import re
import subprocess
import hashlib

def get_available_devices():
    """
    Get a list of device serials connected via adb
    :return: list of str, each str is a device serial number
    """
    try:
        r = subprocess.check_output(["adb", "devices"])
    except Exception:
        return []
        
    if not isinstance(r, str):
        r = r.decode()
    devices = []
    for line in r.splitlines():
        segs = line.strip().split()
        if len(segs) == 2 and segs[1] == "device":
            devices.append(segs[0])
    return devices


def md5(input_str):
    """
    Calculate MD5 hash of a string
    
    :param input_str: input string
    :return: MD5 hex digest
    """
    return hashlib.md5(input_str.encode('utf-8')).hexdigest()