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Writing Apache Modules with Perl and C by Lincoln Stein, Doug MacEachern

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11.2. Customizing the Configuration Process

If Apache's standard configuration mechanism isn't sufficient for you, or you want to do something wild like generating dynamic configuration files on the fly (as mod_perl does in its <Perl> sections), you can reach into the internals of Apache's configuration machinery and make it do what you want. This section covers the more obscure parts of Apache's configuration system and shows you how to achieve advanced effects such as redirecting the configuration process from your own data source.

11.2.1. The configfile_t Structure

Apache uses a clever abstraction for its configuration process. Instead of reading the text of the configuration file directly from a FILE* or file descriptor, Apache interposes the concept of an abstract "configuration stream," the configfile_t pointer. Configuration streams are much like ordinary files, allowing your programs to read from them character by character or line by line, and they are often attached to real files. However, a configfile_t pointer may just as easily be attached to another process or even to a set of internal subroutines that read configuration information from a database. By creating a custom configfile_t pointer, your module can dynamically generate configuration text to feed directly into the Apache configuration machinery.

The configfile_t struct is defined in httpd.h. Its definition is reproduced in Example 11.4. The most important fields are the first three, which are pointers ...

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