Add special 7-bit encoding and decoding functions for USSD codingjolly/7bit_ussd

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.

1 files changed, 2 insertions, 0 deletions

diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index b736de9c..db9b3b28 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);
 
 int gsm_septets2octets(uint8_t *result, const uint8_t *rdata, uint8_t septet_len, uint8_t padding);