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28
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1 # This library is free software; you can redistribute it and/or
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2 # modify it under the terms of the GNU Lesser General Public
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3 # License as published by the Free Software Foundation; either
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4 # version 2.1 of the License, or (at your option) any later version.
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5 #
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6 # This library is distributed in the hope that it will be useful,
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7 # but WITHOUT ANY WARRANTY; without even the implied warranty of
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8 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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9 # Lesser General Public License for more details.
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10 #
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11 # You should have received a copy of the GNU Lesser General Public
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12 # License along with this library; if not, write to the
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13 # Free Software Foundation, Inc.,
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14 # 59 Temple Place, Suite 330,
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15 # Boston, MA 02111-1307 USA
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16
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17 # This file is part of urlgrabber, a high-level cross-protocol url-grabber
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18 # Copyright 2002-2004 Michael D. Stenner, Ryan Tomayko
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19
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20 # $Id: byterange.py,v 1.9 2005/02/14 21:55:07 mstenner Exp $
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21
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22 import os
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23 import stat
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24 import urllib
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25 import urllib2
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26 import email.Utils
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27
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28 try:
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29 from cStringIO import StringIO
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30 except ImportError, msg:
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31 from StringIO import StringIO
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32
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33 class RangeError(IOError):
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34 """Error raised when an unsatisfiable range is requested."""
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35 pass
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36
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37 class HTTPRangeHandler(urllib2.BaseHandler):
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38 """Handler that enables HTTP Range headers.
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39
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40 This was extremely simple. The Range header is a HTTP feature to
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41 begin with so all this class does is tell urllib2 that the
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42 "206 Partial Content" reponse from the HTTP server is what we
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43 expected.
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44
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45 Example:
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46 import urllib2
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47 import byterange
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48
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49 range_handler = range.HTTPRangeHandler()
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50 opener = urllib2.build_opener(range_handler)
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51
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52 # install it
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53 urllib2.install_opener(opener)
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54
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55 # create Request and set Range header
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56 req = urllib2.Request('http://www.python.org/')
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57 req.header['Range'] = 'bytes=30-50'
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58 f = urllib2.urlopen(req)
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59 """
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60
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61 def http_error_206(self, req, fp, code, msg, hdrs):
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62 # 206 Partial Content Response
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63 r = urllib.addinfourl(fp, hdrs, req.get_full_url())
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64 r.code = code
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65 r.msg = msg
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66 return r
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67
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68 def http_error_416(self, req, fp, code, msg, hdrs):
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69 # HTTP's Range Not Satisfiable error
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70 raise RangeError('Requested Range Not Satisfiable')
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71
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72 class RangeableFileObject:
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73 """File object wrapper to enable raw range handling.
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74 This was implemented primarilary for handling range
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75 specifications for file:// urls. This object effectively makes
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76 a file object look like it consists only of a range of bytes in
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77 the stream.
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78
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79 Examples:
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80 # expose 10 bytes, starting at byte position 20, from
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81 # /etc/aliases.
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82 >>> fo = RangeableFileObject(file('/etc/passwd', 'r'), (20,30))
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83 # seek seeks within the range (to position 23 in this case)
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84 >>> fo.seek(3)
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85 # tell tells where your at _within the range_ (position 3 in
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86 # this case)
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87 >>> fo.tell()
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88 # read EOFs if an attempt is made to read past the last
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89 # byte in the range. the following will return only 7 bytes.
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90 >>> fo.read(30)
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91 """
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92
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93 def __init__(self, fo, rangetup):
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94 """Create a RangeableFileObject.
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95 fo -- a file like object. only the read() method need be
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96 supported but supporting an optimized seek() is
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97 preferable.
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98 rangetup -- a (firstbyte,lastbyte) tuple specifying the range
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99 to work over.
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100 The file object provided is assumed to be at byte offset 0.
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101 """
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102 self.fo = fo
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103 (self.firstbyte, self.lastbyte) = range_tuple_normalize(rangetup)
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104 self.realpos = 0
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105 self._do_seek(self.firstbyte)
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106
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107 def __getattr__(self, name):
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108 """This effectively allows us to wrap at the instance level.
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109 Any attribute not found in _this_ object will be searched for
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110 in self.fo. This includes methods."""
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111 if hasattr(self.fo, name):
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112 return getattr(self.fo, name)
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113 raise AttributeError(name)
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114
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115 def tell(self):
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116 """Return the position within the range.
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117 This is different from fo.seek in that position 0 is the
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118 first byte position of the range tuple. For example, if
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119 this object was created with a range tuple of (500,899),
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120 tell() will return 0 when at byte position 500 of the file.
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121 """
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122 return (self.realpos - self.firstbyte)
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123
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124 def seek(self, offset, whence=0):
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125 """Seek within the byte range.
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126 Positioning is identical to that described under tell().
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127 """
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128 assert whence in (0, 1, 2)
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129 if whence == 0: # absolute seek
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130 realoffset = self.firstbyte + offset
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131 elif whence == 1: # relative seek
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132 realoffset = self.realpos + offset
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133 elif whence == 2: # absolute from end of file
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134 # XXX: are we raising the right Error here?
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135 raise IOError('seek from end of file not supported.')
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136
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137 # do not allow seek past lastbyte in range
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138 if self.lastbyte and (realoffset >= self.lastbyte):
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139 realoffset = self.lastbyte
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140
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141 self._do_seek(realoffset - self.realpos)
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142
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143 def read(self, size=-1):
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144 """Read within the range.
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145 This method will limit the size read based on the range.
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146 """
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147 size = self._calc_read_size(size)
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148 rslt = self.fo.read(size)
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149 self.realpos += len(rslt)
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150 return rslt
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151
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152 def readline(self, size=-1):
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153 """Read lines within the range.
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154 This method will limit the size read based on the range.
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155 """
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156 size = self._calc_read_size(size)
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157 rslt = self.fo.readline(size)
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158 self.realpos += len(rslt)
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159 return rslt
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160
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161 def _calc_read_size(self, size):
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162 """Handles calculating the amount of data to read based on
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163 the range.
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164 """
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165 if self.lastbyte:
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166 if size > -1:
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167 if ((self.realpos + size) >= self.lastbyte):
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168 size = (self.lastbyte - self.realpos)
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169 else:
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170 size = (self.lastbyte - self.realpos)
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171 return size
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172
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173 def _do_seek(self, offset):
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174 """Seek based on whether wrapped object supports seek().
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175 offset is relative to the current position (self.realpos).
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176 """
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177 assert offset >= 0
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178 if not hasattr(self.fo, 'seek'):
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179 self._poor_mans_seek(offset)
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180 else:
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181 self.fo.seek(self.realpos + offset)
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182 self.realpos += offset
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183
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184 def _poor_mans_seek(self, offset):
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185 """Seek by calling the wrapped file objects read() method.
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186 This is used for file like objects that do not have native
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187 seek support. The wrapped objects read() method is called
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188 to manually seek to the desired position.
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189 offset -- read this number of bytes from the wrapped
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190 file object.
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191 raise RangeError if we encounter EOF before reaching the
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192 specified offset.
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193 """
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194 pos = 0
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195 bufsize = 1024
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196 while pos < offset:
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197 if (pos + bufsize) > offset:
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198 bufsize = offset - pos
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199 buf = self.fo.read(bufsize)
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200 if len(buf) != bufsize:
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201 raise RangeError('Requested Range Not Satisfiable')
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202 pos += bufsize
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203
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204 class FileRangeHandler(urllib2.FileHandler):
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205 """FileHandler subclass that adds Range support.
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206 This class handles Range headers exactly like an HTTP
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207 server would.
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208 """
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209 def open_local_file(self, req):
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210 import mimetypes
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211 import mimetools
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212 host = req.get_host()
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213 file = req.get_selector()
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214 localfile = urllib.url2pathname(file)
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215 stats = os.stat(localfile)
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216 size = stats[stat.ST_SIZE]
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217 modified = email.Utils.formatdate(stats[stat.ST_MTIME])
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218 mtype = mimetypes.guess_type(file)[0]
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219 if host:
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220 host, port = urllib.splitport(host)
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221 if port or socket.gethostbyname(host) not in self.get_names():
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222 raise urllib2.URLError('file not on local host')
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223 fo = open(localfile,'rb')
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224 brange = req.headers.get('Range', None)
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225 brange = range_header_to_tuple(brange)
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226 assert brange != ()
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227 if brange:
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228 (fb, lb) = brange
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229 if lb == '':
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230 lb = size
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231 if fb < 0 or fb > size or lb > size:
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232 raise RangeError('Requested Range Not Satisfiable')
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233 size = (lb - fb)
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234 fo = RangeableFileObject(fo, (fb, lb))
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235 headers = mimetools.Message(StringIO(
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236 'Content-Type: %s\nContent-Length: %d\nLast-Modified: %s\n' %
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237 (mtype or 'text/plain', size, modified)))
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238 return urllib.addinfourl(fo, headers, 'file:'+file)
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239
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240
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241 # FTP Range Support
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242 # Unfortunately, a large amount of base FTP code had to be copied
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243 # from urllib and urllib2 in order to insert the FTP REST command.
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244 # Code modifications for range support have been commented as
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245 # follows:
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246 # -- range support modifications start/end here
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247
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248 from urllib import splitport, splituser, splitpasswd, splitattr, \
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249 unquote, addclosehook, addinfourl
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250 import ftplib
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251 import socket
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252 import sys
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253 import mimetypes
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254 import mimetools
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255
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256 class FTPRangeHandler(urllib2.FTPHandler):
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257 def ftp_open(self, req):
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258 host = req.get_host()
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259 if not host:
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260 raise IOError('ftp error', 'no host given')
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261 host, port = splitport(host)
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262 if port is None:
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263 port = ftplib.FTP_PORT
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264
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265 # username/password handling
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266 user, host = splituser(host)
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267 if user:
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268 user, passwd = splitpasswd(user)
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269 else:
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270 passwd = None
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271 host = unquote(host)
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272 user = unquote(user or '')
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273 passwd = unquote(passwd or '')
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274
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275 try:
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276 host = socket.gethostbyname(host)
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277 except socket.error, msg:
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278 raise urllib2.URLError(msg)
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279 path, attrs = splitattr(req.get_selector())
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280 dirs = path.split('/')
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281 dirs = map(unquote, dirs)
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282 dirs, file = dirs[:-1], dirs[-1]
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283 if dirs and not dirs[0]:
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284 dirs = dirs[1:]
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285 try:
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286 fw = self.connect_ftp(user, passwd, host, port, dirs)
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287 type = file and 'I' or 'D'
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288 for attr in attrs:
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289 attr, value = splitattr(attr)
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290 if attr.lower() == 'type' and \
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291 value in ('a', 'A', 'i', 'I', 'd', 'D'):
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292 type = value.upper()
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293
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294 # -- range support modifications start here
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295 rest = None
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296 range_tup = range_header_to_tuple(req.headers.get('Range', None))
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297 assert range_tup != ()
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298 if range_tup:
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299 (fb, lb) = range_tup
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300 if fb > 0:
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301 rest = fb
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302 # -- range support modifications end here
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303
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304 fp, retrlen = fw.retrfile(file, type, rest)
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305
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306 # -- range support modifications start here
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307 if range_tup:
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308 (fb, lb) = range_tup
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309 if lb == '':
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310 if retrlen is None or retrlen == 0:
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311 raise RangeError('Requested Range Not Satisfiable due to unobtainable file length.')
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312 lb = retrlen
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313 retrlen = lb - fb
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314 if retrlen < 0:
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315 # beginning of range is larger than file
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316 raise RangeError('Requested Range Not Satisfiable')
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317 else:
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318 retrlen = lb - fb
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319 fp = RangeableFileObject(fp, (0, retrlen))
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320 # -- range support modifications end here
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321
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322 headers = ""
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323 mtype = mimetypes.guess_type(req.get_full_url())[0]
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324 if mtype:
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325 headers += "Content-Type: %s\n" % mtype
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326 if retrlen is not None and retrlen >= 0:
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327 headers += "Content-Length: %d\n" % retrlen
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328 sf = StringIO(headers)
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329 headers = mimetools.Message(sf)
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330 return addinfourl(fp, headers, req.get_full_url())
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331 except ftplib.all_errors, msg:
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332 raise IOError('ftp error', msg), sys.exc_info()[2]
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333
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334 def connect_ftp(self, user, passwd, host, port, dirs):
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335 fw = ftpwrapper(user, passwd, host, port, dirs)
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336 return fw
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337
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338 class ftpwrapper(urllib.ftpwrapper):
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339 # range support note:
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340 # this ftpwrapper code is copied directly from
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341 # urllib. The only enhancement is to add the rest
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342 # argument and pass it on to ftp.ntransfercmd
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343 def retrfile(self, file, type, rest=None):
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344 self.endtransfer()
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345 if type in ('d', 'D'):
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346 cmd = 'TYPE A'
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347 isdir = 1
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348 else:
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349 cmd = 'TYPE ' + type
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350 isdir = 0
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351 try:
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352 self.ftp.voidcmd(cmd)
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353 except ftplib.all_errors:
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354 self.init()
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355 self.ftp.voidcmd(cmd)
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356 conn = None
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357 if file and not isdir:
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358 # Use nlst to see if the file exists at all
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359 try:
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360 self.ftp.nlst(file)
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361 except ftplib.error_perm, reason:
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362 raise IOError('ftp error', reason), sys.exc_info()[2]
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363 # Restore the transfer mode!
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364 self.ftp.voidcmd(cmd)
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365 # Try to retrieve as a file
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366 try:
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367 cmd = 'RETR ' + file
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368 conn = self.ftp.ntransfercmd(cmd, rest)
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369 except ftplib.error_perm, reason:
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370 if str(reason).startswith('501'):
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371 # workaround for REST not supported error
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372 fp, retrlen = self.retrfile(file, type)
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373 fp = RangeableFileObject(fp, (rest,''))
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374 return (fp, retrlen)
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375 elif not str(reason).startswith('550'):
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376 raise IOError('ftp error', reason), sys.exc_info()[2]
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377 if not conn:
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378 # Set transfer mode to ASCII!
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379 self.ftp.voidcmd('TYPE A')
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380 # Try a directory listing
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381 if file:
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382 cmd = 'LIST ' + file
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383 else:
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384 cmd = 'LIST'
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385 conn = self.ftp.ntransfercmd(cmd)
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386 self.busy = 1
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387 # Pass back both a suitably decorated object and a retrieval length
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388 return (addclosehook(conn[0].makefile('rb'),
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389 self.endtransfer), conn[1])
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390
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391
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392 ####################################################################
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393 # Range Tuple Functions
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394 # XXX: These range tuple functions might go better in a class.
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395
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396 _rangere = None
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397 def range_header_to_tuple(range_header):
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398 """Get a (firstbyte,lastbyte) tuple from a Range header value.
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399
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400 Range headers have the form "bytes=<firstbyte>-<lastbyte>". This
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401 function pulls the firstbyte and lastbyte values and returns
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402 a (firstbyte,lastbyte) tuple. If lastbyte is not specified in
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403 the header value, it is returned as an empty string in the
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404 tuple.
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405
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406 Return None if range_header is None
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407 Return () if range_header does not conform to the range spec
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408 pattern.
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409
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410 """
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411 global _rangere
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412 if range_header is None:
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413 return None
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414 if _rangere is None:
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415 import re
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416 _rangere = re.compile(r'^bytes=(\d{1,})-(\d*)')
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417 match = _rangere.match(range_header)
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418 if match:
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419 tup = range_tuple_normalize(match.group(1, 2))
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420 if tup and tup[1]:
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421 tup = (tup[0], tup[1]+1)
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422 return tup
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423 return ()
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424
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425 def range_tuple_to_header(range_tup):
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426 """Convert a range tuple to a Range header value.
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427 Return a string of the form "bytes=<firstbyte>-<lastbyte>" or None
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428 if no range is needed.
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429 """
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430 if range_tup is None:
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431 return None
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432 range_tup = range_tuple_normalize(range_tup)
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433 if range_tup:
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434 if range_tup[1]:
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435 range_tup = (range_tup[0], range_tup[1] - 1)
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436 return 'bytes=%s-%s' % range_tup
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437
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438 def range_tuple_normalize(range_tup):
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439 """Normalize a (first_byte,last_byte) range tuple.
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440 Return a tuple whose first element is guaranteed to be an int
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441 and whose second element will be '' (meaning: the last byte) or
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442 an int. Finally, return None if the normalized tuple == (0,'')
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443 as that is equivelant to retrieving the entire file.
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444 """
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445 if range_tup is None:
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446 return None
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447 # handle first byte
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448 fb = range_tup[0]
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449 if fb in (None, ''):
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450 fb = 0
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451 else:
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452 fb = int(fb)
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453 # handle last byte
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454 try:
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455 lb = range_tup[1]
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456 except IndexError:
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457 lb = ''
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458 else:
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459 if lb is None:
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460 lb = ''
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461 elif lb != '':
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462 lb = int(lb)
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463 # check if range is over the entire file
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464 if (fb, lb) == (0, ''):
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465 return None
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466 # check that the range is valid
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467 if lb < fb:
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468 raise RangeError('Invalid byte range: %s-%s' % (fb, lb))
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469 return (fb, lb)
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