python 解决粘包现象(struct模块)

一. struct模块

　　 该模块可以把一个类型,转换为固定长度的bytes

import struct
lst  = [1,2,4,3,5,]
lst1  = [1,2,4,3,5,7,8,9,]
a = struct.pack('i',len(lst))#将列表的长度转化为固定的4字节
b = struct.pack('i',len(lst1))
print(a,len(a))
print(b,len(b))

　　还可以将想要让服务端/客户端知道的信息做成字典,将字典的长度和字典打包发送 : 

　　符号对应的类型以及转换之后的长度表 : 

　　struct模块实现大文件传输 :

#server端
import socket
import struct
import json
import os

sk = socket.socket()
sk.bind(('127.0.0.1',8989))
sk.listen()
conn,addr = sk.accept()

len_dic = struct.unpack('i',conn.recv(4))[0]#unpack解包接受的是元组类型,索引为0是字典的长度
str_dic = conn.recv(len_dic).decode('utf-8')#根据字典的长度将字典接收为字符串类型
dic = json.loads(str_dic)#将字符串类型的字典转换为字典(dict)
if dic['opt'] == 'upload':
    up_load = 'D:\a\b\c\\' + os.path.basename(dic['filename'])#路径拼接
    # up_load = os.path.join('D:\a\b\c\\',os.path.basename(dic['filename']))
    while dic['filesize'] >0:
        read_size = conn.recv(2048)
        with open(os.path.abspath(up_load),mode='ab') as f1:
            f1.write(read_size)
            dic['filesize'] -= len(read_size)

if dic['opt'] == 'download':
    down_load = 'D:\a\b\c'
    conn.send(json.dumps(os.listdir(down_load)).encode('utf-8'))
    while 1:
        s = conn.recv(2048).decode('utf-8')
        file = os.path.abspath(down_load+'/'+s)
        print(file)
        if os.path.isdir(file):
            dic1 = {'tybe':'dir'}
            len_dic1 = struct.pack('i',len(json.dumps(dic1)))
            conn.send(len_dic1 + json.dumps(dic1).encode('utf-8'))
            conn.send(json.dumps(os.listdir(file)).encode('utf-8'))
            down_load = os.path.abspath(file)
            continue
        elif os.path.isfile(file):
            dic2 = {'tybe':'fil','down_size':os.path.getsize(file)}
            len_dic2 = struct.pack('i',len(json.dumps(dic2)))
            conn.send(len_dic2 + json.dumps(dic2).encode('utf-8'))
            with open(file,mode='rb') as f:
                down_size = os.path.getsize(file)
                while down_size:
                    a = f.read(2048)
                    print(a)###########
                    conn.send(a)
                    down_size -= len(a)
                break

#client端
import socket
import struct
import os
import json

sk = socket.socket()
sk.connect(('127.0.0.1',8989))
def upload():
    dic = {'opt':'upload','filename':None,'filesize':None}
    file = input('请输入一个想要上传的绝对路径: ')
    dic['filename'] = file
    dic['filesize'] = os.path.getsize(file)
    str_dic = json.dumps(dic)
    len_dic = struct.pack('i',len(str_dic))#自动将字典的长度转换为4个bytes类型的长度
    sk.send(len_dic + str_dic.encode('utf-8'))

    with open(dic['filename'],mode='rb') as f:
        while dic['filesize'] > 0:
            read_size = f.read(2048)
            sk.send(read_size)
            dic['filesize'] -= len(read_size)

def download():
    dic = {'opt':'download','filename':None,'filesize':None}
    sk.send(struct.pack('i',len(json.dumps(dic)))+json.dumps(dic).encode('utf-8'))
    while 1:
        lst = json.loads(sk.recv(2048).decode('utf-8'))
        for k, v in enumerate(lst, 1):
            print(k, v)
        file = input('请根据序号输入想要下载的文件: ')
        sk.send(lst[int(file) - 1].encode('utf-8'))
        len_dic = struct.unpack('i',sk.recv(4))[0]
        str_dic = sk.recv(len_dic).decode('utf-8')
        if json.loads(str_dic)['tybe'] == 'dir':
            continue
        elif json.loads(str_dic)['tybe'] == 'fil':
            down_file = 'D:\a\b\c\\'+lst[int(file) - 1]
            while json.loads(str_dic)['down_size']:
                with open(down_file,mode='ab') as f:
                    down_ = sk.recv(2048)
                    f.write(down_)
                json.loads(str_dic)['down_size'] -= len(down_)

if __name__ =='__main__':
    lst = ['上传', '下载']
    def mai():
        for k,v in enumerate(lst,1):
            print(k,v)
        c = input('请按序号输入操作: ')
        if c == '1':
            upload()
        if c == '2':
            download()
        else:
            print('输入错误!')
    mai()