使用Python中的套接字将文件发送到服务器

Question

Mainpage displays my front page and upload is supposed to display the page where you enter the file you wish to store with the server

def upload():
        path_name = raw_input("Enter your file directory")
        open_file = open(path_name,'rb').read()
        name_split = path_name.split("\\")[-1].split('.')
        at = 1

        s.send("SAVE-"+username+"\\"+"".join(name_split[:-1])+"."+str(at)+"."+name_split[-1]+"-")

        while open_file:
            current = open_file[:1024]
            print current
            open_file = open_file[1024:]
            s.send(current)


def mainpage():
        global R2
        R2=Tk()
        gg="white"
        g="blue"
        R2.geometry('720x720')
        R2.title(username + " Dropbox")
        R2.resizable(width=False,height=False)
        logoutbt= Button(R2,text="Logout",width=10,height=2,bg=g,fg=gg,font="5",relief=RAISED,overrelief=RIDGE,command=deslogout)
        upload = Button(R2,text="Upload",width=10,height=2,bg=g,fg=gg,font="5",relief=RAISED,overrelief=RIDGE,command=desupload)
        retrieve = Button(R2,text="Retreive",width=10,height=2,bg=g,fg=gg,font="5",relief=RAISED,overrelief=RIDGE,command=desretreive)
        logoutbt.place(x = 220,y = 500)
        retrieve.place(x = 350,y = 500)
        upload.place(x = 480,y = 500)
        R2.mainloop()    
        open(path_name,'rb').close()

Now when I add the command mainpage() to return back to to my main page after sending the file to the server,the server gets stuck in an infinite loop

ServerCode

if message[0] == "SAVE":
                    if not os.path.exists("C:\Heights\Documents\Projects\HomeWork\Project\Server1\\Files\\"+message[1].split("\\")[0]):
                        os.makedirs("C:\Heights\Documents\Projects\HomeWork\Project\Server1\\Files\\"+message[1].split("\\")[0])
                    file =open("C:\Heights\Documents\Projects\HomeWork\Project\Server1\\Files\\"+ message[1],"wb")
                    content = ""
                    while True:
                        data = current_socket.recv(1024)
                        if not data:
                            break
                        content += data

                    file.write(content)
                    file.close()

The file reaches the server fine when I don't try to return, but the moment I add that one extra line, the server doesn't exit its loop where it receives all the file content. Also,if I try to get a response from the server when it's done writing all the data down, the client and the server get stuck.

Answer 1

Firstly, As a general rule, waiting for the socket to return nothing(empty string or whatever), is a bad idea. That is because in python a socket would only return empty data if the other side closed his socket. But if there was a problem or for any reason the socket was not closed properly, the socket.recv method would hang perhaps infinitely.

Secondly, I see that you intend to instantiate your TKinter App more than once. This is bad practice, and you should consider just hiding your main window.

Hope I was helpful.

Answer 2

Python's socket.recv(...) inherits semantics from Unix recv(2) function, and as stated in recv(2) man:

If no messages are available at the socket, the receive calls wait for a message to arrive, unless the socket is nonblocking

Therefore, since current_socket is blocking, your server just hangs on the line data = current_socket.recv(1024) infinitely right after the whole file has been read to the content variable until the socket on the client becomes properly closed.

To avoid that:

• On the client side send your file size in bytes before sending any of its contents:

   import struct ... file_len_bytes = pack('!i', len(open_file)) s.send(file_len_bytes) while open_file: .... 

• On the server side read your file size and then use it to check whether the whole file has been read:

   import struct ... file_len_bytes = "" while len(file_len_bytes) < 4: file_len_bytes += client.recv(1) file_len = struct.unpack("!i", file_len_bytes[:4])[0] content = "" bytes_read = 0 while bytes_read < file_len: data = current_socket.recv(1024) bytes_read += len(data) content += data