Question about how to read / send SMS from an external program

Hi all, I have been working on a project involved using osmo-nitb and trying to read / send SMS by doing SQL queries directly hlr.sqlite3 in a perl program, but I cannot figure out the encode/decode process on the "user_data" field. From "sms_from_text" function in libmsc/gsm_04_11.c, it appears to me that the content of user_data is a gsm_7bit_encode-ed of text if the SMS is sent with VTY interface. I then tried to port gsm_7bit_decode to perl and the implementation successfully decoded two test strings in libosmocore/tests/sms/sms_test.c. However it does not successfully decode any SMS user_data record in hlr.sqlite3 to the original text. The result looks like just a piece of garbled text, not even close to any human-readable text at all. I also tried briefly to include gsm0338 decoding process, or some other perl-based implementation from CPAN, no success at all. I am currently out of ideas to try. It will be really appreciated if anyone with similar experience can offer insight to my issue here.