mod_linkfreeze

Overview

mod_linkfreeze module provides extended toolset for pattern-based transformation of links on pages to SEO-friendly format.

In general "freezing" idea is based on HTML content modification. Once you've written special rules, the module would carefully modify every hyperlink inside each web-site page if the link matches the rules pattern(s). In a word, mod_linkfreeze turns dynamic links to the static ones. It is a primary idea of the module and at the same time a good SEO practice as long as search robots work much better with static references. And the most interesting thing here—you don't need to modify any part of existent code. The user goes to a web-site and IIS serves the request through the web-site engine. It doesn't matter what the engine is. It can be WordPress, CakePHP or even simple HTML. The important part is that the engine returns HTML response within hyperlinks and then mod_linkfreeze catches and processes the response according to its rules. Dynamic links become static and the user finally gets requested page.

Quick start

Related articles and topics

• Go for SEO with Helicon Ape mod_linkfreeze
• mod_env module
• mod_seo module
• mod_setenvif module (extended syntax supported)

Environment variables

Examples

This is how you can enable mod_linkfreeze for the entire site

# put this line into the .htaccess under the root of your site
SetEnv mod_linkfreeze

and exclude /admin folder from processing by mod_linkfreeze

# put this line into the .htaccess under /admin folder
UnsetEnv mod_linkfreeze

This same behavior may be achieved with one mod_setenvif directive:

# disables mod_linkfreeze for the current context
SetEnvif request_uri !/admin mod_linkfreeze

Note! Sometimes you'll need to explicitly specify the charset for mod_linkfreeze to use as some applications (like PHP) reset it bypassing IIS leaving Ape modules ignorant. To override Charset parameter value of Content-Type header use the following SetEnv line:

# sets Charset for mod_linkfreeze
SetEnv content-type-charset windows-1251

Exact names of charsets may be taken from here.

Directives

LinkFreezeEngine

Enables mod_linkfreeze for the current context. It may be useful to disable mod_linkfreeze (LinkFreezeEngine Off) for the private areas of the site (such as /admin, /private).

Syntax

LinkFreezeEngine On|Off

Default

LinkFreezeEngine On

Example

#put these rules into the httpd.conf file
SetEnv mod_linkfreeze
LinkFreezeRule --- "aspx=htm" [MoveExt]
<Location /admin>
  LinkFreezeEngine off
</Location>

LinkFreezePageSizeLimit

Sets the maximum page size in kilobytes that will be processed by mod_linkfreeze; the part of page exceeding the LinkFreezePageSizeLimit value will be left as is—links in that part won't be frozen (Google also doesn't enjoy parsing huge pages till the end). If the value is set to 0, the check for page size will not be performed.

Syntax

LinkFreezePageSizeLimit 2048|value

Example

LinkFreezePageSizeLimit 4096
SetEnv mod_linkfreeze 
LinkFreezeRule --- "aspx=htm" [ AbsLinks,MoveExt ]

LinkFreezeRule

Determines what links and in what way mod_linkfreeze will process. It is possible to use several LinkFreezeRule directives for the same context.

Syntax

LinkFreezeRule ?&= "old_ext=new_ext" OptionalLinkFilter [ FLAGS ]

Description

• ?&= — any three characters allowed in filenames that will replace "?", "&" and "=" in the URL respectively.

  Note! It is advisable to use rarely used symbols as replacement characters, otherwise conflicts with the same characters in the URLs are inevitable. We recommend the following combinations: ---, ~~~, !!!, |||, ===, ///. The characters may also be combined, e.g.: -=-, !/=, etc.

• "old_ext=new_ext" — old_ext is the file extension to be replaced with new_ext

  Note! You can specify "*" character in case no extension modification is necessary.

  SetEnv mod_linkfreeze
  LinkFreezeRule --- "*"

• LinkFilter — optional parameter that allows to finely configure what types of URLs to freeze. Regular expressions are possible

Example

SetEnv mod_linkfreeze
LinkFreezeRule --- "aspx=htm" "^http://.*"

The above rule says that only URLs beginning with http:// (absolute links) must be processed.

Flags

Flags are used to apply additional conditions to LinkFreezeRule. The following flags are available:

• AbsLinks or A — Transform Absolute links
  
  By default mod_linkfreeze does not process links in absolute format

  <a href="http://localhost/default.aspx?param=val#comment">link</a>

  because most of them point to external resources that won't probably be able to processed them correctly. But if A flag is specified after the rule, such links will be frozen.
  Note that mod_linkfreeze compares SERVER_NAME server variable with the host name for the link

  <a href="http://localhost/default.aspx?param=val#comment">link</a>

  to freeze links to local site only.
• Lowercase or L — Lower case all links before transformation
• MoveExt or M — Move file extension to the end of URL

  Example

  SetEnv mod_linkfreeze
  LinkFreezeRule --- "aspx=htm"  [ MoveExt ]

  The above rule will convert
  

  <a href="/default.aspx?param=val#comment">link</a>

  to
  

  <a href="/default-param-val.htm#comment">link</a>

  Example

  SetEnv mod_linkfreeze
  LinkFreezeRule --- "aspx=htm"

  The above rule will convert
  

  <a href="/default.aspx?param=val#comment">link</a>

  to
  

  <a href="/default.htm-param-val#comment">link</a>

• NoCheckFile or NF — Do not check for physical file
  
  If the request is http://localhost/default-param-val.html and such file physically exists, mod_linkfreeze will show it.
  With NoCheckFile flag after the rule

  SetEnv mod_linkfreeze
  LinkFreezeRule --- "aspx=htm" [MoveExt, NoCheckFile]

  the link will be de-frozen anyway and the user will get response from http://localhost/default.aspx?param=val.
  This is not the most reliable solution, but it works much faster because file existence check is omitted.
• NoLinks or NL — Don't transform links on pages
  The links on pages won't be frozen; only incoming requests will be unfrozen.
• NoRequests or NR — Don't decode incoming requests
  The incoming requests won't be unfrozen; only links on pages will be frozen.
• NoSort or NS — Don't sort parameters in requests/links
  By default is disabled, i.e. parameters will be sorted alphabetically.
• Redirect or R — Redirect old style requests to the static form
  
  mod_linkfreeze will perform redirect to new style URL to avoid duplicate content penalty if:

  1. the old-format URL is requested;

     Example

     SetEnv mod_linkfreeze
     LinkFreezeRule --- "aspx=htm" [ MoveExt, Redirect ]

     With the above rule in place the request to
     http://localhost/default.aspx?param=val#comment
     will be 301-redirected to
     http://localhost/default-param-val.html#comment.
  2. the requested URL has wrong format (incorrect order of parameters; old extension; parameters out of Params list (see below); etc.).

     Example

     SetEnv mod_linkfreeze
     LinkFreezeRule --- "aspx=htm" [ MoveExt, Redirect, Params="id|page" ]

     With the above rule in place the request to
     http://localhost/default.aspx?id=val&other=val2
     or
     http://localhost/default-id-val-other-val2.html
     will be 301-redirected to
     http://localhost/default-id-val.html?other=val2,
     which means that all unwanted parameters are left outside the Google-indexed part of the URL (in the query string) and hence won't harm your pagerank.
• Params="param1|param2| param3..." — Freeze specified parameters only

  Example

  SetEnv mod_linkfreeze
  LinkFreezeRule --- "aspx=htm" [MoveExt, Params="aaa|bbb"]

  With the above rule in place only "aaa" and "bbb" parameters will be frozen. So,
  <a href="/default.aspx?aaa=val1&otherParam=etc">link</a>
  will become
  <a href="/default-aaa-val1.htm?otherParam=etc">link</a>.
  mod_linkfreeze performs sorting of parameters before freezing to avoid duplicate content penalty (also true for Redirect).
  The script doesn't care what the order of parameters is:

  <a href="/default.aspx?aaa=val&bbb=val">link</a>
  <a href="/default.aspx?bbb=val&aaa=val">link</a>

  But for the file-system these are different filenames that will then return the same content:

  <a href="/default-bbb-val-aaa-val.htm">link</a>
  <a href="/default-aaa-val-bbb-val.htm">link</a>

  mod_linkfreeze guarantees the same parameters order in both cases:

  <a href="/default-aaa-val-bbb-val.htm">link</a>