Add static asset cache busting

Calculates MD5 hash of static assets on server start. These are appended to the file name's when url_for is used, telling browsers to download the latest version of the files, e.g. style.css?q=81cf0ee.

Inspired by https://github.com/ChrisTM/Flask-CacheBust but uses query strings instead of rewriting the path because fonts inside CSS files break when the path is rewritten.
This commit is contained in:
Jonathan Rehm 2017-08-13 09:21:19 -07:00
parent 08d0404e9c
commit a27848b351
2 changed files with 59 additions and 0 deletions

57
cps/cache_buster.py Normal file
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@ -0,0 +1,57 @@
# Inspired by https://github.com/ChrisTM/Flask-CacheBust
# Uses query strings so CSS font files are found without having to resort to absolute URLs
import hashlib
import os
def init_cache_busting(app):
"""
Configure `app` to so that `url_for` adds a unique query string to URLs generated
for the `'static'` endpoint.
This allows setting long cache expiration values on static resources
because whenever the resource changes, so does its URL.
"""
static_folder = app.static_folder # the rooted path to the static file folder
hash_table = {} # map of file hashes
app.logger.debug('Computing cache-busting values...')
# compute file hashes
for dirpath, dirnames, filenames in os.walk(static_folder):
for filename in filenames:
# compute version component
rooted_filename = os.path.join(dirpath, filename)
with open(rooted_filename, 'r') as f:
version = hashlib.md5(f.read()).hexdigest()[:7]
# save version to tables
file_path = rooted_filename.replace(static_folder + "/", "")
hash_table[file_path] = version
app.logger.debug('Finished computing cache-busting values')
def bust_filename(filename):
return hash_table.get(filename, "")
def unbust_filename(filename):
return filename.split("?", 1)[0]
@app.url_defaults
def reverse_to_cache_busted_url(endpoint, values):
"""
Make `url_for` produce busted filenames when using the 'static' endpoint.
"""
if endpoint == 'static':
values["q"] = bust_filename(values['filename'])
def debusting_static_view(filename):
"""
Serve a request for a static file having a busted name.
"""
return original_static_view(filename=unbust_filename(filename))
# Replace the default static file view with our debusting view.
original_static_view = app.view_functions['static']
app.view_functions['static'] = debusting_static_view

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@ -21,6 +21,7 @@ from flask import (Flask, render_template, request, Response, redirect,
url_for, send_from_directory, make_response, g, flash,
abort, Markup, stream_with_context)
from flask import __version__ as flaskVersion
import cache_buster
import ub
from ub import config
import helper
@ -200,6 +201,7 @@ mimetypes.add_type('image/vnd.djvu', '.djvu')
app = (Flask(__name__))
app.wsgi_app = ReverseProxied(app.wsgi_app)
cache_buster.init_cache_busting(app)
gevent_server = None