Apache: The Definitive Guide, 3rd Edition

Optional Function Example

As with optional hooks, this example consists of three files which can be found in .../modules/experimental: mod_optional_fn_export.c, mod_optional_fn_export.h and mod_optional_fn_import.c. (Note that comments for this example follow the code line(s) to which they refer.)

First the header, mod_optional_fn_export.h:

#include "apr_optional.h"

Get the optional function support from APR.

APR_DECLARE_OPTIONAL_FN(int,TestOptionalFn,(const char *));

And declare our optional function, which really looks like int TestOptionalFn(const char *).

Now the exporting file, mod_optional_fn_export.c:

#include "httpd.h"
#include "http_config.h"
#include "http_log.h"
#include "mod_optional_fn_export.h"

As always, we start with the headers, including our own.

static int TestOptionalFn(const char *szStr)
{
    ap_log_error(APLOG_MARK,APLOG_ERR,OK,NULL,
                 "Optional function test said: %s",szStr);

    return OK;
}

This is the optional function — all it does is log the fact that it was called.

static void ExportRegisterHooks(apr_pool_t *p)
{
    APR_REGISTER_OPTIONAL_FN(TestOptionalFn);
}

During hook registration we register the optional function.

module optional_fn_export_module=
{
    STANDARD20_MODULE_STUFF,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    ExportRegisterHooks
};

And finally, we see the module structure containing just the hook registration function.

Now the module that uses the optional function, mod_optional_fn_import.c:

#include "httpd.h" #include "http_config.h" #include "mod_optional_fn_export.h" #include ...