Change in osmo-msc[master]: msc/gsm_data.h: fix and clarify GSM 03.40 TP-UD Length

[Vadim Yanitskiy]

Vadim Yanitskiy has uploaded this change for review. ( https://gerrit.osmocom.org/13484


Change subject: msc/gsm_data.h: fix and clarify GSM 03.40 TP-UD Length
......................................................................

msc/gsm_data.h: fix and clarify GSM 03.40 TP-UD Length

As per 3GPP TS 03.40, section 9.2.3.16 "TP-User-Data-Length (TP-UDL)",
if the TP-User-Data is coded using the GSM 7-bit default alphabet,
the TP-User-Data-Length field indicates the *number of septets*
within the TP-User-Data field to follow. Otherwise, e.g. in case
of 8-bit or UCS-2 encoded data, the *number of octets* is indicated.

It's a good question from where does this value come from:

  #define SMS_TEXT_SIZE 256

Let's replace it with two new definitions:

  #define GSM340_UDL_OCT_MAX 140
  #define GSM340_UDL_SPT_MAX 160

which correspond to the maximum TP-UD field length indicated
in octets and septets respectively.

Change-Id: I2a49f9d24cd075234190b3b92999256bce01ca77
---
M include/osmocom/msc/gsm_data.h
1 file changed, 14 insertions(+), 4 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-msc refs/changes/84/13484/1

diff --git a/include/osmocom/msc/gsm_data.h b/include/osmocom/msc/gsm_data.h
index 1a0d144..77f76b7 100644
--- a/include/osmocom/msc/gsm_data.h
+++ b/include/osmocom/msc/gsm_data.h
@@ -239,7 +239,9 @@
 	SMS_SOURCE_SMPP,	/* received via SMPP */
 };
 
-#define SMS_TEXT_SIZE	256
+/* TODO: Move these defines to libosmogsm (gsm/protocol/gsm_03_40.h) */
+#define GSM340_UDL_OCT_MAX 140  /*!< Maximum TP-UD length (in octets) for 7-bit encoding */
+#define GSM340_UDL_SPT_MAX 160  /*!< Maximum TP-UD length (in seplets) for 8-bit and UCS-2 encoding */
 
 struct gsm_sms_addr {
 	uint8_t ton;
@@ -274,10 +276,18 @@
 	uint8_t protocol_id;
 	uint8_t data_coding_scheme;
 	uint8_t msg_ref;
-	uint8_t user_data_len;
-	uint8_t user_data[SMS_TEXT_SIZE];
 
-	char text[SMS_TEXT_SIZE];
+	/* Depending on DCS value in use, TP-UDL may indicate the length of
+	 * TP-UD either in septets, or in octets. See 3GPP TS 03.40,
+	 * section 9.2.3.16 "TP-User-Data-Length (TP-UDL)" for details. */
+	uint8_t user_data_len;
+	/* Since we always store TP-UD in octets, even if it does contain
+	 * data encoded in septets (i.e. 7-bit default encoding), this
+	 * buffer is limited to 140 bytes. */
+	uint8_t user_data[GSM340_UDL_OCT_MAX];
+
+	/* Up to 160 symbols decoded from TP-UD + '\0' */
+	char text[GSM340_UDL_SPT_MAX + 1];
 };
 
 /* control interface handling */

-- 
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Gerrit-Project: osmo-msc
Gerrit-Branch: master
Gerrit-MessageType: newchange
Gerrit-Change-Id: I2a49f9d24cd075234190b3b92999256bce01ca77
Gerrit-Change-Number: 13484
Gerrit-PatchSet: 1
Gerrit-Owner: Vadim Yanitskiy <axilirator at gmail.com>
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