nat: Move paging by lac handling code into the utils file

Moving it here means we can more easily test this code, there is one
behaviour change with the code that we only support paging messages
with one LAC and will silently ignore the others.

1 files changed, 40 insertions, 0 deletions

diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index a3242317b..2428cbc2e 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -24,9 +24,15 @@
 
 #include <openbsc/bsc_nat.h>
 #include <openbsc/gsm_data.h>
+#include <openbsc/bssap.h>
+#include <openbsc/debug.h>
 
+#include <osmocore/linuxlist.h>
 #include <osmocore/talloc.h>
 
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
 struct bsc_nat *bsc_nat_alloc(void)
 {
 	struct bsc_nat *nat = talloc_zero(tall_bsc_ctx, struct bsc_nat);
@@ -66,3 +72,37 @@ struct bsc_config *bsc_config_alloc(struct bsc_nat *nat, const char *token, unsi
 	return conf;
 }
 
+struct bsc_connection *bsc_nat_find_bsc(struct bsc_nat *nat, struct msgb *msg)
+{
+	struct bsc_connection *bsc;
+	int data_length;
+	const u_int8_t *data;
+	struct tlv_parsed tp;
+	int i = 0;
+
+	tlv_parse(&tp, gsm0808_att_tlvdef(), msg->l3h + 3, msgb_l3len(msg) - 3, 0, 0);
+	if (!TLVP_PRESENT(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST)) {
+		LOGP(DNAT, LOGL_ERROR, "No CellIdentifier List inside paging msg.\n");
+		return NULL;
+	}
+
+	data_length = TLVP_LEN(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST);
+	data = TLVP_VAL(&tp, GSM0808_IE_CELL_IDENTIFIER_LIST);
+	if (data[0] !=  CELL_IDENT_LAC) {
+		LOGP(DNAT, LOGL_ERROR, "Unhandled cell ident discrminator: %c\n", data[0]);
+		return NULL;
+	}
+
+	/* Currently we only handle one BSC */
+	for (i = 1; i < data_length - 1; i += 2) {
+		unsigned int _lac = ntohs(*(unsigned int *) &data[i]);
+		llist_for_each_entry(bsc, &nat->bsc_connections, list_entry) {
+			if (!bsc->authenticated || _lac != bsc->lac)
+				continue;
+
+			return bsc;
+		}
+	}
+
+	return NULL;
+}