python socket file transfer

Question

I'm trying to write transfer files or chunks of data over a socket. I feel as if I'm reinventing the wheel, but my searches for a simple solution have failed (everything I find is either too simple or too complex). The server would run on a phone running python 2.5.4. The intended application would be to sync music files between the phone and a host computer.

This is the guts of what I have, which appears to work. I send and receive 'ok' to break up streams.

Is sending 'ok' back and forth essentially as stop bits to break up streams of data a reasonable technique?

Is there a standard way to do this?

Running any sort of library server (ftp, http) on the phone is not a useful solution given the limits of the phone's memory and processing power.

server:

import socket

c = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
c.bind(('', 1234))
c.listen(1)
s,a = c.accept()

while True:
    data = s.recv(1024)
    cmd = data[:data.find('\n')]

    if cmd == 'get':
        x, file_name, x = data.split('\n', 2)
        s.sendall('ok')
        with open(file_name, 'rb') as f:
            data = f.read()
        s.sendall('%16d' % len(data))
        s.sendall(data)
        s.recv(2)

    if cmd == 'end':
        s.close()
        c.close()
        break

client:

import socket

s = socket.socket()
s.connect(('192.168.1.2', 1234))

def get_file(s, file_name):
    cmd = 'get\n%s\n' % (file_name)
    s.sendall(cmd)
    r = s.recv(2)
    size = int(s.recv(16))
    recvd = ''
    while size > len(recvd):
        data = s.recv(1024)
        if not data: 
            break
        recvd += data
    s.sendall('ok')
    return recvd

print get_file(s, 'file1')
print get_file(s, 'file2')
s.sendall('end\n')

Answer 1

Is sending 'ok' back and forth essentially as stop bits to break up streams of data a reasonable technique?

Most protocols use some terminator or another. Popular alternatives are '\r\n', '\r\n\r\n' or EOF (ctrl+d), but these are just arbitrarily chosen and no worse or better than your 'ok', as long as your client and server know how to handle it.

Answer 2

Your code looks good.

You don't actually need to send across the size of the file. You can use while True, as the check if not data: break will stop the loop.

while True:
    data = s.recv(1024)

    if not data: print " Done "; break

    recvd += data

Also, why are you sending 'ok' is the other side doesn't check for it? You are just skipping 2 bytes at each side.

Don't you need to cater to multiple clients? No need for multi-threading?

Answer 3

Is there a standard way to do this?

Yes. http://www.faqs.org/rfcs/rfc959.html

Describes the standard way to do this.

Here is an implementation: http://docs.python.org/library/ftplib.html

Answer 4

U may look at this implementation. It also take care of if the file is in a sub-directory. Here is the link!

server

import socket
import os

print('Waiting for clinet to connect...')
c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
c.bind(('', 1234))
c.listen(1)
s, a = c.accept()

print('Connected. Going to receive file.')
s.sendall('getfilename')
filename = s.recv(1024)
if '/' in filename:
    dir = os.path.dirname(filename)
    try:
        os.stat(dir)
    except:
        print('Directory does not exist. Creating directory.')
        os.mkdir(dir)
f = open(filename, 'wb')
print('Filename: ' + filename)

while True:
    s.sendall('getfile')
    size = int(s.recv(16))
    print('Total size: ' + str(size))
    recvd = ''
    while size > len(recvd):
        data = s.recv(1024)
        if not data: 
            break
        recvd += data
        f.write(data)
        #print(len(recvd))
    break
s.sendall('end')
print('File received.')

s.close()
c.close()
f.close()

client

import socket
import sys

if len(sys.argv) > 1 :
    print('Trying to connect...')
    s = socket.socket()
    s.connect(('127.0.0.1', 1234))

    print('Connected. Wating for command.')
    while True:
        cmd = s.recv(32)

        if cmd == 'getfilename':
            print('"getfilename" command received.')
            s.sendall(sys.argv[1])

        if cmd == 'getfile':
            print('"getfile" command received. Going to send file.')
            with open(sys.argv[1], 'rb') as f:
                data = f.read()
            s.sendall('%16d' % len(data))
            s.sendall(data)
            print('File transmission done.')

        if cmd == 'end':
            print('"end" command received. Teminate.')
            break