SS7: do not attempt transfer if AS is down

The attempt to route message via AS which is down will fail anyway:
let's make it explicit.

Add osmo_ss7_as_down() and use it to check AS state before transferring the message.

Change-Id: I0d5f3b6265e7fdaa79e32fbc30f829ef79e7dad1

include/osmocom/sigtran/osmo_ss7.h

@@ -352,6 +352,7 @@ int osmo_ss7_as_del_asp(struct osmo_ss7_as *as, const char *asp_name);
 void osmo_ss7_as_destroy(struct osmo_ss7_as *as);
 bool osmo_ss7_as_has_asp(const struct osmo_ss7_as *as,
 			 const struct osmo_ss7_asp *asp);
+bool osmo_ss7_as_down(const struct osmo_ss7_as *as);
 bool osmo_ss7_as_active(const struct osmo_ss7_as *as);
 bool osmo_ss7_as_tmode_compatible_xua(struct osmo_ss7_as *as, uint32_t m3ua_tmt);
 void osmo_ss7_asp_disconnect(struct osmo_ss7_asp *asp);

src/osmo_ss7.c

@@ -1143,6 +1143,18 @@ bool osmo_ss7_as_active(const struct osmo_ss7_as *as)
 	return as->fi->state == XUA_AS_S_ACTIVE;
 }
 
+/*! Determine if given AS is in the down state.
+ *  \param[in] as Application Server.
+ *  \returns true in case as is down; false otherwise. */
+bool osmo_ss7_as_down(const struct osmo_ss7_as *as)
+{
+	OSMO_ASSERT(as);
+
+	if (!as->fi)
+		return true;
+	return as->fi->state == XUA_AS_S_DOWN;
+}
+
 /***********************************************************************
  * SS7 Application Server Process
  ***********************************************************************/

src/osmo_ss7_hmrt.c

@@ -228,6 +228,12 @@ static int hmrt_message_for_routing(struct osmo_ss7_instance *inst,
 				       dpc, osmo_ss7_pointcode_print(inst, dpc), rt_name);
 			}
 
+			if (osmo_ss7_as_down(as)) {
+				LOGP(DLSS7, LOGL_ERROR, "Unable to route HMRT message: the AS %s is down\n",
+				     as->cfg.name);
+				return -ENETDOWN;
+			}
+
 			rate_ctr_inc2(as->ctrg, SS7_AS_CTR_TX_MSU_TOTAL);
 
 			switch (as->cfg.proto) {