GSUP: implement TCAP-like session management

Unlike TCAP/MAP, GSUP is just a transport layer without the
dialogue/context. This prevents us from having session based
communication, required e.g. for USSD. But we can emulate
TCAP dialogue by adding additional IEs, which would allow
to relate each message to a particular session.

This change introduces the following IEs:

  - OSMO_GSUP_SESSION_ID_IE,
  - OSMO_GSUP_SESSION_STATE_IE,

which optionally can be used to indicate that the message is
related to a session with given ID, and to manage session
state, i.e. initiate, continue, and finish.

Change-Id: I1cee271fed0284a134ffed103c0d4bebbcfde2a8
Related: OS#1597

6 files changed, 58 insertions, 1 deletions

diff --git a/TODO-RELEASE b/TODO-RELEASE
index 8ccfa491..d9848136 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -7,3 +7,5 @@
 # If any interfaces have been added since the last public release: c:r:a + 1.
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what			description / commit summary line
+gsup		gsup.h				the 'osmo_gsup_message' struct extended with
+						session information => ABI changed
diff --git a/include/osmocom/gsm/gsup.h b/include/osmocom/gsm/gsup.h
index a7fa8208..5f456991 100644
--- a/include/osmocom/gsm/gsup.h
+++ b/include/osmocom/gsm/gsup.h
@@ -82,6 +82,9 @@ enum osmo_gsup_iei {
 	OSMO_GSUP_AUTS_IE			= 0x26,
 	OSMO_GSUP_RES_IE			= 0x27,
 	OSMO_GSUP_CN_DOMAIN_IE			= 0x28,
+
+	OSMO_GSUP_SESSION_ID_IE			= 0x30,
+	OSMO_GSUP_SESSION_STATE_IE		= 0x31,
 };
 
 /*! GSUP message type */
@@ -132,6 +135,18 @@ enum osmo_gsup_cn_domain {
 	OSMO_GSUP_CN_DOMAIN_CS			= 2,
 };
 
+/*! TCAP-like session state */
+enum osmo_gsup_session_state {
+	/*! Undefined session state */
+	OSMO_GSUP_SESSION_STATE_NONE		= 0x00,
+	/*! Initiation of a new session */
+	OSMO_GSUP_SESSION_STATE_BEGIN		= 0x01,
+	/*! Communication of an existing session */
+	OSMO_GSUP_SESSION_STATE_CONTINUE	= 0x02,
+	/*! Indication of the session end */
+	OSMO_GSUP_SESSION_STATE_END		= 0x03,
+};
+
 /*! parsed/decoded PDP context information */
 struct osmo_gsup_pdp_info {
 	unsigned int			context_id;
@@ -176,6 +191,12 @@ struct osmo_gsup_message {
 	enum osmo_gsup_cn_domain	cn_domain;
 	const uint8_t			*pdp_charg_enc;
 	size_t				pdp_charg_enc_len;
+
+	/*! Session state \ref osmo_gsup_session_state */
+	enum osmo_gsup_session_state	session_state;
+	/*! Unique session identifier and origination flag.
+         * Encoded only when \ref session_state != 0x00 */
+	uint32_t			session_id;
 };
 
 int osmo_gsup_decode(const uint8_t *data, size_t data_len,
diff --git a/src/gsm/gsup.c b/src/gsm/gsup.c
index b6ac56d9..8663f449 100644
--- a/src/gsm/gsup.c
+++ b/src/gsm/gsup.c
@@ -385,6 +385,14 @@ int osmo_gsup_decode(const uint8_t *const_data, size_t data_len,
 			gsup_msg->pdp_charg_enc_len = value_len;
 			break;
 
+		case OSMO_GSUP_SESSION_ID_IE:
+			gsup_msg->session_id = osmo_decode_big_endian(value, value_len);
+			break;
+
+		case OSMO_GSUP_SESSION_STATE_IE:
+			gsup_msg->session_state = *value;
+			break;
+
 		default:
 			LOGP(DLGSUP, LOGL_NOTICE,
 			     "GSUP IE type %d unknown\n", iei);
@@ -564,6 +572,14 @@ int osmo_gsup_encode(struct msgb *msg, const struct osmo_gsup_message *gsup_msg)
 				gsup_msg->pdp_charg_enc_len, gsup_msg->pdp_charg_enc);
 	}
 
+	if ((u8 = gsup_msg->session_state)) {
+		size_t len = sizeof(gsup_msg->session_id);
+		uint8_t *sid = osmo_encode_big_endian(gsup_msg->session_id, len);
+
+		msgb_tlv_put(msg, OSMO_GSUP_SESSION_ID_IE, len, sid);
+		msgb_tlv_put(msg, OSMO_GSUP_SESSION_STATE_IE, sizeof(u8), &u8);
+	}
+
 	return 0;
 }
 
diff --git a/tests/gsup/gsup_test.c b/tests/gsup/gsup_test.c
index acc7274f..6ead7d28 100644
--- a/tests/gsup/gsup_test.c
+++ b/tests/gsup/gsup_test.c
@@ -171,6 +171,15 @@ static void test_gsup_messages_dec_enc(void)
 			0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10,
 	};
 
+	static const uint8_t dummy_session_ies[] = {
+		0x2b, /* Dummy value, we only interested in IE coding */
+		TEST_IMSI_IE,
+
+		/* Session ID and state */
+		0x30, 0x04, 0xde, 0xad, 0xbe, 0xef,
+		0x31, 0x01, 0x01,
+	};
+
 	static const struct test {
 		char *name;
 		const uint8_t *data;
@@ -204,6 +213,8 @@ static void test_gsup_messages_dec_enc(void)
 			send_auth_info_res_umts, sizeof(send_auth_info_res_umts)},
 		{"Send Authentication Info Request with AUTS and RAND (UMTS)",
 			send_auth_info_req_auts, sizeof(send_auth_info_req_auts)},
+		{"Dummy message with session IEs",
+			dummy_session_ies, sizeof(dummy_session_ies)},
 	};
 
 	printf("Test GSUP message decoding/encoding\n");
@@ -267,7 +278,7 @@ static void test_gsup_messages_dec_enc(void)
 					osmo_hexdump(t->data + j, ie_end - j));
 
 				OSMO_ASSERT(j <= ie_end - 2);
-				OSMO_ASSERT(t->data[j+0] <= OSMO_GSUP_CN_DOMAIN_IE);
+				OSMO_ASSERT(t->data[j+0] <= OSMO_GSUP_SESSION_STATE_IE);
 				OSMO_ASSERT(t->data[j+1] <= ie_end - j - 2);
 
 				ie_end = j;
diff --git a/tests/gsup/gsup_test.err b/tests/gsup/gsup_test.err
index 05c64fe4..5c010e6c 100644
--- a/tests/gsup/gsup_test.err
+++ b/tests/gsup/gsup_test.err
@@ -40,6 +40,9 @@
   generated message: 08 01 08 21 43 65 87 09 21 43 f5 26 0e 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 20 10 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 
   original message:  08 01 08 21 43 65 87 09 21 43 f5 26 0e 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 20 10 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 
   IMSI:              123456789012345
+  generated message: 2b 01 08 21 43 65 87 09 21 43 f5 30 04 de ad be ef 31 01 01 
+  original message:  2b 01 08 21 43 65 87 09 21 43 f5 30 04 de ad be ef 31 01 01 
+  IMSI:              123456789012345
   message 0: tested 11 truncations, 11 parse failures
   message 1: tested 14 truncations, 13 parse failures
   message 2: tested 83 truncations, 81 parse failures
@@ -54,6 +57,7 @@
   message 11: tested 13 truncations, 12 parse failures
   message 12: tested 211 truncations, 209 parse failures
   message 13: tested 45 truncations, 43 parse failures
+  message 14: tested 20 truncations, 18 parse failures
 DLGSUP Stopping DLGSUP logging
   message 0: tested 2816 modifications, 510 parse failures
   message 1: tested 3584 modifications, 768 parse failures
@@ -69,3 +73,4 @@ DLGSUP Stopping DLGSUP logging
   message 11: tested 3328 modifications, 767 parse failures
   message 12: tested 54016 modifications, 4622 parse failures
   message 13: tested 11520 modifications, 1026 parse failures
+  message 14: tested 5120 modifications, 1026 parse failures
diff --git a/tests/gsup/gsup_test.ok b/tests/gsup/gsup_test.ok
index 49a85ba6..1f599025 100644
--- a/tests/gsup/gsup_test.ok
+++ b/tests/gsup/gsup_test.ok
@@ -27,4 +27,6 @@ Test GSUP message decoding/encoding
           Send Authentication Info Result with IK, CK, AUTN and RES (UMTS) OK
   Testing Send Authentication Info Request with AUTS and RAND (UMTS)
           Send Authentication Info Request with AUTS and RAND (UMTS) OK
+  Testing Dummy message with session IEs
+          Dummy message with session IEs OK
 Done.