[Zope-dev] Streaming Response

[Shane Hathaway]

[Oliver]
>>> You might want to stream multimedia files with a streaming server but 
>>> manage them in zope, 

[Shane]
>  > To do this, we'd need minimal support from the application.  OFS.File
>  > needs to delegate the specifics of data storage and retrieval to a
>  > subobject.  Ape could take the opportunity to replace that subobject
>  > with something that reads and writes the file directly.

[Oliver]
> But this doesn't expose enough, what you'd need would be something like 
> an "external path", which could be the filesystem path in case of Ape or 
> something more exotic when you are using other storages, which offer 
> alternative ways to serve their data (oracle file system for instance).

Here's what I have in mind.  Simplified, OFS/File.py would change to 
something like this:


class SimpleFileData:

     def __init__(self, bytes):
         self.bytes = bytes

     def send(self, RESPONSE):
         RESPONSE.write(self.bytes)


class File(SimpleItem):

     def upload(self, data):
         self.data = SimpleFileData(data)

     def __call__(self, RESPONSE):
         self.data.send(RESPONSE)


An Ape mapper could replace the self.data attribute with an instance of 
the following class.  The mapper would supply the filesystem path to the 
instance through the constructor.

class StreamedFileData:

     def __init__(self, path):
         self.path = path

     def send(self, RESPONSE):
         bytes = open(path, 'rb').read()
         RESPONSE.write(bytes)


An even better implementation of StreamedFileData would arrange for the 
file to be sent asynchronously, but HTTPResponse doesn't currently 
expose such an API.

> Since this information is only known to the storage, but can be 
> valuable, there should be a way to get it.

What I'm suggesting is that the storage might transparently enhance the 
application.  On second thought, though, maybe that's not a good 
pattern, since it might surprise someone to find a StreamedFileData when 
they expected a SimpleFileData instance.  Maybe this stuff should stay 
at the application layer.

Shane