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django-mediasync

One of the more significant development roadblocks we have relates to local vs. deployed media. Ideally all media (graphics, css, scripts) development would occur locally and not use production media. Then, when ready to deploy, the media should be pushed to production. That way there can be significant changes to media without disturbing the production web site.

The goal of mediasync is to develop locally and then flip a switch in production that makes all the media URLs point to remote media URLs instead of the local media directory.

All code is under a BSD-style license, see LICENSE for details.

Source: http://github.com/sunlightlabs/django-mediasync/

Requirements

  • django >= 1.0
  • boto >= 1.8d
  • slimmer == 0.1.30 (optional)
  • python-cloudfiles == 1.7.5 (optional, for Rackspace Cloud Files backend)

Upgrading from mediasync 1.x

  1. Update your mediasync settings as described in the next section.
  2. Run ./manage.py syncmedia --force to force updates of all files:
    • gzip instead of deflate compression
    • sync both compressed and original versions of files
  3. add "django.core.context_processors.request" to TEMPLATE_CONTEXT_PROCESSORS

An important note about Django 1.3

When DEBUG = True and the project is run with manage.py runserver, Django 1.3 automatically adds django.views.static.serve to urlpatterns. While this feature makes local development easier for most people, it screws everything up if you've added mediasync.urls to urlpatterns. As of now, the only way I can find to disable the automatic addition of django.views.static.serve is to use a full URL for STATIC_URL instead of just a path:

STATIC_URL = "http://localhost:8000/static/"

Configuration

settings.py

Add to INSTALLED_APPS:

'mediasync'

Add to TEMPLATE_CONTEXT_PROCESSORS:

'django.core.context_processors.request'

Make sure your STATIC_ROOT setting is the correct path to your media:

STATIC_ROOT = '/path/to/media'

When media is being served locally (instead of from S3 or Cloud Files), mediasync serves media through a Django view. Set your STATIC_URL to what you'd like that local media URL to be. This can be whatever you'd like, as long as you're using the {% media_url %} tag (more details on this later):

STATIC_URL = 'http://localhost:8000/devmedia/'

STATIC_URL is the URL that will be used in debug mode. Otherwise, the STATIC_URL will be loaded from the backend settings. Please see An important note about Django 1.3.

The following settings dict must also be added:

MEDIASYNC = {
    'BACKEND': 'path.to.backend',
}

If you want to use a different media URL than that specified in settings.STATIC_URL, you can add STATIC_URL to the MEDIASYNC settings dict:

MEDIASYNC = {
    ...
    'STATIC_URL': '/url/to/media/', # becomes http://yourhost.com/url/to/media/
    ...
}

Same goes for STATIC_ROOT:

MEDIASYNC = {
    ...
    'STATIC_ROOT': '/path/to/media/',
    ...
}

mediasync supports pluggable backends. Please see below for information on the provided backends as well as directions on implementing your own.

Media expiration

If the client supports media expiration, all files are set to expire 365 days after the file was synced. You may override this value by adding EXPIRATION_DAYS to the MEDIASYNC settings dict.

# Expire in 10 years.
MEDIASYNC['EXPIRATION_DAYS'] = 365 * 10

Serving media remote (S3/Cloud Files) or locally

The media URL is selected based on the SERVE_REMOTE attribute in the MEDIASYNC dict in settings.py. When False, media will be served locally instead of from S3.

# This would force mediasync to serve all media through the value
# specified in settings.STATIC_URL.
MEDIASYNC['SERVE_REMOTE'] = False

# This would serve all media through S3/Cloud Files.
MEDIASYNC['SERVE_REMOTE'] = True

# This would serve media locally while in DEBUG mode, and remotely when
# in production (DEBUG == False).
MEDIASYNC['SERVE_REMOTE'] = not DEBUG

When serving files locally, you can emulate the CSS/JS combo/minifying behavior we get from using media processors by specifying the following.

MEDIASYNC['SERVE_REMOTE'] = False
MEDIASYNC['EMULATE_COMBO'] = True

Note that this will only work if your STATIC_URL is pointing at your Django dev server. Also keep in mind that some processors may take a while, and is best used to check things over before rolling out to production.

DOCTYPE

link and script tags are written using XHTML syntax. The rendering can be overridden by using the DOCTYPE setting. Allowed values are 'html4', 'html5', or 'xhtml'. The default in mediasync 2.0 is html5, just as the DOCTYPE on your site should be.

MEDIASYNC['DOCTYPE'] = 'html5'

For each doctype, the following tags are rendered:

html4
<link rel="stylesheet" href="..." type="text/css" media="...">
<script type="text/javascript" charset="utf-8" src="..."></script>
html5
<link rel="stylesheet" href="..." media="...">
<script src="..."></script>
xhtml
<link rel="stylesheet" href="..." type="text/css" media="..." />
<script type="text/javascript" charset="utf-8" src="..."></script>

SSL

mediasync will attempt to intelligently determine if your media should be served using HTTPS. In order to use automatic SSL detection, django.core.context_processors.request must be added to TEMPLATE_CONTEXT_PROCESSORS in settings.py:

TEMPLATE_CONTEXT_PROCESSORS = (
    ...
    'django.core.context_processors.request',
    ...
)

The USE_SSL mediasync setting can be used to override the SSL URL detection.

# Force HTTPS.
MEDIASYNC['USE_SSL'] = True

or

# Force HTTP.
MEDIASYNC['USE_SSL'] = False

Some backends will be unable to use SSL. In these cases USE_SSL and SSL detection will be ignored.

urls.py

To serve local media through mediasync, add a reference to mediasync.urls in your main urls.py file.

urlpatterns = ('',
    ...
    url(r'^', include('mediasync.urls)),
    ...
)

Backends

mediasync now supports pluggable backends. A backend is a Python module that contains a Client class that implements a mediasync-provided BaseClient class.

S3

MEDIASYNC['BACKEND'] = 'mediasync.backends.s3'
Settings

The following settings are required in the mediasync settings dict:

MEDIASYNC = {
    'AWS_KEY': "s3_key",
    'AWS_SECRET': "s3_secret",
    'AWS_BUCKET': "bucket_name",
}

Optionally you may specify a path prefix:

MEDIASYNC['AWS_PREFIX'] = "key_prefix"

Assuming a correct DNS CNAME entry, setting AWS_BUCKET to assets.sunlightlabs.com and AWS_PREFIX to myproject/media would sync the media directory to http://assets.sunlightlabs.com/myproject/media/.

Amazon allows users to create DNS CNAME entries to map custom domain names to an AWS bucket. MEDIASYNC can be configured to use the bucket as the media URL by setting AWS_BUCKET_CNAME to True.

MEDIASYNC['AWS_BUCKET_CNAME'] = True

If you would prefer to not use gzip compression with the S3 client, it can be disabled:

MEDIASYNC['AWS_GZIP'] = False
Tips

Since files are given a far future expires header, one needs a way to do "cache busting" when you want the browser to fetch new files before the expire date arrives. One of the best and easiest ways to accomplish this is to alter the path to the media files with some sort of version string using the key prefix setting:

MEDIASYNC['AWS_PREFIX'] = "myproject/media/v20001201"

Given that and the above DNS CNAME example, the media directory URL would end up being http://assets.sunlightlabs.com/myproject/media/v20001201/. Whenever you need to update the media files, simply update the key prefix with a new versioned string.

A CACHE_BUSTER settings can be added to the main MEDIASYNC settings dict to add a query string parameter to all media URLs. The cache buster can either be a value or a callable which is passed the media URL as a parameter.

MEDIASYNC['CACHE_BUSTER'] = 1234567890

The above setting will generate a media path similar to:

http://yourhost.com/url/to/media/image.png?1234567890

An important thing to note is that if you're running your Django site in a multi-threaded or multi-node setup, you'll want to be careful about using a time-based cache buster value. Each worker/thread will probably have a slightly different value for datetime.now(), which means your users will find themselves having cache misses randomly from page to page.

Rackspace Cloud Files

MEDIASYNC['BACKEND'] = 'mediasync.backends.cloudfiles'
Settings

The following settings are required in the mediasync settings dict:

MEDIASYNC = {
    'CLOUDFILES_CONTAINER': 'container_name',
    'CLOUDFILES_USERNAME': 'cf_username',
    'CLOUDFILES_API_KEY': 'cf_apikey',
}
Tips

The Cloud Files backend lacks support for the following features:

  • setting HTTP Expires header
  • setting HTTP Cache-Control header
  • content compression (gzip)
  • SSL support
  • conditional sync based on file checksum

Custom backends

You can create a custom backend by creating a Python module containing a Client class. This class must inherit from mediasync.backends.BaseClient. Additionally, you must implement two methods:

def remote_media_url(self, with_ssl):
    ...

remote_media_url returns the full base URL for remote media. This can be either a static URL or one generated from mediasync settings:

def put(self, filedata, content_type, remote_path, force=False):
    ...

put is responsible for pushing a file to the backend storage.

  • filedata - the contents of the file
  • content_type - the mime type of the file
  • remote_path - the remote path (relative from remote_media_url) to which the file should be written
  • force - if True, write file to remote storage even if it already exists

If the client supports gzipped content, you will need to override supports_gzip to return True:

def supports_gzip(self):
        return True

File Processors

File processors allow you to modify the content of a file as it is being synced or served statically.

Mediasync ships with three processor modules:

  1. slim is a minifier written in Python and requires the slimmer Python package. The Python package can be found here: http://pypi.python.org/pypi/slimmer/
  2. yuicompressor is a minifier written in Java and can be downloaded from YUI's download page: http://developer.yahoo.com/yui/compressor/. This processor also requires an additional setting, as defined below. yuicompressor is new and should be considered experimental until the mediasync 2.1 release.
  3. closurecompiler is a javascript compiler provided by Google.

Custom processors can be specified using the PROCESSORS entry in the mediasync settings dict. PROCESSORS should be a list of processor entries. Each processor entry can be a callable or a string path to a callable. If the path is to a class definition, the class will be instantiated into an object. The processor callable should return a string of the processed file data, None if it chooses to not process the file, or raise mediasync.SyncException if something goes terribly wrong. The callable should take the following arguments:

def proc(filedata, content_type, remote_path, is_active):
        ...
filedata
the content of the file as a string
content_type
the mimetype of the file being processed
remote_path
the path to which the file is being synced (contains the file name)
is_active
True if the processor should... process

If the PROCESSORS setting is used, you will need to include the defaults if you plan on using them:

'PROCESSORS': (
    'mediasync.processors.slim.css_minifier',
    'mediasync.processors.slim.js_minifier',
        ...
),

mediasync will attempt to use slimmer by default if you have the package installed and do not use the PROCESSORS setting.

Google Closure Compiler

Google's JavaScript Closure Compiler provides an API that allows files to be compressed without installing anything locally. To use the service:

'PROCESSORS': ('mediasync.processors.closurecompiler.compile',)

YUI Compressor

To configure YUI Compressor you need to define a PROCESSORS and YUI_COMPRESSOR_PATH as follows, assuming you placed the ".jar" file in your ~/bin path:

'PROCESSORS': ('mediasync.processors.yuicompressor.css_minifier',
               'mediasync.processors.yuicompressor.js_minifier'),
'YUI_COMPRESSOR_PATH': '~/bin/yuicompressor.jar',

Features

Ignored Directories

Any directory in STATIC_ROOT that is hidden or starts with an underscore will be ignored during syncing.

Template Tags

When referring to media in HTML templates you can use custom template tags. These tags can by accessed by loading the media template tag collection.

{% load media %}

Any tag that has a path argument can use either a string or a variable:

{% media_url "images/avatar.png" }
{% media_url user.profile.avatar_path %}

If you'd like to make the mediasync tags global, you can add the following to your master urls.py file:

from django.template import add_to_builtins
add_to_builtins('mediasync.templatetags.media')

Some backends (S3) support https URLs when the requesting page is secure. In order for the https to be detected, the request must be placed in the template context with the key 'request'. This can be done automatically by adding 'django.core.context_processors.request' to TEMPLATE_CONTEXT_PROCESSORS in settings.py

media_url

Renders the STATIC_URL from settings.py with trailing slashes removed.

<img src="{% media_url %}/images/stuff.png">

STATIC_URL takes an optional argument that is the media path. Using the argument allows mediasync to add the CACHE_BUSTER to the URL if one is specified.

<img src="{% media_url '/images/stuff.png' %}">

If CACHE_BUSTER is set to 12345, the above example will render as:

<img src="http://assets.example.com/path/to/media/images/stuff.png?12345">

NOTE: Don't use this tag to serve CSS or JS files. Use the js and css tags that were specifically designed for the purpose.

js

Renders a script tag with the correct include.

{% js "myfile.js" %}

css

Renders a <link> tag to include the stylesheet. It takes an optional second parameter for the media attribute; the default media is "screen, projector".

{% css "myfile.css" %}
{% css "myfile.css" "screen" %}

css_print

Shortcut to render as a print stylesheet.

{% css_print "myfile.css" %}

which is equivalent to

{% css "myfile.css" "print" %}

Writing Style Sheets

Users are encouraged to write stylesheets using relative URLS. The media directory is synced with S3 as is, so relative local paths will still work when pushed remotely.

background: url(../images/arrow_left.png);

Joined files

When serving media in production, it is beneficial to combine JavaScript and CSS into single files. This reduces the number of connections the browser needs to make to the web server. Fewer connections can dramatically decrease page load times and reduce the server-side load.

Joined files are specified in the MEDIASYNC dict using JOINED. This is a dict that maps individual media to an alias for the joined files.

'JOINED': {
    'styles/joined.css': ['styles/reset.css','styles/text.css'],
    'scripts/joined.js': ['scripts/jquery.js','scripts/processing.js'],
},

Files listed in JOINED will be combined and pushed to S3 with the name of the alias. The individual CSS files will also be pushed to S3. Aliases must end in either .css or .js in order for the content-type to be set appropriately.

The existing template tags may be used to refer to the joined media. Simply use the joined alias as the argument:

{% css_print "joined.css" %}

When served locally, template tags will render an HTML tag for each of the files that make up the joined file:

<link rel="stylesheet" href="/media/styles/reset.css" type="text/css" media="screen, projection" />
<link rel="stylesheet" href="/media/styles/text.css" type="text/css" media="screen, projection" />

When served remotely, one HTML tag will be rendered with the name of the joined file:

<link rel="stylesheet" href="http://bucket.s3.amazonaws.com/styles/joined.css" type="text/css" media="screen, projection" />

Smart GZIP for S3

In previous versions of mediasync's S3 client, certain content was always pushed in a compressed format. This can cause major issues with clients that do not support gzip. New in version 2.0, mediasync will push both a gzipped and an uncompressed version of the file to S3. The template tags look at the request and direct the user to the appropriate file based on the ACCEPT_ENCODING HTTP header. Assuming a file styles/layout.css, the following would be synced to S3:

styles/layout.css
styles/layout.css.gzt

Note the altered use of the .gz extension. Some versions of the Safari browser on OSX ignore the Content-Type header for files ending in .gz and treat them instead as files to download. This altered extension allows Safari to deflate and utilize the files correctly without affecting functionality in any other tested browsers.

Signals

mediasync provides two signals that allow you to hook into the syncing process. pre_sync is sent after the client is opened, but before the first file is synced. post_sync is sent after the last file is synced, but before the client is closed. This allows you to call commands on the client without having to worry about its state. The signals allow you to do common tasks such as calling Django 1.3's collectstatic command, process SASS stylesheets, or clean up files generated during a pre_sync process.

collectstatic receiver

A receiver for calling the collectstatic management command is provided:

from mediasync.signals import pre_sync, collectstatic_receiver

# run collectstatic before syncing media
pre_sync.connect(collectstatic_receiver)

SASS receiver

A receiver for compiling SASS into CSS is provided:

from mediasync.signals import pre_sync, sass_receiver

# compile SASS files before syncing media
pre_sync.connect(sass_receiver)

Any file in static root that has the sass or scss file extension will be compiled into CSS. The compiled CSS file will be placed in the same directory and the original extension will be replaced with css. If a file exists with the same css extension, it will be overwritten.

By default mediasync uses the sass command with no options. If you would like to specify your own command, specify SASS_COMMAND in settings:

MEDIASYNC = {
    ...
    'SASS_COMMAND': 'sass -scss -l',
    ...
}

Running MEDIASYNC

./manage.py syncmedia

Change Log

2.2.0

  • added pre_sync and post_sync signals
  • provide basic receiver for calling collectstatic before syncing
  • provide receiver for compiling SASS before syncing
  • show media directory listing when serving locally in debug mode
  • add processor for Google's Closure Compiler API for JavaScript
  • template tags can now take a variable as the path argument

2.1.0

  • default to using STATIC_URL and STATIC_ROOT (Django 1.3), falling back to MEDIA_URL and MEDIA_ROOT if the STATIC_* settings are not set
  • add AWS_GZIP setting to optionally disable gzip compression in S3 client

Thanks to Rob Hudson and Dolan Antenucci for their contributions to this release.

2.0.0

  • updated Rackspace Cloud Files backend
  • use gzip instead of deflate for compression (better browser support)
  • smart gzip client support detection
  • add pluggable backends
  • add pluggable file processors
  • experimental YUI Compressor
  • settings refactor
  • allow override of settings.MEDIA_URL
  • Improvements to the logic that decides which files to sync. Safely ignore a wider variety of hidden files/directories.
  • Make template tags aware of whether the current page is SSL-secured. If it is, ask the backend for an SSL media URL (if implemented by your backend).
  • made SERVE_REMOTE setting the sole factor in determining if media should be served locally or remotely
  • add many more tests
  • deprecate CSS_PATH and JS_PATH

Thanks to Greg Taylor, Peter Sanchez, Jonathan Drosdeck, Rich Leland, and Rob Hudson for their contributions to this release.

1.0.1

  • add application/javascript and application/x-javascript to JavaScript mimetypes
  • break out of CSS and JS mimetypes
  • add support for HTTPS URLs to S3
  • allow for storage of S3 keys in ~/.boto configuration file

Thanks to Rob Hudson and Peter Sanchez for their contributions.

1.0.0

Initial release.