《Python 黑帽子》学习笔记 - Python3 实现 netcat - Day 8

原书的代码主要考虑的是如何实现功能，在字符编码，socket 阻塞和数据交互，异常处理等方面存在一些问题，造成了程序功能不完善，逻辑出差和退出等情况。

本篇笔记记录用 Python3 实现原书的 netcat, 脚本功能和步骤主要是参照原书的实现思路，会对部分代码的逻辑进行更合理的调整，并学习字符编码，异常处理，调试日志记录等知识点。

功能和实现思路见上一篇笔记。

Python3 代码

#!/usr/bin/env python3
# -*- code: utf-8 -*-

import sys
import getopt
import socket
import subprocess
import threading
import logging

logging.basicConfig(level=logging.DEBUG,
                    format='%(filename)s[line:%(lineno)d] %(levelname)s: %(message)s',
                    # format='%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s: %(message)s',
                    # datefmt='%Y/%m/%d %H:%M:%S',
                    # filename='myapp.log',
                    filemode='a')

# define some global variables
listen = False
command = False
upload = False
execute = ""
target = ""
upload_destination = ""
port = 0

def run_command(command):
    """
    execute the shell command, or file received from client.
    :param command: 
    :return: output: shell command result. 
    """
    # trim the newline.(delete the characters of the string end.)
    command = command.rstrip()

    # run the command and get the output back
    try:
        # run command with arguments and return its output.
        output = subprocess.check_output(command, stderr=subprocess.STDOUT, shell=True)
        logging.debug(output)
    except Exception as e:
        logging.error(e)
        output = b"Failed to execute command.\r\n"

    # send the output back to the client
    return output

def client_handler(client_socket):
    """
    the thread function of handling the client. 
    :param client_socket: 
    :return: 
    """
    global upload
    global execute
    global command

    # upload file
    if len(upload_destination):
        # read in all of the bytes and write to our destination
        file_buffer = ""
        # keep reading data until none is available
        while True:
            data = client_socket.recv(1024)
            file_buffer += data.decode("utf-8")
            logging.debug(data)

            # "#EOF#" tell the server, file is end.
            if "#EOF#" in file_buffer:
                file_buffer = file_buffer[:-6]
                break
            # for interaciton, like heart packet.
            client_socket.send(b"#")

        # now we take these bytes and try to write them out
        try:
            with open(upload_destination, "wb") as fw:
                fw.write(file_buffer.encode("utf-8"))
            client_socket.send(