Parse BSSMAP in conn-oriented data

Add functions to parse the BSSMAP part of BSSAP messages, and in theory
do other things than just forwarding the messages depending on the
BSSMAP message type. This will be used in follow-up patches to change
the AoIP transport layer address in Assignment Request and related
messages.

Related: SYS#5560
Change-Id: I3e2599a9a07925afdbe69f7b8dbcec227681dfa2

include/osmocom/bsc_nat/bssap.h

@@ -22,7 +22,13 @@
 #include <osmocom/core/msgb.h>
 #include <osmocom/bsc_nat/bsc_nat.h>
 
+/* connection-less */
 int bssap_handle_udt(struct bsc_nat_sccp_inst *sccp_inst, struct osmo_sccp_addr *addr, struct msgb *msgb,
 		     unsigned int length);
 
 int bssmap_tx_reset(struct bsc_nat_sccp_inst *sccp_inst, struct osmo_sccp_addr *addr);
+
+/* connection-oriented */
+struct subscr_conn;
+
+int bssap_handle_dt(enum bsc_nat_net net, struct subscr_conn *subscr_conn, struct msgb *msgb, unsigned int length);

src/osmo-bsc-nat/Makefile.am

@@ -30,6 +30,7 @@ osmo_bsc_nat_SOURCES = \
 	bsc_nat.c \
 	bsc_nat_fsm.c \
 	bssap.c \
+	bssap_conn.c \
 	logging.c \
 	main.c \
 	msc.c \

src/osmo-bsc-nat/bsc_nat_fsm.c

@@ -126,14 +126,7 @@ static int sccp_sap_up_cn(struct osmo_prim_hdr *oph, void *scu)
 			goto error;
 		}
 
-		LOGP(DMAIN, LOGL_DEBUG, "Fwd via %s\n", talloc_get_name(subscr_conn));
-
-		msgb_pull_to_l2(oph->msg);
-		osmo_sccp_tx_data(g_bsc_nat->ran.sccp_inst->scu,
-				  subscr_conn->ran.id,
-				  oph->msg->data,
-				  msgb_length(oph->msg));
-		rc = 0;
+		rc = bssap_handle_dt(BSC_NAT_NET_CN, subscr_conn, oph->msg, msgb_l2len(oph->msg));
 		break;
 
 	case OSMO_PRIM(OSMO_SCU_PRIM_N_DISCONNECT, PRIM_OP_INDICATION):
@@ -253,14 +246,7 @@ static int sccp_sap_up_ran(struct osmo_prim_hdr *oph, void *scu)
 			goto error;
 		}
 
-		LOGP(DMAIN, LOGL_DEBUG, "Fwd via %s\n", talloc_get_name(subscr_conn));
-
-		msgb_pull_to_l2(oph->msg);
-		osmo_sccp_tx_data(g_bsc_nat->cn.sccp_inst->scu,
-				  subscr_conn->cn.id,
-				  oph->msg->data,
-				  msgb_length(oph->msg));
-		rc = 0;
+		rc = bssap_handle_dt(BSC_NAT_NET_RAN, subscr_conn, oph->msg, msgb_l2len(oph->msg));
 		break;
 
 	case OSMO_PRIM(OSMO_SCU_PRIM_N_DISCONNECT, PRIM_OP_INDICATION):

src/osmo-bsc-nat/bssap_conn.c

@@ -0,0 +1,120 @@
+/* (C) 2022 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * Author: Oliver Smith <osmith@sysmocom.de>
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/lienses/>.
+ *
+ */
+
+#include "config.h"
+#include <osmocom/core/msgb.h>
+#include <osmocom/gsm/gsm0808.h>
+#include <osmocom/sigtran/sccp_helpers.h>
+#include <osmocom/bsc_nat/logging.h>
+#include <osmocom/bsc_nat/subscr_conn.h>
+
+static int bssap_fwd_to_cn(struct subscr_conn *subscr_conn, struct msgb *msg, unsigned int length)
+{
+	LOGP(DMAIN, LOGL_DEBUG, "Fwd BSSAP to CN via %s\n", talloc_get_name(subscr_conn));
+
+	msgb_pull_to_l2(msg);
+
+	return osmo_sccp_tx_data(g_bsc_nat->cn.sccp_inst->scu, subscr_conn->cn.id, msg->data, msgb_length(msg));
+}
+
+static int bssap_fwd_to_ran(struct subscr_conn *subscr_conn, struct msgb *msg, unsigned int length)
+{
+	LOGP(DMAIN, LOGL_DEBUG, "Fwd BSSAP to RAN via %s\n", talloc_get_name(subscr_conn));
+
+	msgb_pull_to_l2(msg);
+
+	return osmo_sccp_tx_data(g_bsc_nat->ran.sccp_inst->scu, subscr_conn->ran.id, msg->data, msgb_length(msg));
+}
+
+static int bssmap_cn_rcvmsg_dt(struct subscr_conn *subscr_conn, struct msgb *msg, unsigned int length)
+{
+	int ret = 0;
+
+	switch (msg->l3h[0]) {
+	default:
+		ret = bssap_fwd_to_ran(subscr_conn, msg, length);
+		break;
+	}
+
+	return ret;
+}
+
+static int bssmap_ran_rcvmsg_dt(struct subscr_conn *subscr_conn, struct msgb *msg, unsigned int length)
+{
+	int ret = 0;
+
+	switch (msg->l3h[0]) {
+	default:
+		ret = bssap_fwd_to_cn(subscr_conn, msg, length);
+		break;
+	}
+
+	return ret;
+}
+
+static int bssmap_rcvmsg_dt(enum bsc_nat_net net, struct subscr_conn *subscr_conn, struct msgb *msg,
+				 unsigned int length)
+{
+	if (length < 1) {
+		LOGP(DMAIN, LOGL_ERROR, "Not enough room: %u\n", length);
+		return -1;
+	}
+
+	LOGP(DMAIN, LOGL_NOTICE, "Rx DT BSSMAP %s\n", gsm0808_bssmap_name(msg->l3h[0]));
+
+	if (net == BSC_NAT_NET_CN)
+		return bssmap_cn_rcvmsg_dt(subscr_conn, msg, length);
+	return bssmap_ran_rcvmsg_dt(subscr_conn, msg, length);
+}
+
+int bssap_handle_dt(enum bsc_nat_net net, struct subscr_conn *subscr_conn, struct msgb *msgb, unsigned int length)
+{
+	struct bssmap_header *bs;
+	int rc = -1;
+
+	LOGP(DMAIN, LOGL_DEBUG, "Rx DT: %s\n", osmo_hexdump(msgb->l2h, length));
+
+	if (length < sizeof(*bs)) {
+		LOGP(DMAIN, LOGL_ERROR, "The header is too short\n");
+		return -1;
+	}
+
+	switch (msgb->l2h[0]) {
+	case BSSAP_MSG_BSS_MANAGEMENT:
+		bs = (struct bssmap_header *)msgb->l2h;
+		if (bs->length < length - sizeof(*bs)) {
+			LOGP(DMAIN, LOGL_ERROR, "Failed to parse BSSMAP header\n");
+			return -1;
+		}
+		msgb->l3h = &msgb->l2h[sizeof(*bs)];
+		rc = bssmap_rcvmsg_dt(net, subscr_conn, msgb, length - sizeof(*bs));
+		break;
+	case BSSAP_MSG_DTAP:
+		LOGP(DMAIN, LOGL_DEBUG, "Rx DT DTAP\n");
+		if (net == BSC_NAT_NET_CN)
+			rc = bssap_fwd_to_ran(subscr_conn, msgb, length);
+		else
+			rc = bssap_fwd_to_cn(subscr_conn, msgb, length);
+		break;
+	default:
+		LOGP(DMAIN, LOGL_ERROR, "%s(%s) is not implemented!\n", __func__, gsm0808_bssap_name(msgb->l2h[0]));
+	}
+
+	return rc;
+}