gsm0808: add encoder for cause codes and use it

At the moment the all gsm0808 cause codes are encoded directly using the
tlv API directly to put a one byte TLV field. This works ok for most
situations where the cause code consists of a single byte. However,
gsm0808 specifies a two byte cause code model where cause codes may be
extended up to two bytes. Instead of implementing the encoding over and
over and again, let's rather have an encoder function we can call.

- Add an encoder function that can generate single byte and extended
  cause codeds and makes the length decision automatically.

- Use only this function to append cause codes

Change-Id: I71d58fad89502a43532f60717ca022c15c73f8bb

3 files changed, 43 insertions, 12 deletions

diff --git a/src/gsm/gsm0808.c b/src/gsm/gsm0808.c
index c0d5f39d..e951ab1f 100644
--- a/src/gsm/gsm0808.c
+++ b/src/gsm/gsm0808.c
@@ -141,7 +141,7 @@ struct msgb *gsm0808_create_reset(void)
 		return NULL;
 
 	msgb_v_put(msg, BSS_MAP_MSG_RESET);
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, 1, &cause);
+	gsm0808_enc_cause(msg, cause);
 	msg->l3h = msgb_tv_push(msg, BSSAP_MSG_BSS_MANAGEMENT, msgb_length(msg));
 
 	return msg;
@@ -190,7 +190,7 @@ struct msgb *gsm0808_create_clear_command(uint8_t cause)
 
 	msg->l3h = msgb_tv_put(msg, BSSAP_MSG_BSS_MANAGEMENT, 4);
 	msgb_v_put(msg, BSS_MAP_MSG_CLEAR_CMD);
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, 1, &cause);
+	gsm0808_enc_cause(msg, cause);
 
 	return msg;
 }
@@ -273,7 +273,7 @@ struct msgb *gsm0808_create_cipher_reject(enum gsm0808_cause cause)
 
 	msgb_v_put(msg, BSS_MAP_MSG_CIPHER_MODE_REJECT);
 
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, 1, (const uint8_t *)&cause);
+	gsm0808_enc_cause(msg, cause);
 
 	msg->l3h = msgb_tv_push(msg, BSSAP_MSG_BSS_MANAGEMENT, msgb_length(msg));
 
@@ -286,18 +286,22 @@ struct msgb *gsm0808_create_cipher_reject(enum gsm0808_cause cause)
  *  \returns callee-allocated msgb with BSSMAP Cipher Mode Reject message */
 struct msgb *gsm0808_create_cipher_reject_ext(enum gsm0808_cause_class class, uint8_t ext)
 {
-	uint8_t c[2];
+	uint16_t cause;
 	struct msgb *msg = msgb_alloc_headroom(BSSMAP_MSG_SIZE, BSSMAP_MSG_HEADROOM,
 					       "bssmap: cipher mode reject");
 	if (!msg)
 		return NULL;
 
-	c[0] = 0x80 | (class << 4); /* set the high bit to indicate extended cause */
-	c[1] = ext;
+	/* Set cause code class in the upper byte */
+	cause = 0x80 | (class << 4);
+	cause = cause << 8;
+
+	/* Set cause code extension in the lower byte */
+	cause |= ext;
 
 	msgb_v_put(msg, BSS_MAP_MSG_CIPHER_MODE_REJECT);
 
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, 2, c);
+	gsm0808_enc_cause(msg, cause);
 
 	msg->l3h = msgb_tv_push(msg, BSSAP_MSG_BSS_MANAGEMENT, msgb_length(msg));
 
@@ -572,7 +576,7 @@ struct msgb *gsm0808_create_ass_fail(uint8_t cause, const uint8_t *rr_cause,
 		return NULL;
 
 	msgb_v_put(msg, BSS_MAP_MSG_ASSIGMENT_FAILURE);
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, 1, &cause);
+	gsm0808_enc_cause(msg, cause);
 
 	/* RR cause 3.2.2.22 */
 	if (rr_cause)
@@ -614,7 +618,7 @@ struct msgb *gsm0808_create_clear_rqst(uint8_t cause)
 		return NULL;
 
 	msgb_v_put(msg, BSS_MAP_MSG_CLEAR_RQST);
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, 1, &cause);
+	gsm0808_enc_cause(msg, cause);
 	msg->l3h = msgb_tv_push(msg, BSSAP_MSG_BSS_MANAGEMENT, msgb_length(msg));
 
 	return msg;
@@ -751,7 +755,7 @@ struct msgb *gsm0808_create_handover_required(const struct gsm0808_handover_requ
 	msgb_v_put(msg, BSS_MAP_MSG_HANDOVER_REQUIRED);
 
 	/* Cause, 3.2.2.5 */
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, params->cause & 0x80? 2 : 1, (const uint8_t*)&params->cause);
+	gsm0808_enc_cause(msg, params->cause);
 
 	/* Cell Identifier List, 3.2.2.27 */
 	gsm0808_enc_cell_id_list2(msg, &params->cil);
@@ -876,7 +880,7 @@ struct msgb *gsm0808_create_handover_failure(const struct gsm0808_handover_failu
 	msgb_v_put(msg, BSS_MAP_MSG_HANDOVER_FAILURE);
 
 	/* Cause, 3.2.2.5 */
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, params->cause & 0x80? 2 : 1, (const uint8_t*)&params->cause);
+	gsm0808_enc_cause(msg, params->cause);
 
 	/* RR Cause, 3.2.2.22 */
 	if (params->rr_cause_present)
@@ -907,7 +911,7 @@ struct msgb *gsm0808_create_handover_performed(const struct gsm0808_handover_per
 	msgb_v_put(msg, BSS_MAP_MSG_HANDOVER_PERFORMED);
 
 	/* Cause, 3.2.2.5 */
-	msgb_tlv_put(msg, GSM0808_IE_CAUSE, gsm0808_cause_ext(params->cause) ? 2 : 1, (const uint8_t *)&params->cause);
+	gsm0808_enc_cause(msg, params->cause);
 
 	/* Cell Identifier, 3.2.2.17 */
 	gsm0808_enc_cell_id(msg, &params->cell_id);
diff --git a/src/gsm/gsm0808_utils.c b/src/gsm/gsm0808_utils.c
index c58d8284..38a8664c 100644
--- a/src/gsm/gsm0808_utils.c
+++ b/src/gsm/gsm0808_utils.c
@@ -48,6 +48,32 @@
  *  \file gsm0808_utils.c
  */
 
+/*! Encode TS 08.08 AoIP Cause IE
+ *  \param[out] msg Message Buffer to which to append IE
+ *  \param[in] cause Cause code to be used in IE
+ *  \returns number of bytes added to \a msg */
+uint8_t gsm0808_enc_cause(struct msgb *msg, uint16_t cause)
+{
+	/* See also 3GPP TS 48.008 3.2.2.5 Cause */
+	uint8_t *old_tail;
+	bool extended;
+
+	old_tail = msg->tail;
+
+	extended = gsm0808_cause_ext(cause >> 8);
+
+	msgb_put_u8(msg, GSM0808_IE_CAUSE);
+	if (extended) {
+		msgb_put_u8(msg, 2);
+		msgb_put_u16(msg, cause);
+	} else {
+		msgb_put_u8(msg, 1);
+		msgb_put_u8(msg, (uint8_t) (cause & 0xFF));
+	}
+
+	return (uint8_t) (msg->tail - old_tail);
+}
+
 /*! Encode TS 08.08 AoIP transport address IE
  *  \param[out] msg Message Buffer to which to append IE
  *  \param[in] ss Socket Address to be used in IE
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index e9a9e4f2..dc4e0a69 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -183,6 +183,7 @@ gsm0808_create_handover_complete;
 gsm0808_create_handover_failure;
 gsm0808_create_handover_performed;
 gsm0808_prepend_dtap_header;
+gsm0808_enc_cause;
 gsm0808_enc_aoip_trasp_addr;
 gsm0808_dec_aoip_trasp_addr;
 gsm0808_enc_speech_codec;