Add function to properly encode RAI

Add gsm48_encode_ra() which takes appropriate struct as [out] parameter
instead of generic buffer. Using uint8_t buffer instead of proper struct
type prooved to be error-prone - see Coverity CID57877, CID57876.

Old gsm48_construct_ra() is made into tiny wrapper around new
function. The test output is adjusted because of the change in function
return value which was constant and hence ignored anyway.

Related: OS#1640
Change-Id: I31f9605277f4945f207c2c44ff82e62399f8db74

1 files changed, 21 insertions, 20 deletions

diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index a7daea47..88760599 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -689,33 +689,34 @@ void gsm48_parse_ra(struct gprs_ra_id *raid, const uint8_t *buf)
 	raid->rac = buf[5];
 }
 
-/*! Encode a TS 04.08 Routing Area Identifier
- *  \param[out] buf Caller-provided output buffer of 6 bytes
+/*! Encode a 3GPP TS 24.008 § 10.5.5.15 Routing area identification
+ *  \param[out] out Caller-provided packed struct
  *  \param[in] raid Routing Area ID to be encoded
- *  \returns number of bytes used in \a buf */
-int gsm48_construct_ra(uint8_t *buf, const struct gprs_ra_id *raid)
+ */
+void gsm48_encode_ra(struct gsm48_ra_id *out, const struct gprs_ra_id *raid)
 {
-	uint16_t mcc = raid->mcc;
-	uint16_t mnc = raid->mnc;
-	uint16_t _lac;
+	out->lac = osmo_htons(raid->lac);
+	out->rac = raid->rac;
 
-	buf[0] = ((mcc / 100) % 10) | (((mcc / 10) % 10) << 4);
-	buf[1] = (mcc % 10);
+	out->digits[0] = ((raid->mcc / 100) % 10) | (((raid->mcc / 10) % 10) << 4);
+	out->digits[1] = raid->mcc % 10;
 
-	/* I wonder who came up with the stupidity of encoding the MNC
-	 * differently depending on how many digits its decimal number has! */
-	if (mnc < 100) {
-		buf[1] |= 0xf0;
-		buf[2] = ((mnc / 10) % 10) | ((mnc % 10) << 4);
+	if (raid->mnc < 100) {
+		out->digits[1] |= 0xf0;
+		out->digits[2] = ((raid->mnc / 10) % 10) | ((raid->mnc % 10) << 4);
 	} else {
-		buf[1] |= (mnc % 10) << 4;
-		buf[2] = ((mnc / 100) % 10) | (((mnc / 10) % 10) << 4);
+		out->digits[1] |= (raid->mnc % 10) << 4;
+		out->digits[2] = ((raid->mnc / 100) % 10) | (((raid->mnc / 10) % 10) << 4);
 	}
+}
 
-	_lac = osmo_htons(raid->lac);
-	memcpy(buf + 3, &_lac, 2);
-
-	buf[5] = raid->rac;
+/*! Encode a TS 04.08 Routing Area Identifier
+ *  \param[out] buf Caller-provided output buffer of 6 bytes
+ *  \param[in] raid Routing Area ID to be encoded
+ *  \returns number of bytes used in \a buf */
+int gsm48_construct_ra(uint8_t *buf, const struct gprs_ra_id *raid)
+{
+	gsm48_encode_ra((struct gsm48_ra_id *)buf, raid);
 
 	return 6;
 }