dns: expose multiaddress connect code.

Internally the dns code has the ability to try connecting to multiple
addresses in a sequence.  Expose this, as we'll want it for reconnection.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

daemon/dns.c

@@ -154,6 +154,29 @@ static struct io_plan *start_connecting(struct io_conn *conn,
 	return io_close(conn);
 }
 
+struct dns_async *multiaddress_connect_(struct lightningd_state *dstate,
+		  const struct netaddr *addresses,
+		  struct io_plan *(*init)(struct io_conn *,
+					  struct lightningd_state *,
+					  const struct netaddr *,
+					  void *arg),
+		  void (*fail)(struct lightningd_state *, void *arg),
+		  void *arg)
+{
+	struct dns_async *d = tal(dstate, struct dns_async);
+
+	d->dstate = dstate;
+	d->init = init;
+	d->fail = fail;
+	d->arg = arg;
+	d->name = "names from address list";
+	d->num_addresses = tal_count(addresses);
+	d->addresses = tal_dup_arr(d, struct netaddr, addresses,
+				   d->num_addresses, 0);
+	try_connect_one(d);
+	return d;
+}
+
 static struct io_plan *read_addresses(struct io_conn *conn, struct dns_async *d)
 {
 	d->addresses = tal_arr(d, struct netaddr, d->num_addresses);

daemon/dns.h

@@ -29,4 +29,25 @@ struct dns_async *dns_resolve_and_connect_(struct lightningd_state *dstate,
 		  void (*fail)(struct lightningd_state *, void *arg),
 		  void *arg);
 
+/* Don't do lookup, just try to connect to these addresses. */
+#define multiaddress_connect(dstate, addresses, initfn, failfn, arg) \
+	multiaddress_connect_((dstate), (addresses),			\
+			typesafe_cb_preargs(struct io_plan *, void *, \
+					    (initfn), (arg),		\
+					    struct io_conn *,		\
+					    struct lightningd_state *,	\
+					    const struct netaddr *),	\
+			typesafe_cb_preargs(void, void *, (failfn), (arg), \
+					    struct lightningd_state *), \
+				 (arg))
+
+struct dns_async *multiaddress_connect_(struct lightningd_state *dstate,
+		  const struct netaddr *addresses,
+		  struct io_plan *(*init)(struct io_conn *,
+					  struct lightningd_state *,
+					  const struct netaddr *,
+					  void *arg),
+		  void (*fail)(struct lightningd_state *, void *arg),
+		  void *arg);
+
 #endif /* PETTYCOIN_DNS_H */