# 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() |