Openwrt + Huawei E367 + balance of mts.by with bash and c

7bit_hex_to_char.c

#include <stdint.h>
#include <stdio.h>
#include <string.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 get_data_pair(const char *input, uint8_t *output) {
  uint8_t data;

  if (get_data(*input, &data) != 0) {
    return 1;
  }

  *output = data << 4;

  if (get_data(*(input + 1), &data) != 0) {
    return 2;
  }

  *output = *output | data;

  return 0;
}

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

  char *hex = argv[1];
  uint16_t data = 0;
  uint8_t data_length = 0;

  while (*hex != '\0') {
    uint8_t new_data;
    if (get_data_pair(hex, &new_data) != 0) {
      fprintf(stderr, "invalid hex: bad pair %.2s\n", hex);
      return 2;
    }
    hex += 2;

    data = new_data << data_length | data;
    data_length += 8;

    while (data_length >= 7) {
      putchar(data & 0x7f);
      data = data >> 7;
      data_length -= 7;
    }
  }

  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 7bit_hex_to_char.c -o 7bit_hex_to_char
	$(TOOLCHAIN_DIR)/mips-openwrt-linux-strip 7bit_hex_to_char

ussd.sh

#!/bin/sh

# Huawei E367 + mts.by
device="/dev/ttyUSB1"
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 ./7bit_hex_to_char

cp /dev/null "$tmp_file"

./ussd.sh 20