author | Sverre Rabbelier <srabbelier@gmail.com> |
Wed, 04 Mar 2009 23:11:33 +0000 | |
changeset 1672 | 9b6cc71dd70c |
parent 109 | 620f9b141567 |
permissions | -rw-r--r-- |
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1 |
WebOb File-Serving Example |
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========================== |
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This document shows how you can make a static-file-serving application |
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using WebOb. We'll quickly build this up from minimal functionality |
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to a high-quality file serving application. |
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.. comment: |
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>>> import webob, os |
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>>> base_dir = os.path.dirname(os.path.dirname(webob.__file__)) |
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>>> doc_dir = os.path.join(base_dir, 'docs') |
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>>> from dtopt import ELLIPSIS |
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First we'll setup a really simple shim around our application, which |
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we can use as we improve our application: |
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.. code-block:: |
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|
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>>> from webob import Request, Response |
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>>> import os |
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>>> class FileApp(object): |
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... def __init__(self, filename): |
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... self.filename = filename |
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... def __call__(self, environ, start_response): |
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... res = make_response(self.filename) |
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... return res(environ, start_response) |
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>>> import mimetypes |
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>>> def get_mimetype(filename): |
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... type, encoding = mimetypes.guess_type(filename) |
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... # We'll ignore encoding, even though we shouldn't really |
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... return type or 'application/octet-stream' |
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Now we can make different definitions of ``make_response``. The |
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simplest version: |
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.. code-block:: |
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>>> def make_response(filename): |
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... res = Response(content_type=get_mimetype(filename)) |
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... res.body = open(filename, 'rb').read() |
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... return res |
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Let's give it a go. We'll test it out with a file ``test-file.txt`` |
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in the WebOb doc directory: |
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.. code-block:: |
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>>> fn = os.path.join(doc_dir, 'test-file.txt') |
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>>> open(fn).read() |
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'This is a test. Hello test people!\n' |
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>>> app = FileApp(fn) |
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>>> req = Request.blank('/') |
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>>> print req.get_response(app) |
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200 OK |
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content-type: text/plain |
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Content-Length: 36 |
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<BLANKLINE> |
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This is a test. Hello test people! |
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<BLANKLINE> |
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Well, that worked. But it's not a very fancy object. First, it reads |
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everything into memory, and that's bad. We'll create an iterator instead: |
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.. code-block:: |
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>>> class FileIterable(object): |
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... def __init__(self, filename): |
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... self.filename = filename |
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... def __iter__(self): |
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... return FileIterator(self.filename) |
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>>> class FileIterator(object): |
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... chunk_size = 4096 |
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... def __init__(self, filename): |
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... self.filename = filename |
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... self.fileobj = open(self.filename, 'rb') |
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... def __iter__(self): |
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... return self |
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... def next(self): |
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... chunk = self.fileobj.read(self.chunk_size) |
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... if not chunk: |
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... raise StopIteration |
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... return chunk |
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>>> def make_response(filename): |
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... res = Response(content_type=get_mimetype(filename)) |
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... res.app_iter = FileIterable(filename) |
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... res.content_length = os.path.getsize(filename) |
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... return res |
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|
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And testing: |
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.. code-block:: |
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>>> req = Request.blank('/') |
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>>> print req.get_response(app) |
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200 OK |
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content-type: text/plain |
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Content-Length: 36 |
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99 |
<BLANKLINE> |
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This is a test. Hello test people! |
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101 |
<BLANKLINE> |
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|
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Well, that doesn't *look* different, but lets *imagine* that it's |
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different because we know we changed some code. Now to add some basic |
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105 |
metadata to the response: |
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.. code-block:: |
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109 |
>>> def make_response(filename): |
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... res = Response(content_type=get_mimetype(filename), |
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... conditional_response=True) |
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... res.app_iter = FileIterable(filename) |
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... res.content_length = os.path.getsize(filename) |
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114 |
... res.last_modified = os.path.getmtime(filename) |
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115 |
... res.etag = '%s-%s-%s' % (os.path.getmtime(filename), |
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116 |
... os.path.getsize(filename), hash(filename)) |
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117 |
... return res |
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118 |
|
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119 |
Now, with ``conditional_response`` on, and with ``last_modified`` and |
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120 |
``etag`` set, we can do conditional requests: |
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121 |
|
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122 |
.. code-block:: |
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123 |
|
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124 |
>>> req = Request.blank('/') |
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125 |
>>> res = req.get_response(app) |
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126 |
>>> print res |
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127 |
200 OK |
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128 |
content-type: text/plain |
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129 |
Content-Length: 36 |
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130 |
Last-Modified: ... GMT |
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131 |
ETag: ...-... |
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132 |
<BLANKLINE> |
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133 |
This is a test. Hello test people! |
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134 |
<BLANKLINE> |
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135 |
>>> req2 = Request.blank('/') |
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136 |
>>> req2.if_none_match = res.etag |
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137 |
>>> req2.get_response(app) |
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138 |
<Response ... 304 Not Modified> |
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139 |
>>> req3 = Request.blank('/') |
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140 |
>>> req3.if_modified_since = res.last_modified |
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141 |
>>> req3.get_response(app) |
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142 |
<Response ... 304 Not Modified> |
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143 |
|
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144 |
We can even do Range requests, but it will currently involve iterating |
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145 |
through the file unnecessarily. When there's a range request (and you |
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146 |
set ``conditional_response=True``) the application will satisfy that |
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147 |
request. But with an arbitrary iterator the only way to do that is to |
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148 |
run through the beginning of the iterator until you get to the chunk |
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149 |
that the client asked for. We can do better because we can use |
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150 |
``fileobj.seek(pos)`` to move around the file much more efficiently. |
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151 |
|
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152 |
So we'll add an extra method, ``app_iter_range``, that ``Response`` |
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153 |
looks for: |
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154 |
|
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155 |
.. code-block:: |
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156 |
|
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157 |
>>> class FileIterable(object): |
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158 |
... def __init__(self, filename, start=None, stop=None): |
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159 |
... self.filename = filename |
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160 |
... self.start = start |
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161 |
... self.stop = stop |
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162 |
... def __iter__(self): |
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163 |
... return FileIterator(self.filename, self.start, self.stop) |
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164 |
... def app_iter_range(self, start, stop): |
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165 |
... return self.__class__(self.filename, start, stop) |
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166 |
>>> class FileIterator(object): |
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167 |
... chunk_size = 4096 |
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168 |
... def __init__(self, filename, start, stop): |
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169 |
... self.filename = filename |
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170 |
... self.fileobj = open(self.filename, 'rb') |
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171 |
... if start: |
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172 |
... self.fileobj.seek(start) |
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173 |
... if stop is not None: |
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174 |
... self.length = stop - start |
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175 |
... else: |
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176 |
... self.length = None |
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177 |
... def __iter__(self): |
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178 |
... return self |
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179 |
... def next(self): |
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180 |
... if self.length is not None and self.length <= 0: |
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181 |
... raise StopIteration |
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182 |
... chunk = self.fileobj.read(self.chunk_size) |
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183 |
... if not chunk: |
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184 |
... raise StopIteration |
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185 |
... if self.length is not None: |
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186 |
... self.length -= len(chunk) |
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187 |
... if self.length < 0: |
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|
188 |
... # Chop off the extra: |
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189 |
... chunk = chunk[:self.length] |
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190 |
... return chunk |
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191 |
|
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192 |
Now we'll test it out: |
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193 |
|
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194 |
.. code-block:: |
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195 |
|
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196 |
>>> req = Request.blank('/') |
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197 |
>>> res = req.get_response(app) |
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198 |
>>> req2 = Request.blank('/') |
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199 |
>>> # Re-fetch the first 5 bytes: |
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|
200 |
>>> req2.range = (0, 5) |
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201 |
>>> res2 = req2.get_response(app) |
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202 |
>>> res2 |
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203 |
<Response ... 206 Partial Content> |
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204 |
>>> # Let's check it's our custom class: |
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205 |
>>> res2.app_iter |
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206 |
<FileIterable object at ...> |
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207 |
>>> res2.body |
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208 |
'This ' |
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209 |
>>> # Now, conditional range support: |
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210 |
>>> req3 = Request.blank('/') |
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211 |
>>> req3.if_range = res.etag |
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212 |
>>> req3.range = (0, 5) |
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213 |
>>> req3.get_response(app) |
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214 |
<Response ... 206 Partial Content> |
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215 |
>>> req3.if_range = 'invalid-etag' |
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216 |
>>> req3.get_response(app) |
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217 |
<Response ... 200 OK> |