How can I compare the content of two (or more) MSI files?

Question

How can I do a "content compare" of two (or more) MSI files and see what is actually different inside the files - instead of doing a useless binary compare? (which obviously only tells me if I am dealing with copies of the same file or not).

Some relevant and typical problem scenarios:

• Our build system spits out MSI files like crazy, and sometimes we need to figure out what differences exist between different MSI files (read: something changed, and now we are failing deployment).
• We have MSI files compiled from the same sources in different locations, and some of them fail to run reporting System.BadImageFormatException - how can we debug what the differences in the MSI files are? (an answer dealing with this error specifically here: Are applications dependent on the environment where it was compiled?).
• MSI files can be compiled with all kinds of tools, but for stackoverflow users such files are probably most commonly created using WiX or Visual Studio Installer Projects (free toolkits).

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This is a Q/A-style question on the topic of comparing your compiled MSI files to determine what real "content differences" exist.

Answer 1

Microsoft Orca: If you have Visual Studio installed, try searching for Orca-x86_en-us.msi - under Program Files (x86) - and install it. Then find Orca in the start menu.

• Current path: C:\Program Files (x86)\Windows Kits\10\bin\10.0.17763.0\x86
• Change version numbers as appropriate

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About MSI Files

Roughly speaking MSI files are COM-structured storage files - essentially a file system within a file - with streams of different content, one of which is a stripped down SQL Server database (in the most generic of terms I believe). Provided the MSI files are readable, the content (of various formats and types) can be compared.

Tech Note: It is conceivable that an MSI which triggers a System.BadImageFormatException is just not runnable (msiexec.exe can't run it), but it may still be readable - and hence comparable (please add a comment to verify this if you experience it).

Streams: Some streams in the MSI are tables with string values. There may also be streams for embedded cab-archives used to store files to deploy, and tables with binary content only - such as the Binary table where compiled and uncompiled custom actions alike are stored along with other binary content the setup needs. And there is a special "summary stream" and a table with icons stored in their native, binary format, and the list goes on... For most of the tables we can compare the strings in each table pretty much like we compare text in a Word document (which also used to be OLE / COM files - though newer versions now use Open Office XML) and get a detailed report of differences. In order to do this, you obviously need a special-purpose tool for the job - one capable of finding its way though all the relevant streams. Some commercial and free tools for this are listed below.

Binary content: Before elaborating this, I should note that comparing content in the Binary Table, Cabs Table, Icon Table - or any other binary table, will generally allow you a binary compare only (particularly for compiled custom action dll and exe files). Script custom actions - in the binary table - can be compared as text, but compiled custom actions are binary compare only. So if your problem emanates from a compiled custom action, you can't really see it in a direct compare (you see the binary difference only). You need to hit your source control system to see what code was used for compiled custom actions of any kind - hopefully you have a good label practice so you can find the actual source code used in each setup. I don't use this practice, but for internal, corporate releases perhaps you can even include your debug-build dll for your compiled custom action, and attempt to attach the debugger to the running code to really figure out what is going on? I wouldn't use a debug mode dll for a public release though - unless I'd clarified any risks. Debug code may be riddled with (unexpected) debug message boxes (used as entry points to attach the debugger) and other problems that should never hit a production package.

Come to think of it, your cab files and icon files can definitely be compared to their corresponding versions in older (or newer) MSI files by using the technique to decompile MSI files using dark.exe - which is described below. Then, using a good compare tool (Beyond Compare is mentioned below), you can do a full diff on the cab file content between different MSI versions (and some of the files could be text files, that could be text compared). I guess cabs and icons are sort of "transparent binaries" in an open format as opposed to compiled binaries (with custom actions and more) which are not inherently decompilable or inspectable (unless you know how to decompile managed binaries).

In conclusion: MSI files are fully transparent with the exception of compiled custom actions. This transparency is one of the core benefits of MSI. Most Windows Installer benefits, over previous deployment technologies, generally center around corporate deployment benefits. Unfortunately developers may only see the bad aspects of MSI: the (potential) MSI anti-patterns (towards bottom - very messy and ad-hoc for now). Admittedly some of these problems are very serious and violate "the principle of least astonishment". Developers - why have other and equally important things to do - may frankly be left scratching their heads in disbelief.

Leave no mistake about it though: MSI has massive corporate deployment benefits (see same link as above, towards bottom). Condensed: reliable silent running, remote management, rollback, logging, implicit uninstall feature, elevated rights, standardized command line, transparency, transforms for standardized setup customization and admin install to reliably extract files. Just to name the big ones quickly. Benefits in list form here.

A lot of digressions so far - let's get to the point. What tools can be used to compare MSI files?

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Commercial Tools

Several commercial deployment tools such as Installshield, Advanced Installer and many other MSI tools have support for viewing and comparing MSI files. Maybe I add too many links, but let me use my usual policy of "if you link to one, you link to everyone" - it should save some time and some Google searches.

As a special note - a nostalgic one - the best MSI-diff feature I ever saw was in Wise Package Studio. It was head and shoulders above the rest to be honest - always working, neatly color coded and just easy to comprehend. This tool is no longer for sale as described here: What installation product to use? InstallShield, WiX, Wise, Advanced Installer, etc (if you have a packaging team in your corporation, maybe they have a spare license laying around?).

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Free Tools

The commercial tools are good, but there are also several free alternatives that can be used to compare MSI files - and below is a list of some of them along with some hints for how to use each tool (in a rather minimalistic way).

There are some more details added for dark.exe - which is not a comparison tool for COM-structured storage files at all, but a way to decompile MSI files to WiX XML source files and extract all support files (icons, binaries, cabs, setup files) - allowing them to be compared with regular text / binary compare tools afterwards.

1. Orca (MSI SDK)

Microsoft's own MSI SDK tool / viewer called Orca can view MSI files and edit them, but there is no direct support for comparing two MSI files (that I know about). I suppose you could export the tables and then compare them, but other tools have more built-in features. This option is mentioned since you may already have Orca installed and then this is probably a quick way to get a simple diff done. The "poor man's option".

You may already have the installer. If you have Visual Studio installed, try searching for Orca-x86_en-us.msi - under Program Files (x86) - and install it. Then find Orca in the start menu. Technically Orca is installed as part of the Windows SDK (large, but free download). If you don't have Visual Studio installed, perhaps you know someone who does? Just have them search for this MSI and send you (it is a tiny half mb file) - should take them seconds. If not, you can always download the Windows SDK

2. Super Orca (free third party tool)

Super Orca will allow a rudimentary compare of two MSI files. My smoke test seems to reveal that advanced fields such as the Summary Stream may be ignored. In other words a straight table compare only. There could be other limitations. Maybe it is good enough? It is easy to use.

Note: I have not been able to verify for sure, but I believe this tool saved my MSI without warning once. That was very undesirable at the time.

3. widiffdb.vbs (MSI SDK)

The MSI SDK has a VBScript you can use to view differences between two MSI files. It is called widiffdb.vbs (msdn). With this tool I can see the Summary Stream differences ignored by Super Orca. Anything MSI SDK is authoritative.

UPDATE: All MSI SDK API scripts on github.com (the actual VBScript code).

• Throwing in a link to the full list of such MSI SDK VBScripts - for various purposes. Don't be confused, only widiffdb.vbs is needed for comparing MSI files, but there are many useful scripts for other purposes to be found.
• If you have Visual Studio installed, just search for widiffdb.vbs. Launch with cscript.exe and pass in full path to two MSI files to compare them. Output in console.

Usage:

cscript.exe widiffdb.vbs "Setup 1.msi" "Setup 2.msi"

Sample Output:

Property Value           [ALLUSERS] {1}->{2}
Property Value           [MSIINSTALLPERUSER] {}->{1}
Property INSERT          [MSIINSTALLPERUSER]
\005SummaryInformation   [9] {{00000000-0000-0000-0000-000000000000}}->{{00000000-0000-0000-0000-000000000001}}
\005SummaryInformation   [12] {28.03.2019 15:20:02}->{28.03.2019 14:40:52}
\005SummaryInformation   [13] {28.03.2019 15:20:02}->{28.03.2019 14:40:52}
\005SummaryInformation   [15] {2}->{10}

To find the script, you can search for it under Program Files (x86) if you have Visual Studio installed (it is part of the Windows SDK which will also be installed along with Visual Studio) - (currently the path is: C:\Program Files (x86)\Windows Kits\10\bin\10.0.17763.0\x86 - just replace the version numbers as appropriately and you should find the MSI quicker).

4. dark.exe (WiX toolkit - open source)

The dark.exe binary from the WiX toolset (a toolkit which was likely used to compile some of your MSI files). This dark.exe is a "disassembler" or "decompiler" for MSI files. It will convert MSI files to wxs XML format (WiX's own format used to compile MSI files in the first place), along with a number of extracted binary files (if you use the correct decompile options and flags).

The wxs source files can be compared as regular text source files (my favorite tool for this is Beyond Compare, but it is a commercial tool - there are plenty of text compare tools - including those in Visual Studio). The binary files can obviously be binary compared. Any extracted CAB file can be compared to another, similar cab file from another MSI setup version for example.

Here is a sample command line:

dark.exe -x outputfolder MySetup.msi

• In many cases this will yield a very good compare of the MSI files and you should be able to determine what is really different.

• The extracted binaries could be script files (VBScripts, etc...) or any number of other binaries (for example compiled DLL custom actions). In the latter case you can't really decompile it further - unless it is a .NET binary and you have expertise in decompiling such binaries.

• However, it should be noted that WiX-generated MSI files compiled using the exact same WiX source files can be different for a couple of reasons:

  • The same WiX source file can also be compiled with different compiler and linker settings, and this can affect the generated MSI file in several different ways. To see all switches, download and install WiX and just write candle.exe or light.exe into a command prompt and hit enter.

  • Certain fields such as package GUIDs and product GUIDs can be set to auto-generate in the wxs file. The resultant, corresponding field in the generated MSI file will obviously be different for every build in this case.

    • I don't have a full list of what fields can be set to auto-generate at this point (if you know, maybe hit edit and modify this in situ).

    • The mentioned auto-generated fields can also be hard-coded (which is not good for the package GUID, but that is another, long story - just know that if you find two MSI files that are binary different with the same package GUID, then you are in serious trouble - if they are in the wild - Windows Installer will treat them as the same file by definition). Package codes should always be auto-generated. Digression.

  • The MSI files themselves obviously have different file date information having been compiled separately - just to state the obvious.

And a special note somewhat unrelated to the topic at hand, but important nonetheless: you can use dark.exe to decompile executables compiled with WiX's Burn feature. This is WiX's bootstrapper feature used to install one or more MSI and / or EXE files in sequence - one after the other. These bootstrappers are EXE files and you can decompress them into their constituent MSI and/or EXE files:

dark.exe -x outputfolder setup.exe

Just open a command prompt, CD to the folder where the setup.exe resides. Then specify the above command. Concrete sample: dark.exe -x outputfolder MySetup.exe. The output folder will contain a couple of sub-folders containing both extracted MSI and EXE files and manifests and resource file for the Burn GUI. Any MSI files can then be disassembled as described above to produce a WiX source file (wxs).

5. InstEd (free third party tool - with plus version available)

For some reason I have never used this tool actively, but tested it several times. Testing it again it does seem to do the job of comparing two MSI files, albeit from a strange menu option (which made me think the feature did not work before).

• Open an MSI, then go to Transform => Compare Against... and browse to the MSI you want to compare the first one to.
• Comparison seems OK, and I see that there are changes in the Summary Stream - for example - but the diff doesn't seem to show what is different (unless I just don't see it).
• To see the summary stream changes, open both files in separate InstEd instances and go Tables => Summary Info... in both instances. Now compare the information in the property sheets. Alternatively use the widiffdb.vbs script listed above.

6. Other Tools... (COM-structured storage file viewers)

There are no doubt many other tools capable of viewing COM-structured storage files, but I think the above options should suffice for most users. I'll add a link to installsite.org's list of MSI tools again.

7. Advanced Installer (commercial tool with some free features)

This commercial tool will be able to function as a viewer and allow some basic operations on MSI files even without running with a full license. The nice bit is that you don't even need to use the raw tables, but can use a much nicer user interface to "hotfix" various things in the MSI. For example various upgrade parameters (continue or fail when major upgrade uninstalls fail, etc...).

Changes made in the Table Editor view (straight-up table view) will not be visible in the other "wizard views". The reason for this is explained here.

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Links

• The same (similar) information written for system administrators.