# dkim_set_dns_callback()

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SYNOPSIS |
    #include <dkim.h>
    DKIM_STAT dkim_set_dns_callback(
    	DKIM_LIB *libopendkim,
            void (*func)(const void *context),
            unsigned int interval);
    );
Define a function which should be called from time to time while waiting for a DNS response to become available. This is particularly meant for use when libopendkim is being used by an application which is timeout-sensitive where a heartbeat ("still alive, operation in progress") message is desirable. When defined, the specified function will be called at the specified interval even if the DNS response has not yet arrived, using the caller-specific context pointer set by the `dkim_set_user_context()` function (if any) as the parameter to that function.
DESCRIPTION |
Called When | `dkim_set_dns_callback()` can called at any time.
ARGUMENTS |
Argument | Description
--- | ---
libopendkim | Library-specific handle, returned by `dkim_init()`.
func | A pointer to a function which takes a single void pointer which should be called at the requested interval while waiting for a DNS reply. If NULL, no callback will be used.
interval | Desired interval, in seconds, between calls to `func`.
RETURN VALUES | DKIM_STAT_OK -- the callback and interval were successfully registered DKIM_STAT_NOTIMPLEMENT -- the underlying DNS resolution service does not provide a callback facility

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