Openwrt + Huawei E3372 + balance of velcom.by with bash and c

hex_to_utf16be.c

#include <locale.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <wchar.h>

uint8_t get_data(char input, uint8_t *output) {
  if (input - '0' >= 0 && '9' - input >= 0) {
    *output = input - '0';
  } else if (input - 'a' >= 0 && 'f' - input >= 0) {
    *output = input - 'a' + 10;
  } else if (input - 'A' >= 0 && 'F' - input >= 0) {
    *output = input - 'A' + 10;
  } else {
    return 1;
  }

  return 0;
}

uint8_t print_data_group(const char *input) {
  wchar_t data_group = 0;
  uint8_t data;

  for (uint8_t index = 0; index < 4; index++) {
    if (get_data(*(input + index), &data) != 0) {
      return 1;
    }

    data_group = data_group << 4 | data;
  }

  putwchar(data_group);

  return 0;
}

int main(int argc, char *argv[]) {
  if (argc != 2) {
    fputs("required argument: hex\n", stderr);
    return 1;
  }

  char *hex = argv[1];
  setlocale(LC_CTYPE, "");

  for (size_t index = 0; index + 4 <= strlen(hex); index += 4) {
    if (print_data_group(hex + index) != 0) {
      fprintf(stderr, "invalid hex: %s\n", hex);
      return 2;
    }
  }

  return 0;
}

Makefile

# system type : Atheros AR9330 rev 1
# machine     : GL.Inet GL-AR150
# cpu model   : MIPS 24Kc V7.4

STAGING_DIR = openwrt-sdk-18.06.4-ar71xx-generic_gcc-7.3.0_musl.Linux-x86_64/staging_dir
export STAGING_DIR
TOOLCHAIN_DIR = $(STAGING_DIR)/toolchain-mips_24kc_gcc-7.3.0_musl/bin

all:
	$(TOOLCHAIN_DIR)/mips-openwrt-linux-gcc -Wall -Os -march=mips32r2 -mtune=24kc hex_to_utf16be.c -o hex_to_utf16be
	$(TOOLCHAIN_DIR)/mips-openwrt-linux-strip hex_to_utf16be

ussd.sh

#!/bin/sh

# Huawei E3372 + velcom.by
device="/dev/ttyUSB2"
command="AT+CUSD=1,\"AA180C3602\",15\r"

tmp_file="/tmp/ussd_response.txt"

if ! echo "$1" | egrep -q "^[0-9]+$" ; then
  >&2 echo "sleep time is required (first argument)"
  exit 1
fi
sleep_time=$1

cp /dev/null "$tmp_file"
cat "$device" > "$tmp_file" &
bg_pid=$!

fault () {
  kill $bg_pid
  cp /dev/null "$tmp_file"
  exit 2
}
trap "fault" SIGINT

quit () {
  kill $bg_pid
  cp /dev/null "$tmp_file"
}
trap "quit" EXIT

# at least 1 ussd response
ussd_responses=""
while [ -z "$ussd_responses" ]; do
  echo -e "$command" > "$device"
  sleep $sleep_time

  # response will be like '+CUSD: 1,"C23..",15'
  ussd_responses=$(cat /tmp/ussd_response.txt | sed -nr "\
s/\
\+CUSD:\
[[:space:]]*?[01]\
[[:space:]]*?,\
[[:space:]]*?\"\
([0-9a-f]+?)\"\
.*$\
/\1/gip\
  ")
done

echo -e "$ussd_responses" | xargs -n1 ./hex_to_utf16be

cp /dev/null "$tmp_file"

./ussd.sh 20