Django Files — A Short Talk (slides only)

Files
in an exciting adventure with dinosaurs

TZ=CET ls -ltr talk/
-rwxr--r-- 1 jaylett django 6 6 Nov 14:01 Files
-rwxr--r-- 1 jaylett django 5 6 Nov 14:02 Files and HTTP
-rwxr--r-- 1 jaylett django 15 6 Nov 14:04 Files in the ORM
-rwxr--r-- 1 jaylett django 13 6 Nov 14:08 Storage backends
-rwxr--r-- 1 jaylett django 25 6 Nov 14:20 Static files
-rwxr--r-- 1 jaylett django 8 6 Nov 14:35 Form media
-rwxr--r-- 1 jaylett django 29 6 Nov 14:40 Asset pipelines
-rwxr--r-- 1 jaylett django 6 6 Nov 14:55 What next?

The File family
• File — or ImageFile, if it might be an image
• ContentFile / SimpleUploadedFile in tests
• which have a different parameter order

• #10541 cannot save ﬁle from a pipe

UploadedFile
• “behaves somewhat like a ﬁle object”
• temporary ﬁle and memory variants
• custom upload handlers

forms.FileField
# forms-filefield.py
class FileForm(forms.Form):
uploaded = forms.FileField()
def upload(request):
if request.method == 'POST':
form = FileForm(request.POST, request.FILES)
if form.is_valid():
request.FILES['uploaded'] # do something!
return HttpResponseRedirect('/next/')
else:
form = FileForm()
return render_to_response(
'upload.html',
{'form': form},
)

• #15879 multipart/form-data filename="" 
not handled as file
• #17955 Uploading a file without using django forms
• #18150 Uploading a file ending with a 
backslash fails
• #20034 Upload handlers provide no way to retrieve
previously parsed POST variables
• #21588 "Modifying upload handlers on the fly"
documentation doesn't replicate internal magic

Files in the ORM
# orm-file.py
class Wub(models.Model):
infosheet = models.FileField()
>>> w = Wub(infosheet="relative/to/media/root.pdf")
>>> print w.infosheet.url
https://media.root/relative/to/media/root.pdf
>>> w.infosheet = ContentFile("A boring bit of text",
“file.txt")
https://media.root/file.txt

• #5619 FileField and ImageField return the wrong path/url 
before calling save_FOO_ﬁle()
• #10244 FileFields can't be set to NULL in the db
• #13809 FileField open method is only accepting 'rb' modes
• #14039 FileField special-casing breaks MultiValueField including a
FileField
• #13327 FileField/ImageField accessor methods throw unnecessary
exceptions when they are blank or null.
• #17224 determine and document the use of default option in context
of FileField
• #25547 refresh_from_db leaves FieldFile with reference to db_instance

Files in the ORM
# orm-file.py
http://media.root/relative/to/media/root.pdf
“file.txt")
http://media.root/file.txt
>>> w.infosheet = None

Files in the ORM
# orm-file.py
http://media.root/relative/to/media/root.pdf
“file.txt")
http://media.root/file.txt
>>> print type(w.infosheet)
FieldFile <class 'django.db.models.fields.files.FieldFile'>

FieldFile
• magical autoconversion for anything (within
reason)
• this happens using FileDescriptor classes
which, well, let’s just ignore that

FileField
# orm-fieldfile.py
>>> w = Wub(infosheet="relative/to/media/
root.pdf")
>>> w.infosheet == None
True
>>> w.infosheet is None
False

• #18283 FileField should not reuse FieldFiles

In ModelForms
# modelforms-filefield.py
class WubCreate(CreateView):
model = Wub
fields = ['infosheet']

ImageField
# orm-imagefile.py
photo = models.ImageField()
>>> w = Wub(infosheet="relative/to/media/
root.pdf", photo="relative/to/media/
root.png")
>>> w.photo.width, w.photo.height
(480, 200)

• #15817 ImageField having 
[width|height]_field set sytematically compute 
the image dimensions in ModelForm validation
process
• #18543 Non image file can be saved to
ImageField
• #19215 ImageField's “Currently” and “Clear”
Sometimes Don't Appear
• #21548 Add the ability to limit file extensions for
ImageField and FileField

ImageField
# orm-imagefile-proxies.py
photo = models.ImageField(width_field='photo_width',
height_field='photo_height')
photo_width = models.PositiveIntegerField(blank=True)
photo_height = models.PositiveIntegerField(blank=True)
>>> w = Wub(infosheet="relative/to/media/root.pdf",
photo="relative/to/media/root.png")
>>> w.photo.width, w.photo.height
(480, 200)
>>> w.photo_width, w.photo_height
(480, 200)

• #8307 ImageFile use of width_field and
height_field is slow with remote storage
backends
• #13750 ImageField accessing height or width
and then data results in "I/O operation on
closed file”

Storing ﬁles
• Stored in MEDIA_ROOT
• Served from MEDIA_URL
• Uses FileSystemStorage…by default

What can Storage do?
• oriented around ﬁles, rather than a general FS API
• open / save / delete / exists / size / path / url
• make an available name, ie one that doesn’t clash
• modiﬁed, created, accessed times
• … also listdir

Choosing storage
# configuring-storage-settings.py
DEFAULT_FILE_STORAGE = 'dotted.path.Class'
MEDIA_ROOT = '/my-root'
MEDIA_URL = 'https://media.root/'
class MyStorage(FileSystemStorage):
def __init__(self, **kwargs):
kwargs.setdefault(
'location',
'/my-root'
)
kwargs.setdefault(
'base_url',
'https://media.root/'
)
return super(
MyStorage,
self
).__init__(**kwargs)

Choosing storage
# models.py
from mystorage import BetterStorage
storage_instance = BetterStorage()
class MyModel(models.Model):
upload = models.FileField(
storage=storage_instance
)

• #9586 Shall upload_to return an urlencoded 
string or not?
• #12157 FileSystemStorage does file I/O inefficiently, despite
providing options to permit larger blocksizes
• #15799 Document what exception should be raised when trying
to open non-existent file
• #21602 FileSystemStorage._save() Should Save to a Temporary
Filename and Rename to Attempt to be Atomic
• #23759 Storage.get_available_name should preserve all file
extensions, not just the first one
• #23832 Storage API should provide a timezone aware approach

Reasons to override
• Model ﬁelds with different options
• Different storage engine entirely

Protected storage
FSS = FileSystemStorage
pstore = FSS(
location=‘/protected’,
base_url="/p/",
)
urlpatterns += patterns(
url(
r'^p/(?P<path>.*)$',
protected,
),
)
class
Profile(models.Model):
resume = FileField(
null=True,
blank=True,
storage=pstore,
)
@login_required
def protected(request,
path):
f = pstore.open(path)
return HttpResponse(
f.chunks()
)

S3BotoStorage
• One of many in django-storages-redux
• Millions of options, somewhat undocumented
• conﬁgure with AWS_ACCESS_KEY_ID,
AWS_SECRET_ACCESS_KEY,
AWS_STORAGE_BUCKET_NAME
• defaults for the rest mostly sane

Fun with S3Boto
AWS_S3_CUSTOM_DOMAIN='cdn.eg.com'
AWS_HEADERS={
'Cache-Control': 'max-age=31536000'
} # a year or so
AWS_PRELOAD_METADATA=True

Protected S3 storage
protected_storage = S3BotoStorage(
acl='private',
querystring_auth=True,
querystring_expire=600,
# 10 minutes, try to ensure people
# won’t / can't share
)
model.field.url # works as expected

Code that uses storage
• Please test on both Windows and Linux/Unix
• Please test with something remote like S3Boto
• Please write your own tests to work with different
storage backends

How it works

{% load static %}
<img
src='{% static "asset/path.png" %}'
width='200' height='100' alt=''>

<img
src='https://static.root/asset/path.png'
width='200' height='100' alt=‘'>

• #24336 static server should skip for protocol-
relative STATIC_URL
• #25022 collectstatic create self-referential
symlink

• #23563 Make `staticﬁles_storage` a public API
• #25484 static template tag outputs invalid HTML
if storage class's url() returns a URI with '&'
characters.

I make it sound bad
Really, it’s not

Cached (1.4) / Manifest (1.7)
• Cache uses the main cache, or a dedicated one
• Manifest writes a JSON manifest ﬁle to the
conﬁgured storage backend

The problem

<script src=“/static/admin/js/
collapse.min.c1a27df1b997.js”>
<script src=“/admin/editorial/
article/2/autosave_variables.js">
<script src=“/static/autosave/js/
autosave.js”>

The problem

<script src=“/static/admin/js/
collapse.min.c1a27df1b997.js”>
<script src=“/admin/editorial/
article/2/autosave_variables.js">
<script src=“/static/autosave/js/
autosave.js?v=2”>

Manifests for artefacts
class LocalManifestMixin(ManifestFilesMixin):
_local_storage = None
def __init__(self, *args, **kwargs):
super(LocalManifestMixin, self).__init__(*args, **kwargs)
self._local_storage = FileSystemStorage()
def read_manifest(self):
try:
with self._local_storage.open(self.manifest_name) as manifest:
return manifest.read().decode('utf-8')
except IOError:
return None
def save_manifest(self):
payload = {
'paths': self.hashed_files,
'version': self.manifest_version,
}
if self._local_storage.exists(self.manifest_name):
self._local_storage.delete(self.manifest_name)
contents = json.dumps(payload).encode('utf-8')
self._local_storage._save(
self.manifest_name, ContentFile(contents)
)

• #18929 CachedFilesMixin is not compatible with S3BotoStorage
• #19528 CachedFilesMixin does not rewrite rules for css 
selector with path
• #19670 CachedFilesMixin Doesn't Limit Substitutions to Extension Matches
• #20620 CachedFileMixin.post_process breaks when cache size is exceeded
• #21080 collectstatic post-processing fails for references inside comments
• #22353 CachedStaticFilesMixin lags in updating hashed names of other static files
referenced in CSS
• #22972 HashedFilesMixin.patterns should limit URL matches to their respective filetypes
• #24243 Allow HashedFilesMixin to handle file name fragments
• #24452 Staticfiles backends using HashedFilesMixin don't update CSS files' hash
when referenced media changes
• #25283 ManifestStaticFilesStorage does not works in edge cases while 
importing url font-face with IE hack

Some options for 3PA
• Fiat: All 3PAs use staticfiles
• Shim: all 3PAs use the admin approach, wrapping
it in their own taglib. Duplication!
• Bless: move staticfiles into core and make the
simple `load static` the same as `load staticfiles`
• Weakly bless staticfiles so `load static` behaves
like the admin, and the admin static stuff goes
away, and everyone just uses `load static`

Widgets, Forms, Admin
• Widgets might have specific assets to render
properly: typically CSS & JS
• Forms might have specific assets to render properly,
too. They’re made out of widgets and some other bits,
so they use the same system
• Then individual admin screens (ModelAdmin) might
have specific assets as well; they have Forms which
have Widgets
• Amazingly this hasn’t escaped into View

This is a good thing
from django.contrib import admin
from django.contrib.staticfiles.templatetags.staticfiles
import static
class ArticleAdmin(admin.ModelAdmin):
# ...
class Media:
js = [
'//tinymce.cachefly.net/4.1/tinymce.min.js',
static('js/tinymce_setup.js'),
]

This isn’t a good thing
from django.contrib.staticfiles.templatetags.staticfiles
import static
from django.contrib.admin.templatetags.admin_static
import static

• #9357 Unable to subclass form Media class
• #12264 calendar.js depends on jsi18n but date widgets using 
it do not specify as required media
• #12265 Media (js/css) collection strategy in Forms has no order dependence
concept
• #13978 Allow inline js/css in forms.Media
• #18455 Added hooks to Media for staticfiles app
• #21221 Widgets and Admin's Media should use the configured staticfiles
storage to create the right path to a file
• #21318 Clarify the ordering of the various Media classes
• #21987 Allow Media objects to have their own MEDIA_TYPES
• #22298 Rename Media to Static

Some options
• Fiat: all 3PAs use staticfiles explicitly
• Shim: all 3PAs use the admin approach explicitly
• Bless: move staticfiles into core;
Media.absolute_path uses its storage
backend
• Weakly bless staticfiles, ie
Media.absolute_path uses the admin trick

This world’s a mess anyway
• no convenient API to get (CSS, JS) media
• can’t dedupe between forms if you have many
on one page

This world’s a mess anyway
• no convenient API to get (CSS, JS) media
• can’t dedupe between forms if you have many
on one page
• some things are global, eg jQuery, and can’t
easily dedupe between a widget and a site-wide
library
• to say nothing of different versions

What? Why?
• compilation
• concatenation

What? Why?
• compilation
• concatenation or linking/encapsulation

What? Why?
• compilation
• miniﬁcation

What? Why?
• compilation
• miniﬁcation
• hashing and caching

Writing the HTML

<script type='text/javascript'
src='site.min.48fb66c7.js'>
<link rel='stylesheet' type='text/
css' href=‘site.min.29557b4f.css'>

Focus on targets

<script type='text/javascript'  
src='{% static "site.js" %}'>
<link rel='stylesheet' 
type=‘text/css'
href='{% static "site.css" %}'>

Focus on sources

<script type='text/javascript' src='menu.js'>
<script type='text/javascript' src='index.js'>
<link rel='stylesheet' type='text/css' href='nav.css'>
<link rel='stylesheet' type='text/css' href='footer.css'>
<link rel='stylesheet' type='text/css' href='index.css'>

{% asset js 'menu.js' %}
{% asset js 'index.js' %}
{% asset css 'nav.css' %}
{% asset css 'footer.css' %}
{% asset css 'index.css' %}

Rails / Sprocket
<%= stylesheet_link_tag
"application", media: "all" %>
<%= javascript_include_tag
"application" %>

Rails / Sprocket
//= require home
//= require moovinator
//= require slider
//= require phonebox

Rails / Sprocket
.class {
background-image: url(
<%= asset_path 'image.png' %>
)
}

Rails / Sprocket
rake assets:precompile

Rails / Sprocket
rake assets:clean

Sprocket clones
• asset-pipeline (Express/node.js)
• sails (node.js)
• grails asset pipeline (Groovy)
• Pipe (PHP)

node.js
• express-cdn
• Broccoli
• Sigh
• gulp
• Webpack

gulp (node.js)
var gulp = require('gulp');
var sass = require('gulp-sass');
var sourcemaps = require('gulp-sourcemaps');
var rev = require('gulp-rev');
gulp.task('default', ['compile-scss']);
gulp.task('compile-scss', function() {
gulp.src('source/stylesheets/**/*.scss')
.pipe(sourcemaps.init())
.pipe(sass(
{indentedSyntax: false, errLogToConsole: true }
))
.pipe(sourcemaps.write())
.pipe(rev())
.pipe(gulp.dest('static'));
});

gulp (node.js)
var gulp = require('gulp');
var sass = require('gulp-sass');
var sourcemaps = require('gulp-sourcemaps');
var rev = require('gulp-rev');
gulp.task('default', ['compile-scss']);
gulp.task('compile-scss', function() {
gulp.src('source/stylesheets/**/*.scss')
.pipe(sourcemaps.init())
.pipe(sass(
{indentedSyntax: false, errLogToConsole: true }
))
.pipe(sourcemaps.write())
.pipe(rev())
.pipe(gulp.dest('static'))
.pipe(rev.manifest())
.pipe(gulp.dest('static'));
});

Django options
• Plain django (external pipeline + staticﬁles)
• django-compressor
• django-pipeline

Plain Django
• Pipeline external to Django (use what you want)
• Hashes computed by staticﬁles
• Sourcemap support is ﬁddly if you want hashes

django-compressor
• Integrated pipeline, supports precompilers &c
• Source ﬁles listed in templates
• Integrated hashing
• Can be used with staticﬁles, but feels awkward
• Can support sourcemaps, via a plugin

django-pipeline
• Internal pipeline, supports precompilers &c
• Source to output mapping in Django settings
• Integrates with staticﬁles better than compressor
• Hashing via staticﬁles
• Doesn’t support sourcemaps directly

Django + webpack
• webpack-bundle-tracker + django-webpack-
loader (Owais Lone 2015)
• Pipeline run by Webpack, emits a mapping ﬁle
• Template tag to resolve the bundle name to a
URL relative to STATIC_ROOT

Django options
• django-compressor: fixed pipeline
• django-pipelines: fixed pipeline (+ config woes)
• staticfiles: doesn’t get hashes right
• webpack-loader: isn’t generic

The future?
• pipeline builds named bundles into output files
• pipeline writes manifest.json: a mapping of
bundle name to output filename
• staticfiles storage reads in manifest.json on boot
• templates refer to the bundle name
• useful for staticfiles to be able to list static
directories (eg for node pipeline search paths)

Third-party apps
• can’t cooperate with your project’s pipeline
• don’t want to force a dependency on a pipeline
• so must precompile into ﬁles in your sdist
• possibly for staticﬁles to sweep up (but we’ve
discussed this bit before)

What next?
• bless or semi-bless staticﬁles?
• deprecate CachedStaticFilesStorage?
• document the boundaries of our hashing?
• rename? kill? expand? form.Media
• asset management / document external pipelines
• ﬁx some bugs ;-)

• #9433 File locking broken on AFP mounts
• #17686 file.save crashes on unicode filename
• #18233 file_move_safe overwrites destination file
• #18655 Media files should be served using file
storage API
• #22961 StaticFilesHandler should not run
middleware on 404

😨🐉
• Durbed (durbed.deviantart.com) under CC By-
SA 3.0
• “Happy New Year from Hell Creek”
• “Primal feathers”

Django Files — A Short Talk (slides only)

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