Chromium Blog
News and developments from the open source browser project
Build Chrome Packaged Apps with the MediaGalleries API
2012年11月20日火曜日
Many popular applications today help users consume, share, manage, and edit media content, as evidenced by the rise of web apps like
Google Play Music
and
YouTube
. For
Chrome packaged app developers
, the new
Media Galleries API
introduces a simple way for apps to access media stored on a user’s device (with the user’s permission, of course).
To use the API, you first have to determine what kind of permission your app needs to access user’s media:
read-only
: allows media content to be read, but not modified
read-write
: allows media content to be read and modified
add-files
: allows media to be added to the galleries but prevents modifying existing media files.
Currently, only read-only access is supported. Support for read-write and add-files will be introduced in a future release.
To retrieve media content, use
getMediaFilesystems()
. If this is the first time your app is accessing the user’s media libraries, the system will prompt the user to grant access:
You can also make your app explicitly ask the user to designate specific galleries. This is useful if, for example, your app is only interested in pictures. Once access is granted, your app can then retrieve a list of
LocalFileSystem
structures. At that point, you can use the
W3C FileSystem API
to access the media gallery content.
NOTE
: The file system APIs will only return files that the Chrome platform
natively supports
, and only the
asynchronous version
of the FileSystem API is currently supported.
We’re eager to see what great applications you will build with the Media Galleries API and the Chrome Packaged Apps platform. To get started, clone our
samples repository
and look at the Media Galleries
sample application
. Have questions or comments? Subscribe to
chromium-apps
and follow us on our
Google+ page
!
Posted by Joe Marini, Developer Advocate
A safer playground for your Linux and Chrome OS renderers
2012年11月19日月曜日
Sandboxing
is a layer of security that Chrome places between attackers and their computer, aiming to isolate an attacker who has successfully exploited a vulnerability. When contained in a sandbox jail, an attacker will typically look for porous or fragile bits in the walls to throw rocks at. That is, he’ll try to gain additional privileges by taking advantage of other vulnerabilities. Our job is to make the virtual walls of the sandbox as strong and impenetrable as possible.
One juicy target for attackers is the operating system’s kernel: a large and complex code base. The latest stable version of Chrome introduces a new layer of sandboxing of Chrome renderers for the 64-bit versions of Chrome OS and Linux, based on a new kernel feature called
seccomp-bpf
. With seccomp-bpf we’ll install a small filter in the kernel that will quickly reject many of the rocks thrown by an attacker. A simple example: if we know that Chrome renderers don’t need a system call such as
vmsplice
, or a facility such as “inotify”, we can just deny them completely. We use a
broker process model
to keep the list of allowed system calls small.
Installing this filter in the kernel improves the security of our users. But it is just the beginning: using this new facility, we’ll continue to make the sandbox safer.
This new sandbox layer is automatically baked into the latest version of Chrome OS. On Linux, you can check by going to
chrome://sandbox
and look for “Seccomp-BPF sandbox Yes”. If this is not available, ask your Linux distribution to include and enable seccomp-bpf in its kernel, as
Ubuntu
has done since version 12.04.
As always, you can report bugs and issues
here
, by clicking on “New issue”.
Posted by Julien Tinnes, Software Engineer
Build smoother web apps with Chrome Developer Tools
2012年11月16日金曜日
Whether your web app involves scrolling down a long list of news headlines or a game with
flying birds
and crumbling structures, you want your web app to look as smooth as native apps. It used to be tricky to chase down the cause of animation jitter and lag in user actions with
Chrome Developer Tools
. This is why
we’ve added
the Frame Mode to our Timeline panel
to help you pinpoint offending long frames and understand what’s causing them to run slowly.
So, what’s a frame
? A frame includes all the tasks that the browser needs to perform in order to update the screen upon a user action or a tick of the animation timer. A complex, but not uncommon, sequence might be:
run JavaScript animations and other event handlers
update CSS animations
recalculate styles and lay out the elements in the DOM
re-paint the updated layers of the page
compose them and present to the user
Delivering a butter-smooth animation means completing all of the above in
less than 16.6ms
(common 60Hz refresh rate).
If you are not done by then, you’ll miss the frame
and the animation will appear janky.
To see how using Timeline can help you, run your favorite browser-based game, then open Developer Tools and record the Timeline while the game is running some animation. The Timeline Frame mode will now show you colored bars, each representing a frame. The colors correspond to different types of timeline events:
network activity and HTML parsing (blue)
running JavaScript (yellow)
performing style recalculation and layout (violet)
painting and compositing (green)
You can zoom in by selecting several frames or by clicking on a particular frame of interest. Looking at a specific frame in detailed view will show you the frame duration, and you can find more detailed statistics by hovering on it.
Even if your web app doesn’t have animation in it, the notion of a frame is still useful because the browser performs a repeated sequence of actions while processing input events such as keypress, mouse actions, scrolling etc. Leaving enough time to process such events inside a frame makes your app more
responsive and interactiv
e, resulting in a better overall experience for users.
In large web applications with huge DOM trees, layout typically takes time and resources. Doing it in a loop makes things much worse. So we’ve
added a warning mark on layouts that were forced, by requesting positional properties
(e.g. offsetWidth and offsetHeight) of DOM elements from JavaScript. If you hover over the layout event, you can see two stacks -- one that invalidated the DOM and another that caused layout synchronously. You can also see the area that had to be re-laid highlighted on the screen.
Finally, don’t forget that the
best practice
for dealing with animations is to use the
requestAnimationFrame
API, which guarantees that Chromium will call back your animation code in sync with the display refresh.
You can learn more about optimizing rendering performance of a page in
Tom Wiltzius’ article
on html5rocks.com. Follow
Google Chrome Developers
on Google+ or
@ChromiumDev
on Twitter for more news on Chrome Developer Tools.
Posted by Andrey Kosyakov, Software Engineer
Restricting extension APIs in legacy packaged apps
2012年11月15日木曜日
Even though Chrome extensions and
legacy packaged apps
are similar at a technical level, users have very different expectations for how extensions and apps should look and behave. Users expect extensions to interact with the whole browser, whereas they expect apps to act solely in their containing tab or window.
Until now, all Chrome legacy packaged apps could request the same permissions and use the same APIs as extensions to interact with Chrome. In order to make the capabilities of legacy packaged apps more closely align with user expectations, we’ve decided to limit the extensions permissions that legacy packaged apps can request.
Beginning this week, you won’t be able to publish legacy packaged apps in the Chrome Web Store that request any of the following permissions:
(a) any host permissions, including "
< all urls >
"
(b) the top-level "content_scripts" key
(c) the "debugger", "devtools", "pageCapture", "plugin", "proxy", "tabs'", "history", "webNavigation" permissions
(d) the top-level "npapi" key
Existing legacy packaged apps in the Chrome Web Store will not be affected, and those existing apps can continue to be updated without being subject to these new restrictions.
If you have questions, please get in touch with us on the
Chromium extensions
or
Chromium apps
groups.
Posted by Peter Ludwig, Product Manager
Backstage at JAM with Chrome
2012年11月8日木曜日
Earlier today
we launched
JAM with Chrome.
JAM with Chrome
is an interactive web application that enables friends in different locations to play music together in the Chrome browser on their computers.
JAM with Chrome was built with the
latest browser technologies
:
Web Audio
for high fidelity playback without resorting to lots of pre-recorded audio samples.
WebSockets
is used to deliver immediate real-time playback across all the members of the band ensuring they stay in sync and playing from the same tab sheet.
Finally,
CSS3
,
SVG
and
Canvas
provide rich visuals and an immersive experience.
To learn more about how we built this experience, check out “
How we made the Audio rock
”. This is the first of three HTML5 Rocks articles that describes how the team used Web Audio to deliver an absorbing auditory experience. Stay tuned for more developer stories by following
+Google Chrome Developers
.
Enjoy playing music with friends at
www.jamwithchrome.com
and be sure to open Chrome’s
developer tools
to see what’s going on backstage!
Posted by Paul Kinlan, Developer Advocate
A web developer’s guide to the latest Chrome Beta
2012年11月8日木曜日
Today’s Chrome
Beta channel release
includes a slew of awesome new developer features.
Datalist support in date and time
datalist
allows you to specify a list of suggested dates and times for input elements. Of course, users still have the freedom to enter arbitrary dates and times. One use case is helping users choose when their food should be ready for pickup:
MathML
Now you can write mathematical content in
MathML
and expect it to be consistently beautiful across the web. Special kudos to
WebKit
volunteer
Dave Barton
for implementing this on his own accord.
Other new features in this release
CSS custom filters
have landed behind a
flag
. They enable sweet cinematic effects like page flipping with just CSS and HTML. You can turn them on with
chrome://flags
.
Chromium now parses the
autocomplete
attribute
according to spec
. Use it to specify which type of saved user data the browser should use to prefill input elements. Examples are
name
and
street-address
.
A few brand new features landed with a prefix:
-webkit-hyphens
gives you more control over hyphenation at line breaks, and
-webkit-clip-path
enables you to
clip DOM content
to an SVG shape.
Un-prefixed APIs
APIs un-prefixed in today’s Beta release include:
IndexedDB
, a client-side storage API offering fast access to large amounts of structured data
Intl
, which adds support for JavaScript internationalization of date format, number format, collation and non-standard segmentation, and more time zones
postMessage
, a feature enabling cross-origin communication (including
support for fast transferable objects
)
requestAnimationFrame
for silky smooth JavaScript animations
performance.now()
for reliable, high-resolution timing
Today’s Beta release supports these APIs in both their prefixed and un-prefixed forms. If you’re currently using the prefixed versions, you should switch to the un-prefixed versions after today’s Beta release reaches the Stable channel. At that point the prefixed versions will be deprecated, and future releases may not support them.
Experiments removed in this release
As the web platform evolves, support for some experiments has been removed. The
Blob
constructor
should now be used instead of the
WebKitBlobBuilder A
PI, and the
Blob.webkitSlice()
method is deprecated in favor of
Blob.slice()
.
We also gathered a lot of valuable data and feedback from our experimental support for
Web Intents
and
decided to disable
the feature in today's Beta release.
Stay in the loop
Visit
chromestatus.com
for a complete overview of Chrome’s developer features, and circle
+Google Chrome Developers
for more frequent updates.
We hope you enjoy this Beta release as much as we’ve enjoyed working on it!
Posted by Peter Beverloo, Software Engineer and Web Platform Enthusiast
Introducing TCP Listen, a new API for Chrome packaged apps
2012年11月2日金曜日
Chrome packaged apps
aim to deliver an app experience with the appearance and capabilities of native apps, but built using the growing capabilities of HTML5. These apps can access APIs for better filesystem handling, direct access to hardware devices, raw network communication and
many others
. One of the new APIs that just landed in an experimental state is
TCP Listen
, which allows an app to accept incoming TCP connections.
Since the developer preview launch
earlier this year
, Chrome packaged apps have been able to connect to remote servers using TCP or UDP, and bind to a UDP port. For example, this
Media Center application
searches for and connects to media servers in the local network. Now, through the new TCP Listen API, a Chrome packaged app can also act as a TCP server itself and accept incoming connections on specified ports.
You can use this API, for example, to create a
HTTP server
on a development environment application, to
automate a browser window
for page load testing (see image below) or even to augment the
Media Center application
with a
DLNA®/UPnP
media server and show your PicasaWeb pictures on your DLNA® enabled television.
To get started, clone this
GitHub repository
and look at the
webserver
and the
TCP server
samples. You may also want to watch the
Chrome Apps Office Hours
where we specifically talk about the TCP Listen API.
We are curious to see what clever ideas you will come up with. Have questions or comments? Subscribe to
chromium-apps
and let us know!
Posted by Renato Mangini, Developer Advocate
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