bug page 2 - Dave's Blog

Search
My timeline on Mastodon

A New Species Discovered ... On Flickr (npr.org)

2012 Aug 11, 9:17

Winterton, a senior entomologist at the California Department of Food and Agriculture, has seen a lot of bugs. But he hadn’t seen this species before.

There’s no off switch when you’re the senior entomologist. If you’re browsing the web you find your way to Flickr photos of insects or start correcting Wikipedia articles on insects.

PermalinkCommentsflickr insect science photos

The Fiddler Book: "Debugging with Fiddler: The official reference from the developer of Fiddler"

2012 Jun 23, 9:19

THE Fiddler Book straight from the source, EricLaw - the developer of Fiddler!

Fiddler is a wonderful tool with never ending extensibility. With this book I shall master it!

PermalinkCommentstechnical programming book ericlaw fiddler http

Sometimes the bug isn't in your code, it's in the CPU (dragonflybsd.org)

2012 Mar 7, 8:00

Fascinating, but really most of the time it is in your code.  Really you should look there first.  Usually not the compiler’s fault, or the OS’s fault, or a loose wire in the CPU…

PermalinkCommentstechnical programming cpu

Show request's timestamp in Fiddler? - Stack Overflow

2012 Jan 13, 2:33PermalinkCommentstechnical fiddler http debug tool timestamp

Bug Spotting: Ctors with default parameters

2011 Dec 1, 4:59

The following code compiled just fine but did not at all act in the manner I expected:

BOOL CheckForThing(__in CObj *pObj, __in IFigMgr* pFigMgr, __in_opt LPCWSTR url)
{
BOOL fCheck = FALSE;
if (SubCheck(pObj))
{
...
I’m calling SubCheck which looks like:
bool SubCheck(const CObj& obj);

Did you spot the bug? As you can see I should be passing in *pObj not pObj since the method takes a const CObj& not a CObj*. But then why does it compile?

It works because CObj has a constructor with all but one param with default values and CObj is derived from IUnknown:

CObj(__in_opt IUnknown * pUnkOuter, __in_opt LPCWSTR pszUrl = NULL);
Accordingly C++ uses this constructor as an implicit conversion operator. So instead of passing in my CObj, I end up creating a new CObj on the stack passing in the CObj I wanted as the outer object which has a number of issues.

The lesson is unless you really want this behavior, don't make constructors with all but 1 or 0 default parameters. If you need to do that consider using the 'explicit' keyword on the constructor.

More info about forcing single argument constructors to be explicit is available on stack overflow.

PermalinkCommentsc++ technical bug programming

URI Empty Path Segments Matter

2011 Nov 23, 11:00

Shortly after joining the Internet Explorer team I got a bug from a PM on a popular Microsoft web server product that I'll leave unnamed (from now on UWS). The bug said that IE was handling empty path segments incorrectly by not removing them before resolving dotted path segments. For example UWS would do the following:

A.1. http://example.com/a/b//../
A.2. http://example.com/a/b/../
A.3. http://example.com/a/
In step 1 they are given a URI with dotted path segment and an empty path segment. In step 2 they remove the empty path segment, and in step 3 they resolve the dotted path segment. Whereas, given the same initial URI, IE would do the following:
B.1. http://example.com/a/b//../
B.2. http://example.com/a/b/
IE simply resolves the dotted path segment against the empty path segment and removes them both. So, how did I resolve this bug? As "By Design" of course!

The URI RFC allows path segments of zero length and does not assign them any special meaning. So generic user agents that intend to work on the web must not treat an empty path segment any different from a path segment with some text in it. In the case above IE is doing the correct thing.

That's the case for generic user agents, however servers may decide that a URI with an empty path segment returns the same resource as a the same URI without that empty path segment. Essentially they can decide to ignore empty path segments. Both IIS and Apache work this way and thus return the same resource for the following URIs:

http://exmaple.com/foo//bar///baz
http://example.com/foo/bar/baz
The issue for UWS is that it removes empty path segments before resolving dotted path segments. It must follow normal URI procedure before applying its own additional rules for empty path segments. Not doing that means they end up violating URI equivalency rules: URIs (A.1) and (B.2) are equivalent but UWS will not return the same resource for them.
PermalinkCommentsuser agent url ie uri technical web browser

Features of image type input tags in HTML

2011 Nov 21, 11:00

A bug came up the other day involving markup containing <input type="image" src="http://example.com/.... I knew that "image" was a valid input type but it wasn't until that moment that I realized I didn't know what it did. Looking it up I found that it displays the specified image and when the user clicks on the image, the form is submitted with an additional two name value pairs: the x and y positions of the point at which the user clicked the image.

Take for example the following HTML:

<form action="http://example.com/">
<input type="image" name="foo" src="http://deletethis.net/dave/images/davebefore.jpg">
</form>
If the user clicks on the image, the browser will submit the form with a URI like the following:http://example.com/?foo.x=145&foo.y=124.

This seemed like an incredibly specific feature to be built directly into the language when this could instead be done with javascript. I looked a bit further and saw that its been in HTML since at least HTML2, which of course makes much more sense. Javascript barely existed at that point and sending off the user's click location in a form may have been the only way to do something interesting with that action.

PermalinkCommentsuri technical form history html

Chris Harrison | A New Angle on Cheap LCDs

2011 Oct 25, 5:33
Its not a bug -- its a feature! Very cool unread mail demo.
PermalinkCommentstechnical

Bug Spotting: Smart pointers and parameter evaluation order

2011 Oct 19, 5:58PermalinkCommentsc++ technical bug programming smart-pointer cpp

Thread Local Storage, part 1: Overview « Nynaeve

2011 Aug 6, 1:53Description of the inner workings of both of Window's TLS options, the Win32 APIs like TlsAlloc as well as __declspec(thread). I didn't know that the max number of TLS indices is now 1088.PermalinkCommentsblog programming development windows debug tls thread-local-storage

WPAD Server Fiddler Extension Update v1.0.1

2011 Jun 12, 3:34
As it turns out the WPAD Server Fiddler Extension I made a while back actually has a non-malicious purpose. Apparently its useful for debugging HTTP on the WP7 phone (or so I'm told). Anyway I took some requests and I've fixed a few minor bugs (start button not updating correctly), changed the dialog to be a Fiddler tab so you can use it non-modally, and the WPAD server is now always off when Fiddler starts.
PermalinkCommentsextension fiddler technical update wpad

Re: [FileAPI] File.slice spec bug from Jonas Sicking on 2011-04-12 (public-webapps@w3.org from April to June 2011)

2011 Apr 14, 11:27If only all web compat issues were so easily fixed: "If someone knows about any websites I can personally take care of contacting them and trying to get them fixed."PermalinkCommentsw3c reference file api standard

An Analysis of Browser Domain-Isolation Bugs

2010 Oct 28, 7:49PermalinkCommentsdavid-ross security browser research web webbrowser technical todo system:filetype:pdf system:media:document

High Performance Web Sites :: HAR to Page Speed

2010 May 2, 2:52'HAR to Page Speed' is a tool that takes a HAR file (Http ARchive) supported by various HTTP debuggers and produces a page speed score. This is a great example of the value of a cross HTTP debugger file format.PermalinkCommentshttp tool debug performance web technical

HTML 5 Video Seeking and Redirects

2010 Apr 26, 3:09Firefox developer on the topic of HTML5 video and the issues of using HTTP range requests to seek within an HTML5 video.PermalinkCommentshtml html5 http range technical video firefox web browser bug code programming

The Old New Thing : Advantages of knowing your x86 machine code

2010 Feb 19, 2:27Raymond's tips for modifying x86 assembly code while debugging.PermalinkCommentstutorial debug debugging technical assembly x86 windows raymond-chen tips

Annotated x64 Disassembly

2010 Feb 19, 2:26A short tutorial on debugging amd64 assemblyPermalinkCommentsmicrosoft tutorial msdn debug debugging technical assembly x64 amd64 windows documentation

Annotated x86 Disassembly

2010 Feb 19, 2:25A short tutorial on debugging x86 assembly code.PermalinkCommentsmicrosoft tutorial msdn debug debugging technical assembly x86 windows documentation

WPAD Server Fiddler Extension

2010 Jan 5, 7:42

I've made a WPAD server Fiddler extension and in a fit of creativity I've named it: WPAD Server Fiddler Extension.

Of course you know about Fiddler, Eric's awesome HTTP debugger tool, the HTTP proxy that lets you inspect, visualize and modify the HTTP traffic that flows through it. And on the subject you've probably definitely heard of WPAD, the Web Proxy Auto Discovery protocol that allows web browsers like IE to use DHCP or DNS to automatically discover HTTP proxies on their network. While working on a particularly nasty WPAD bug towards the end of IE8 I really wished I had a way to see the WPAD requests and responses and modify PAC responses in Fiddler. Well the wishes of me of the past are now fulfilled by present day me as this Fiddler extension will respond to WPAD DHCP requests telling those clients (by default) that Fiddler is their proxy.

When I started working on this project I didn't really understand how DHCP worked especially with respect to WPAD. I won't bore you with my misconceptions: it works by having your one DHCP server on your network respond to regular DHCP requests as well as WPAD DHCP requests. And Windows I've found runs a DHCP client service (you can start/stop it via Start|Run|'services.msc', scroll to DHCP Client or via the command line with "net start/stop 'DHCP Client'") that caches DHCP server responses making it just slightly more difficult to test and debug my extension. If a Windows app uses the DHCP client APIs to ask for the WPAD option, this service will send out a DHCP request and take the first DHCP server response it gets. That means that if you're on a network with a DHCP server, my extension will be racing to respond to the client. If the DHCP server wins then the client ignores the WPAD response from my extension.

Various documents and tools I found useful while working on this:

PermalinkCommentsproxy fiddler http technical debug wpad pac tool dhcp

Developing on a Device | Android Developers

2009 Dec 26, 7:11Wow, that was easy to setup. After installing the driver Eclipse just asks me if I want to debug on my phone or my virtual device.PermalinkCommentstechnical reference android programming development cellphone g1 documentation google
Older EntriesNewer Entries Creative Commons License Some rights reserved.