HTTP debugging for Silverlight developers (Mac OS X edition)

ddietric — Mon, 08 Jun 2009 13:00:00 GMT

Many posts have been written about how to debug problems with issuing HTTP requests from Silverlight applications, particularly in the context of web services and WCF (see for example Debugging Web Service Usage in Silverlight 2 or Faults and Exceptions when using Web Services in Silverlight 2). As they point out there are severe limitations to what information is passed to applications in case of non-200 HTTP status codes. And they also point out that sometimes you need to know what requests and responses are exactly sent over the wire in order to figure out what's going on, usually mentioning Fiddler for doing so. It is a very powerful tool allowing you to not only monitor HTTP traffic from certain applications but also letting you manipulate requests and responses (which is probably more than you need for "simple" debugging anyway).

This is all great until you hit an issue that only seems to repro on that other platform. Using a Windows application to debug on Mac OS X is impractical at best (impossible would be the better word in this case though). So, what to use instead? For my personal application development I use Wireshark which some of you may have encountered in the past under its old name, Ethereal. There are, however, a couple of differences. Wireshark is open source released under the GPL 2 but more importantly it is a sniffer and not an "HTTP debugging proxy". This means that in comparison to Fiddler it does not necessarily "know" HTTP as well since to Wireshark it is just another high-level protocol. It also means that a typical Wireshark capture picks up much more traffic than we care for (not using promiscuous mode in case of shared medium topologies at least reduces the amount of noise in the capture).

Wireshark is an X11 application so be sure that you have X11 installed and that it is up-to-date. Also, the OS X version of Wireshark uses BPFs to capture network traffic; however, access to those is denied for all users except for root (see also Enabling and using the "root" user in Mac OS X) so their permissions need to be changed first. This has to be redone after every reboot. While automatically making these changes during every startup or login has some appeal to it I prefer making them manually when they are needed. Given the nature of BPFs, keeping them locked down seems like a good idea to me.

Now we're finally ready to start Wireshark. The first start of the application can take a while (if I remember correctly this is due to X11 filling its font cache) so be patient. Also, all builds I have tried so far greet you with a nice pop-up error message. Luckily just ignoring it doesn't cause any trouble at least not in case of what I'm talking about in this post. At this point you can start capturing by simply selecting an interface from the list.

As mentioned before, this will give you much more information than you need since you'll see all traffic sent to/from your machine or all traffic hitting your interface if you are using promiscuous mode which is on by default. The screenshot below indicates 12752 captured packets after about 100 seconds which shouldn't surprise you since unlike Fiddler which is only concerned about HTTP Wireshark is capturing Ethernet frames. The simplest way to get to the information you really care about is to filter for http which is also shown in the screenshot. There's a lot more you can do like filtering for source or destination address so pay a visit to the Wireshark Wiki.

Lastly I'd like to mention that you can view a packet in its own window by selecting the command Show Packet in New Window from the View menu or by simply double-clicking on a packet in case you're running the latest development release.

This posting is provided "AS IS" with no warranties, and confers no rights.

Setting up Silverlight 2 remote debugging on Mac OS X

ddietric — Thu, 06 Mar 2008 00:20:00 GMT

Let's face it: Silverlight is awesome! So are the Visual Studio Tools for Silverlight. One reason why it is so awesome is that you can run your applications on Windows and Mac OS X. But what if you need to debug an application while it is running on a Macintosh? Since there are no development tools for the Mac we have to resort to remote debugging which will allow us to debug the application running on OS X using Visual Studio on Windows. In order to do this we need to set up the CoreCLR debugging proxy on the Mac and then configure VS accordingly.

We start off by configuring the Mac. Everything we need on the Mac is part of the VS Tools for Silverlight installation and can be found in the directory %ProgramFiles%\Microsoft Visual Studio 9.0\Silverlight\MacIntel\ (or %ProgramFiles(x86)\Microsoft Visual Studio 9.0\Silverlight\MacIntel\ if you're running a 64-bit version of Windows). We just copy the whole folder over to the Mac e.g. into /Applications/ (you may also want to rename the copy on the Mac as MacIntel doesn't really describe the content that well). After that we have to mark the files configcoreclrdebug and coreclr_dbg_proxy as executable and then run configcoreclrdebug which will set up the debugging proxy and create a Windows executable containing all the information required to set up VS. It only requires two inputs: A port number in the range from 49152 to 65535 which will be used by the proxy to listen for incoming connections (you can also just hit Enter to accept the default in squared brackets) and a password used to protect the data in the Windows executable.

HOSTNAME:~ username$ cd /Applications/MacIntel/

HOSTNAME:MacIntel username$ ls -la

total 384

drwxr-x--- 6 username admin 204 Mar 3 05:25 .

drwxrwxr-x+ 42 root admin 1428 Mar 3 05:26 ..

-rw-r----- 1 username admin 62464 Mar 3 05:25 ConfigureWindowsCoreCLRDebuggingBase.exe

-rw-r----- 1 username admin 55383 Mar 3 05:25 MacDebuggingReadme.rtf

-rw-r----- 1 username admin 23604 Mar 3 05:25 configcoreclrdebug

-rw-r----- 1 username admin 48944 Mar 3 05:25 coreclr_dbg_proxy

HOSTNAME:MacIntel username$ chmod u+x configcoreclrdebug

HOSTNAME:MacIntel username$ chmod u+x coreclr_dbg_proxy

HOSTNAME:MacIntel username$ ./configcoreclrdebug

Generating debugger certificate and private key...

Done.

[...]

Select a TCP port number to be used for debugging: (49152-65535) [58752]:

[...]

Please specify a password at least eight characters long that will be used to

protect the debugging private key during transportation to the Windows machine

from which debugging will be performed.

Password:

Re-type password:

The CoreCLR debugging environment has been successfully configured on this

machine for the current user. In order to enable debugging from a remote machine

running Windows it will be necessary to propagate these same configuration

settings. To aid in this a Windows executable has been created in the following

file:

/Users/username/.coreclrdbg/ConfigureWindowsCoreCLRDebugging.exe

[...]

HOSTNAME:MacIntel username$

We now copy ConfigureWindowsCoreCLRDebugging.exe from the location mentioned in the output of configcoreclrdebug back to our Windows machine and execute it. All it will ask us for is the password we used to generate the executable.

C:\Users\username\Desktop>ConfigureWindowsCoreCLRDebugging.exe

Password: ********

This machine and user account has been successfully configured.

C:\Users\username\Desktop>

And we're done. We can now test this by creating a little app, copy the ClientBin folder over to the Mac and execute it there. Then we'll attach to it by using the Attach to Process... command from VS' Debug menu. We select CoreCLR Remote Cross-platform Debugging as the transport and enter the name or IP address of the Mac as the qualifier which will get us a list of the processes running on the remote machine. We just need to select the right instance of the web browser hosting the Silverlight runtime (its type will be CoreCLR Remote) and hit Attach. After that we can set breakpoints, check the value of variables and so on as usual.

This posting is provided "AS IS" with no warranties, and confers no rights.

Dennis "D.C." Dietrich : Mac OS X

HTTP debugging for Silverlight developers (Mac OS X edition)

Setting up Silverlight 2 remote debugging on Mac OS X