The Httperr#.log file enables IIS to log invalid requests separately from valid requests. Both logs are used to log information about client requests that are made to the Web server. However, IIS log entries are created when the send has completed. The error logging occurs after the driver has initiated the send but before the send has completed. Therefore, not all fields that can be logged in the W3C Extended Log file can be logged in the Httperr#.log file.
Software update informationA supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.
If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.
Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.
File informationThe English version of this software update has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.
Date Time Version Size File name
02-Feb-2004 22:47 5.2.3790.125 337,408 Http.sys
Implementation informationWarning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
After you apply this software update, create the following registry key:
If you set the wrong field value, or if you set the field value to zero, or if the registry parameter is not present, the Http.sys parser uses the default fields. The bit value for each log field that is available is listed in the following table. To log all available fields, set the value of the ErrorLoggingFields registry key to 7DFF4E7 (hexadecimal).
To customize the fields that are logged, open the Windows Calculator, view the scientific version of the calculator, and then enter the hexadecimal values in the following table. Use the OR function to combine the values.
Note If you change the error logging configuration, you must restart the Http.sys parser.
|Log field||Default field||Available||Field bit value|
When an HTTP 400 Bad Request is logged, this error implies that the request did not comply with HTTP RFC 2616. Therefore, everything in the header is treated as suspicious and invalid.
When the Http.sys parser experiences an error while parsing a URL, fields such as user-agent and referrer will not be available. The fields that are not available are logged as dashes (-) in the Httperr#.log file. Sometimes, a request can be fully parsed but can still be logged in the error log file for errors other than parsing. These errors may include timeouts or malformed requests that cause the IIS worker process to fail. When this behavior occurs, fields such as user-agent and referrer are available.
After you apply this software update, you must add an entry to the registry and then set its value appropriately before you can configure the list of fields that are available to log in the Httperr#.log file. By default, the field combination is the same field combination that is included with Windows Server 2003. However, some W3C Extended Log file fields are not available for error logging.
The following table compares error logging and IIS W3C Extended Log file logging. Unless otherwise noted, the interpretation and the values of the fields the same.
Note The new fields that this software update adds to error logging appear as bold text.
|Log field||Error logging before update||Error logging after update||W3C Extended Logging||Comments|
|TIME||Yes||Yes||Yes||Unlike IIS log files, the time field does not incorporate the time that is spent while sending the request. The time stamp is taken just after the driver has sent the error response.|
|S-SITENAME||No||No||Yes||Error logs report the site ID instead.|
|CS-USERNAME||No||No||Yes||Authentication occurs in user-mode IIS. It is not available in kernel-mode error logging time.|
|CS-URI-STEM||No||No||Yes||Error logs report URI and Query as the single field CS-URI.|
|CS-URI-QUERY||No||No||Yes||Error logs report URI and Query as the single field CS-URI.|
|SC-SUBSTATUS||No||No||Yes||Substatus from IIS is not available at error logging time.|
|SC-WIN32-STATUS||No||No||Yes||Win32 user-mode status from IIS is not available at error logging time.|
|TIME-TAKEN||No||Yes||Yes||Unlike IIS log files, the TIME-TAKEN field does not incorporate the time that is spent while sending the request. Typically, processing time in kernel mode is less than one millisecond, especially for entries that are created for error such as parse errors. Therefore, the value in this field is typically zero.|
|S-QUEUENAME||Yes||Yes||No||This field shows the application pool name that the IIS worker process uses.|
Article ID: 832975 - Last Review: Mar 29, 2017 - Revision: 2