python-3.x - 如何使用Python告诉客户端服务器中不存在文件

Question

我正在编写一个简单的客户端服务器简单应用程序，其中客户端向服务器请求某个文件。如果文件存在，则服务器发送文件及其大小；否则，服务器将发送文件。如果不存在，则服务器将向客户端发送一条消息，指出找不到该文件。我在服务器中包含了异常，但是我不知道如何在客户端中包含if子句:如果文件存在，则接收文件；如果文件存在，则接收文件。否则，收到消息说它不存在。我想我已经在服务器端做到了这一点，但是我不确定如何编写此代码，以便仅在服务器中找不到文件的情况下才在客户端中打印“文件未找到”消息。
这是服务器端代码

import socket
import os
import sys
import pickle

def Main():
    host = '127.0.0.1'
    port = 8881

    s = socket.socket()
    s.bind((host,port))
    print("Server", host, "waiting on port", port)
    s.listen(1)
    while True:
        c, addr = s.accept()
        print("Connected to: " + str(addr))
        filename = ''
        while True:
            data = c.recv(1024).decode('utf-8')
            if not data:
                break
            filename += data
        print("File requested: " + filename)
        if os.path.isfile(filename):
            lista = []
            myfile = os.path.getsize(filename)
            size = ('File size: ',myfile,' bytes')
            texto = ''
            for i in size:
                texto = texto + '{:>4}'.format(i)
            print(texto)
            lista.append(texto)
            file_size = pickle.dumps(lista)
            c.send(file_size)
            file2send = open(filename, "rb")
            c.send(file2send.read())
            c.close()
        else:
            print("File not found")
            msg = ('File not found')
            s.send(msg.encode('utf-8'))
            

if __name__ == '__main__':
    Main()

和客户端:

import socket, os.path, datetime, sys, pickle

def Main():
    host = '127.0.0.1'
    port = 8881

    s = socket.socket()
    s.connect((host, port))

    Filename = input("File name and extension: ")
    s.send(Filename.encode('utf-8'))
    s.shutdown(socket.SHUT_WR)
    file_size = s.recv(1024)
    lista = pickle.loads(file_size)
    print(lista)
    data = s.recv(1024).decode('utf-8')
    print(data)
    msg = s.recv(1024).decode('utf-8')
    print(msg)
    s.close()

if __name__ == '__main__':
    Main()

Answer 1

在服务器中，您正在将“找不到文件”消息发送到服务器套接字s，而是应将其发送到客户端c，并且根据您的逻辑，应先发送消息长度，然后发送消息，然后再关闭连接。
请引用下面的服务器代码。
服务器:

import socket
import os
import sys
import pickle

def Main():
    host = '127.0.0.1'
    port = 8881

    s = socket.socket()
    s.bind((host,port))
    print("Server", host, "waiting on port", port)
    s.listen(1)
    while True:
        c, addr = s.accept()
        print("Connected to: " + str(addr))
        filename = ''
        while True:
            data = c.recv(1024).decode('utf-8')
            if not data:
                break
            filename += data
        print("File requested: " + filename)
        if os.path.isfile(filename):
            lista = []
            myfile = os.path.getsize(filename)
            size = ('File size: ',myfile,' bytes')
            texto = ''
            for i in size:
                texto = texto + '{:>4}'.format(i)
            print(texto)
            lista.append(texto)
            file_size = pickle.dumps(lista)
            c.send(file_size)
            file2send = open(filename, "rb")
            c.send(file2send.read())
            c.close()
        else:
            print("File not found")
            msg = ('File not found')
            c.send(str(len(msg)).encode('utf-8'))
            c.send(msg.encode('utf-8'))
            c.close()
            

if __name__ == '__main__':
    Main()