[webkit-dev] WebKit blog post proposal: Remote debugging with Web Inspector.
Pavel Feldman
pfeldman at chromium.org
Sat Apr 30 22:11:42 PDT 2011
I see. It might be unfortunate branding, but the large amount of Web
Inspector users refer to it as "Developer Tools". We use every opportunity
to tell users that it is the same thing, but this is not enough. The first
question we always get is "Do you guys upstream any of your Chrome Dev Tools
code into the WebKit?". Which sounds crazy, because 100% of the code is
upstream. So it is probably just me trying to use both names to fix this. It
sounds like I should be more formal in this case and make the letter of the
post conform to its WebKit spirit.
- I changed the phrasing to use "Web Inspector" only, there is no mention of
"Chrome Dev Tools" anymore.
- Removed all "Chrome" mentions as well
- There is now single mention of "Chromium" in the example scenario that I
am eager to keep. I truly believe that the example makes the post more
lively. There is nothing easier than posting this whole thing at
chromium.org, but it will harm the "unified WebKit Remote Debugging
Protocol" message we are trying to deliver.
<provocative>In return, can I ask to rename the WebKit blog from "Surfin'
Safari" to something more WebKit-specific?</provocative>
So here is another update (posting the first topics that have changed).
Mark, Evan, do you think it is better now?
WebKit Remote Debugging <http://www.webkit.org/blog/?p=1620>Posted by *Pavel
Feldman* on Saturday, April 30th, 2011 at 10:06 pm
As you might know, WebKit Web Inspector is implemented as an HTML + CSS +
JavaScript web application. What you might not know is that Web Inspector
can run outside of the rendering engine environment and still provide
complete set of its features to the end user.
Debugging over the wire
Running debugger outside the rendering engine is interesting because mobile
platforms do not often provide enough screen real estate for quality
debugging; they have network stack and CPU specifics that often affect page
load and runtime. Still, they are based on the WebCore rendering engine,
they could have Web Inspector instrumentation running and hence expose
valuable debugging information to the end user. Now that Web Inspector is
functioning out-of-process over the serialized-message-channel, attaching
Web Inspector window to the remote rendering engine is possible. Here is an
example of the remote debugging session using Chromium:
1. Start your target browser with the remote-debugging-port command line
switch:
Chromium --remote-debugging-port=9222
2. Open several pages there.
3. Navigate to the given port from your client browser instance (WebKit
nightly will do) and it will list inspectable pages opened in the browser as
web links.
[image: Tab discovery page]
4. Follow any of these links to start remote debugging session for the
corresponding page.
[image: Tab attached page]
You will find remote debugging interface very similar to the Web Inspector
and here is why:
- Target browser acts as a web server bound to the port 9222 on the
localhost.
- Once you follow the link, your client browser fetches HTML, JavaScript
and CSS files of the Web Inspector front-end over HTTP.
- Upon load event, Web Inspector establishes Web Socket connection back
to the target browser and starts interchanging JSON messages with it.
In fact, pretty much the same scenario takes place within any WebKit-based
browser when user opens Web Inspector. The only difference is that the
transports being used for the JSON message interchange may vary. Note, that
in case of mobile devices, front-end files can also be served from the
cloud.
On Sun, May 1, 2011 at 1:32 AM, Evan Martin <evan at chromium.org> wrote:
> I think Mark's point was more about phrasing like "WebKit Web Inspector
> (aka Chrome Developer Tools)" or "You will find remote debugging interface
> very similar to the Web Inspector / Chrome Developer Tools and here is
> why: Target Chrome browser acts as". I think that objection is reasonable.
>
> Perhaps you could rearrange the post to be solely about the WebKit-specific
> parts, and include a link to a Chrome blog post with details for Chrome
> users.
>
>
> On Sat, Apr 30, 2011 at 3:23 AM, Mark Rowe <mrowe at apple.com> wrote:
>
>> This seems rather Chrome-centric for a webkit.org blog post.
>>
>> - Mark
>>
>> On 2011-04-30, at 01:55, Pavel Feldman wrote:
>>
>> An update.
>>
>> Pavel
>>
>> WebKit Remote Debugging <http://www.webkit.org/blog/?p=1620> Posted by *Pavel
>> Feldman* on Saturday, April 30th, 2011 at 1:53 am
>>
>> As you might know, WebKit Web Inspector (aka Chrome Developer Tools) is
>> implemented as an HTML + CSS + JavaScript web application. What you might
>> not know is that Web Inspector can run outside of the rendering engine
>> environment and still provide complete set of its features to the end user.
>> Debugging over the wire
>>
>> Running debugger outside the rendering engine is interesting because
>> mobile platforms do not often provide enough screen real estate for quality
>> debugging; they have network stack and CPU specifics that often affect page
>> load and runtime. Still, they are based on the WebCore rendering engine,
>> they could have Web Inspector instrumentation running and hence expose
>> valuable debugging information to the end user. Now that Web Inspector is
>> functioning out-of-process over the serialized-message-channel, attaching
>> Web Inspector window to the remote rendering engine is possible. Here is an
>> example of the remote debugging session using Chrome Developer Tools:
>>
>> 1. Start your target browser (recent Chromium build or Google Chrome will
>> do) with the remote-debugging-port command line switch:
>>
>> Chromium.app/Contents/MacOS/Chromium --remote-debugging-port=9222
>>
>> 2. Open several pages there.
>>
>> 3. Navigate to the given port from your client browser instance (WebKit
>> nightly or another Chrome instance will do) and it will list inspectable
>> pages opened in the browser as web links.
>> [image: Tab discovery page]
>>
>> 4. Follow any of these links to start remote debugging session for the
>> corresponding page.
>> [image: Tab attached page]
>>
>> You will find remote debugging interface very similar to the Web Inspector
>> / Chrome Developer Tools and here is why:
>>
>> - Target Chrome browser acts as a web server bound to the port 9222 on
>> the localhost.
>> - Once you follow the link, your client browser fetches HTML,
>> JavaScript and CSS files of the Developer Tools front-end over HTTP.
>> - Upon load event, Developer Tools establishes Web Socket connection
>> back to the target browser and starts interchanging JSON messages with it.
>>
>> In fact, pretty much the same scenario takes place within any WebKit-based
>> browser when user opens Web Inspector. The only difference is that the
>> transports being used for the JSON message interchange may vary. Note, that
>> in case of mobile devices, front-end files can also be served from the
>> cloud.
>> Remote Debugging Protocol
>>
>> Another scenario for remote debugging is IDE integration. Web IDEs would
>> like to provide seamless debugging experience integrated into their
>> environments to the end user. Exposing unified WebKit remote debugging
>> protocol would allow them to use alternate front-ends for the WebKit
>> debugging.
>>
>> Under the hood, Web Inspector front-end is talking to the browser backend
>> by means of the Remote Debugging Protocol. This protocol is based on the JSON-RPC
>> 2.0 <http://groups.google.com/group/json-rpc/web/json-rpc-2-0> specification.
>> It is bidirectional: clients send asynchronous requests to the server,
>> server responds to these requests and/or generates notifications. Since API
>> surface for general purpose web debugging is huge, we divided it into a
>> number of domains. Each domain contains requests and notifications specific
>> to some area. Here is the list of the domains supported so far:
>>
>> - *Browser Debugger* – allows setting breakpoints on particular DOM
>> operations and events. JavaScript execution will stop on these operations as
>> if there was a regular breakpoint set.
>> - *Console* – defines methods and events for interaction with the
>> JavaScript console.
>> - *CSS* – exposes raw CSS read / write operations.
>> - *Debugger* – exposes JavaScript debugging functions; allows setting
>> and removing breakpoints, stepping through execution, exploring stack
>> traces, etc.
>> - *DOM* – This domain exposes DOM read/write operations.
>> - *Network* – allows tracking network activities of the page; exposes
>> information about HTTP and WebSocket requests and responses, their headers,
>> bodies, raw timing, etc.
>> - *Page* – actions and events related to the inspected page.
>> - *Runtime* – exposes JavaScript runtime by means of remote evaluation
>> and mirror objects.
>> - *Timeline* – provides its clients with instrumentation records that
>> are generated during the page runtime.
>>
>> You can find JSON schema defining the protocol here<http://trac.webkit.org/browser/trunk/Source/WebCore/inspector/Inspector.json>.
>> For your convenience, we generated documentation from this schema and
>> published it on the Chrome DevTools page<http://code.google.com/chrome/devtools/docs/remote-debugging.html>.
>> Note that there are few unlisted domains such as Application Cache, DOM
>> Storage, and Database, but they are not ready for the prime time yet.
>> What’s next
>>
>> We are now open to the feedback on the WebKit Remote Debugging Protocol.
>> We will collect all the feedback in the form of the bug reports<http://webkit.org/new-inspector-bug> and
>> the Chrome DevTools forum<http://groups.google.com/group/google-chrome-developer-tools> messages.
>> We will then address initial feedback, polish the protocol a bit and publish
>> its first draft with a specific version. Once we have the protocol defined,
>> developers can come up with the alternate front-ends (IDEs and such) that
>> will interact with the WebKit instrumentation running in various browsers.
>> We also expect all the WebKit ports to expose WebSocket interfaces similar
>> to explained above or to come up with any other transport and bridge it with
>> the Web Inspector front-end. Stay tuned!
>> - Show quoted text -
>> Comments are closed.
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>
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