#####
Nginx
#####

If you serve Django behind Nginx, then you can delegate the file download
service to Nginx and get increased performance:

* lower resources used by Python/Django workers ;
* faster download.

See `Nginx X-accel documentation`_ for details.


****************************
Configure some download view
****************************

As an example, let's consider an application called "myapp".

:file:`settings.py`:

.. code-block:: python

   INSTALLED_APPS = (
       # ...
       'myapp',
       # ...
   )
   MYAPP_STORAGE_LOCATION = '/var/www/files/'  # Could be MEDIA_ROOT for public
                                               # files.

This application holds a ``Document`` model.

:file:`myapp/models.py`:

.. code-block:: python

   from django.conf import settings
   from django.core.files.storage import FileSystemStorage
   from django.db import models


   storage = FileSystemStorage(location=settings.MYAPP_STORAGE_LOCATION)


   class Document(models.Model):
       file = models.FileField(storage=storage, upload_to='document')

Notice the ``storage`` and ``upload_to`` parameters: files for ``Document``
model live in :file:`/var/www/files/document/` folder.

Then we configured a download view for this model, restricted to authenticated
users:

:file:`myapp/urls.py`:

.. code-block:: python

   from django.conf.urls import url, url_patterns
   from django.contrib.auth.decorators import login_required

   from django_downloadview import ObjectDownloadView

   from myapp.models import Document


   download = login_required(ObjectDownloadView.as_view(model=Document))

   url_patterns = ('',
       url('^document/(?P<pk>[0-9]+/download/$', download, name='download'),
   )

As is, Django is to serve the files, i.e. load chunks into memory and stream
them.

Nginx is much more efficient for the actual streaming... Let's use it!


***************
Configure Nginx
***************

See `Nginx X-accel documentation`_ for details.

Here is what you could have in :file:`/etc/nginx/sites-available/default`:

.. code-block:: nginx

   charset utf-8;

   # Django-powered service.
   upstream frontend {
       server 127.0.0.1:8000 fail_timeout=0;
   }

   server {
       listen 80 default;

       # File-download proxy.
       #
       # Will serve /var/www/files/myfile.tar.gz when passed URI
       # like /optimized-download/myfile.tar.gz
       #
       # See http://wiki.nginx.org/X-accel
       # and https://github.com/benoitbryon/django-downloadview
       location /optimized-download {
           internal;
           # Location to files on disk.
           # See Django's settings.NGINX_DOWNLOAD_MIDDLEWARE_MEDIA_ROOT
           alias /var/www/files/;
       } 

       # Proxy to Django-powered frontend.
       location / {
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
           proxy_set_header Host $http_host;
           proxy_redirect off;
           proxy_pass http://frontend;
       }
   }

... where specific configuration is the ``location /optimized-download``
section.  

.. note::

   ``/optimized-download`` is not available for the client, i.e. users
   won't be able to download files via ``/optimized-download/<filename>``.

.. warning::

   Make sure Nginx can read the files to download! Check permissions.


************************************************
Global delegation, with XAccelRedirectMiddleware
************************************************

If you want to delegate all file downloads to Nginx, then use
:py:class:`django_downloadview.nginx.XAccelRedirectMiddleware`.

Register it in your settings:

.. code-block:: python

   MIDDLEWARE_CLASSES = (
       # ...
       'django_downloadview.nginx.XAccelRedirectMiddleware',
       # ...
   )

Setup the middleware:

.. code-block:: python

   NGINX_DOWNLOAD_MIDDLEWARE_MEDIA_ROOT = MYAPP_STORAGE_LOCATION
   NGINX_DOWNLOAD_MIDDLEWARE_MEDIA_URL = '/optimized-download'

Optionally fine-tune the middleware. Default values are ``None``, which means
"use Nginx's defaults".

.. code-block:: python

   NGINX_DOWNLOAD_MIDDLEWARE_EXPIRES = False  # Force no expiration.
   NGINX_DOWNLOAD_MIDDLEWARE_WITH_BUFFERING = False  # Force buffering off.
   NGINX_DOWNLOAD_MIDDLEWARE_LIMIT_RATE = False  # Force limit rate off.


*************************************************
Local delegation, with x_accel_redirect decorator
*************************************************

If you want to delegate file downloads to Nginx on a per-view basis, then use
:py:func:`django_downloadview.nginx.x_accel_redirect` decorator.

Adapt :file:`myapp/urls.py`:

.. code-block:: diff

   from django.conf.urls import url, url_patterns
   from django.contrib.auth.decorators import login_required

   from django_downloadview import ObjectDownloadView
   + from django_downloadview.nginx import x_accel_redirect

   from myapp.models import Document


   download = login_required(ObjectDownloadView.as_view(model=Document))
   + download = x_accel_redirect(download,
   +                             media_root=settings.MY_APP_STORAGE_LOCATION,
   +                             media_url='/optimized-download')

   url_patterns = ('',
       url('^document/(?P<pk>[0-9]+/download/$', download, name='download'),
   )


*************
Common issues
*************

``Unknown charset "utf-8" to override``
=======================================

Add ``charset utf-8;`` in your nginx configuration file.

``open() "path/to/something" failed (2: No such file or directory)``
====================================================================

Check your ``settings.NGINX_DOWNLOAD_MIDDLEWARE_MEDIA_ROOT`` in Django
configuration VS ``alias`` in nginx configuration: in a standard configuration,
they should be equal.


**********
References
**********

.. target-notes::

.. _`Nginx X-accel documentation`: http://wiki.nginx.org/X-accel