Archive for August, 2009

Writing Data-Driven Custom Actions

Whenever Windows Installer’s built-in actions do not suffice to perform a specific task, a Custom Action needs to be written. Needless to say, Custom Actions, can be a bit tricky — not only can they be laborious to write and cumbersome to debug, they also run the risk of interfering with Windows Installer’s declarative, transactional way of performing installs.

It is not really surprising that Windows Installer therefore more or less discourages the use of Custom Actions unless it is absolutely necessary. Moreover, as a result of its declarative nature, it is understadable that Windows Installer prefers Custom Actions to be data-driven.

What this means in practice is that a Custom Action should not perform a hard-coded task — rather, it should query one or more (custom) tables containing the necessary information (in a declarative manner) about what is to be performed and should act accordingly.

Using WiX, creating custom tables turns out to be pretty easy. Let’s assume we create a Custom Action that, based on some condition, does something with a specific file. An appropriate table could look like this:

<CustomTable Id="MyCustomTable">
  <Column Id="Id" Type="string" PrimaryKey="yes"/>
  <Column Id="Path" Type="string"/>
  <Column Id="Condition" Type="string"/>

    <Data Column="Id">Foo</Data>
    <Data Column="Path">[INSTALLLOCATION]foo.txt</Data>
    <Data Column="Condition"><![CDATA[ &FeatureFoo=3 ]]></Data>
    <Data Column="Id">Bar</Data>
    <Data Column="Path">[INSTALLLOCATION]bar.txt</Data>
    <Data Column="Condition"><![CDATA[ &FeatureBar=3 ]]></Data>

To query this table, we have to open a view and fetch the records one by one:

PMSIHANDLE Database = MsiGetActiveDatabase( InstallHandle );
ASSERT( Database != NULL );

UINT Result = MsiDatabaseOpenView(
  L"SELECT `Condition`, `Path`, FROM `MyCustomTable`",
  &View );
if ( ERROR_SUCCESS != Result )

Result = MsiViewExecute( View, NULL );
if ( ERROR_SUCCESS != Result )

for ( ;; )
  Result = MsiViewFetch( View, &Record );
  if ( Result == ERROR_NO_MORE_ITEMS  )
  else if ( ERROR_SUCCESS != Result )

  // Read condition. 
  // N.B. Do not format -- this is done by 
  // MsiEvaluateCondition itself.

  WCHAR Condition[ 256 ];
  DWORD Length = _countof( Condition );
  Result = MsiRecordGetString(
    &Length );
  if ( ERROR_SUCCESS != Result )

  if ( MSICONDITION_TRUE != MsiEvaluateCondition(
    Condition ) )
    // This record can be skipped.

  // Read remaing fields.

  Length = _countof( VszPath );
  Result = GetFormattedRecord(
    &Length );
  if ( ERROR_SUCCESS != Result )


With GetFormattedRecord being the following utility routine:

static UINT GetFormattedRecord(
  __in MSIHANDLE InstallHandle,
  __in MSIHANDLE Record,
  __in UINT Field,
  __out PWSTR Value,
  __inout PDWORD Length
  DWORD RecLength = *Length;
  UINT Result = MsiRecordGetString(
    &RecLength );
  if ( ERROR_SUCCESS != Result )
    *Length = RecLength;
    return Result;

  PMSIHANDLE FormattingRecord = MsiCreateRecord( 1 );
  Result = MsiRecordSetString( FormattingRecord, 0, Value );
  if ( ERROR_SUCCESS != Result )
    return Result;

  return MsiFormatRecord(
    Length );

Some things are worth noting:

  • I use PMSIHANDLE, which, as you probably already know, is not a typedef for MSIHANDLE* but rather a smart-pointer like class that automatically closes the handle when it goes out of scope.
  • The use of backticks in the query.
  • It must have been a Visual Basic programmer implementing MsiRecordGetString: Field Indexes start with 1, not 0. To make matters worse, reading from index 0 does not fail but returns arbitrary data. Finally, to confuse people further, indexes are 0-based for MsiRecordSetString.
  • If the field contains formatted data, you have to MsiFormatRecord it yourself. For conditions, however, MsiEvaluateCondition handles that for you.

So far, so good. There is, however, one thing to notice: To access the installer database, the custom action must be a nondeferred action:

You cannot access the current installer session or all property data from a deferred execution custom action

The problem with nondeferred actions, however, is that they execute in user context — in contrast to deferred actions, which execute in system context. On pre-Vista platforms, a per-machine installer package can be expected to always be launched by an administrator (otherwise it will fail anyway) — in this case, the differences between user and system context may not be important — both, for example, have r/w access to files in %ProgramFiles%. On Vista and later OS, however, it is common to have a regular user launch an installation which causes an elevation prompt once it reaches the main install phase. In this case, the user context is significantly less privileged than system context.

For a hypothetical custom action that is intended to edit a file installed to %ProgramFiles%, this means that (disregarding rollback considerations and assuming proper scheduling) performing this action from within the nondeferred custom action will work fine on pre-Vista OS. When run on Vista, though, it is likely to fail due to lack of write access to %ProgramFiles%. In practice, this means that all system-changing tasks usually have to be performed by a deferred action.

To sum up: To be data-driven, you have to use nondeferred actions. To be able to perform any serious, system state-changing tasks, however, you have to use deferred actions.


As it turns out, however, there is a way to escape this catch-22, and it is carefully buried in the Windows Installer documentation:

[…] Actions that update the system, such as the InstallFiles and WriteRegistryValues actions, cannot be run by calling MsiDoAction. The exception to this rule is if MsiDoAction is called from a custom action that is scheduled in the InstallExecuteSequence table between the InstallInitialize and InstallFinalize actions. […]

[From the Remarks section of MsiDoAction]

In fact, the way I came across this solution was by looking at the source code of the WiX XmlFile action, which I knew manages to both be data-driven (uses a custom table) and alter system state (edits XML files). The way it does this, and the point where the above remark comes into play, is as follows: In the nondeferred action, you do not perform any actions changing system state. Rather, you collect the information from the installer tables and stuff it (yuck) into the CustomActionData property. Then, leveraging MsiDoAction and passing said CustomActionData, you schedule another custom action — this time a deferred one — which parses the CustomActioData (yuck) and, based on this data, finally performs the actual modifications — in system context.

It really could not be easier and more intuitive, right?


Overview on Designing High-Performance Windows Applications

Back in 2008, the Windows Server Performance Team Blog, which I came across recently, ran a series of posts on Designing Applications for High Performance:

If you are interested in developing server side applications for Windows, these articles are definitely worth reading.

Vote for cfix

The Automated Testing Institute has elected cfix to be one of the finalists for the Autmation Honors award. The winners of the award will be highlighted in a Special December Edition of the Automated Software Testing Magazine.

If you are a cfix user, be sure to vote for cfix here.

And by the way, I think The Grinder, which is a really neat web performance testing framework, also deserves being voted for…

cfix studio Beta 2 to add support for EXE-based unit tests

N.B. cfix studio was the code name of what has become Visual Assert

The biggest shortcoming of the current cfix studio version certainly is that it requires all tests be implemented in a DLL. Conceptually, keeping test cases separated from the remaining code certainly is a good idea — and implementing tests in a DLL is a way to accomplish this. However, there are many projects in which such separation is either not feasible or just too much effort.

The good news is that with Beta 2, this will finally change: EXEs become first class-citizens in cfix studio and it will not matter any more whether your tests are part of a DLL or EXE project — you can just put them where you think is appropriate.

Take a classic MFC/GUI application project as an example: It is pretty common for these kinds of projects that most, if not all, application logic is part of a single Visual Studio project that compiles into a single EXE. There may be some additional DLLs or LIBs, but by and large, the EXE itself is where most of the interesting things happen.

The upcoming Beta 2 release now allows you to implement all your unit tests as part of the same EXE project. This means that your tests have access to all classes, functions and resources that are part of the project — all of which you would not easily have access to if you implemented the tests in a separate DLL.

Of course, embedding unit tests into an executable raises two questions:

  1. How to strip the tests from the final release?
  2. How on earth will you be able to run these tests without having main() create windows, load files, play sounds, etc each time?

Thankfully, C/C++ has a preprocessor and Visual C++ has the “exclude from build” feature which allows you to exclude certain files whenever the project is built using a specific configuration. Using any of these two features, the first question is easily answered.

The second problem is more tricky — but thankfully, it has already been solved for you: When cfix studio runs unit tests, it is well aware of that running main() might have, let’s say interesting effects — so what it does is simple: It just makes sure that main() is never run! Not only does this ensure that the tests run silently, i.e. without windows popping up etc, it also has the benefit that all unit tests “see” the application in a pristine state: Rather than having to worry about which state main() has brought the application into, you can initialize and clean up any state you need in your Setup and Teardown functions1.

To make a long story short: You can write unit tests in EXE projects in exactly the same manner as you would in a DLL project. No special considerations needed, no project settings that need to be changed, no additional boilerplate code to write. And when you run the EXE outside cfix studio, i.e. hit F5 in Visual Studio or launch the EXE directly, you will not even notice that the EXE houses some unit tests — everything works as normal.

Sounds good? Then wait a few more days and see it in action!

1: Needless to say, all global variables are initialized, constructors are run, etc. All CRT initialization happens as normal; only main()/WinMain() is not run. And yes, it also works for apps that link statically to MFC and therefore do not have a “regular” WinMain().

More Context Menu Handlers for Everyday Use

Although Windows Explorer may actually not be the brightest spot of Windows, it is still, for most users, among the most often used pograms. Customizing it to speed up certain tasks is thus a natural desire.

A while ago, I wrote about how to extend the context menu by new commands that allow MSI packages to be installed/uninstalled with logfiles being created. The registry entries I used were:

Windows Registry Editor Version 5.00

@="&Logged Install"

@="msiexec.exe /l* \"%1-install.log\" /i \"%1\" %*"

@="L&ogged Uninstall"

@="msiexec.exe /l* \"%1-uninstall.log\" /x \"%1\" %*"

@="msiexec.exe /l* \"%1.log\" /i \"%1\" %*"

While I do not use Windows Installer every day, I am a heavy user of cmd.exe command prompts. Another set of custom verbs I use on my machines therefore deal with opening command line windows. Getting Windows Explorer to open a “normal” command prompt using the context menu is not hard and it has been demonstrated on various places. The idea becomes truly powerful, though, when the commands are specialized to open special kinds of command windows:

  • A plain command prompt
  • An elevated command prompt (using elevate.exe)
  • A WDK command prompt (WLH-chk)
  • A WDK command prompt (WLHA64-chk)
  • A Visual Studio 2005 command prompt
  • etc …

To distinguish the different types of consoles, I like to use different colors — The Visual Studio command prompt is white/green, the elevated prompt is green/blue, and so on. The following script puts it all together (mind the static paths):

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\Directory\shell\Open DDK Console here (WLH-chk)]
@="Open DD&K Console here (WLH-chk)"

[HKEY_CLASSES_ROOT\Directory\shell\Open DDK Console here (WLH-chk)\command]
@="C:\\Windows\\System32\\cmd.exe /k C:\\WinDDK\\6000\\bin\\setenv.bat C:\\WinDDK\\6000\\ chk WLH && cd /D %1 && color 1f"

[HKEY_CLASSES_ROOT\Directory\shell\Open DDK Console here (WLHA64-chk)]
@="Open DD&K Console here (WLHA64-chk)"

[HKEY_CLASSES_ROOT\Directory\shell\Open DDK Console here (WLHA64-chk)\command]
@="C:\\Windows\\System32\\cmd.exe /k C:\\WinDDK\\6000\\bin\\setenv.bat C:\\WinDDK\\6000\\ chk AMD64 && cd /D %1 && color 1f"

[HKEY_CLASSES_ROOT\Directory\shell\Open Default Console here]
@="Open Default Conso&le here"

[HKEY_CLASSES_ROOT\Directory\shell\Open Default Console here\command]
@="cmd.exe /K \"title %1 && cd /D %1\""

[HKEY_CLASSES_ROOT\Directory\shell\Open Elevated Console here]
@="Open Ele&vated Console here"

[HKEY_CLASSES_ROOT\Directory\shell\Open Elevated Console here\command]
@="d:\\bin\\elevate.exe /K \"title %1 && color 1a && cd /D %1\""

[HKEY_CLASSES_ROOT\Directory\shell\Open VS.Net 2005 Console here]
@="Open VS.Net 200&5 Console here"

[HKEY_CLASSES_ROOT\Directory\shell\Open VS.Net 2005 Console here\command]
@="cmd.exe /K \"cd /D %1 && \"C:\\Program Files (x86)\\Microsoft Visual Studio 8\\VC\\vcvarsall.bat\" && color 2f\""

Finally, if you perform backups to the cloud from time to time and do want to upload unencrypted data or for other reasons encrypt specific files occasionaly, it may also be practical to have two GPG commands in your context menu — one to (symetrically) encrypt, and one to decrypt:

Windows Registry Editor Version 5.00





@="\"c:\\Program Files (x86)\\GNU\\GnuPG\\gpg.exe\" -d -i -o %1.plain %1"

@="Encrypt with GPG (symmetric)"

@="\"c:\\Program Files (x86)\\GNU\\GnuPG\\gpg.exe\" -c %1"


About me

Johannes Passing lives in Berlin, Germany and works as a Solutions Architect at Google Cloud.

While mostly focusing on Cloud-related stuff these days, Johannes still enjoys the occasional dose of Win32, COM, and NT kernel mode development.

He also is the author of cfix, a C/C++ unit testing framework for Win32 and NT kernel mode, Visual Assert, a Visual Studio Unit Testing-AddIn, and NTrace, a dynamic function boundary tracing toolkit for Windows NT/x86 kernel/user mode code.

Contact Johannes: jpassing (at) hotmail com

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