ws page 30 - Dave's Blog

Outline View Internet Explorer Extension

I've made another extension for IE8, Outline View, which gives you a side bar in IE that displays an outline of the current page and lets you make intrapage bookmarks.

The outline is generated based on the heading tags in the document (e.g. h1, h2, etc), kind of like what W3C's Semantic data extractor tool displays for an outline. So if the page doesn't use heading tags the way the HTML spec intended or just sticks img tags in them, then the outline doesn't look so hot. On a page that does use headings as intended though it looks really good. For instance a section from the HTML 4 spec shows up quite nicely and I find its actually useful to be able to jump around to the different sections. Actually, I've been surprised going to various blogs how well the outline view is actually working -- I thought a lot more webdevs would be abusing their heading tags.

I've also added intrapage bookmarks. When you make a text selection and clear it, that selected text is added as a temporary intrapage bookmark which shows up in the correct place in the outline. You can navigate to the bookmark or right click to make it permanent. Right now I'm storing the permanent intrapage bookmarks in IE8's new per-domain DOM storage because I wanted to avoid writing code to synchronize a cross process store of bookmarks, it allowed me to play with the DOM storage a bit, and the bookmarks will get cleared appropriately when the user clears their history via the control panel.

Internet Explorer 8 Released

IE8, the software I've been working on for some time now, has finally been released at MIX09.

• Download IE8.
• Dean's MIX09 Keynote releasing IE8 is viewable here.
• Louis pointed me to this humorous IE8 advertising that doesn't make me cringe. On the contrary it has Ask a Ninja, Janeane Garofalo, and several comedians I recall collectively from either 'I Love the [decade]' or 'Best Week Ever'.
• It seems like only a year ago that IE8 Beta was released.
• IE Blog: IE8 Released.

Notes on Creating Internet Explorer Extensions in C++ and COM

Working on Internet Explorer extensions in C++ & COM, I had to relearn or rediscover how to do several totally basic and important things. To save myself and possibly others trouble in the future, here's some pertinent links and tips.

First you must choose your IE extensibility point. Here's a very short list of the few I've used:

• Explorer Bars and IE Toolbars
• IE Tools, IE Help, and IE Context Menu menu items
• IE Toolbar Buttons

Once you've created your COM object that implements IObjectWithSite and whatever other interfaces your extensibility point requires as described in the above links you'll see your SetSite method get called by IE. You might want to know how to get the top level browser object from the IUnknown site object passed in via that method.

After that you may also want to listen for some events from the browser. To do this you'll need to:

1. Implement the dispinterface that has the event you want. For instance DWebBrowserEvents2, or HTMLDocumentEvents, or HTMLWindowEvents2. You'll have to search around in that area of the documentation to find the event you're looking for.
2. Register for events using AtlAdvise. The object you need to subscribe to depends on the events you want. For example, DWebBrowserEvents2 come from the webbrowser object, HTMLDocumentEvents come from the document object assuming its an HTML document (I obtained via get_Document method on the webbrowser), and HTMLWindowEvents2 come from the window object (which oddly I obtained via calling the get_script method on the document object). Note that depending on when your SetSite method is called the document may not exist yet. For my extension I signed up for browser events immediately and then listened for events like NavigateComplete before signing up for document and window events.
3. Implement IDispatch. The Invoke method will get called with event notifications from the dispinterfaces you sign up for in AtlAdvise. Implementing Invoke manually is a slight pain as all the parameters come in as VARIANTs and are in reverse order. There's some ATL macros that may make this easier but I didn't bother.
4. Call AtlUnadvise at some point -- at the latest when SetSite is called again and your site object changes.

If you want to check if an IHTMLElement is not visible on screen due how the page is scrolled, try comparing the Body or Document Element's client height and width, which appears to be the dimensions of the visible document area, to the element's bounding client rect which appears to be its position relative to the upper left corner of the visible document area. I've found this to be working for me so far, but I'm not positive that frames, iframes, zooming, editable document areas, etc won't mess this up.

Be sure to use pointers you get from the IWebBrowser/IHTMLDocument/etc. only on the thread on which you obtained the pointer or correctly marshal the pointers to other threads to avoid weird crashes and hangs.

Obtaining the HTML document of a subframe is slightly more complicated then you might hope. On the other hand this might be resolved by the new to IE8 method IHTMLFrameElement3::get_contentDocument

Check out Eric's IE blog post on IE extensibility which has some great links on this topic as well.

The 'Is It UTF-8?' Quick and Dirty Test

I've found while debugging networking in IE its often useful to quickly tell if a string is encoded in UTF-8. You can check for the Byte Order Mark (EF BB BF in UTF-8) but, I rarely see the BOM on UTF-8 strings. Instead I apply a quick and dirty UTF-8 test that takes advantage of the well-formed UTF-8 restrictions.

Unlike other multibyte character encoding forms (see Windows supported character sets or IANA's list of character sets), for example Big5, where sticking together any two bytes is more likely than not to give a valid byte sequence, UTF-8 is more restrictive. And unlike other multibyte character encodings, UTF-8 bytes may be taken out of context and one can still know that its a single byte character, the starting byte of a three byte sequence, etc.

The full rules for well-formed UTF-8 are a little too complicated for me to commit to memory. Instead I've got my own simpler (this is the quick part) set of rules that will be mostly correct (this is the dirty part). For as many bytes in the string as you care to examine, check the most significant digit of the byte:

F:

This is byte 1 of a 4 byte encoded codepoint and must be followed by 3 trail bytes.

E:

This is byte 1 of a 3 byte encoded codepoint and must be followed by 2 trail bytes.

C..D:

This is byte 1 of a 2 byte encoded codepoint and must be followed by 1 trail byte.

8..B:

This is a trail byte.

0..7:

This is a single byte encoded codepoint.

Subst Allows Non-Letter Drive Letters

I knew that the command line tool subst would create virtual drives that map to existing directories but I didn't know that subst lets you name the virtual drives with characters that aren't US-ASCII letters. For instance you can run 'subst 4: C:\windows' and then 'more 4:\win.ini' to dump C:\windows\win.ini. This also works for non-US-ASCII characters like, "Ｃ" (aka U+FF23, Fullwidth Latin Capital Letter C), which when displayed by cmd.exe via some best fit style character conversions looks just like the regular US-ASCII 'C'. None of Explorer, IE, or the common file dialogs allow the use of these odd virtual drives -- just cmd.exe, so I'm not sure how this would ever be useful but I thought it was odd and I wanted to share.