gsm/gsm0480.c: introduce gsm0480_extract_ie_by_tag()
In some cases, there is no need to parse the whole message,
e.g. during the conversion from DTAP to GSUP/MAP. This
function can be used to extract given IE from a message.
Change-Id: I3989d061903352473305f80712f1a1560d05df3d
diff --git a/src/gsm/gsm0480.c b/src/gsm/gsm0480.c
index 5c73e5b..dfd9877 100644
--- a/src/gsm/gsm0480.c
+++ b/src/gsm/gsm0480.c
@@ -33,6 +33,7 @@
#include <osmocom/gsm/protocol/gsm_04_80.h>
#include <string.h>
+#include <errno.h>
static inline unsigned char *msgb_wrap_with_TL(struct msgb *msgb, uint8_t tag)
{
@@ -214,6 +215,93 @@
uint16_t length,
struct ss_request *req);
+/*! Get pointer to the IE of a given type
+ * \param[in] hdr Pointer to the message starting from header
+ * \param[in] msg_len Length of the whole message + header
+ * \param[out] ie External pointer to be set
+ * \param[out] ie_len External IE length variable
+ * \param[in] ie_tag Tag value of the required IE
+ * \returns 0 in case of success, otherwise -ERRNO
+ *
+ * This function iterates over existing IEs within a given
+ * message (depending on its type), and looks for the one with
+ * given \ref ie_tag value. If the IE is found, the external
+ * pointer pointed by \ref ie will be set to its value part
+ * (omitting TL), and \ref ie_len will be set to the length.
+ * Otherwise, e.g. in case of parsing error, both \ref ie
+ * and \ref ie_len are set to NULL and 0 respectively.
+ */
+int gsm0480_extract_ie_by_tag(const struct gsm48_hdr *hdr, uint16_t msg_len,
+ uint8_t **ie, uint16_t *ie_len, uint8_t ie_tag)
+{
+ uint8_t pdisc, msg_type;
+ uint8_t *tlv, len;
+
+ /* Init external variables */
+ *ie_len = 0;
+ *ie = NULL;
+
+ /* Drop incomplete / corrupted messages */
+ if (msg_len < sizeof(*hdr))
+ return -EINVAL;
+
+ pdisc = gsm48_hdr_pdisc(hdr);
+ msg_type = gsm48_hdr_msg_type(hdr);
+
+ /* Drop non-SS related messages */
+ if (pdisc != GSM48_PDISC_NC_SS)
+ return -EINVAL;
+
+ len = msg_len - sizeof(*hdr);
+ tlv = (uint8_t *) hdr->data;
+
+ /* Parse a message depending on its type */
+ switch (msg_type) {
+ /* See table 2.5: RELEASE COMPLETE message content */
+ case GSM0480_MTYPE_RELEASE_COMPLETE:
+ /* See tables 2.3 and 2.4: REGISTER message content */
+ case GSM0480_MTYPE_REGISTER:
+ /* Iterate over TLV-based IEs */
+ while (len > 2) {
+ if (tlv[0] == ie_tag) {
+ *ie_len = tlv[1];
+ *ie = tlv + 2;
+ return 0;
+ }
+
+ len -= tlv[1] + 2;
+ tlv += tlv[1] + 2;
+ continue;
+ }
+
+ /* The Facility IE is mandatory for REGISTER */
+ if (msg_type == GSM0480_MTYPE_REGISTER)
+ if (ie_tag == GSM0480_IE_FACILITY)
+ return -EINVAL;
+ break;
+
+ /* See table 2.2: FACILITY message content */
+ case GSM0480_MTYPE_FACILITY:
+ /* There is no other IEs */
+ if (ie_tag != GSM0480_IE_FACILITY)
+ break;
+
+ /* Mandatory LV-based Facility IE */
+ if (len < 2)
+ return -EINVAL;
+
+ *ie_len = tlv[0];
+ *ie = tlv + 1;
+ return 0;
+
+ default:
+ /* Wrong message type, out of specs */
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
/* Decode a mobile-originated USSD-request message */
int gsm0480_decode_ussd_request(const struct gsm48_hdr *hdr, uint16_t len,
struct ussd_request *req)