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Robin Zimmermann Kaazing
HTML5 Offline Web Applications
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Intuit
• Whether helping balance a checkbook, run a small
business, or pay income taxes, our innovative
solutions have simplified millions of people’s lives
Copyright © 2010 - Kaazing Corporation. All rights reserved.
Thanks to our Sponsors:
Kaazing
• A high-performance Web platform that
enables full-duplex communication over
the Web
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• About Offline Web Apps
• Creating Offline Web Apps
• Server Configuration
• Tips, Tricks, and Q&A
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Offline Web Applications • New HTML5 Specification
• Also known as Application Cache (AppCache)
• WHATWG: http://www.whatwg.org/specs/web-
apps/current-work/multipage/offline.html#offline
• W3C:
http://dev.w3.org/html5/spec/offline.html#offline
• Spec is primarily aimed at browser developers
to ensure interoperability…
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Data for the current section. The format that data lines must take
depends on the current section. When the current section is
the explicit section, data lines must consist of zero or more
U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters,
a valid URL identifying a resource other than the manifest itself,
and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION
(tab) characters. When the current section is the fallback section,
data lines must consist of zero or more U+0020 SPACE and U+0009
CHARACTER TABULATION (tab) characters, a valid URL identifying a
resource other than the manifest itself, one or more U+0020 SPACE
and U+0009 CHARACTER TABULATION (tab) characters, another valid URL
identifying a resource other than the manifest itself, and then
zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab)
characters. When the current section is the online whitelist
section, data lines must consist of zero or more U+0020 SPACE and
U+0009 CHARACTER TABULATION (tab) characters, either a single
U+002A ASTERISK character (*) or a valid URL identifying a resource
other than the manifest itself, and then zero or more U+0020 SPACE
and U+0009 CHARACTER TABULATION (tab) characters…
Copyright © 2010 - Kaazing Corporation. All rights reserved.
WHATWG spec
The Spec…
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And the Slightly Simpler Version…
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Sweet! I’m offline! How easy was that!
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Offline Web Applications • Allow you to keep using web apps and sites without a
network connection
(for example, on an airplane, in rural areas, subways)
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Offline without AppCache
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Noooooooo!
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Traditional Caching • Cache duration can be controlled through
Web Server’s Cache HTTP headers
o For example, in Apache’s .htaccess file (see
example on next slide)
• Not reliable for offline use
• Browser caching settings also apply
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<IfModule mod_expires.c>
Header set cache-control: public
ExpiresActive on
# your document html
ExpiresByType text/html "access"
# rss feed
ExpiresByType application/rss+xml "access plus 1 hour"
# favicon (cannot be renamed)
ExpiresByType image/vnd.microsoft.icon "access plus 1 week"
# media: images, video, audio
ExpiresByType image/png "access plus 1 month"
ExpiresByType image/jpg "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType video/ogg "access plus 1 month"
ExpiresByType audio/ogg "access plus 1 month"
ExpiresByType video/mp4 "access plus 1 month"
# webfonts
ExpiresByType font/ttf "access plus 1 month"
ExpiresByType font/woff "access plus 1 month"
ExpiresByType image/svg+xml "access plus 1 month"
# css and javascript
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/javascript "access plus 1 month"
ExpiresByType text/javascript "access plus 1 month"
</IfModule>
Copyright © 2010 - Kaazing Corporation. All rights reserved.
.htaccess File
Web Server Caching Settings
Source: Paul Irish & Divya Manian http://html5boilerplate.com/
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Offline Web Applications • Allow you to cache pages that have not been
visited
• Browsers cache data in an Application Cache
• Once resources are cached, you can access them
very quickly (without a network request)
• HTML5 also allows online and offline detection
• Using offline mechanism allows you to easily
prefetch site resources (speeds up pages, but
uses bandwidth)
• Pages served using TLS (SSL) can also be
included to work offline Copyright © 2010 - Kaazing Corporation. All rights reserved.
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Demo Copyright © 2010 - Kaazing Corporation. All rights reserved.
Source Files: http://bit.ly/9pJ1Zq or: http://tech.kaazing.com/training/offline/peter-lubbers-html5-offline-web-apps-presentation-code.zip
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Browser Support for Offline Web Applications
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Source: http://caniuse.com/ (the best site for checking browser support for HTML5 features)
Hi-res browser logos: http://paulirish.com/2010/high-res-browser-icons/
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Offline Emulation • HTML5 Gears Project by Brad Neuberg,
Google:
http://code.google.com/p/html5-gears/
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Developing Offline Web Applications
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CACHE MANIFEST
# manifest version 1.0.1
# Files to cache
CACHE:
index.html
cache.html
html5.css
img/foo.gif
http://www.example.com/styles.css
# Use from network if available
NETWORK:
network.html
# Fallback content
FALLBACK:
/ fallback.html
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Manifest File
The Manifest File
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<!DOCTYPE html>
<html manifest="offline.manifest">
<head>
<title>HTML5 Application Cache</title>
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HTML
Using a Manifest File in HTML
• Reference the manifest file:
o <name>.manifest – it must match the name of the manifest file
o Add as attribute to HTML element
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Browser Notification • Users may have to opt in (similar to
Geolocation)
• Configurable and not default in all browsers
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The Manifest File • Manifest file has three sections:
o CACHE:
o NETWORK:
o FALLBACK:
• Multiple sections (of the same kind) are allowed
• First line must be CACHE MANIFEST
• Comments start with # (don’t use inline
comments)
• An application cache is created using the
manifest’s complete URL (you can have multiple
manifest files in a site)
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CACHE: Section • To cache files in the AppCache, include them in
the CACHE: section or list files directly under
CACHE MANIFEST (default is to cache files)
• Add one file per line (full name required)
• Files can contain path information or even be an
absolute URL
• Application caches can’t include fragment identifiers (#) or wildcards
• Case sensitive
• Files that reference the manifest file will
automatically be cached
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NETWORK: Section • Also called the online whitelist
• Files listed in this section listed will not be
loaded from the cache, but retrieved over the
network (from the server) if online
• You can specify “*” o Sets the online whitelist wildcard flag to “open”
o Access to resources on other origins will not be blocked
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FALLBACK: Section • Provides a way to fall back if resources
cannot be found
• Specify a fallback namespace and a fallback page for that namespace:
/ fallback.html
• You can only list one fallback namespace
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Initial Cache Sequence 1. Access the page (with the manifest attribute)
2. Page is loaded and page’s resources are loaded
(from the server)
3. Manifest is encountered and parsed, all files
flagged for caching are loaded in the background
4. Go offline (regular caching is also in effect, so
watch for false positives)
5. Access a CACHE: resource (loads from cache)
6. Access a NETWORK resource (FALLBACK content
is served, files will be available if you go back
online)
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Step 1: First Page Load
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Step 2: Going Offline
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Step 3: Offline Web Page
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Step 4: Network Page
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Consecutive Load Sequence 1 1. Go back to online mode
2. Change the cache.html page on the server
3. Reload the cache.html page in the browser
4. The (old) page loads from the application cache
(The changes do not appear!)
5. The browser checks to see if the referenced manifest file has been updated and does
nothing since it has not been modified
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Consecutive Load Sequence 2 6. Update the manifest file (make a trivial change,
like a version number comment update)
7. Reload the cache page in the browser
8. The (old) page loads from the application cache
(This is always the first action from the browser,
so the changes still don’t appear!)
9. The browser checks to see if the referenced
manifest has been updated and since it has, it
downloads all the files flagged to be cached
10.The new files are now in the application cache,
reload the page once more to see the latest
changes Copyright © 2010 - Kaazing Corporation. All rights reserved.
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// Simple method
if(window.applicationCache) {
// this browser supports offline web apps
}
//Or just use Modernizr (source: http://www.modernizr.com/) if (Modernizr.applicationcache){
// We have offline web app support! Continue
operation,
// indicating to the user that the app will sync up
once they get back online
} else {
// No offline support, show errors if the user goes
offline
}
Copyright © 2010 - Kaazing Corporation. All rights reserved.
JavaScript
Checking for Browser Support
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Copyright © 2010 - Kaazing Corporation. All rights reserved.
Checking for Online and Offline Events
window.addEventListener("online", function(e) {
log("Application is now online");
}, true);
window.addEventListener("offline", function(e) {
log("Application is now offline");
}, true);
JavaScript
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Using Web Pages Offline • Test offline pages using the
“Work Offline” feature if available
(Not in Chrome and
Safari)
• Disconnect your
computer (does not
work for localhost)
• Watch out for false
positives (regular
browser caching)
Copyright © 2010 - Kaazing Corporation. All rights reserved.
Opera
Firefox
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Working Offline
Browser Work Offline
Chrome Disconnect from the network
Firefox File > Work Offline
Safari Disconnect from the network
Opera File > Work Offline
Internet Explorer N/A (Does not support App Cache)
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ApplicationCache Events • The window.applicationCache object fires
several events related to the state of the cache
• window.applicationCache.status is a
numerical property indicating the state of the
cache
o 0 UNCACHED
o 1 IDLE
o 2 CHECKING
o 3 DOWNLOADING
o 4 UPDATEREADY
o 5 OBSOLETE
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Event Callback Attributes
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Callback Attribute Event
onchecking CHECKING
ondownloading DOWNLOADING
onupdateready UPDATEREADY
onobsolete OBSOLETE
oncached CACHED
onerror ERROR
onnoupdateready NOUPDATE
onprogress PROGRESS
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Checking App Cache Status
window.applicationCache.onchecking = function(e) {
log("Checking for application update");
}
window.applicationCache.onnoupdate = function(e) {
log("No application update found");
}
window.applicationCache.onupdateready = function(e) {
log("Application update ready");
window.applicationCache.swapCache();
}
window.applicationCache.onobsolete = function(e) {
log("Application obsolete");
}
JavaScript
Forces correct behavior in some browsers
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Copyright © 2010 - Kaazing Corporation. All rights reserved.
Checking App Cache Status
window.applicationCache.ondownloading = function(e) {
log("Downloading application update");
}
window.applicationCache.oncached = function(e) {
log("Application cached");
}
window.applicationCache.onerror = function(e) {
log("Application cache error");
}
window.applicationCache.onprogress = function(e) {
log("Application Cache progress");
}
JavaScript
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Serving the Manifest File • Manifest files have the MIME type text/cache-manifest
• Most web servers need to be configured to
serve the manifest files correctly
o Served correctly by default by Python's SimpleHTTPServer on Ubuntu Linux
o For Python on Windows/Mac OS X or Apache, update the configuration files with the MIME type
• Verify how the manifest file is served by using
network or curl –I http://offline.example.com/offline.manifest
Copyright © 2010 - Kaazing Corporation. All rights reserved.
Source: Introducing HTML5, Offline Chapter, Bruce Lawson and Remy Sharp
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Verifying the MIME Type • Using curl (see previous
slide)
• Firefox add-on:
Live HTTP Headers
• Chrome developer tools
• Server log
• It works
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# Apache mimetype configuration
# APACHE_HOME/conf/mime.types
text/cache-manifest manifest
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mime.types File
Apache Configuration
# Apache mimetype configuration
AddType text/cache-manifest .manifest
.htaccess File
Or:
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# Cache settings for the manifest file
<IfModule mod_expires.c>
Header set cache-control: public
ExpiresActive on
.
.
.
# Prevent receiving a cached manifest
ExpiresByType text/cache-manifest "access plus 0 seconds"
.
.
.
</IfModule>
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.htaccess File
Apache Configuration
Source: Introducing HTML5, Offline Chapter, Bruce Lawson and Remy Sharp
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mimetypes.py File
Python Configuration
Windows: PYTHON_HOME/Lib/mimetypes.py, for example: C:\Python26\Lib\mimetypes.py
Mac: PYTHON_HOME/Lib/mimetypes.py, for example: /System/Library/Frameworks/Python.framework/Versions/2.6/lib/
python2.6/mimetypes.py
Important: If you do not have a mimetypes.py file, you can use mimetypes.py
from the offline/ mac-config-file example folder. If you already have a compiled mimetypes.pyc file in the same directory, ensure that the permissions
on this file are changed to read/write. When you start Python with the new file, Python compiles it and generates or overwrites the mimetypes.pyc.
# Python SimpleHTTPServer mimetype Configuration
# python –m SimpleHTTPServer 9999)
'.manifest' : 'text/cache-manifest',
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Microsoft IIS Configuration
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Offline Web Applications Tips and Tricks
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Debugging Offline Cache
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Chrome: Chrome Developer Tools > Storage Note: Not available in Safari Web Inspector yet…
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Accessing Offline Resources
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Accessing the Offline Cache
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Firefox: about:cache
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Accessing the Offline Cache
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Firefox SQLite Manager Add-on: https://addons.mozilla.org/en-US/firefox/addon/5817/
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Accessing the Offline Cache
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File System Access
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Browser Offline Cache Settings and
Clearing the Cache
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Offline Cache Settings
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Firefox: Tools > Options (Preferences on Mac OS X) >
Advanced > Network
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Offline Cache Settings
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Opera: opera:config
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Clearing the Cache
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Chrome: Settings Menu > Tools > Clear Browsing Data
Opera: Tools > Preferences > Storage
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Clearing the Cache
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Firefox: Tools > Clear Recent History
Safari: Settings Menu > Reset Safari
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Clearing the Cache Browser Steps to Clear the Cache
Chrome Settings Menu > Tools > Clear Browsing Data
Firefox Tools > Clear Recent History (and Tools > Options (Preferences on Mac OS X) > Advanced > Network > Remove for app cache)
Safari Settings Menu > Reset Safari
Opera Tools > Preferences > Storage (+ Tools > Clear Private Data)
Internet Explorer Coming soon…
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Note: Close any offline pages before you do this to avoid problems
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Private Browsing • Most private browsing modes prevent writing
to application cache
o For example, Safari’s Private Browsing mode, and Chrome’s Incognito Mode
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Security Considerations • Others browsing the same site (on the same
machine in the same browser) can potentially
access your cached data (data is cached
based on the manifest file URL)
• Do not store sensitive,
personal data in the
application cache
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Best Practices • Manifest errors are fatal (case sensitive entries)
• If you are adding and removing (lots of files) files,
remember to update the manifest file
o Use a predeployment script
o Use a version Comment in the manifest file
• Host your site on different domain names
o You can do this on your local machine by hacking the hosts file (see example on the next slide)
o Windows:\WINDOWS\system32\drivers\etc\hosts
o UNIX: /etc/hosts
• To see if files are requested, watch the server log Copyright © 2010 - Kaazing Corporation. All rights reserved.
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Checking Server Access
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# For example
127.0.0.1 localhost
127.0.0.1 offline0.example.com
127.0.0.1 offline1.example.com
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hosts file
hosts File for Testing
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Disk Quota • Don’t assume success and check for errors
o Example in Chrome: Application Cache Error event: Failed to commit new
cache to storage, would exceed quota
• In the future,
browsers will
hopefully have
graceful quota
upgrade
mechanisms like
Opera’s for Local Storage
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Works Well With HTML5 Web Storage…
if (navigator.onLine) {
//Send updates to server
} else {
window.localStorage.myLocalKey = ‘Some Data'; }
}
JavaScript
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CACHE MANIFEST
styles.css
FALLBACK:
/ /offline.html
NETWORK:
*
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Manifest File
Cache-As-You-Go • If you add the manifest attribute, files will be
added to the cache implicitly
• Subresources and dependencies may not be
loaded properly (CSS, JS, etc.)
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This work is licensed under a Creative Commons Attribution 3.0 License.
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Kaazing Jobs: http://www.kaazing.com/about/careers.html
E-mail: [email protected]
Twitter: @peterlubbers
LinkedIN: Peter Lubbers
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Resources • WHATWG Offline Web Apps spec:
http://www.whatwg.org/specs/web-apps/current-
work/multipage/offline.html#offline
• W3C Offline Web Apps spec:
http://dev.w3.org/html5/spec/offline.html#offline
• Offline example source files: http://bit.ly/9pJ1Zq
• Pro HTML5 Programming, Offline chapter, Peter
Lubbers, Brian Albers, and Frank Salim
• Introducing HTML5, Offline chapter, Bruce
Lawson and Remy Sharp
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Copyright © 2010 Kaazing Corporation, All rights reserved. All materials, including labs and other handouts are property of Kaazing Corporation. Except when
expressly permitted by Kaazing Corporation, you may not copy, reproduce, publish, or display any part of this training material, in any form, or by any means.
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`