套接字编程； 在多个设备上传输时文件损坏

Question

The problem I'm having is to get a file from the server to client across devices. Everything works fine on localhost. Lets say I want to "get ./testing.pdf" which sends the pdf from the server to the client. It sends but it is always missing bytes. Is there any problems with how I am sending the data. If so how can I fix it? I left out the code for my other functionalities since they are not used for this function.

sending a txt file with "hello" in it works perfectly

server.py

import socket, os, subprocess          # Import socket module

s = socket.socket()         # Create a socket object
host = socket.gethostname() # Get local machine name
#host = ''
port = 5000                # Reserve a port for your service.
bufsize = 4096
s.bind((host, port))        # Bind to the port
s.listen(5)                 # Now wait for client connection.

while True:
    c, addr = s.accept()     # Establish connection with client.
    print 'Got connection from', addr

    while True:
      userInput = c.recv(1024)


    .... CODE ABOUT OTHER FUNCTIONALITY

      elif userInput.split(" ")[0] == "get":
      print "inputed get"
      somefile = userInput.split(" ")[1]
      size = os.stat(somefile).st_size
      print size
      c.send(str(size))

      bytes = open(somefile).read()
      c.send(bytes)
      print c.recv(1024)

c.close()  

client.py

import socket, os               # Import socket module

s = socket.socket()         # Create a socket object
host = socket.gethostname() # Get local machine name
#host = '192.168.0.18'
port = 5000                # Reserve a port for your service.
bufsize = 1

s.connect((host, port))

print s.recv(1024)
print "Welcome to the server :)"

while 1 < 2:
    userInput = raw_input()

   .... CODE ABOUT OTHER FUNCTIONALITY

    elif userInput.split(" ")[0] == "get":
        print "inputed get"
        s.send(userInput)
        fName = os.path.basename(userInput.split(" ")[1])
        myfile = open(fName, 'w')
        size = s.recv(1024)
        size = int(size)
        data = "" 

        while True:
            data += s.recv(bufsize)
            size -= bufsize
            if size < 0: break
            print 'writing file .... %d' % size

        myfile = open('Testing.pdf', 'w')
        myfile.write(data)
        myfile.close()
        s.send('success')

 s.close 

Answer 1

I can see two problems right away. I don't know if these are the problems you are having, but they are problems. Both of them relate to the fact that TCP is a byte stream, not a packet stream. That is, recv calls do not necessarily match one-for-one with the send calls.

1. size = s.recv(1024) It is possible that this recv could return only some of the size digits. It is also possible that this recv could return all of the size digits plus some of the data. I'll leave it for you to fix this case.

2. data += s.recv(bufsize) / size -= bufsize There is no guarantee that that the recv call returns bufsize bytes. It may return a buffer much smaller than bufsize. The fix for this case is simple: datum = s.recv(bufsize) / size -= len(datum) / data += datum .