“ AttributeError”我在做什么错？

Question

I'm developing a server monitoring utility in Python that I want to work on everything from macOS to Haiku. It's split into a client that connects to and queries multiple servers. Right now I'm testing the client on a macOS host with the server running on Debian in a Parallels VM. However, I didn't commit the new changes I made that did work to GitHub, and then made some changes that broke the whole thing. I'm only going to include the parts of my code that are relevant.

This is from the client.

def getServerInfoByName(serverName):
    serverIndex = serverNames.index(serverName)
    serverAddress = serverAddressList[serverIndex]
    serverPort = serverPorts[serverIndex]
    serverUsername = serverUsernames[serverIndex]
    return serverAddress, serverPort, serverUsername



for server in serverNames:
    try:
        if server != None:
            serverInfo = getServerInfoByName(server)
            exec(server + "Socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)")
            exec(server + "Socket.connect(('" + serverInfo[0] + "', " + serverInfo[1] + "))")

    except ConnectionRefusedError:
        print("Could not establish a connection to " + server + ".")
        print(divider)
        sys.exit()




def clientLoop():
    sys.stdout.write(termcolors.BLUE + "-> " + termcolors.ENDC)
    commandInput = input()
    splitCommand = commandInput.split(' ')
    whichServer = splitCommand[0]

    if splitCommand[0] == "exit":
        sys.exit()

    # Insert new one word client commands here

    elif len(splitCommand) < 2:
        print("Not enough arguments")
        print(divider)
        clientLoop()

    elif splitCommand[1] == "ssh":
        serverInfo = getServerInfoByName(whichServer)
        os.system("ssh " + serverInfo[2] + "@" + serverInfo[0])
        print(divider)
        clientLoop()

    # Insert new external commands above here (if any, perhaps FTP in the 
    # future).
    # NOTE: Must be recursive or else we'll crash with an IndexError
    # TODO: Possibly just catch the exception and use that to restart the 
    # function

    else:
        whichServer = splitCommand[0]
        commandToServer = splitCommand[1]
        exec(whichServer + "Socket.send(commandToServer.encode('utf-8'))")

        response = exec(whichServer + "Socket.recv(1024)")
        print(response.decode('utf-8'))
        print(divider)
        clientLoop()

clientLoop()

And this is from the server.

### Start the server

try:
    incomingSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    incomingSocket.bind((address, port))

except OSError:
    print("The configured address is already in use.")
    print("The problem should solve itself in a few seconds.")
    print("Otherwise, make sure no other services are using")
    print("the configured address.")
    sys.exit()

incomingSocket.listen(1)

### Main loop for the server
while True:

    clientSocket, clientAddress = incomingSocket.accept()
    incomingCommand = clientSocket.recv(1024)
    command = incomingCommand.decode('utf-8')

    if command != None:
        if command == "os":
            clientSocket.send(osinfo[0].encode('utf-8'))

        elif command == "hostname":
            clientSocket.send(osinfo[1].encode('utf-8'))

        elif command == "kernel":
            clientSocket.send(osinfo[2].encode('utf-8'))

        elif command == "arch":
            clientSocket.send(osinfo[3].encode('utf-8'))

        elif command == "cpu":
            cpuOverall = getOverall()
            cpuOverallMessage = "Overall CPU usage: " + str(cpuOverall) + "%"
            clientSocket.send(cpuOverallMessage.encode('utf-8'))

        elif command == "stopserver":
            incomingSocket.close()
            clientSocket.close()
            sys.exit()

        else:
            clientSocket.send("Invalid command".encode('utf-8'))

Any time I try to send a command to the server, the client crashes with AttributeError: 'NoneType' object has no attribute 'decode' as soon as it tries to decode the response from the server. Eventually I want to encrypt the sockets with AES but I can't do that if it doesn't even work in plain text.

Answer 1

exec does not return anything. You should not generate variable names with exec but use dictionaries to store the sockets.

servers = {}
for name, address, port, username in zip(serverNames, serverAddressList, serverPorts, serverUsernames):
    try:
      server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      server.connect((address, port))
      servers[name] = server, address, port, username
    except ConnectionRefusedError:
        print("Could not establish a connection to {}.".format(name))
        print(divider)
        sys.exit()

def client_loop():
    while True:
        sys.stdout.write("{}-> {}".format(termcolors.BLUE,termcolors.ENDC))
        command = input().split()
        which_server = command[0]

        if which_server == "exit":
            break
        elif len(command) < 2:
            print("Not enough arguments")
            print(divider)
        elif command[1] == "ssh":
            _, address, _, username = servers[which_server]
            os.system("ssh {}@{}".format(username, address))
            print(divider)
        else:
            server = servers[which_server][0]
            server.sendall(command[1].encode('utf-8'))
            response = server.recv(1024)
            print(response.decode('utf-8'))
            print(divider)

client_loop()