Big File Upload

To handle big files without using all the available memory a generator can be used. The generator will return the file in small chunks:

#!/usr/bin/env python
import cgi, os
import cgitb; cgitb.enable()

try: # Windows needs stdio set for binary mode.
    import msvcrt
    msvcrt.setmode (0, os.O_BINARY) # stdin  = 0
    msvcrt.setmode (1, os.O_BINARY) # stdout = 1
except ImportError:
    pass

form = cgi.FieldStorage()

# Generator to buffer file chunks
def fbuffer(f, chunk_size=10000):
   while True:
      chunk = f.read(chunk_size)
      if not chunk: break
      yield chunk
      
# A nested FieldStorage instance holds the file
fileitem = form['file']

# Test if the file was uploaded
if fileitem.filename:

   # strip leading path from file name to avoid directory traversal attacks
   fn = os.path.basename(fileitem.filename)
   f = open('files/' + fn, 'wb', 10000)

   # Read the file in chunks
   for chunk in fbuffer(fileitem.file):
      f.write(chunk)
   f.close()
   message = 'The file "' + fn + '" was uploaded successfully'

else:
   message = 'No file was uploaded'
   
print """\
Content-Type: text/html\n
<html><body>
<p>%s</p>
</body></html>
""" % (message,)

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Big File Upload