python - 需要有关 Python 套接字编程的帮助(初学者)

Question

我正在学习套接字编程和 python。我需要创建一个向服务器发送命令的客户端(list 或 get )。服务器然后验证该命令。我的客户端程序可以显示 "list"或 "get"，但是当我输入其他东西时它不显示错误信息。
而且，它只能工作一次；当我在收到服务器的回复后输入不同的命令时，出现以下错误:

追溯(最近一次调用最后一次): 文件“fclient.py”，第 49 行，位于 client_socket.send(命令) 文件“/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.py”，第 170 行，在 _dummy 中 引发错误(EBADF，“错误的文件描述符”)

我完全迷路了。在客户端程序中获取命令行输入并将其发送到服务器并要求服务器验证命令行参数的最佳方法是什么？有人可以看一下并指出正确的方向吗？非常感谢您的帮助。

客户端.py

import socket   #for sockets
import sys      #for exit

command = ' '
socksize = 1024

#return a socket descriptor which can be used in other socket related functions
#properties: address family: AF_INET (IP v4)
#properties: type: SOCK_STREAM (connection oriented TCP protocol)

try:
    #create an AF_INET, STREAM socket (TCP)
    client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
except socket.error, msg:               #error handling
    print 'Failed to create socket. Error code: ' + str(msg[0]) + ', Error message: ' + msg[1]
    sys.exit();

print 'Socket Created'

#Get the IP address of the remote host/url
#connect to IP on a certain 'port' using the connect
#host = 'flip3.engr.oregonstate.edu'
#port = 30021
#host = 'www.google.com'
#port = 80
host = ''       #symbolic name meaning the local host
port = 8888     #arbitrary non-privileged port

try:
    remote_ip = socket.gethostbyname(host)
except socket.gaierror:
    #could not resolve
    print 'Hostname could not be resolved. Existing'
    sys.exit()
print 'IP address of ' + host + ' is ' + remote_ip

#Connect to remote server
client_socket.connect((remote_ip, port))
print 'Socket Connected to ' + host + ' on ip ' + remote_ip


#Send some data to remote server
while True:
    print 'Enter a command: list or get <filename>'
    command = raw_input()
    if command.strip() == 'quit':
        break
    client_socket.send(command)

    data = client_socket.recv(socksize)
    print data

#Close the socket
client_socket.close()

服务器.py

import socket
import sys
from thread import *

#HOST = 'flip3.engr.oregonstate.edu' #symbolic name meaning all available interfaces
#PORT = 30021
HOST = ''
PORT = 8888

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'

try:
    server_socket.bind((HOST, PORT))    #bind to a address(and port)
except socket.error, msg:
    print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
    sys.exit()

print 'Socket bind complete'

#put the socket in listening mode
server_socket.listen(10)     #maximum 10 connections
print 'TCP Server Waiting for client on port 30021'

#wait to accept a connection - blocking call
client, addr = server_socket.accept()
#display client information
print 'Connected with ' + addr[0] + ':' + str(addr[1])

#keep talking with the client
while 1:
    #Receiving from client
    data = client.recv(1024)

    if (data == 'list' or data == 'get'):
        reply = 'receive: ' + data
        client.send(reply)
        break;
    else:
        reply = 'wrong command'
        client.send(reply)

client.close()

Answer 1

第一个问题是您在循环内部关闭了客户端套接字，在收到对第一个命令的回复后将其关闭。将关闭套接字移出循环并引入退出条件以退出循环:

#Connect to remote server
client_socket.connect((remote_ip, port))

print 'Socket Connected to ' + host + ' on ip ' + remote_ip

#Send some data to remote server
while True:
    print 'Enter a command: list or get <filename>'
    command = raw_input()
    if command.strip() == 'quit':
        break
    client_socket.send(command)

    data = client_socket.recv(socksize)
    print data

# Close the socket
client_socket.close()

您正在服务器端做类似的事情:您尝试在每次迭代时重新打开监听套接字。将这部分也移出循环:

#wait to accept a connection - blocking call
client, addr = server_socket.accept()

#display client information
print 'Connected with ' + addr[0] + ':' + str(addr[1])

你的命令解析不起作用的原因是因为这个声明:

if (data == 'list' or 'get'):

你想在这里写的是

if (data == 'list' or data == 'get'):

第一个表达式的计算结果如下:

• 是 data == 'list' 吗？
• 如果是，则该子表达式的计算结果为 True，因此 a 或 b 将返回。
• 如果不是，则选择 or 的第二个操作数，即字符串 'get'。
• or 表达式的结果现在将被 if 语句隐式转换为 bool 值:
• 情况 1:True 已经是 True
• 情况 2:转换为 bool 值的非空字符串的计算结果也为 True

因此您的 if 语句将始终评估为 True，这就是您的命令解析不起作用的原因。

写

if (data == 'list' or data == 'get'):

以更好的形式，我建议使用

if (data.strip() in ('list'  'get')):

最后，您应该将套接字代码包装在 try..finally 中，以确保套接字始终关闭，即使发生了类似 KeyboardInterrupt 的异常:

try:
    #keep talking with the client
    while 1:
        #Receiving from client
        data = client.recv(1024)

        if (data.strip() in ('list'  'get')):
            reply = 'receive: ' + data
            client.send(reply)
        else:
            reply = 'wrong command'
            client.send(reply)
except KeyboardInterrupt:
    print "Exiting gracefully."
finally:
    server_socket.close()

(finally 子句在所有情况下都会执行 - 无论是否发生已处理或未处理的异常)