# 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, end=' ')
code = line[:3]
if line[3:4] == '-':
while 1:
line = f.readline()
if not line: break # Really an error
print(line, end=' ')
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)')
def raw_input(prompt):
sys.stdout.write(prompt)
sys.stdout.flush()
return sys.stdin.readline()
# Get a command from the user.
#
def getcommand():
try:
while 1:
line = input('ftp.py> ')
if line: return line
except EOFError:
return ''
# Call the main program.
#
if __name__ == '__main__':
main()
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