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<H1><A NAME="SECTION0023000000000000000000">
22. How to stream uploaded files directly to disk</A>
</H1>
<P>
By default, CherryPy handles in the same way all data posted to the server through a form. In all cases, CherryPy
converts that data to a string or a list of strings. This data can be a short string or a big file that's being uploaded.
<P>
In most cases, this is very convenient and it works very well. However, if your application requires users to upload very
big files, then converting them to a string and having this string in memory can be a problem ...
<P>
In that case, you may want to write these files directly to a file instead of having them in memory.
<P>
Here is how this can be done:
<UL>
<LI>Use the <var>initRequestBeforeParse</var> special function to tell CherryPy not to parse the POST data itself (by setting <var>request.parsePostData</var> to 0).
</LI>
<LI>Use the <var>FieldStorage</var> class of the <var>cgi</var> module to parse the POST data (by reading <var>request.rfile</var>) and stream the uploaded file to disk.
</LI>
</UL>
<P>
Here is an example code that does this:
<P>
<div class="verbatim"><pre>
import cgi
def initRequestBeforeParse():
if request.path == 'postFile':
request.parsePostData = 0
CherryClass Root:
mask:
def index(self):
<html><body>
<form method=post action=postFile enctype="multipart/form-data">
Upload a file: <input type=file name=myFile><br>
<input type=submit>
</form>
</body></html>
view:
def postFile(self):
# Use cgi.FieldStorage to parse the POST data
dataDict = cgi.FieldStorage(fp=request.rfile, headers=request.headerMap, environ={'REQUEST_METHOD':'POST'}, keep_blank_values=1)
value = dataDict['myFile']
# Value has 2 attributes:
# - filename contains the name of the uploaded file
# - file is an input stream opened for reading
f = open('/tmp/myFile', 'wb')
while 1:
data = value.file.read(1024 * 8) # Read blocks of 8KB at a time
if not data: break
f.write(data)
f.close()
return "<html><body>The file has been saved in /tmp/myFile</body></html>"
</pre></div>
<P>
Note that the file is not streamed directly from the browser to <span class="file">/tmp/myFile</span>. Instead, it is saved in a <var>tempfile</var>
by the <var>cgi</var> module and then streamed from this <var>tempfile</var> to <span class="file">/tmp/myFile</span>.
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<span class="release-info">Release 0.10, documentation updated on 19 March 2004.</span>
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