[webkit-dev] Determine whether all resources have been successfully loaded

Plessl Christian christian at plesslweb.ch
Fri Aug 3 01:50:13 PDT 2007

Hi Webkit developers

I have posted this question a couple of weeks ago on the webkit-sdk  
mailinglist, but did not get any answer. I assume that subscribers of  
this list are more familiar with the implementation of webkit and  
might know the answer.

I'm working on a command-line applications that uses WebKit for  
creating PDF documents from webpages (http://wkpdf.plesslweb.ch).

While I found WebKit intuitive to use, I'm stuck with a seemingly  
simple problem: how can I check, whether all resources referenced by  
a webpage have been loaded successfully?

To get information about the loading of frames and resources, I'm  
implementing the following delegate methods.

  WebResourceLoadDelegate methods:

  - webView:identifierForInitialRequest:fromDataSource:
  - webView:resource:didFinishLoadingFromDataSource:
  - webView:resource:didFailLoadingWithError:fromDataSource:

  WebFramLoadDelegate methods:

  - webView:didStartProvisionalLoadForFrame:(WebFrame *)frame;
  - webView:didFinishLoadForFrame:
  - webView:didCommitLoadForFrame:
  - webView:didFailLoadWithError:forFrame:
  - webView:didFailProvisionalLoadWithError:forFrame:

The problem is, that didFinishLoadingFromDataSource is called, _even_  
if not all resources could be loaded successfully.

I have created a minimal test case to show you what I mean.

The main function creates a WebView, adds delegates, and load the URL  
request like this:

   WebView * webView = [[WebView alloc] initWithFrame:NSMakeRect 
   [webView setFrameLoadDelegate: controller];
   [webView setResourceLoadDelegate: controller];
   NSURLRequest * request = ... @"test_missing_frame.html"
		[[webView mainFrame] loadRequest:request];

The HTML file test_missing_frame.html is a frameset referencing two  
frames (frame1.html,frame2.html), where frame2 references a missing  
resource. The code for these HTML files is shown below.

I have instrumented all delegate methods to generate a trace listing  
the call sequence and the most important arguments to the delegate  
calls. identifierForInitialRequest returns an identifier that  
contains a unique number and the name of the resource:

     didStartProvisionalLoadForFrame myFrame
     identifierForInitialRequest -> (id:0 (http://xxx/ 
     didCommitLoadForFrame myFrame
     didStartProvisionalLoadForFrame f1
     identifierForInitialRequest -> (id:1 (http://xxx/frame1.html))
     didStartProvisionalLoadForFrame f2
     identifierForInitialRequest -> (id:2 (http://xxx/frame2.html))
     didFinishLoadingFromDataSource id: id:0 (http://xxx/ 
     didCommitLoadForFrame f1
     didFinishLoadForFrame f1
     didFinishLoadingFromDataSource id: id:1 (http://xxx/frame1.html)
     didCommitLoadForFrame f2
     identifierForInitialRequest -> (id:3 (http://xxx/missing.jpg))
     didFinishLoadingFromDataSource id: id:2 (http://xxx/frame2.html)
->  didFinishLoadForFrame f2
->  didFinishLoadForFrame myFrame
->  didFinishLoadingFromDataSource id: id:3 (http://xxx/missing.jpg)

This call sequence shows 3 surprises (or bugs):

  1) didFinishLoadingFromDataSource is also called for the _missing_  
resource. I would have expected that didFailLoadingWithError is called

  2) didFinishLoadForFrame myFrame is called, before all resources of  
frame f2 have been loaded

  3) didFinishLoadForFrame is called although the load was not  
successfull although. This contradicts Apple's documentation that  
says: "This method is invoked when a location request for frame has  
successfully; that is, when all the resources are done  
loading." (Although the first part of this sentence is unclear and  

What is the recommended way to find out, whether all resources have  
been loaded successfully?

Did I misunderstand something or is this a bug in WebKit? Should I  
file a bugreport with WebKit?

I would appreciate any help.


-- test_missing_frame.html ---------------
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
	<title>missing resources test</title>
<frameset cols="200,*">
	<frame src="frame1.html" name="f1">
   <frame src="frame2.html" name="f2">

-- frame1.html ---------------------------
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
   <h1>This is frame1</h1>
   <p>No resource is missing for this frame!</p>

-- frame2.html ---------------------------
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
   <h1>This is frame2</h1>
   <p>There is 1 resource missing for this frame.<img  

Christian Plessl christian at plesslweb.ch http://plesslweb.ch

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