset) pairs containing each of the |
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65 | decoded parts of the header. Charset is None for non-encoded parts of the |
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66 | header, otherwise a lower-case string containing the name of the character |
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67 | set specified in the encoded string. |
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68 | |
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69 | An email.errors.HeaderParseError may be raised when certain decoding error |
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70 | occurs (e.g. a base64 decoding exception). |
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71 | """ |
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72 | # If no encoding, just return the header |
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73 | header = str(header) |
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74 | if not ecre.search(header): |
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75 | return [(header, None)] |
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76 | decoded = [] |
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77 | dec = '' |
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78 | for line in header.splitlines(): |
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79 | # This line might not have an encoding in it |
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80 | if not ecre.search(line): |
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81 | decoded.append((line, None)) |
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82 | continue |
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83 | parts = ecre.split(line) |
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84 | while parts: |
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85 | unenc = parts.pop(0).strip() |
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86 | if unenc: |
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87 | # Should we continue a long line? |
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88 | if decoded and decoded[-1][1] is None: |
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89 | decoded[-1] = (decoded[-1][0] + SPACE + unenc, None) |
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90 | else: |
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91 | decoded.append((unenc, None)) |
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92 | if parts: |
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93 | charset, encoding = [s.lower() for s in parts[0:2]] |
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94 | encoded = parts[2] |
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95 | dec = None |
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96 | if encoding == 'q': |
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97 | dec = email.quoprimime.header_decode(encoded) |
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98 | elif encoding == 'b': |
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99 | paderr = len(encoded) % 4 # Postel's law: add missing padding |
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100 | if paderr: |
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101 | encoded += '==='[:4 - paderr] |
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102 | try: |
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103 | dec = email.base64mime.decode(encoded) |
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104 | except binascii.Error: |
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105 | # Turn this into a higher level exception. BAW: Right |
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106 | # now we throw the lower level exception away but |
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107 | # when/if we get exception chaining, we'll preserve it. |
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108 | raise HeaderParseError |
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109 | if dec is None: |
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110 | dec = encoded |
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111 | |
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112 | if decoded and decoded[-1][1] == charset: |
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113 | decoded[-1] = (decoded[-1][0] + dec, decoded[-1][1]) |
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114 | else: |
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115 | decoded.append((dec, charset)) |
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116 | del parts[0:3] |
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117 | return decoded |
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118 | |
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119 | |
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120 | |
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121 | def make_header(decoded_seq, maxlinelen=None, header_name=None, |
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122 | continuation_ws=' '): |
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123 | """Create a Header from a sequence of pairs as returned by decode_header() |
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124 | |
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125 | decode_header() takes a header value string and returns a sequence of |
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126 | pairs of the format (decoded_string, charset) where charset is the string |
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127 | name of the character set. |
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128 | |
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129 | This function takes one of those sequence of pairs and returns a Header |
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130 | instance. Optional maxlinelen, header_name, and continuation_ws are as in |
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131 | the Header constructor. |
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132 | """ |
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133 | h = Header(maxlinelen=maxlinelen, header_name=header_name, |
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134 | continuation_ws=continuation_ws) |
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135 | for s, charset in decoded_seq: |
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136 | # None means us-ascii but we can simply pass it on to h.append() |
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137 | if charset is not None and not isinstance(charset, Charset): |
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138 | charset = Charset(charset) |
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139 | h.append(s, charset) |
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140 | return h |
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141 | |
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142 | |
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143 | |
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144 | class Header: |
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145 | def __init__(self, s=None, charset=None, |
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146 | maxlinelen=None, header_name=None, |
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147 | continuation_ws=' ', errors='strict'): |
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148 | """Create a MIME-compliant header that can contain many character sets. |
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149 | |
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150 | Optional s is the initial header value. If None, the initial header |
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151 | value is not set. You can later append to the header with .append() |
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152 | method calls. s may be a byte string or a Unicode string, but see the |
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153 | .append() documentation for semantics. |
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154 | |
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155 | Optional charset serves two purposes: it has the same meaning as the |
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156 | charset argument to the .append() method. It also sets the default |
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157 | character set for all subsequent .append() calls that omit the charset |
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158 | argument. If charset is not provided in the constructor, the us-ascii |
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159 | charset is used both as s's initial charset and as the default for |
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160 | subsequent .append() calls. |
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161 | |
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162 | The maximum line length can be specified explicit via maxlinelen. For |
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163 | splitting the first line to a shorter value (to account for the field |
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164 | header which isn't included in s, e.g. `Subject') pass in the name of |
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165 | the field in header_name. The default maxlinelen is 76. |
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166 | |
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167 | continuation_ws must be RFC 2822 compliant folding whitespace (usually |
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168 | either a space or a hard tab) which will be prepended to continuation |
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169 | lines. |
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170 | |
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171 | errors is passed through to the .append() call. |
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172 | """ |
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173 | if charset is None: |
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174 | charset = USASCII |
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175 | if not isinstance(charset, Charset): |
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176 | charset = Charset(charset) |
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177 | self._charset = charset |
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178 | self._continuation_ws = continuation_ws |
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179 | cws_expanded_len = len(continuation_ws.replace('\t', SPACE8)) |
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180 | # BAW: I believe `chunks' and `maxlinelen' should be non-public. |
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181 | self._chunks = [] |
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182 | if s is not None: |
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183 | self.append(s, charset, errors) |
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184 | if maxlinelen is None: |
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185 | maxlinelen = MAXLINELEN |
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186 | if header_name is None: |
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187 | # We don't know anything about the field header so the first line |
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188 | # is the same length as subsequent lines. |
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189 | self._firstlinelen = maxlinelen |
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190 | else: |
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191 | # The first line should be shorter to take into account the field |
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192 | # header. Also subtract off 2 extra for the colon and space. |
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193 | self._firstlinelen = maxlinelen - len(header_name) - 2 |
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194 | # Second and subsequent lines should subtract off the length in |
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195 | # columns of the continuation whitespace prefix. |
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196 | self._maxlinelen = maxlinelen - cws_expanded_len |
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197 | |
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198 | def __str__(self): |
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199 | """A synonym for self.encode().""" |
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200 | return self.encode() |
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201 | |
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202 | def __unicode__(self): |
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203 | """Helper for the built-in unicode function.""" |
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204 | uchunks = [] |
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205 | lastcs = None |
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206 | for s, charset in self._chunks: |
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207 | # We must preserve spaces between encoded and non-encoded word |
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208 | # boundaries, which means for us we need to add a space when we go |
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209 | # from a charset to None/us-ascii, or from None/us-ascii to a |
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210 | # charset. Only do this for the second and subsequent chunks. |
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211 | nextcs = charset |
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212 | if uchunks: |
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213 | if lastcs not in (None, 'us-ascii'): |
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214 | if nextcs in (None, 'us-ascii'): |
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215 | uchunks.append(USPACE) |
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216 | nextcs = None |
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217 | elif nextcs not in (None, 'us-ascii'): |
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218 | uchunks.append(USPACE) |
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219 | lastcs = nextcs |
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220 | uchunks.append(unicode(s, str(charset))) |
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221 | return UEMPTYSTRING.join(uchunks) |
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222 | |
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223 | # Rich comparison operators for equality only. BAW: does it make sense to |
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224 | # have or explicitly disable <, <=, >, >= operators? |
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225 | def __eq__(self, other): |
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226 | # other may be a Header or a string. Both are fine so coerce |
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227 | # ourselves to a string, swap the args and do another comparison. |
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228 | return other == self.encode() |
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229 | |
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230 | def __ne__(self, other): |
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231 | return not self == other |
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232 | |
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233 | def append(self, s, charset=None, errors='strict'): |
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234 | """Append a string to the MIME header. |
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235 | |
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236 | Optional charset, if given, should be a Charset instance or the name |
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237 | of a character set (which will be converted to a Charset instance). A |
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238 | value of None (the default) means that the charset given in the |
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239 | constructor is used. |
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240 | |
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241 | s may be a byte string or a Unicode string. If it is a byte string |
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242 | (i.e. isinstance(s, str) is true), then charset is the encoding of |
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243 | that byte string, and a UnicodeError will be raised if the string |
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244 | cannot be decoded with that charset. If s is a Unicode string, then |
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245 | charset is a hint specifying the character set of the characters in |
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246 | the string. In this case, when producing an RFC 2822 compliant header |
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247 | using RFC 2047 rules, the Unicode string will be encoded using the |
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248 | following charsets in order: us-ascii, the charset hint, utf-8. The |
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249 | first character set not to provoke a UnicodeError is used. |
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250 | |
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251 | Optional `errors' is passed as the third argument to any unicode() or |
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252 | ustr.encode() call. |
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253 | """ |
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254 | if charset is None: |
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255 | charset = self._charset |
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256 | elif not isinstance(charset, Charset): |
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257 | charset = Charset(charset) |
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258 | # If the charset is our faux 8bit charset, leave the string unchanged |
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259 | if charset != '8bit': |
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260 | # We need to test that the string can be converted to unicode and |
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261 | # back to a byte string, given the input and output codecs of the |
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262 | # charset. |
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263 | if isinstance(s, str): |
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264 | # Possibly raise UnicodeError if the byte string can't be |
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265 | # converted to a unicode with the input codec of the charset. |
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266 | incodec = charset.input_codec or 'us-ascii' |
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267 | ustr = unicode(s, incodec, errors) |
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268 | # Now make sure that the unicode could be converted back to a |
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269 | # byte string with the output codec, which may be different |
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270 | # than the iput coded. Still, use the original byte string. |
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271 | outcodec = charset.output_codec or 'us-ascii' |
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272 | ustr.encode(outcodec, errors) |
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273 | elif isinstance(s, unicode): |
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274 | # Now we have to be sure the unicode string can be converted |
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275 | # to a byte string with a reasonable output codec. We want to |
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276 | # use the byte string in the chunk. |
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277 | for charset in USASCII, charset, UTF8: |
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278 | try: |
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279 | outcodec = charset.output_codec or 'us-ascii' |
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280 | s = s.encode(outcodec, errors) |
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281 | break |
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282 | except UnicodeError: |
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283 | pass |
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284 | else: |
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285 | assert False, 'utf-8 conversion failed' |
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286 | self._chunks.append((s, charset)) |
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287 | |
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288 | def _split(self, s, charset, maxlinelen, splitchars): |
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289 | # Split up a header safely for use with encode_chunks. |
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290 | splittable = charset.to_splittable(s) |
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291 | encoded = charset.from_splittable(splittable, True) |
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292 | elen = charset.encoded_header_len(encoded) |
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293 | # If the line's encoded length first, just return it |
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294 | if elen <= maxlinelen: |
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295 | return [(encoded, charset)] |
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296 | # If we have undetermined raw 8bit characters sitting in a byte |
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297 | # string, we really don't know what the right thing to do is. We |
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298 | # can't really split it because it might be multibyte data which we |
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299 | # could break if we split it between pairs. The least harm seems to |
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300 | # be to not split the header at all, but that means they could go out |
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301 | # longer than maxlinelen. |
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302 | if charset == '8bit': |
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303 | return [(s, charset)] |
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304 | # BAW: I'm not sure what the right test here is. What we're trying to |
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305 | # do is be faithful to RFC 2822's recommendation that ($2.2.3): |
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306 | # |
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307 | # "Note: Though structured field bodies are defined in such a way that |
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308 | # folding can take place between many of the lexical tokens (and even |
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309 | # within some of the lexical tokens), folding SHOULD be limited to |
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310 | # placing the CRLF at higher-level syntactic breaks." |
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311 | # |
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312 | # For now, I can only imagine doing this when the charset is us-ascii, |
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313 | # although it's possible that other charsets may also benefit from the |
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314 | # higher-level syntactic breaks. |
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315 | elif charset == 'us-ascii': |
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316 | return self._split_ascii(s, charset, maxlinelen, splitchars) |
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317 | # BAW: should we use encoded? |
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318 | elif elen == len(s): |
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319 | # We can split on _maxlinelen boundaries because we know that the |
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320 | # encoding won't change the size of the string |
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321 | splitpnt = maxlinelen |
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322 | first = charset.from_splittable(splittable[:splitpnt], False) |
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323 | last = charset.from_splittable(splittable[splitpnt:], False) |
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324 | else: |
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325 | # Binary search for split point |
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326 | first, last = _binsplit(splittable, charset, maxlinelen) |
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327 | # first is of the proper length so just wrap it in the appropriate |
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328 | # chrome. last must be recursively split. |
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329 | fsplittable = charset.to_splittable(first) |
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330 | fencoded = charset.from_splittable(fsplittable, True) |
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331 | chunk = [(fencoded, charset)] |
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332 | return chunk + self._split(last, charset, self._maxlinelen, splitchars) |
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333 | |
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334 | def _split_ascii(self, s, charset, firstlen, splitchars): |
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335 | chunks = _split_ascii(s, firstlen, self._maxlinelen, |
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336 | self._continuation_ws, splitchars) |
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337 | return zip(chunks, [charset]*len(chunks)) |
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338 | |
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339 | def _encode_chunks(self, newchunks, maxlinelen): |
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340 | # MIME-encode a header with many different charsets and/or encodings. |
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341 | # |
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342 | # Given a list of pairs (string, charset), return a MIME-encoded |
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343 | # string suitable for use in a header field. Each pair may have |
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344 | # different charsets and/or encodings, and the resulting header will |
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345 | # accurately reflect each setting. |
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346 | # |
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347 | # Each encoding can be email.utils.QP (quoted-printable, for |
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348 | # ASCII-like character sets like iso-8859-1), email.utils.BASE64 |
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349 | # (Base64, for non-ASCII like character sets like KOI8-R and |
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350 | # iso-2022-jp), or None (no encoding). |
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351 | # |
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352 | # Each pair will be represented on a separate line; the resulting |
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353 | # string will be in the format: |
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354 | # |
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355 | # =?charset1?q?Mar=EDa_Gonz=E1lez_Alonso?=\n |
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356 | # =?charset2?b?SvxyZ2VuIEL2aW5n?=" |
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357 | chunks = [] |
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358 | for header, charset in newchunks: |
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359 | if not header: |
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360 | continue |
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361 | if charset is None or charset.header_encoding is None: |
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362 | s = header |
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363 | else: |
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364 | s = charset.header_encode(header) |
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365 | # Don't add more folding whitespace than necessary |
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366 | if chunks and chunks[-1].endswith(' '): |
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367 | extra = '' |
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368 | else: |
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369 | extra = ' ' |
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370 | _max_append(chunks, s, maxlinelen, extra) |
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371 | joiner = NL + self._continuation_ws |
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372 | return joiner.join(chunks) |
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373 | |
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374 | def encode(self, splitchars=';, '): |
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375 | """Encode a message header into an RFC-compliant format. |
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376 | |
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377 | There are many issues involved in converting a given string for use in |
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378 | an email header. Only certain character sets are readable in most |
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379 | email clients, and as header strings can only contain a subset of |
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380 | 7-bit ASCII, care must be taken to properly convert and encode (with |
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381 | Base64 or quoted-printable) header strings. In addition, there is a |
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382 | 75-character length limit on any given encoded header field, so |
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383 | line-wrapping must be performed, even with double-byte character sets. |
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384 | |
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385 | This method will do its best to convert the string to the correct |
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386 | character set used in email, and encode and line wrap it safely with |
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387 | the appropriate scheme for that character set. |
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388 | |
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389 | If the given charset is not known or an error occurs during |
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390 | conversion, this function will return the header untouched. |
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391 | |
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392 | Optional splitchars is a string containing characters to split long |
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393 | ASCII lines on, in rough support of RFC 2822's `highest level |
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394 | syntactic breaks'. This doesn't affect RFC 2047 encoded lines. |
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395 | """ |
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396 | newchunks = [] |
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397 | maxlinelen = self._firstlinelen |
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398 | lastlen = 0 |
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399 | for s, charset in self._chunks: |
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400 | # The first bit of the next chunk should be just long enough to |
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401 | # fill the next line. Don't forget the space separating the |
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402 | # encoded words. |
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403 | targetlen = maxlinelen - lastlen - 1 |
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404 | if targetlen < charset.encoded_header_len(''): |
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405 | # Stick it on the next line |
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406 | targetlen = maxlinelen |
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407 | newchunks += self._split(s, charset, targetlen, splitchars) |
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408 | lastchunk, lastcharset = newchunks[-1] |
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409 | lastlen = lastcharset.encoded_header_len(lastchunk) |
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410 | value = self._encode_chunks(newchunks, maxlinelen) |
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411 | if _embeded_header.search(value): |
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412 | raise HeaderParseError("header value appears to contain " |
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413 | "an embedded header: {!r}".format(value)) |
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414 | return value |
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415 | |
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416 | |
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417 | |
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418 | def _split_ascii(s, firstlen, restlen, continuation_ws, splitchars): |
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419 | lines = [] |
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420 | maxlen = firstlen |
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421 | for line in s.splitlines(): |
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422 | # Ignore any leading whitespace (i.e. continuation whitespace) already |
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423 | # on the line, since we'll be adding our own. |
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424 | line = line.lstrip() |
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425 | if len(line) < maxlen: |
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426 | lines.append(line) |
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427 | maxlen = restlen |
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428 | continue |
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429 | # Attempt to split the line at the highest-level syntactic break |
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430 | # possible. Note that we don't have a lot of smarts about field |
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431 | # syntax; we just try to break on semi-colons, then commas, then |
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432 | # whitespace. |
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433 | for ch in splitchars: |
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434 | if ch in line: |
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435 | break |
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436 | else: |
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437 | # There's nothing useful to split the line on, not even spaces, so |
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438 | # just append this line unchanged |
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439 | lines.append(line) |
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440 | maxlen = restlen |
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441 | continue |
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442 | # Now split the line on the character plus trailing whitespace |
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443 | cre = re.compile(r'%s\s*' % ch) |
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444 | if ch in ';,': |
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445 | eol = ch |
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446 | else: |
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447 | eol = '' |
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448 | joiner = eol + ' ' |
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449 | joinlen = len(joiner) |
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450 | wslen = len(continuation_ws.replace('\t', SPACE8)) |
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451 | this = [] |
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452 | linelen = 0 |
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453 | for part in cre.split(line): |
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454 | curlen = linelen + max(0, len(this)-1) * joinlen |
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455 | partlen = len(part) |
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456 | onfirstline = not lines |
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457 | # We don't want to split after the field name, if we're on the |
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458 | # first line and the field name is present in the header string. |
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459 | if ch == ' ' and onfirstline and \ |
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460 | len(this) == 1 and fcre.match(this[0]): |
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461 | this.append(part) |
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462 | linelen += partlen |
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463 | elif curlen + partlen > maxlen: |
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464 | if this: |
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465 | lines.append(joiner.join(this) + eol) |
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466 | # If this part is longer than maxlen and we aren't already |
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467 | # splitting on whitespace, try to recursively split this line |
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468 | # on whitespace. |
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469 | if partlen > maxlen and ch != ' ': |
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470 | subl = _split_ascii(part, maxlen, restlen, |
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471 | continuation_ws, ' ') |
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472 | lines.extend(subl[:-1]) |
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473 | this = [subl[-1]] |
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474 | else: |
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475 | this = [part] |
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476 | linelen = wslen + len(this[-1]) |
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477 | maxlen = restlen |
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478 | else: |
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479 | this.append(part) |
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480 | linelen += partlen |
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481 | # Put any left over parts on a line by themselves |
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482 | if this: |
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483 | lines.append(joiner.join(this)) |
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484 | return lines |
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485 | |
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486 | |
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487 | |
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488 | def _binsplit(splittable, charset, maxlinelen): |
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489 | i = 0 |
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490 | j = len(splittable) |
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491 | while i < j: |
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492 | # Invariants: |
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493 | # 1. splittable[:k] fits for all k <= i (note that we *assume*, |
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494 | # at the start, that splittable[:0] fits). |
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495 | # 2. splittable[:k] does not fit for any k > j (at the start, |
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496 | # this means we shouldn't look at any k > len(splittable)). |
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497 | # 3. We don't know about splittable[:k] for k in i+1..j. |
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498 | # 4. We want to set i to the largest k that fits, with i <= k <= j. |
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499 | # |
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500 | m = (i+j+1) >> 1 # ceiling((i+j)/2); i < m <= j |
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501 | chunk = charset.from_splittable(splittable[:m], True) |
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502 | chunklen = charset.encoded_header_len(chunk) |
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503 | if chunklen <= maxlinelen: |
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504 | # m is acceptable, so is a new lower bound. |
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505 | i = m |
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506 | else: |
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507 | # m is not acceptable, so final i must be < m. |
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508 | j = m - 1 |
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509 | # i == j. Invariant #1 implies that splittable[:i] fits, and |
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510 | # invariant #2 implies that splittable[:i+1] does not fit, so i |
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511 | # is what we're looking for. |
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512 | first = charset.from_splittable(splittable[:i], False) |
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513 | last = charset.from_splittable(splittable[i:], False) |
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514 | return first, last |
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