Question

I have an Elmah filter setup in web.config to stop notification of certain error messages. But they still seem to come through. What could be the cause?

 <httpModules>
  <add name="ErrorMail" type="Elmah.ErrorMailModule, Elmah" />
  <add name="SecuritySwitch" type="SecuritySwitch.SecuritySwitchModule, SecuritySwitch" />
  <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah" />
  <add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah" />
</httpModules>

<errorFilter>
  <test>
    <regex binding="Exception.Message" pattern="(?ix: \b This \b.+?\b is \b.+?\b an \b.+?\b invalid \b.+?\b webresource \b.+?\b request \b )" />
  </test>
  <test>
    <regex binding="Exception.Message" pattern="(?ix: \b Path \b.+?\b eurl.axd \b )" />
  </test>
  <test>
    <regex binding="Exception.Message" pattern="(?ix: \b potentially \b.+?\b dangerous \b.+?\b value \b.+?\b detected \b.+?\b client \b )" />
  </test>
</errorFilter>

Answer 1

I believe you can only have single test element. The key is to start with an <or></or> element and nest your filters in that. This certainly works for us.

<errorFilter>
    <test>
        <or>
            <!-- Don't email 404 errors -->
            <and>
                <equal binding="HttpStatusCode" value="404" type="Int32" />
                <regex binding="FilterSourceType.Name" pattern="mail" />
            </and>
            <!-- Don't log cancelled downloads -->
            <and>
                <equal binding="HttpStatusCode" value="500" type="Int32" />
                <equal binding="Context.Request.ServerVariables['URL']" value="/Download.aspx" type="String" />
                <or>
                    <regex binding="BaseException.Message" pattern="0x80070016" caseSensitive="false" />
                    <regex binding="BaseException.Message" pattern="0x800704CD" caseSensitive="false" />
                </or>
            </and>
            <!--Viewstate Corruption-->
            <or>
                <regex binding="Exception" type="System.Web.HttpException" pattern="System.FormatException: Invalid length for a Base-64 char array." caseSensitive="false" />
                <regex binding="Exception" type="System.Web.HttpException" pattern="System.FormatException: Invalid character in a Base-64 string." caseSensitive="false" />
            </or>
            <!-- IE8 Bug -->
            <and>
                <regex binding="Context.Request.ServerVariables['HTTP_USER_AGENT']" pattern="Trident\/4\.0" />
                <or>
                    <equal binding="Context.Request.ServerVariables['URL']" value="/ScriptResource.axd" type="String" />
                    <equal binding="Context.Request.ServerVariables['URL']" value="/WebResource.axd" type="String" />
                </or>
            </and>
        </or>
    </test>
</errorFilter>

More information here:

http://www.diaryofaninja.com/blog/2011/09/20/adding-filters-to-your-elmah-installation