[PATCH 2/3] Add special 7-bit encoding and decoding functions for USSD coding

From: Andreas Eversberg &lt;jolly(a)eversberg.eu&gt; Handling 7-bit coding is a little different for USSD, as TS 03.38 states: To avoid the situation where the receiving entity confuses 7 binary zero pad bits as the @ character, the carriage return or <CR> character shall be used for padding in this situation [...]. If <CR> is intended to be the last character and the message (including the wanted <CR>) ends on an octet boundary, then another <CR> must be added together with a padding bit 0. The receiving entity will perform the carriage return function twice, but this will not result in misoperation as the definition of <CR> [...] is identical to the definition of <CR><CR>. The receiving entity shall remove the final <CR> character where the message ends on an octet boundary with <CR> as the last character. Jacob has verified the fix with fakeBTS and the wireshark dissector. Fixes: OW#947 Reviewed-by: Jacob Erlbeck &lt;jerlbeck(a)sysmocom.de&gt; --- include/osmocom/gsm/gsm_utils.h | 2 ++ src/gsm/gsm0480.c | 10 +++++----- src/gsm/gsm_utils.c | 31 +++++++++++++++++++++++++++++++ src/gsm/libosmogsm.map | 2 ++ tests/ussd/ussd_test.c | 22 ++++++++++++++++++++++ tests/ussd/ussd_test.ok | 21 +++++++++++++++++++++ 6 files changed, 83 insertions(+), 5 deletions(-) diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h index a572f50..6cd46e4 100644 --- a/include/osmocom/gsm/gsm_utils.h +++ b/include/osmocom/gsm/gsm_utils.h @@ -57,8 +57,10 @@ const char *gsm_band_name(enum gsm_band band); enum gsm_band gsm_band_parse(const char *mhz); int gsm_7bit_decode(char *decoded, const uint8_t *user_data, uint8_t length); +int gsm_7bit_decode_ussd(char *decoded, const uint8_t *user_data, uint8_t length); int gsm_7bit_decode_hdr(char *decoded, const uint8_t *user_data, uint8_t length, uint8_t ud_hdr_ind); int gsm_7bit_encode(uint8_t *result, const char *data); +int gsm_7bit_encode_ussd(uint8_t *result, const char *data, int *octets_written); int gsm_7bit_encode_oct(uint8_t *result, const char *data, int *octets_written); /* the three functions below are helper functions and here for the unit test */ diff --git a/src/gsm/gsm0480.c b/src/gsm/gsm0480.c index b9b3ed9..cc693fe 100644 --- a/src/gsm/gsm0480.c +++ b/src/gsm/gsm0480.c @@ -105,7 +105,7 @@ struct msgb *gsm0480_create_unstructuredSS_Notify(int alertPattern, const char * msgb_put_u8(msg, ASN1_OCTET_STRING_TAG); ussd_len_ptr = msgb_put(msg, 1); data = msgb_put(msg, 0); - len = gsm_7bit_encode(data, text); + gsm_7bit_encode_ussd(data, text, &len); msgb_put(msg, len); ussd_len_ptr[0] = len; /* USSD-String } */ @@ -172,7 +172,7 @@ struct msgb *gsm0480_create_notifySS(const char *text) msgb_put_u8(msg, 0x82); tmp_len = msgb_put(msg, 1); data = msgb_put(msg, 0); - len = gsm_7bit_encode(data, text); + gsm_7bit_encode_ussd(data, text, &len); tmp_len[0] = len; msgb_put(msg, len); @@ -401,8 +401,8 @@ static int parse_process_uss_req(const uint8_t *uss_req_data, uint16_t length, /* Prevent a mobile-originated buffer-overrun! */ if (num_chars > MAX_LEN_USSD_STRING) num_chars = MAX_LEN_USSD_STRING; - gsm_7bit_decode(req->text, - &(uss_req_data[7]), num_chars); + gsm_7bit_decode_ussd(req->text, + &(uss_req_data[7]), num_chars); rc = 1; } } @@ -423,7 +423,7 @@ struct msgb *gsm0480_create_ussd_resp(uint8_t invoke_id, uint8_t trans_id, const /* First put the payload text into the message */ ptr8 = msgb_put(msg, 0); - response_len = gsm_7bit_encode(ptr8, text); + gsm_7bit_encode_ussd(ptr8, text, &response_len); msgb_put(msg, response_len); /* Then wrap it as an Octet String */ diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c index 54b965e..3dd1537 100644 --- a/src/gsm/gsm_utils.c +++ b/src/gsm/gsm_utils.c @@ -172,6 +172,19 @@ int gsm_7bit_decode(char *text, const uint8_t *user_data, uint8_t septet_l) return gsm_7bit_decode_hdr(text, user_data, septet_l, 0); } +int gsm_7bit_decode_ussd(char *text, const uint8_t *user_data, uint8_t length) +{ + int i; + + gsm_7bit_decode_hdr(text, user_data, length, 0); + i = strlen(text); + /* remove last <CR>, if it fits up to the end of last octet */ + if (i && (user_data[gsm_get_octet_len(length) - 1] >> 1) == '\r') + text[--i] = '\0'; + + return i; +} + /* GSM 03.38 6.2.1 Prepare character packing */ int gsm_septet_encode(uint8_t *result, const char *data) { @@ -254,6 +267,24 @@ int gsm_7bit_encode(uint8_t *result, const char *data) return gsm_7bit_encode_oct(result, data, &out); } +int gsm_7bit_encode_ussd(uint8_t *result, const char *data, int *octets) +{ + int y; + + y = gsm_7bit_encode_oct(result, data, octets); + /* if last octet contains only one bit, add <CR> */ + if (((y * 7) & 7) == 1) + result[(*octets) - 1] |= ('\r' << 1); + /* if last character is <CR> and completely fills last octet, add + * another <CR>. */ + if (y && ((y * 7) & 7) == 0 && (result[(*octets) - 1] >> 1) == '\r') { + result[(*octets)++] = '\r'; + y++; + } + + return y; +} + int gsm_7bit_encode_oct(uint8_t *result, const char *data, int *octets) { int y = 0; diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map index 8a020db..1b985e1 100644 --- a/src/gsm/libosmogsm.map +++ b/src/gsm/libosmogsm.map @@ -132,8 +132,10 @@ gsm48_parse_ra; gsm48_rr_att_tlvdef; gsm_7bit_decode; +gsm_7bit_decode_ussd; gsm_7bit_decode_hdr; gsm_7bit_encode; +gsm_7bit_encode_ussd; gsm_7bit_encode_oct; gsm_arfcn2band; diff --git a/tests/ussd/ussd_test.c b/tests/ussd/ussd_test.c index 55384f1..d41c141 100644 --- a/tests/ussd/ussd_test.c +++ b/tests/ussd/ussd_test.c @@ -22,6 +22,7 @@ #include <osmocom/core/application.h> #include <osmocom/core/logging.h> #include <osmocom/gsm/gsm0480.h> +#include <osmocom/gsm/gsm_utils.h> #include <stdio.h> #include <stdlib.h> #include <string.h> @@ -68,6 +69,20 @@ static int parse_mangle_ussd(const uint8_t *_data, int len) struct log_info info = {}; +void gsm_7bit_ussd(char *text) +{ + uint8_t coded[256]; + char decoded[256]; + int y; + + printf("original = %s\n", osmo_hexdump((uint8_t *)text, strlen(text))); + gsm_7bit_encode_ussd(coded, text, &y); + printf("encoded = %s\n", osmo_hexdump(coded, y)); + gsm_7bit_decode_ussd(decoded, coded, y * 8 / 7); + y = strlen(decoded); + printf("decoded = %s\n\n", osmo_hexdump((uint8_t *)decoded, y)); +} + int main(int argc, char **argv) { struct ussd_request req; @@ -93,5 +108,12 @@ int main(int argc, char **argv) printf("Result for %d is %d\n", rc, i); } + printf("<CR> case test for 7 bit encode\n"); + gsm_7bit_ussd("01234567"); + gsm_7bit_ussd("0123456"); + gsm_7bit_ussd("01234567\r"); + gsm_7bit_ussd("0123456\r"); + gsm_7bit_ussd("012345\r"); + return 0; } diff --git a/tests/ussd/ussd_test.ok b/tests/ussd/ussd_test.ok index 1b6316e..91f2a31 100644 --- a/tests/ussd/ussd_test.ok +++ b/tests/ussd/ussd_test.ok @@ -51,3 +51,24 @@ Result for 0 is 8 Result for 0 is 7 Result for 0 is 6 Result for 1 is 5 +<CR> case test for 7 bit encode +original = 30 31 32 33 34 35 36 37 +encoded = b0 98 6c 46 ab d9 6e +decoded = 30 31 32 33 34 35 36 37 + +original = 30 31 32 33 34 35 36 +encoded = b0 98 6c 46 ab d9 1a +decoded = 30 31 32 33 34 35 36 + +original = 30 31 32 33 34 35 36 37 0d +encoded = b0 98 6c 46 ab d9 6e 0d +decoded = 30 31 32 33 34 35 36 37 0d + +original = 30 31 32 33 34 35 36 0d +encoded = b0 98 6c 46 ab d9 1a 0d +decoded = 30 31 32 33 34 35 36 0d 0d + +original = 30 31 32 33 34 35 0d +encoded = b0 98 6c 46 ab 35 1a +decoded = 30 31 32 33 34 35 0d + -- 1.7.9.5