Transfer A Text File Via Socket In Python

Question

I have a project in PYTHON that is two machines (A , B) , 1) request machine A send a request to B to list a directory(in my code i set it to current directory) 2) in second request machine A wants to download the Text file of the directory. (Put a text file in machine B's directory) 3) after that machine A changes the text file and send back to the machine B. 4) and At the end machine A send two number and machine B send back the result of it. it work till step 2 but nothing happen after that it's like a true while I can't understand why?! Here is my Code Machine A (Client):

# -*- coding: UTF-8 -*-
import os
import socket
PORT = 9000
HOST = 'localhost'
socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.connect((HOST, PORT))
store=[]
direc = raw_input("Enter The Directory to List : ")
socket.sendall(direc)
len_data = socket.recv(2048)
print int(len_data)
for i in range(int(len_data)):
    data = socket.recv(2048)
    store.append(data)
print("List of Files:")
for i in store:
    print(i)
txt_file = raw_input("Please Choose a TEXT file :")
if store.count(txt_file) is 0:
    print("There no such a TXT file!!")
else:
    socket.sendall(txt_file)

def write_file(name):
    fname = open(name,'ab')
    while True:
        string = socket.recv(2048)
        if string:
            fname.write(string)
        else:
            fname.write("changed")
            fname.close()
            break
def read_file(name):
    fileToSend = open(name, 'rb')
    while True:
        data = fileToSend.readline()
        if data:
            socket.send(data)
        else:
            fileToSend.close()
            break

write_file(txt_file)
read_file(txt_file)
x = raw_input("Enter The First Num: ")
socket.send(x)
y = raw_input("Enter The Second Num: ")
socket.send(y)
result = socket.recv(1024)
print result
raw_input()
socket.sendall('')
socket.close()
exit()

and the Machine B (Server):

import os,sys,socket
PORT = 9000
HOST = 'localhost'
tcpsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_address = (HOST, PORT)
print >>sys.stderr, 'starting up on %s port %s' % server_address
socket.bind((HOST,PORT))
socket.listen(1)
conn, addr = socket.accept()
directory = conn.recv(2048)
if os.listdir(os.curdir):
    data = os.listdir(os.curdir)
len_data = data.__len__()
print(len_data)
if len_data:
        conn.send(str(len_data))
for i in data:
    if i:
        print >>sys.stderr, 'sending data back to the client'
        conn.send(i)
    else:
        break
txt_file_name = conn.recv(2048)
def write_file(name):
    with open(name,'wb') as fname:
        while True:
            string = conn.recv(2048)
            if string:
                fname.write(string)
            else:
                fname.close()
                break
def read_file(name):
    with open(name, 'rb') as fileToSend:
        while True:
            data = fileToSend.readline()
            if data:
                conn.send(data)
            else:
                fileToSend.close()
                break

def add (x,y):
    return str(x+y)

read_file(txt_file_name)
write_file(txt_file_name)

x = conn.recv(1024)
y = conn.recv(1024)
conn.send(add(x,y))
conn.sendall('')
conn.close()
exit()

Hai Vu · Accepted Answer

I am fascinated with your problem and looked into it. While we can solve it using socket. I lean toward HTTP protocol for several reasons:

You don't have to make up your own "hand shake". The HTTP protocol has provision for requesting file, uploading a file, and do some processing (your step #4)
You can test your server using a web browser
Web services are very popular now. This is a baby step to learn about web services.

Here is the server code (server.py):

from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler
import os

class MyHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        global running
        if self.path == '/':
            self.list_files()
        elif self.path.startswith('/calculation'):
            self.send_calculation()
        elif self.path.startswith('/quit'):
            self.send_response(200)
            running = False
        else:
            self.send_file(self.path[1:])

    def do_POST(self):
        filename = self.path[1:] # Remove the / from the path
        filesize = int(self.headers['Content-Length'])
        contents = self.rfile.read(filesize)

        with open(filename, 'w') as f:
            f.write(contents.decode())

        self.send_response(200)

    def send_file(self, filename):
        # Check to see if file exists and is a file, not directory
        if os.path.isfile(filename):
            self.send_response(200)
            self.send_header('Content-Type', 'text/plain')
            self.end_headers()

            # Read and send the contents of the file
            with open(filename) as f:
                contents = f.read()
            self.wfile.write(contents)
        else:
            self.send_response(404)
            self.send_header('Content-Type', 'text/plain')
            self.end_headers()
            self.wfile.write('Dude! File not found')

    def send_calculation(self):
        empty, operation, number1, number2 = self.path.split('/')
        result = int(number1) + int(number2)
        self.send_response(200)
        self.send_header('Content-Type', 'text/plain')
        self.end_headers()
        self.wfile.write(result)

    def list_files(self):
        file_list = os.listdir(os.curdir)
        if file_list:
            self.send_response(200)
            self.send_header('Content-Type', 'text/plain')
            self.end_headers()
            for filename in file_list:
                self.wfile.write('{}
'.format(filename))

#
# Main
#
running = True
server = HTTPServer(('', 9000), MyHandler)
print 'Server started on host:{}, port:{}'.format(*server.server_address)
while running:
    server.handle_request()

And here is the client code (client.py):

import urllib2
import urlparse

def make_url(server, port, path, scheme='http'):
    netloc = '{}:{}'.format(server, port)
    url = urlparse.urlunsplit((scheme, netloc, path, '', ''))
    return url

#
# Main
#
server = '10.0.0.5'
port = 9000

# 1 - Request directory listing
url = make_url(server, port, '/')
file_list = urllib2.urlopen(url).read()
print 'Files from server:'
for filename in file_list.splitlines():
    print '- {}'.format(filename)

# 2 - Request contents of a file
filename = raw_input('Type a file name: ')
url = make_url(server, port, filename)
contents = urllib2.urlopen(url).read()
print 'Contents:'
print contents

# 3 - Upload a file to the server
contents = 'hello, world.
The End'
filename = 'foo.txt'
url = make_url(server, port, filename)
f = urllib2.urlopen(url, data=contents)

# 4 - Do some calculation
n1 = 19
n2 = 5
path = '/calculation/{}/{}'.format(n1, n2)
url = make_url(server, port, path)
result = int(urllib2.urlopen(url).read())
print '{} + {} = {}'.format(n1, n2, result)

# Send quit signal

url = make_url(server, port, '/quit')
urllib2.urlopen(url).read()

Web Service

The server is really a web service, which provides the following services:

Get a directory listing

GET http://server:port/

This service will return a list of files in the current directory.

Get contents of a file

GET http://server:port/filename

Returns the contents of a file in plain text format.

Upload a file

POST http://server:port/filename

Copy a file from the client to the server. If the file already exists on the server, override it.

Do some calculation

GET http://server:port/calculation/x/y

Returns x + y

Shut down the server

GET http://server:port/quit

Tells the server to quit.

Error Handling

For the sake of brevity and clarity, I did not add and error handling to the code. Here are a few error condition that I can think of:

Retrieve a non-existing file, or a directory (server)
Upload failed because of the lack of file write permission (server)
In the calculation service, the parameters are not numbers (server)
The server has not started, wrong port, wrong server (client)

Other Discussions

In a general, GET means data flow from the server to the client, and POST the opposite direction.
To test GET action from the server, you can use your browser. For example, to retrieve the directory contents from 192.168.1.5, port 9000, point your web browser to:
```
http://192.168.1.5:900/  
```
Testing POST is trickier, see the client code in the upload section for idea of using POST.
In the server code, the do_GET() function handles all the GET requests, and the do_POST() function handles all the POST requests.