add bindings for the checkout layer

This one was missing from the current bindings. The checkout layer
runs when the worker attempts to send a DNS query to given upstream
when the address is already determined. The layer can add EDNS options
or update outbound query, or block particular addresses / protocol.

diff --git a/lib/resolve.c b/lib/resolve.c
index af1f317f23efed102fc64a4ca462b8b83606cd0d..fd0312a5e97a948f2fc18fb270c3694164a36d30 100644 (file)
--- a/lib/resolve.c
+++ b/lib/resolve.c
@@ -1537,7 +1537,9 @@ int kr_resolve_checkout(struct kr_request *request, struct sockaddr *src,
        }
        struct kr_query *qry = array_tail(rplan->pending);
 
-       /* Run the checkout layers and cancel on failure. */
+       /* Run the checkout layers and cancel on failure.
+        * The checkout layer doesn't persist the state, so canceled subrequests
+        * don't affect the resolution or rest of the processing. */
        int state = request->state;
        ITERATE_LAYERS(request, qry, checkout, packet, dst, type);
        if (request->state == KR_STATE_FAIL) {