gsm0808: Implement helper functions for CONFUSION BSSMAP message decoding.

Also add a test for an actual CONFUSION message parsing.

Change-Id: If8afd2d096fb66c6c2f255a08fc1129de3d09cec

include/osmocom/gsm/gsm0808.h

@@ -319,6 +319,9 @@ const char *gsm0808_cause_class_name(enum gsm0808_cause_class class);
  * \returns Cause value */
 enum gsm0808_cause gsm0808_get_cause(const struct tlv_parsed *tp);
 
+const char *gsm0808_diagnostics_octet_location_str(uint8_t pointer);
+const char *gsm0808_diagnostics_bit_location_str(uint8_t bit_pointer);
+
 extern const struct value_string gsm0808_lcls_config_names[];
 extern const struct value_string gsm0808_lcls_control_names[];
 extern const struct value_string gsm0808_lcls_status_names[];

include/osmocom/gsm/protocol/gsm_08_08.h

@@ -663,3 +663,16 @@ enum gsm0808_lcls_status {
 	GSM0808_LCLS_STS_LOCALLY_SWITCHED	= 0x04,
 	GSM0808_LCLS_STS_NA			= 0xFF
 };
+
+/* 3GPP TS 48.008 3.2.2.32 Diagnostics */
+struct gsm0808_diagnostics {
+	uint8_t error_pointer_octet;
+#if OSMO_IS_LITTLE_ENDIAN
+	uint8_t error_pointer_bit_spare:4,
+			error_pointer_bit:4;
+#elif OSMO_IS_BIG_ENDIAN
+/* auto-generated from the little endian part above (libosmocore/contrib/struct_endianess.py) */
+	uint8_t error_pointer_bit:4, error_pointer_bit_spare:4;
+#endif
+	uint8_t msg[0]; /*! received message which provoked the error */
+} __attribute__((packed));

src/gsm/gsm0808.c

@@ -21,6 +21,8 @@
  *
  */
 
+#include <string.h>
+
 #include <osmocom/core/byteswap.h>
 #include <osmocom/gsm/gsm0808.h>
 #include <osmocom/gsm/gsm0808_utils.h>
@@ -34,6 +36,9 @@
  *  message generation/encoding.
  */
 
+/*! Char buffer to return strings from functions */
+static __thread char str_buff[512];
+
 /*! Create "Complete L3 Info" for AoIP, legacy implementation.
  * Instead use gsm0808_create_layer3_aoip2(), which is capable of three-digit MNC with leading zeros.
  *  \param[in] msg_l3 msgb containing Layer 3 Message
@@ -1670,6 +1675,39 @@ enum gsm0808_cause gsm0808_get_cause(const struct tlv_parsed *tp)
 	return buf[0];
 }
 
+const char *gsm0808_diagnostics_octet_location_str(uint8_t pointer)
+{
+	switch (pointer) {
+	case 0:
+		return "Error location not determined";
+	case 1:
+		return "The first octet of the message received (i.e. the message type) was found erroneous (unknown)";
+	case 0xfd:
+		return  "The first octet of the BSSAP header (Discrimination) was found erroneous";
+	case 0xfe:
+		return  "(DTAP only) The DLCI (second) octet of the BSSAP header was found erroneous";
+	case 0xff:
+		return  "The last octet of the BSSAP header (length indicator) was found erroneous";
+	default:
+		snprintf(str_buff, sizeof(str_buff), "The %d octet of the message received was found erroneous", pointer);
+		return str_buff;
+	}
+}
+
+const char *gsm0808_diagnostics_bit_location_str(uint8_t bit_pointer)
+{
+	if (bit_pointer == 0) {
+		return "No particular part of the octet is indicated";
+	} else if (bit_pointer > 8) {
+		return "Reserved value";
+	}
+
+	snprintf(str_buff, sizeof(str_buff),
+	         "An error was provoked by the field whose most significant bit is in bit position %d",
+	         bit_pointer);
+	return str_buff;
+}
+
 const struct value_string gsm0808_lcls_config_names[] = {
 	{ GSM0808_LCLS_CFG_BOTH_WAY, "Connect both-way" },
 	{ GSM0808_LCLS_CFG_BOTH_WAY_AND_BICAST_UL,

src/gsm/libosmogsm.map

@@ -159,6 +159,8 @@ gsm0808_bssmap_name;
 gsm0808_cause_name;
 gsm0808_cause_class_name;
 gsm0808_get_cause;
+gsm0808_diagnostics_octet_location_str;
+gsm0808_diagnostics_bit_location_str;
 gsm0808_create_ass;
 gsm0808_create_ass2;
 gsm0808_create_assignment_completed;

tests/gsm0808/gsm0808_test.c

@@ -379,6 +379,55 @@ static void test_create_sapi_reject()
 	msgb_free(msg);
 }
 
+static void test_dec_confusion()
+{
+	static const uint8_t hex[] =
+		{ 0x26, 0x04, 0x01, 0x52, 0x1f, 0x07, 0x00, 0xff, 0x00, 0x03, 0x25, 0x03, 0x25 };
+	struct tlv_parsed tp;
+	int diag_len;
+	enum gsm0808_cause cause;
+	enum gsm0808_cause_class cause_class;
+	struct gsm0808_diagnostics *diag;
+
+	printf("Testing decoding CONFUSION\n");
+
+	tlv_parse(&tp, gsm0808_att_tlvdef(), hex+1, sizeof(hex)-1, 0, 0);
+
+	/* Check for the Cause and Diagnostic mandatory elements */
+	if (!TLVP_PRESENT(&tp, GSM0808_IE_CAUSE) || !TLVP_PRESENT(&tp, GSM0808_IE_DIAGNOSTIC)) {
+		printf("Either Cause or Diagnostic mandatory IE are not detected\n");
+		return;
+	}
+
+	diag_len = TLVP_LEN(&tp, GSM0808_IE_DIAGNOSTIC);
+	if (diag_len < 5) {
+		printf("Diagnostic length is too short: %d (expected > 5)\n",
+		       diag_len);
+		return;
+	}
+
+	cause = gsm0808_get_cause(&tp);
+	if ((int)cause < 0) {
+		printf("ERROR: failed (%s) to extract Cause, aborting\n", strerror(-(int)cause));
+		return;
+	}
+	cause_class = gsm0808_cause_class(cause);
+	printf("  Cause class %d/0x%x (%s)\n",
+	       cause_class, cause_class, gsm0808_cause_class_name(cause_class));
+	printf("  Cause %d/0x%x (%s)\n",
+	       cause, cause, gsm0808_cause_name(cause));
+
+	diag = (struct gsm0808_diagnostics *)TLVP_VAL(&tp, GSM0808_IE_DIAGNOSTIC);
+	printf("  Diagnostics error octet location %d (%s)\n",
+	       diag->error_pointer_octet,
+	       gsm0808_diagnostics_octet_location_str(diag->error_pointer_octet));
+	printf("  Diagnostics error bit location %d (%s)\n",
+	       diag->error_pointer_bit,
+	       gsm0808_diagnostics_bit_location_str(diag->error_pointer_bit));
+	printf("  Diagnostics message that provoked the error: %s\n",
+	       osmo_hexdump(diag->msg, diag_len-2));
+}
+
 static void test_create_ass()
 {
 	static const uint8_t res1[] =
@@ -2422,6 +2471,8 @@ int main(int argc, char **argv)
 
 	test_gsm0808_cell_id_to_from_cgi();
 
+	test_dec_confusion();
+
 	printf("Done\n");
 	return EXIT_SUCCESS;
 }

tests/gsm0808/gsm0808_test.ok

@@ -910,4 +910,10 @@ cid unknown 0x1a7:unknown 0x1a7 -> cgi 777-007-7777-7777 -> cid unknown 0x1a7:un
   --> gsm0808_cell_id{LAC-CI} = LAC-CI:7777-7777
   --> gsm0808_cell_id{LAI} = LAI:777-007-7777
   --> gsm0808_cell_id{CGI} = CGI:777-007-7777-7777
+Testing decoding CONFUSION
+  Cause class 5/0x5 (Invalid message)
+  Cause 82/0x52 (INFORMATION ELEMENT OR FIELD MISSING)
+  Diagnostics error octet location 0 (Error location not determined)
+  Diagnostics error bit location 15 (Reserved value)
+  Diagnostics message that provoked the error: 00 03 25 03 25 
 Done