7.5 Rewriter Issues

7.5.1 Discovering the Issue

To isolate a rewriter issue:

  1. Go to the Web server, access the page that is causing the rewriter problem, use view source option of the browser, then copy the source to a text file.

  2. Access the page from Access Manager, view the source, and copy it to a text file.

  3. Use a diff tool to compare the differences between the two files.

    This should help you identify the URLs that need to be rewritten but aren’t being rewritten.

7.5.2 Rewriting Fails on a Page with Numerous HREFs

Although the rewriting failure occurs when downloading large amounts of data from a protected Web server, it is not the size or the timeout of the page that is the issue. It is the number of links to be rewritten. The Access Gateway has a data size limit for the number of references that the rewriter can rewrite on a page.

The solution is to reduce the number of HREFs on the page that need to be rewritten. If the problem is occurring because the rewriter is rewriting HTTP to HTTPS, you can solve this problem by disabling multi-homing for the Web server and by rewriting the Web page to use relative links. This reduces the number of links that need to be rewritten.

7.5.3 Links Are Broken Because the Rewriter Sends the Request to the Wrong Proxy Service

When links on the Web server are rewritten to the wrong proxy service, the reverse proxy and Web servers might have the following configuration:

  • The initial request from the browser is to a path-based multi-homing proxy service.

  • The reverse proxy is configured to service one or more path-based proxy services.

  • The path-based proxy services are configured to Forward Received Host Name and to Remove Path on Fill.

  • The Web servers protected by these path-based proxy services have links to each other.

With this configuration, the rewriter cannot determine whether the link is to the current proxy service, one of the other path-based proxy services, or the parent proxy service. With the path removed, all the path-based proxy services have the same name. For example if one proxy service has the published name of mycompany.provo.novell.com/sales and a second path-based proxy service has a name of mycompany.provo.novell.com/app, the names are the same as the parent proxy service when the path is removed. The HTTP header does not help, because the proxy services are forwarding the same host name: mycompany.provo.novell.com.

There are a number of ways to solve this problem. One of the easiest ways is to set up DNS names for the Web servers, then configure the proxy services so that the Host Header option is set to Web Server Host Name and the DNS name of the Web server is specified in the Web Server Host Name field. This places the DNS name of the Web Server name in the HTTP Host header, allowing the rewriter to distinguish it from the other Web servers protected by the reverse proxy.

7.5.4 Reading Configuration Files

If the rewriter is successful in reading the configuration files, and you have enabled the log level to LOG_INFO, the following message is displayed in the /var/log/ics_dyn.log file:

Reading Config File 

Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:Configuration information read successfully

For more information on configuring log levels, see Configuring Log Levels.

If the rewriter fails to read the configuration files, the following message is displayed:

Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:Reading configuration failed for ssTypeName=www.mynovell.com

If this happens, re-create the corresponding proxy service and restart the Linux Access Gateway service.

7.5.5 Rewriter Does Not Rewrite Content in Files with a Non-Default Extension

If the Web server sends data, whose file extensions do not match with any of the default rewriter profiles, then rewriter does not rewrite the content. The following content-type extensions that are rewritten by default are html, htm, shtml, jhtml, asp, jsp, js, php, and css. In order to work around this problem, do the following:

  1. In the Administration Console, click Devices > Access Gateways > Edit > [Name of Reverse Proxy] > [Name of Proxy Service] > HTML Rewriting.

  2. Do one of the following:

    • If the Web server sends a different content type for a non-default file extension, then configure the new content type in the Content-Type Header.

    • If the Web Server does not send any content type for a non-default extension, then configure extension/<file_extension> as the Content-Type Header. For example, if the data sent is http://www.myproxy.com/test.mytxt, then you must configure the Content-Type Header as extension/mytxt.

7.5.6 Additional DNS Name Without a Scheme Is Not Rewritten

Rewriter rewrites URLS based on the port configured for Connect Port, when domain name without scheme is added to the additional URL list. For example, if the Connect port is configured as 80, Web server rewrites only HTTP URLs and not HTTPs URLs. To work around this problem,

  1. In the Administration Console, click Devices > Access Gateways > Edit > [Name of Reverse Proxy] > [Name of Proxy Service] > HTML Rewriting

  2. Add the additional DNS name with the scheme in the Additional DNS Names List in the following format:

    scheme://DNS_name

    For example, https://example.com

7.5.7 Rewriting a URL

Set the log level to LOG_DEBUG to view rewriter log messages in the /var/log/ics_dyn.log file. (See Configuring Log Levels.)

For example, if the Rewriter successfully rewrites the URL, the following messages are displayed:

Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:URL:'http://www.mynovell.com:9090/common/inc/nav/main.js' Content type match, Will Rewrite
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:URL:'http://www.mynovell.com:9090/common/inc/nav/main.js' Unknown Content-Type - automatic match - Will Rewrite
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0::'http://www.mynovell.com:9090/common/inc/nav/main.js' NULL Content-Type - automatic match - Will Rewrite
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:In RewriterOption::shouldRewriteUrl, returning TRUE.
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:URL:'http://www.mynovell.com:9090/common/inc/nav/main.js' Unknown extension - automatic match - Will Rewrite
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:URL:'http://www.mynovell.com:9090/common/inc/nav/main.js' NULL extension - automatic match - Will Rewrite
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:URL:'http://www.mynovell.com:9090/common/inc/nav/main.js' Extension type match - Will Rewrite

If the conditions for rewriting a URL fail, the following messages are displayed:

Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:URL:'http://www.mynovell.com:9090/favicon.ico' - Did not match INCLUDE list, Content-Type and Extension type
Aug 16 04:16:51 proxy140 LINUX_AG:REWRITER:0:In RewriterOption::shouldRewriteUrl, returning FALSE.

Check the rewriter configuration. Ensure that your content type, extension type, and include URL list are valid.