# django-tahoestorage

Let's you use a Tahoe Grid as the storage backend for a Django
FileField. 

Written by Anders Pearson at the Columbia Center For New Media
Teaching and Learning (http://ccnmtl.columbia.edu/)

## how to use it

It would look something like this (in your apps' models.py):


    from tahoestorage.storage import TahoeStorage
    ts = TahoeStorage()
    
    class Whatever(models.Model):
        file = models.FileField(upload_to='a/b/c/', storage=ts)

### settings

This expects a certain configuration though. You (obviously) need to
have a Tahoe grid running. In your settings, you will then need to
set:

TAHOE_STORAGE_BASE_URL

The base URL for accessing your grid. 
Probably something like "http://localhost:3456/"

A localhost URL is recommended, which means you need to run a Tahoe
Node (it doesn't have to be a storage node) on the same machine as
your Django app is running on.

TAHOE_STORAGE_BASE_CAP

A R/W directory CAP to use as the "root" of your django
storage. You'll want to use the Tahoe web or commandline api to make a
new directory in your Tahoe grid and then take note of the CAP. This
becomes a very important value which you will want to take precautions
to not lose. If you manage to lose/forget the base CAP, you will
effectively lose access to everything stored under it. Tattoo it on
your forehead if necessary.

TAHOE_PUBLIC_BASE_URL

If your django app is going to be public facing, you will need at
least one Tahoe node that is configured to accept connections from
outside hosts. Either configure a node this way or run one behind an
apache/lighttpd/nginx proxy (this can be a good setup since you can
restrict it to read-only GET requests and avoid making your grid
publically writeable). This value will then be the base of download
URLs generated. If the django app is for internal use only and
everyone has a Tahoe node running on their machine, you can set this
to "http://localhost:3456/" and file downloads will come directly via
Tahoe (this is the most efficient way to do it as it will take full
advantage of the bittorrent style swarming that Tahoe does). But
obviously, that won't work for a public site. 

## Performance

Probably not very good. The way Tahoe works and the way Django expects
to interact with a storage layer are not the most compatible. Tahoe
doesn't provide a way to traverse multiple directory levels in a
single step. Each directory level it has to go down requires a
synchronous HTTP request/response. 

As a consequence, I recommend as minimal an 'upload_to' structure as
you think you can get away with. The catch is that if there are too
many files in a directory, the amount of data sent back on each query
gets very large and also slows things down, so you don't want to go
too minimal. 

I'm working on some other approaches and caching can help, but this
will probably never be as performant as a local filestorage backend. 

I'd also recommend trying to avoid using this for very large file
uploads. This code will stream the uploads and is careful to not try
to load an entire file into memory on the upload, but it could still
get very slow and it must block during the upload.