== link:index.html[Index] -> link:modules.html[Modules] -> link:modules_handlers.html[Handlers]
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Last checked: 2010/08/17 Cherokee 1.0.9b
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Handler: Redirection
--------------------

The main idea of a redirection is telling the web client to go to
another URL when the requested URL matches a rule. It could happen
that this is not precisely what you are looking for. Check the
link:modules_handlers_proxy.html[reverse proxy] handler if you are
looking for more complex layer 7 operations.  However, for URL
redirections this handler is the place to go. A very common scenario
would be rewriting URLS.

Lets suppose you have URLs like::
+
----
    http://example.com/inst/photogallery/viewphoto?photoid=1235
    http://example.com/inst/photogallery/viewcomments?photoid=1235
    http://example.com/inst/photogallery/admin?photoid=1235&method=delete
----

You probably would prefer URLs like::
+
----
    http://example.com/photo/1235
    http://example.com/photo/1235/cmts
    http://example.com/photo/1235/delete
----

[[parameters]]
Parameters
~~~~~~~~~~

This directive uses PCRE (Perl Compatible Regular Expressions) to make
the substitution.

* Type: [External | Internal]

  - *Internal*:
    The redirection will happen internally, hence the internal URL in
    which the address is translated will be invisible for the client.

  - *External*:
    It works in the same way as the previous one, but in this case, it
    will redirect the connection to the new resource.

* *Regular Expression* and *Substitution* are the matching request and
   the intended target of such petition. Getting into details of
   regular expressions is out of the scope of this document. Besides,
   there are many link:http://perldoc.perl.org/perlre.html[Perl
   regular expressions] references. Macros can be used for these
   substitutions, which is specially handy for some cases that cannot
   be covered any other way, such as uniformly managing virtual
   servers with multiple matches. Take a look at the examples at the
   end of this section for further clarification.
+
[options="header"]
|=========================================================================
|Variable           |Example          |Description
|`${host}`          |example.com      |Host of the matching virtual server
|=========================================================================
+

This macro uses the standard template subsystem , which provides
link:config_virtual_servers_evhost.html#slicing[slicing support]. You
should read more about this powerful feature if you are not already
familiar with it.

The maximum allowed number of substitutions on an expression is
limited to 20, and even though it could be raised even more, this
wouldn't actually make any difference for any real-life case.


[[vhosts]]
Virtual hosts and redirections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The internal redirections, using the `internal` keyword, are limited to
work in the same virtual host. All the internal redirections will be
processed in the original virtual host, which makes a lot of sense in
terms of security.

In case you do need to redirect a resource to another virtual host
and/or domain, you will have to use an explicit redirection using the
`external` keyword.

[[rule_type]]
The influence of the rule type
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Any rule type can be used with the redirection handler: Directory,
Extensions, Regular Expression, etc. Only the case where the type is
*Regular Expression* will require some more extra information.
Because of Cherokee's design, modularity and inheritance is heavily
used throughout the code base. This one is a special case because the
regex entry of the redirection handler can be empty whenever the
matching rule used is a regular expression (because it is inherited by
it).

The logic behind this is that you can set up a regular expression to
match the rule, but once you're in the redirection handler you could
or could not be needing another matching to be performed. If not, the
original one (the one from the rule) will be enough. If you do, you
can specify a completely different expression to be matched. For
instance, you could match the rule taking just the beginning part of
the request as meaningful, and once you are into the handler you might
want to consider just the end of it before making the substitution.

[[examples]]
Examples
~~~~~~~~

This example will perform internal redirections:

[cols="30%,70%",options="header"]
|=======================================================================================
|Regular Expression    |Substitution
|__/(\d+)$__           |http://example.com/inst/photogallery/viewphoto?photoid=$1
|__/(\d+)/cmts__       |http://example.com/viewcomments?photoid=$1
|__/(\d+)/delete__     |http://example.com/inst/photogallery/admin?photoid=$1&method=delete
|__/https_redir/(\d+)__|https://${host}/secure?photoid=$1
|=======================================================================================

Which would translate into the following redirections for the listed
matching requests:

[cols="30%,70%",options="header"]
|===========================================================================================
|Request               |Internal translation
|__/photo/123__        |http://example.com/inst/photogallery/viewphoto?photoid=123
|__/photo/213/cmts__   |http://example.com/viewcomments?photoid=213
|__/photo/501/delete__ |http://example.com/inst/photogallery/admin?photoid=501&method=delete
|__/https_redir/555__  |https://example.com/secure?photoid=555
|===========================================================================================

You might also want to check out the cookbook entry titled
link:cookbook_http_to_https.html[HTTP to HTTPS] on how to redirect all
traffic from HTTP to HTTPS.


[[global]]
Global redirections
~~~~~~~~~~~~~~~~~~~

If you want to implement global redirections that can be defined once
and apply to every virtual server on your configuration, you will also
have to perform matches against the host part of the request. This can
be done by creating an additional virtual server using "Regular
Expression" as method to match the host, which can be specified
through the the `Host Match` tab. You will then have to define a
substitution that uses both type of regex matches:

.Match groups
[cols="20%,80%"]
|======================================
| `^1,^2,^3,..` | These are substituted by the host name match.
| `$1,$2,$3,..` | These are substituted by either the handler match (if any) or its own match groups.
|======================================

For more information, check out the practical example in the cookbook
describing how to implement
link:cookbook_redirs.html#global-redirs[global redirections].