[Zope3-dev] Returning large amounts of data to a client

[Peter Mayne]

I have a resource class that returns binary data (PNG images in this 
case) to the client, along the following lines:

class MyResource(BrowserView, Resource):
     implements(IBrowserPublisher)

...

     def GET(self):
         request = self.request
         response = request.response
         response.setHeader('Content-Type', CONTENT_TYPE)
         data = /generate binary data here/

         return data

This is fine when the amount of data is small, but what if there are 
many bytes involved.

The obvious thing to try was

         response.write(data)
         return None

and guessing that I can write a sequence of (say) 64KB chunks so I don't 
use too much memory, but I get

   File "C:\opt\Python23\Lib\site-packages\zope\server\buffers.py", line 
186, in append
     self.strbuf = strbuf + s
UnicodeDecodeError: 'ascii' codec can't decode byte 0x89 in position 
283: ordinal not in range(128)

which implies that ZX3 is expecting (possibly UTF-8) encoded characters, 
rather than binary data, when writing to the response. Furthermore, I 
possibly wouldn't want to buffer the large amount of data, which is what 
the classes in buffers.py seem to do.

What is the right thing to do when returning potentially large amounts 
of data to a client?

Thanks.

PJDM
-- 
Peter Mayne
Spherion Technology Solutions
Canberra, ACT, Australia
"I'm after rebellion, I'll settle for lies" - Blue Oyster Cult