import argparse
import socket
import shlex
import subprocess
import sys
import textwrap
import threading

def execute(cmd):
    cmd = cmd.strip()
    if not cmd:
        return
    output = subprocess.check_output(shlex.split(cmd),stderr=subprocess.STDOUT)

#subprocess。这个库提供了一组强大的进程创建接口，让你可以通过多种方式调用其他程序return output.decode()

class Netcat:
    def __init__(self,args,buffer=None):
        self.args = args
        self.buffer = buffer
        self.socket = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
        self.socket.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
#利用传进来的参数，初始化一个NetCat对象，然后创建一个socket对象
    def run(self):
        if self.args.listen:
            self.listen()
        else:
            self.send()#run函数作为NetCat对象的执行入口，它的逻辑其实相当简单：直接把后续的执行移交给其他两个函数。如果我们的NetCat对象是接收方，run就执行listen函数；如果是发送方，run就执行send函数

    def send(self):
        self.socket.connect((self.args.target,self.args.port))
        if self.buffer:
            self.socket.send(self.buffer)
        try:
            while True:
                recv_len = 1
                response = ''
                while recv_len:
                    data = self.socket.recv(4096)
                    recv_len = len(data)
                    response += data.decode()
                    if recv_len < 4096:
                        break
                if response:
                    print(response)
                    buffer = input('>')
                    buffer += '\n'
                    self.socket.send(buffer.encode())
        except KeyboardInterrupt:
            print('User terminated')
            self.socket.close()
            sys.exit()
#先连接到target和port，之后利用try/catch块，这样就能直接用Ctrl+C组合键手动关闭连接，再通过通过循环接收数据
    def listen(self):
        self.socket.bind((self.args.target,self.args.port))
        self.socket.listen(5)
        while True:
            client_socket,_ = self.socket.accept()
            client_thread = threading.Thread(target=self.handle,args=(client_socket,))
            client_thread.start()
#listen函数把socket对象绑定到target和port上，然后开始用一个循环监听新连接，并把已连接的socket对象传递给handle函数。
    def handle(self,client_socket):
        if self.args.execute:
            output = execute(self.args.execute)
            client_socket.send(output.encode())
        elif self.args.upload:
            file_buffer = b''
            while True:
                data = client_socket.recv(4096)
                print(data.decode)
                if data:
                    file_buffer += data
                else:
                    break
            with open(self.args.upload,'wb') as f:
                f.write(file_buffer)
            message = f'Saved file {self.args.upload}'
            client_socket.send(message.encode())
        elif self.args.command:
            cmd_buffer = b''
            while True:
                try:
                    client_socket.send(b'ailx10:#>')
                    while '\n' not in cmd_buffer.decode():
                        cmd_buffer += client_socket.recv(64)
                    response = execute(cmd_buffer.decode())
                    if response:
                        client_socket.send(response.encode())
                    cmd_buffer = b''
                except Exception as e:
                    print(f'server killed {e}')
                    self.socket.close()
                    sys.exit()#handle函数会根据它收到的命令行参数来执行相应的任务：执行命令、上传文件，或是打开一个shell。#如果要执行命令，handle函数就会把该命令传递给execute函数，然后把输出结果通过socket发回去#如果要执行命令，handle函数就会把该命令传递给execute函数，然后把输出结果通过socket发回去#最后，如果要创建一个shell，我们还是创建一个循环，向发送方发一个提示符，然后等待其发回命令
if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="simple netcat tool",
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     epilog=textwrap.dedent("""Example:
                                     netcat.py -t 192.168.0.108 -p 5555 -l -c # command shell
                                     netcat.py -t 192.168.0.108 -p 5555 -l -u=mytest.txt # upload file
                                     netcat.py -t 192.168.0.108 -p 5555 -l -e=\"cat /etc/passwd\" # execute command
                                     echo 'ABC' | ./netcat.py -t 192.168.0.108 -p 135 # echo text to server port 135
                                     netcat.py -t 192.168.0.108 -p 5555 # connect to server
                                     """))
    parser.add_argument('-c','--command',action='store_true',help='command shell')
    parser.add_argument('-e','--execute',help='execute specified command')
    parser.add_argument('-l','--listen',action='store_true',help='listen')
    parser.add_argument('-p','--port',type=int,default=5555,help='specified port')
    parser.add_argument('-t','--target',default='192.168.0.108',help='specified ip')
    parser.add_argument('-u','--upload',help='upload file')

    args = parser.parse_args()
    if args.listen:
        buffer = ''
    else:
        buffer = sys.stdin.read()

    nc = Netcat(args,buffer.encode())
    nc.run()