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Zope Image to filesystem image
filesystem, zodb, chunks, 2^16, 65kb, stream, blob, sascha welter, betabug, #zope, irc
16th of March 2007
Today I bumped into a nasty challenge when trying to copy a Zope image from ZODB to the filesystem. The reason why it wasn't easy was that Zope splits the file up into chunks if it's upload size is more than 65Kb (2^16 bytes) which I guess it does for being able to "stream" the file back into the browser when viewing the image instead of sending one large blob.
So, this didn't work:
Image
>>> open(temp_file_path,'wb').write(imgobj.data)
...if the data is big because sometimes imgobj.data is a string (the binary data) and sometimes is a ImplicitAcquirerWrapper that you have to iterate over.
That's when Sascha Welter stepped up on the #zope channel on IRC with a snippet of code that does it properly:
"""
Write data from a file from the ZODB / Zope
to a tempfile on the filesystem.
input:
- source (a zope object, not just a string with the object id!!)
- temp_file (a writable file object)
"""
data = source.data
if isinstance(data, StringType): #StringType
temp_file.write( str(data) )
else:
(start,end) = (0,source.getSize())
pos = 0
while source.data is not None:
l = len(data.data)
pos = pos + l
if pos > start:
# We are within the range
lstart = l - (pos - start)
if lstart < 0: lstart = 0
# find the endpoint
if end <= pos:
lend = l - (pos - end)
temp_file.write(data[lstart:lend])
break
# Not yet at the end, transmit what we have.
temp_file.write(data[lstart:])
data = data.next
temp_file.flush()
temp_file.seek(0, 0)
This is pretty neat. I have a similar issue with trying to use a Python script to return a .mp3 from a Zope file object. Whenever the script is called it *renders* the .mp3 instead of passing the data.
Do I need to do something similar to your script to make this work properly?
I doubt that it *renders* the mp3 file. Perhaps you mean that it starts playing or something. There's a solution to that, set the Content-Type to something like "application/octet-stream"