From f1158c7719c1b746f0fb303efabf8e6a4670646b Mon Sep 17 00:00:00 2001
From: "Mychaela N. Falconia" <falcon@freecalypso.org>
Date: Sat, 26 Aug 2023 01:06:57 +0000
Subject: [PATCH] SMS over GSUP: implement forwarding of MT SMS

When an SMSC tries to deliver an SM to a subscriber, it will send us
an MT-forwardSM.req GSUP message.  We look up the subscriber by IMSI
and see if they are attached to a VLR.  If the subscriber is attached,
we forward the message to the MSC/VLR, otherwise return an error
to the SMSC.

Related: OS#6135
Change-Id: Ib3551bf7839690606c677461758c5cfef5f0aa7b
---
 include/osmocom/hlr/hlr_sms.h |  1 +
 src/hlr.c                     |  3 +++
 src/hlr_sms.c                 | 28 ++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/include/osmocom/hlr/hlr_sms.h b/include/osmocom/hlr/hlr_sms.h
index 6e68a858..b3beea6f 100644
--- a/include/osmocom/hlr/hlr_sms.h
+++ b/include/osmocom/hlr/hlr_sms.h
@@ -29,3 +29,4 @@ struct hlr_smsc_route *smsc_route_alloc(struct hlr *hlr, const char *num_addr,
 void smsc_route_del(struct hlr_smsc_route *rt);
 
 void forward_mo_sms(struct osmo_gsup_req *req);
+void forward_mt_sms(struct osmo_gsup_req *req);
diff --git a/src/hlr.c b/src/hlr.c
index 501eabc9..eae9e843 100644
--- a/src/hlr.c
+++ b/src/hlr.c
@@ -560,6 +560,9 @@ static int read_cb(struct osmo_gsup_conn *conn, struct msgb *msg)
 	case OSMO_GSUP_MSGT_MO_FORWARD_SM_REQUEST:
 		forward_mo_sms(req);
 		break;
+	case OSMO_GSUP_MSGT_MT_FORWARD_SM_REQUEST:
+		forward_mt_sms(req);
+		break;
 	default:
 		LOGP(DMAIN, LOGL_DEBUG, "Unhandled GSUP message type %s\n",
 		     osmo_gsup_message_type_name(req->gsup.message_type));
diff --git a/src/hlr_sms.c b/src/hlr_sms.c
index ebf40994..ac4d50d6 100644
--- a/src/hlr_sms.c
+++ b/src/hlr_sms.c
@@ -191,3 +191,31 @@ void forward_mo_sms(struct osmo_gsup_req *req)
 			     strlen(smsc->name) + 1);
 	osmo_gsup_forward_to_local_peer(req->cb_data, &dest_peer, req, NULL);
 }
+
+/***********************************************************************
+ * forwarding of MT SMS from SMSCs to MSC/VLR based on IMSI
+ ***********************************************************************/
+
+void forward_mt_sms(struct osmo_gsup_req *req)
+{
+	struct hlr_subscriber subscr;
+	struct osmo_cni_peer_id dest_peer;
+	int rc;
+
+	rc = db_subscr_get_by_imsi(g_hlr->dbc, req->gsup.imsi, &subscr);
+	if (rc < 0) {
+		osmo_gsup_req_respond_err(req, GMM_CAUSE_IMSI_UNKNOWN,
+					  "IMSI unknown");
+		return;
+	}
+	/* is this subscriber currently attached to a VLR? */
+	if (!subscr.vlr_number[0]) {
+		osmo_gsup_req_respond_err(req, GMM_CAUSE_IMPL_DETACHED,
+					  "subscriber not attached to a VLR");
+		return;
+	}
+	osmo_cni_peer_id_set(&dest_peer, OSMO_CNI_PEER_ID_IPA_NAME,
+			     (const uint8_t *) subscr.vlr_number,
+			     strlen(subscr.vlr_number) + 1);
+	osmo_gsup_forward_to_local_peer(req->cb_data, &dest_peer, req, NULL);
+}