[gsm48] Introduce a gsm48_generate_mid_from_imsi method

Prefix generate_mid_from_tmsi with a gsm48_, create a new method
to binary encode the imsi. Add a unit test for parsing and decoding.

The implementation can parse the data it generated and the
last octet seems to be filled with the end mark.

openbsc/include/openbsc/gsm_04_08.h

@@ -708,7 +708,8 @@ int gsm48_tx_mm_auth_req(struct gsm_lchan *lchan, u_int8_t *rand);
 int gsm48_tx_mm_auth_rej(struct gsm_lchan *lchan);
 struct msgb *gsm48_msgb_alloc(void);
 int gsm48_sendmsg(struct msgb *msg, struct gsm_trans *trans);
-int generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi);
+int gsm48_generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi);
+int gsm48_generate_mid_from_imsi(u_int8_t *buf, const char* imsi);
 int gsm48_mi_to_string(char *string, const int str_len, const u_int8_t *mi, const int mi_len);
 
 int gsm48_send_rr_release(struct gsm_lchan *lchan);

openbsc/src/gsm_04_08.c

@@ -899,7 +899,7 @@ int gsm0408_loc_upd_acc(struct gsm_lchan *lchan, u_int32_t tmsi)
 		     bts->network->network_code, bts->location_area_code);
 
 	mid = msgb_put(msg, GSM48_MID_TMSI_LEN);
-	generate_mid_from_tmsi(mid, tmsi);
+	gsm48_generate_mid_from_tmsi(mid, tmsi);
 
 	DEBUGP(DMM, "-> LOCATION UPDATE ACCEPT\n");
 

openbsc/src/gsm_04_08_utils.c

@@ -164,6 +164,12 @@ static char bcd2char(u_int8_t bcd)
 		return 'A' + (bcd - 0xa);
 }
 
+/* only works for numbers in ascci */
+static u_int8_t char2bcd(char c)
+{
+	return c - 0x30;
+}
+
 
 void gsm0408_generate_lai(struct gsm48_loc_area_id *lai48, u_int16_t mcc,
 			 u_int16_t mnc, u_int16_t lac)
@@ -187,7 +193,7 @@ void gsm0408_generate_lai(struct gsm48_loc_area_id *lai48, u_int16_t mcc,
 	lai48->lac = htons(lac);
 }
 
-int generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi)
+int gsm48_generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi)
 {
 	u_int32_t *tptr = (u_int32_t *) &buf[3];
 
@@ -199,6 +205,35 @@ int generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi)
 	return 7;
 }
 
+int gsm48_generate_mid_from_imsi(u_int8_t *buf, const char *imsi)
+{
+	unsigned int length = strlen(imsi), i, off = 0;
+	u_int8_t odd = (length & 0x1) == 1;
+
+	buf[0] = GSM48_IE_MOBILE_ID;
+	buf[2] = char2bcd(imsi[0]) << 4 | GSM_MI_TYPE_IMSI | (odd << 3);
+
+	/* if the length is even we will fill half of the last octet */
+	if (odd)
+		buf[1] = (length + 1) >> 1;
+	else
+		buf[1] = (length + 2) >> 1;
+
+	for (i = 1; i < buf[1]; ++i) {
+		u_int8_t lower, upper;
+
+		lower = char2bcd(imsi[++off]);
+		if (!odd && off + 1 == length)
+			upper = 0x0f;
+		else
+			upper = char2bcd(imsi[++off]) & 0x0f;
+
+		buf[2 + i] = (upper << 4) | lower;
+	}
+
+	return 2 + buf[1];
+}
+
 /* Section 9.1.8 / Table 9.9 */
 struct chreq {
 	u_int8_t val;

openbsc/src/paging.c

@@ -99,7 +99,7 @@ static void page_ms(struct gsm_paging_request *request)
 
 	page_group = calculate_group(request->bts, request->subscr);
 	tmsi = strtoul(request->subscr->tmsi, NULL, 10);
-	mi_len = generate_mid_from_tmsi(mi, tmsi);
+	mi_len = gsm48_generate_mid_from_tmsi(mi, tmsi);
 	rsl_paging_cmd(request->bts, page_group, mi_len, mi,
 			request->chan_type);
 }

openbsc/tests/gsm0408/gsm0408_test.c

@@ -24,13 +24,20 @@
 #include <stdlib.h>
 
 #include <openbsc/gsm_04_08.h>
+#include <openbsc/gsm_subscriber.h>
+#include <openbsc/debug.h>
 
 #define COMPARE(result, op, value) \
     if (!((result) op (value))) {\
 	fprintf(stderr, "Compare failed. Was %x should be %x in %s:%d\n",result, value, __FILE__, __LINE__); \
 	exit(-1); \
     }
-	
+
+#define COMPARE_STR(result, value) \
+	if (strcmp(result, value) != 0) { \
+		fprintf(stderr, "Compare failed. Was %s should be %s in %s:%d\n",result, value, __FILE__, __LINE__); \
+		exit(-1); \
+	}
 
 /*
  * Test Location Area Identifier formatting. Table 10.5.3 of 04.08
@@ -58,9 +65,38 @@ static void test_location_area_identifier(void)
     COMPARE(lai48.lac, ==, htons(0x000f));
 }
 
+static void test_mi_functionality(void)
+{
+	const char *imsi_odd  = "987654321098763";
+	const char *imsi_even = "9876543210987654";
+	const u_int32_t tmsi = 0xfabeacd0;
+	u_int8_t mi[128];
+	unsigned int mi_len;
+	char mi_parsed[GSM48_MI_SIZE];
+
+	printf("Testing parsing and generating TMSI/IMSI\n");
+
+	/* tmsi code */
+	mi_len = gsm48_generate_mid_from_tmsi(mi, tmsi);
+	gsm48_mi_to_string(mi_parsed, sizeof(mi_parsed), mi + 2, mi_len - 2);
+	COMPARE((u_int32_t)strtoul(mi_parsed, NULL, 10), ==, tmsi);
+
+	/* imsi code */
+	mi_len = gsm48_generate_mid_from_imsi(mi, imsi_odd);
+	gsm48_mi_to_string(mi_parsed, sizeof(mi_parsed), mi + 2, mi_len -2);
+	printf("hex: %s\n", hexdump(mi, mi_len));
+	COMPARE_STR(mi_parsed, imsi_odd);
+
+	mi_len = gsm48_generate_mid_from_imsi(mi, imsi_even);
+	gsm48_mi_to_string(mi_parsed, sizeof(mi_parsed), mi + 2, mi_len -2);
+	printf("hex: %s\n", hexdump(mi, mi_len));
+	COMPARE_STR(mi_parsed, imsi_even);
+}
+
 int main(int argc, char** argv)
 {
-    test_location_area_identifier();
+	test_location_area_identifier();
+	test_mi_functionality();
 }