# A simple FTP client.

#

# The information to write this program was gathered from RFC 959,

# but this is not a complete implementation!  Yet it shows how a simple

# FTP client can be built, and you are welcome to extend it to suit

# it to your needs...

#

# How it works (assuming you've read the RFC):

#

# User commands are passed uninterpreted to the server.  However, the

# user never needs to send a PORT command.  Rather, the client opens a

# port right away and sends the appropriate PORT command to the server.

# When a response code 150 is received, this port is used to receive

# the data (which is written to stdout in this version), and when the

# data is exhausted, a new port is opened and a corresponding PORT

# command sent.  In order to avoid errors when reusing ports quickly

# (and because there is no s.getsockname() method in Python yet) we

# cycle through a number of ports in the 50000 range.

import sys, posix, string

from socket import *

BUFSIZE = 1024

# Default port numbers used by the FTP protocol.

#

FTP_PORT = 21

FTP_DATA_PORT = FTP_PORT - 1

# Change the data port to something not needing root permissions.

#

FTP_DATA_PORT = FTP_DATA_PORT + 50000

# Main program (called at the end of this file).

#

def main():

    hostname = sys.argv[1]

    control(hostname)

# Control process (user interface and user protocol interpreter).

#

def control(hostname):

    #

    # Create control connection

    #

    s = socket(AF_INET, SOCK_STREAM)

    s.connect((hostname, FTP_PORT))

    f = s.makefile('r') # Reading the replies is easier from a file...

    #

    # Control loop

    #

    r = None

    while 1:

        code = getreply(f)

        if code in ('221', 'EOF'): break

        if code == '150':

            getdata(r)

            code = getreply(f)

            r = None

        if not r:

            r = newdataport(s, f)

        cmd = getcommand()

        if not cmd: break

        s.send(cmd + '\r\n')

# Create a new data port and send a PORT command to the server for it.

# (Cycle through a number of ports to avoid problems with reusing

# a port within a short time.)

#

nextport = 0

#

def newdataport(s, f):

    global nextport

    port = nextport + FTP_DATA_PORT

    nextport = (nextport+1) % 16

    r = socket(AF_INET, SOCK_STREAM)

    r.bind((gethostbyname(gethostname()), port))

    r.listen(1)

    sendportcmd(s, f, port)

    return r

# Send an appropriate port command.

#

def sendportcmd(s, f, port):

    hostname = gethostname()

    hostaddr = gethostbyname(hostname)

    hbytes = string.splitfields(hostaddr, '.')

    pbytes = [repr(port//256), repr(port%256)]

    bytes = hbytes + pbytes

    cmd = 'PORT ' + string.joinfields(bytes, ',')

    s.send(cmd + '\r\n')

    code = getreply(f)

# Process an ftp reply and return the 3-digit reply code (as a string).

# The reply should be a line of text starting with a 3-digit number.

# If the 4th char is '-', it is a multi-line reply and is

# terminate by a line starting with the same 3-digit number.

# Any text while receiving the reply is echoed to the file.

#

def getreply(f):

    line = f.readline()

    if not line: return 'EOF'

    print line,

    code = line[:3]

    if line[3:4] == '-':

        while 1:

            line = f.readline()

            if not line: break # Really an error

            print line,

            if line[:3] == code and line[3:4] != '-': break

    return code

# Get the data from the data connection.

#

def getdata(r):

    print '(accepting data connection)'

    conn, host = r.accept()

    print '(data connection accepted)'

    while 1:

        data = conn.recv(BUFSIZE)

        if not data: break

        sys.stdout.write(data)

    print '(end of data connection)'

# Get a command from the user.

#

def getcommand():

    try:

        while 1:

            line = raw_input('ftp.py> ')

            if line: return line

    except EOFError:

        return ''

# Call the main program.

#

main()