URL Rewrite Architecture

URL rewrite or “remapping” means changing the URL used in the in the proxy request. This is initially the same as in the client request and remains so if no URL rewriting is done.

Rewriting is configured by an ordered list of rules. Each rule contains _parameters_ and _arguments_. Parameters are required and describe the basic rule. On top of the parameters are arguments, which are optional and adjust the behavior of the basic rule. These are distinguished by a leading ‘@’ character, which marks an argument. Otherwise it is a parameter.

Implementation

class acl_filter_rule

An access check to determine if a rule is enabled for a request. The filter has a set of matching criteria and an action, which is either ALLOW or DENY. If the filter matches the request the action is used, otherwise the next filter is checked.

class UrlRewrite

The top level remapping structure. This is created from a configuration file and then used during a transaction to perform remapping. Data that is shared or needs to persist as long as the configuration is stored in this class. These are

The rules are stored here in one of several containers. The rule type is implicit in which container contains the rule. It is assumed that all rules in a container have the data needed for the rule type of that container.

class RegexMapping

A container for a regular expression mapping. This contains the base mapping along with the regular expression and a format string. The format string is annotated with the locations of regular expression match group substitutions so that if the regular expression matches, the results can be efficiently assembled in to the output host name.