上传已经ok，下载是一样的

#server

# import socket
# sk=socket.socket()
# sk.bind(('127.0.0.1',9000))
# sk.listen()
# import json,os
#
# conn,addr=sk.accept()
# msg=conn.recv(4)
# length=struct.unpack('i',msg)
# key=conn.recv(length[0])
# li=json.loads(key.decode('utf-8'))
# print(li)
# ret=False
# if li[0]=='zlz' and li[1]=='666':
#     result='登录成功'
#     length=struct.pack('i',len(result.encode('utf-8')))
#     conn.send(length)
#     conn.send(result.encode('utf-8'))
#     ret=True
# else:
#     result='登录失败'
#     length = struct.pack('i', len(result.encode('utf-8')))
#     conn.send(length)
#     conn.send(result.encode('utf-8'))
import socketserver
import struct
import json
import os
class Myserver(socketserver.BaseRequestHandler):
    def handle(self):
        conn = self.request
        while True:
            try:
                msg = conn.recv(4)
                length = struct.unpack('i', msg)
                key = conn.recv(length[0])
                li = json.loads(key.decode('utf-8'))
                print(li)
                ret = False
                if li[0] == 'zlz' and li[1] == '666':
                    result = '登录成功'
                    length = struct.pack('i', len(result.encode('utf-8')))
                    conn.send(length)
                    conn.send(result.encode('utf-8'))
                    ret = True
                else:
                    result = '登录失败'
                    length = struct.pack('i', len(result.encode('utf-8')))
                    conn.send(length)
                    conn.send(result.encode('utf-8'))
                if ret:
                    result = '选择 上传文件 下载文件'
                    length = struct.pack('i', len(result.encode('utf-8')))
                    conn.send(length)
                    conn.send(result.encode('utf-8'))

                    msg = conn.recv(4)
                    length = struct.unpack('i', msg)
                    key = conn.recv(length[0])
                    li = key.decode('utf-8')
                    print(li)

                    msg = conn.recv(4)
                    length = struct.unpack('i', msg)[0]
                    print(length)

                    if li=='上传文件':
                        with open(r'C:UserslenovoDesktop339.tif',mode='wb') as f:
                            while length>0:
                                ret = conn.recv(1024)
                                f.write(ret)
                                length -= len(ret)
                    print('finish')
                    break
            except ConnectionResetError:
                break
        conn.close()
server = socketserver.ThreadingTCPServer(('127.0.0.1',9001),Myserver)
server.serve_forever()
#client

import socket
sk=socket.socket()
import struct
sk.connect(('127.0.0.1',9001))
import sys
import os
import json

class User:
    def __init__(self,account,pwd):
        self.acconut = account
        self.pwd = pwd
        self.info = [self.acconut, self.pwd]
        key = json.dumps(self.info).encode('utf-8')
        length = len(key)
        l=struct.pack('i', length)
        sk.send(l)
        sk.send(key)
while True:
    account=input('输入账号')
    pwd=input('输入密码')
    a=User(account,pwd)
    msg=sk.recv(4)
    length=struct.unpack('i',msg)[0]
    msg=sk.recv(length)
    print(msg.decode('utf-8'))
    msg = sk.recv(4)
    length = struct.unpack('i', msg)[0]
    msg = sk.recv(length)
    print(msg.decode('utf-8'))

    result=input('输入您的操作')
    length = struct.pack('i', len(result.encode('utf-8')))
    sk.send(length)
    sk.send(result.encode('utf-8'))

    path=input('path>>>')
    filesize=os.path.getsize(path)
    length = struct.pack('i', filesize)
    print(length)
    sk.send(length)
    with open(path,mode='rb') as f:
        while filesize>0:
            content=f.read(1024)
            sk.send(content)
            filesize-=1024
    sk.close()
    # r'C:UserslenovoDesktop239.tif'