Apache: The Definitive Guide, 3rd Edition

Per-Directory Configuration

It is also possible for modules to be configured on a per-directory, per-URL, or per-file basis. Again, each module optionally creates its own per-directory configuration (the same structure is used for all three cases). This configuration is made available to modules either directly (during configuration) or indirectly (once the server is running), through the request_rec structure, which is detailed in the next section.

Note that the module doesn’t care how the configuration has been set up in terms of servers, directories, URLs, or file matches — the core of the server works out the appropriate configuration for the current request before modules are called by merging the appropriate set of configurations.

The method differs from per-server configuration, so here’s an example, taken this time from the standard module, modules/metadata/mod_expires.c:

typedef struct {
    int active;
    char *expiresdefault;
    apr_table_t *expiresbytype;
} expires_dir_config;

First we have a per-directory configuration structure:

static void *create_dir_expires_config(apr_pool_t *p, char *dummy)
{
    expires_dir_config *new =
    (expires_dir_config *) apr_pcalloc(p, sizeof(expires_dir_config));
    new->active = ACTIVE_DONTCARE;
    new->expiresdefault = "";
    new->expiresbytype = apr_table_make(p, 4);
    return (void *) new;
}

This is the function that creates it, which will be linked from the module structure, as usual. Note that the active member is set to a default that can’t be set by directives ...