Testing Filter Handlers

The IFilter test suite validates your filter handlers. The test suite does so by: calling IFilter methods and checking the returned values for compliance with the IFilter interface specification; and checking that chunk identifiers are unique and increasing, that the IFilter interface behaves consistently after re-initialization, and that any IFilter method calls with invalid parameters return expected error codes. The test suite programs also dump the output of a file filtered by a filter handler, and check the IFilter registration information in the registry.

This topic is organized as follows:


If a new filter handler for a file type is being installed as a replacement for an existing filter registration, the installer should save the current registration and restore it if the new filter handler is uninstalled. There is no mechanism to chain filters. Hence, the new filter handler is responsible for replicating any necessary functionality of the old filter.

Command-Line Invocation

The IFilter test suite consists of three command-line applications - ifilttst.exe, filtdump.exe, and filtreg.exe and an initialization file, ifilttst.ini.


In Windows 7 and later, filters written in managed code are explicitly blocked. Filters MUST be written in native code due to potential common language runtime (CLR) versioning issues with the process that multiple add-ins run in.


The ifilttst.exe program runs several tests to validate a filter handler. The following example illustrates how to invoke the ifilttst.exe program from the command line:

ifilttst /i test.htm /l /d /v 1

The example performs the following tasks:

  • Directs the program to filter the file test.htm
  • Redirects the log messages to test.htm.log
  • Redirects the dump messages to test.htm.dmp
  • Sets the verbosity to 1

For the preceding command to work, three files must be located in the current working directory: test.htm, ifilttst.exe, and ifilttst.ini. Command-line switches are listed in the following table.

Switch and possible variables Description
/i file name The input file or directory to be filtered. The file name can contain the wildcard characters * and ?.
/l Log messages are directed to a file instead of the screen. Log messages describe the individual tests performed and the pass/fail results of the tests. The log file name is the same as the input file name but with a .log extension.
/d Dump messages are directed to a file instead of the screen. Dump messages describe the contents of the chunks. The chunk structure is dumped when the verbosity level is 3. The dump file name is the same as the input file name but with a .dmp extension.
/-l Disable logging. This flag overrides the /l switch.
/-d Disable dumping. This flag overrides the /d switch.
/v integer The verbosity level. The default is 3.
  • 0 - The test logs only messages concerning specific IFilter interface failures. The test dumps the chunk contents.
  • 1 - The test logs warning messages as well as those for level 0.
  • 2 - The test logs messages concerning tests that passed as well as those for level 1.
  • 3 - The test logs informational messages as well as those for level 2. In addition, the test dumps the structure of the chunk.
/t integer The number of threads to launch. The default is 1.
/r integer] Recursively filters subdirectories. The optional integer parameter specifies the depth to which to exercise recursion. If no integer is specified, or if the integer is 0, full recursion is assumed. By default, the recursion depth is 1.
/c integer The number of times to loop. If the integer is 0, the test loops infinitely. By default, the test loops only once.


You must include a space between the command line switch and the value.


The filtdump.exe program loads a filter handler for a specified document and prints the output produced by the IFilter DLL. The following example illustrates how to invoke the filtdump.exe program.

filtdump filename.ext

Filtdump.exe uses the ILoadFilter::LoadIFilter method to load the IFilter DLL appropriate for the specified file name extension and prints the results. For example, the following command instructs filtdump.exe to load the smpfilt.dll filter handler for the extension .smp, extract all text and properties from the file myfile.smp, and print the results.

filtdump myfile.smp


The filtreg.exe program inspects IFilter installation information in the registry. You invoke the filtreg.exe program from the command line by typing its name, as in the following example.


Filtreg.exe enumerates all file name extensions that have filter handlers associated with them by printing the file name extension and the name of the IFilter DLL for the extension. This is a simple way to verify the correct installation of an IFilter.


An IFilter interface is initialized by calling the IFilter::Init method. The IFilter::Init method takes the following four parameters:

  1. grfFlags
  2. cAttributes
  3. aAttributes
  4. pdwFlags

The user of the ifilttst.exe program of the IFilter test suite can specify the values for these parameters in a file called ifilttst.ini. The following table describes the entries in the ifilttst.ini file that specify the first three parameters(the input parameters). For a sample file, see Sample ifilttst.ini File.


There is no table entry for the pdwFlags parameter because it is an output parameter; it does not need to have any special value prior to the call to the IFilter::Init method.

  Entry Description
Flags The names of the IFILTER_INIT flags that are to be joined by the OR operator to form the grfFlags parameter of the IFilter::Init method. The flag names must all be uppercase, and on the same line.
cAttributes A decimal integer representing the value of the cAttributes parameter.
aAttributes This entry must start with aAttributes and must be different from the other aAttributes entries within the section. Legal names for the aAttributes entry are: aAttributes, aAttributes1, aAttributes2, and so forth. The first token must be a GUID. The GUID must be formatted exactly as illustrated in the [Test3] section of the Sample ifilttst.ini File. The second token can be either a property identifier (PID) consisting of a number in hexadecimal notation, or a pointer to a wide character string (lpwstr). A lpwstr can be specified by enclosing the string in double quotes, as illustrated in the [Test6] section of the Sample ifilttst.ini File.

If the Flags and cAttributes entries are not specified, they default to 0. If you set cAttributes equal to 2, you should specify two aAttributes names. In the [Test5] section of the sample, cAttributes is 1, but no aAttributes have been specified. The test then calls the IFilter::Init method with cAttributes equal to 1 and aAttributes equal to NULL. This is a useful test case because it is likely to cause an access violation in the IFilter::Init method.

If ifilttst.exe cannot find a file named ifilttst.ini in the working directory, a default configuration is used to initialize the IFilter::Init object. The following example illustrates the default configuration.

            cAttributes = 0

Sample ifilttst.ini File

The ifilttst.ini file is organized in sections, with the section name enclosed in square brackets. In the example, the sections are named [Test1], [Test2], and so forth. All section names must be unique. The test reads the values from the first section and initializes the IFilter with those values. Then all the tests are run using this IFilter configuration. Then the IFilter is released and reinitialized, using parameters that are listed above. The process is repeated until all configurations are tested.

; Only extract text from the object
            Flags =
            cAttributes = 0

            // Get all attributes (text-type and internal value-type properties.
            cAttributes = 0

            // This also extracts just text from the object (the GUID is PSGUID_STORAGE, and the propid is
            // PID_STG_CONTENTS).
            cAttributes = 1
            aAttributes1 = b725f130-47ef-101a-a5f1-02608c9eebac 13

            // Only extract requested attribute from the html object (the GUID corresponds to the HTML IFilter.
            cAttributes = 1
            aAttributes1 = 70eb7a10-55d9-11cf-b75b-00aa0051fe20 2

            // Question: what happens if cAttributes is nonzero, but aAttributes is empty?
            cAttributes = 1

            // Here is an attribute with a lpwstr instead of a propid (the lpwstr is enclosed in quotes).
            // The GUID corresponds to the meta tag clsid for the HTML IFilter.
            Flags =
            cAttributes = 1
            aAttributes1 = D1B5D3F0-C0B3-11CF-9A92-00A0C908DBF1 "GENERATOR"

IFilter Test Procedure

After the IFilter has been initialized, the ifilttst.exe program conducts a series of tests on the IFilter. In addition to following the IFilter test procedures, ensure that your IFilter implementation employs secure code practices. See "Secure Code Practices for Windows Search" in Implementing Filter Handlers in Windows Search.

Validation Test

The validation test steps through the object one chunk at a time, verifying each individual chunk and all return codes. The validation test saves all returned STAT_CHUNK structures in a list.

The validation test verifies the following conditions:

  • The STAT_CHUNK.idChunk chunk IDs must be unique and increasing.
  • The STAT_CHUNK.flags parameter is a recognized chunk state, such as CHUNKSTATE, CHUNK_TEXT, or CenabledHUNK_VALUE constants.
  • The STAT_CHUNK.breakType parameter is a recognized break type (0, 1, 2, 3, 4).
  • If the IFilter initialization attributes specify that the IFilter should return only chunks containing internal value-type properties, then idChunkSource must equal 0.
  • If the chunk is not derived that is, if it is not an internal value-type property, then STAT_CHUNK.idChunkSource must equal STAT_CHUNK.idChunk.
  • IFilter::GetChunk returns S_OK or other acceptable return value, such as FILTER_E_END_OF_CHUNKS, FILTER_E_LINK_UNAVAILABLE, and so forth.
  • If the chunk contains text, IFilter::GetText returns S_OK, FILTER_S_LAST_TEXT, or FILTER_E_NO_MORE_TEXT.
  • If IFilter::GetText returns FILTER_S_LAST_TEXT, the next call to IFilter::GetText returns FILTER_E_NO_MORE_TEXT.
  • If the chunk contains a value, IFilter::GetValue returns S_OK or FILTER_E_NO_MORE_VALUES.

Consistency Test

The ifilttxt.exe program re-initializes the IFilter interface with the same parameters as in the validation test and performs a consistency test. If the IFilter implementation has been initialized with the IFILTER_INIT IFILTER_INIT_INDEXING_ONLY flag, the test releases the IFilter interface and re-binds it before making another call to the IFilter::Init method.

The consistency test verifies the following conditions:

  • Each STAT_CHUNK structure returned by the IFilter::GetChunk method is identical to the corresponding STAT_CHUNK returned in the validation test.
  • IFilter::GetChunk returns S_OK or other acceptable return value, such as FILTER_E_END_OF_CHUNKS, FILTER_E_LINK_UNAVAILABLE, and so forth.

Invalid Input Test

The ifilttst.exe program re-initializes the IFilter interface with the same parameters,and performs an invalid input test. This test steps through the document one chunk at a time making function calls incorrectly, such as calling the IFilter::GetValue method when the current chuck contains text. The test checks all return codes for compliance with the IFilter specification.

The invalid input test verifies the following conditions:

  • If the current chunk contains text, IFilter::GetValue returns FILTER_E_NO_VALUES, and a call to IFilter::GetText succeeds.
  • If the current chunk contains a value, IFilter::GetText returns FILTER_E_NO_TEXT, and a call to IFilter::GetValue succeeds.
  • If the previous call to IFilter::GetText returned FILTER_E_NO_MORE_TEXT, successive calls to IFilter::GetText return FILTER_E_NO_MORE_TEXT.
  • If the previous call to IFilter::GetValue returned FILTER_E_NO_MORE_VALUES, successive calls to IFilter::GetValue return FILTER_E_NO_MORE_VALUES.
  • If the previous call to IFilter::GetChunk returned FILTER_E_END_OF_CHUNKS, successive calls to IFilter::GetChunk return FILTER_E_END_OF_CHUNKS.


The invalid input test compares the current chunk structures to those returned in the validation test to make sure they are identical.

Testing Different IFilter Configurations

The ifilttst.exe program releases the IFilter interface and rebinds, this time initializing it with the next set of parameters. The test repeats the cycle: validation test, consistency test, and invalid input test, until all the desired IFilter configurations specified in ifilttst.ini file have been tested.

Ensuring Registered Items Get Indexed

The final test of your IFilter ensures that your IFilter is properly registered and that it is invoked to index the items that you registered to use it. You can use the Catalog Manager to initiate re-indexing, or use the Crawl Scope Manager (CSM) to set up default rules indicating the URLs that you want the indexer to crawl. After indexing is complete, use the Windows Search UI to search for a string in the content or properties of items. If the items were indexed, they will appear in the search results.

For more information about re-indexing, see Using the Catalog Manager and Using the Crawl Scope Manager. The ReindexMatchingUrls code sample demonstrates ways to specify which files to re-index and how. The CrawlScopeCommandLine code sample demonstrates how to define command line options for Crawl Scope Manager (CSM) indexing operations. Both code samples are available on GitHub.

Sample Log File

Upon request, the Ifilttst.exe program can produce a log containing a description of the steps it takes during execution. The following examples are excerpts from a log file, with the verbosity set to the highest possible value 3.

            1. INFO----**** New configuration ****
            3. Section name : Test2
            4. grfFlags     : 63
            5. cAttributes  : 0
            6. aAttributes  : NONE
            7. pdwFlags     : 0
            9. INFO----Successfully bound filter.
            11. PASS----Init() returned a valid value for pdwFlags.
            13. INFO----Successfully initialized filter.
            15. INFO----Performing validation test. In this part of the test, the chunks structures
            16.         returned by the IFilter are checked for correctness, and the return values
            17.         of the IFilter calls are checked.
            19. PASS----GetChunk() succeeded.
            21. PASS----The current chunk has a legal value for the flags field.

The first line is an informational message, indicating that a new configuration has been loaded from the ifilttst.ini file. Line (3) indicates the section name in the ifilttst.ini file from which the current configuration has been read. Lines (4) through (7) list the parameters to IFilter::Init. The lines starting with INFO are informational messages about the binding of the IFilter and the start of the validation test. Lines starting with PASS are messages regarding specific tests that have passed.

The line in the following log example is a warning. Warnings call attention to IFilter behavior that is problematic, although legal. This warning indicates that the IFilter::GetChunk method has returned a text chunk that contains no text.

WARNING-First call to GetText() returned FILTER_E_NO_MORE_TEXT.

The following example error message indicates that the IFilter emitted a chunk that was not requested.

            ERROR---The IFilter has emitted a chunk which it was not requested to emit.
            Check the initialization parameters in section Test1 of the initialization file.
            INFO----Current chunk propid : 0x5

In the case of this example error message, the IFilter emitted a chunk with a PID of 0x5. Inspection of section [Test1] in ifilttst.ini would show that the IFilter was configured to not emit chunks with this PID. For example, if neither IFILTER_INIT_APPLY_INDEX_ATTRIBUTES nor IFILTER_INIT_APPLY_OTHER_ATTRIBUTES were specified in the Flags entry and if cAttributes were 0, then IFilter would emit only chunks with a PID of 0x13 and corresponding to PID_STG_CONTENTS.

Sample Dump File

Upon request, the Ifilttst.exe program can produce a dump containing the chunks it finds and their content. The following example is an excerpt from such a dump file.

                1. Chunk ID: ........... 2
                2. Chunk Break Type: ... END OF SENTENCE
                3. Chunk State: ........ TEXT
                4. Chunk Locale: ....... 0x411
                5. Chunk Source ID: .... 2
                6. Chunk Start Source .. 0x0
                7. Chunk Length Source . 0x0
                8. GUID ................ b725f130-47ef-101a-a5f1-02608c9eebac
                9. Property ID ......... 0x13

                10. This is a HTML IFilter test page

                11. Chunk ID: ........... 3
                12. Chunk Break Type: ... END OF SENTENCE
                13. Chunk State: ........ TEXT
                14. Chunk Locale: ....... 0x411
                15. Chunk Source ID: .... 2
                16. Chunk Start Source .. 0x0
                17. Chunk Length Source . 0x0
                18. GUID ................ f29f85e0-4ff9-1068-ab91-08002b27b3d9
                19. Property ID ......... 0x2

                20. This is a HTML IFilter test page

                21. Chunk ID: ........... 4
                22. Chunk Break Type: ... END OF SENTENCE
                23. Chunk State: ........ VALUE
                24. Chunk Locale: ....... 0x411
                25. Chunk Source ID: .... 2
                26. Chunk Start Source .. 0x0
                27. Chunk Length Source . 0x0
                28. GUID ................ f29f85e0-4ff9-1068-ab91-08002b27b3d9
                29. Property ID ......... 0x2

                30. This is an HTML IFilter test page

The first nine lines describe the current chunk structure. The GUID and the PID correspond to PSGUID_STORAGE / PID_STG_CONTENTS. This is a chunk containing plain text. The text is in the following chunk structure:

10. This is an HTML IFilter test page

The next chunk, starting at line 11, has a different GUID, corresponding to the HTML IFilter, and a different PID, corresponding to an HTML HREF. This is an internal value-type property, exported by the HTML IFilter.

The next chunk, starting at line 21, has the same GUID and PID, but its chunk state is VALUE instead of TEXT. Note that the text in these last two chunks is the same as for the first chunk. But because the IFilter is designed for three attributes (plain text, HTML HREF as text, and HTML HREF as a value) to be applied to this phrase, the results are emitted in three separate chunks.

Additional Resources

Developing Filter Handlers

About Filter Handlers in Windows Search

Best Practices for Creating Filter Handlers in Windows Search

Returning Properties from a Filter Handler

Filter Handlers that Ship with Windows

Implementing Filter Handlers in Windows Search

Registering Filter Handlers