/Demo/sockets/ftp.py

  1# A simple FTP client.
  2#
  3# The information to write this program was gathered from RFC 959,
  4# but this is not a complete implementation!  Yet it shows how a simple
  5# FTP client can be built, and you are welcome to extend it to suit
  6# it to your needs...
  7#
  8# How it works (assuming you've read the RFC):
  9#
 10# User commands are passed uninterpreted to the server.  However, the
 11# user never needs to send a PORT command.  Rather, the client opens a
 12# port right away and sends the appropriate PORT command to the server.
 13# When a response code 150 is received, this port is used to receive
 14# the data (which is written to stdout in this version), and when the
 15# data is exhausted, a new port is opened and a corresponding PORT
 16# command sent.  In order to avoid errors when reusing ports quickly
 17# (and because there is no s.getsockname() method in Python yet) we
 18# cycle through a number of ports in the 50000 range.
 19
 20
 21import sys, posix, string
 22from socket import *
 23
 24
 25BUFSIZE = 1024
 26
 27# Default port numbers used by the FTP protocol.
 28#
 29FTP_PORT = 21
 30FTP_DATA_PORT = FTP_PORT - 1
 31
 32# Change the data port to something not needing root permissions.
 33#
 34FTP_DATA_PORT = FTP_DATA_PORT + 50000
 35
 36
 37# Main program (called at the end of this file).
 38#
 39def main():
 40    hostname = sys.argv[1]
 41    control(hostname)
 42
 43
 44# Control process (user interface and user protocol interpreter).
 45#
 46def control(hostname):
 47    #
 48    # Create control connection
 49    #
 50    s = socket(AF_INET, SOCK_STREAM)
 51    s.connect((hostname, FTP_PORT))
 52    f = s.makefile('r') # Reading the replies is easier from a file...
 53    #
 54    # Control loop
 55    #
 56    r = None
 57    while 1:
 58        code = getreply(f)
 59        if code in ('221', 'EOF'): break
 60        if code == '150':
 61            getdata(r)
 62            code = getreply(f)
 63            r = None
 64        if not r:
 65            r = newdataport(s, f)
 66        cmd = getcommand()
 67        if not cmd: break
 68        s.send(cmd + '\r\n')
 69
 70
 71# Create a new data port and send a PORT command to the server for it.
 72# (Cycle through a number of ports to avoid problems with reusing
 73# a port within a short time.)
 74#
 75nextport = 0
 76#
 77def newdataport(s, f):
 78    global nextport
 79    port = nextport + FTP_DATA_PORT
 80    nextport = (nextport+1) % 16
 81    r = socket(AF_INET, SOCK_STREAM)
 82    r.bind((gethostbyname(gethostname()), port))
 83    r.listen(1)
 84    sendportcmd(s, f, port)
 85    return r
 86
 87
 88# Send an appropriate port command.
 89#
 90def sendportcmd(s, f, port):
 91    hostname = gethostname()
 92    hostaddr = gethostbyname(hostname)
 93    hbytes = string.splitfields(hostaddr, '.')
 94    pbytes = [repr(port//256), repr(port%256)]
 95    bytes = hbytes + pbytes
 96    cmd = 'PORT ' + string.joinfields(bytes, ',')
 97    s.send(cmd + '\r\n')
 98    code = getreply(f)
 99
100
101# Process an ftp reply and return the 3-digit reply code (as a string).
102# The reply should be a line of text starting with a 3-digit number.
103# If the 4th char is '-', it is a multi-line reply and is
104# terminate by a line starting with the same 3-digit number.
105# Any text while receiving the reply is echoed to the file.
106#
107def getreply(f):
108    line = f.readline()
109    if not line: return 'EOF'
110    print line,
111    code = line[:3]
112    if line[3:4] == '-':
113        while 1:
114            line = f.readline()
115            if not line: break # Really an error
116            print line,
117            if line[:3] == code and line[3:4] != '-': break
118    return code
119
120
121# Get the data from the data connection.
122#
123def getdata(r):
124    print '(accepting data connection)'
125    conn, host = r.accept()
126    print '(data connection accepted)'
127    while 1:
128        data = conn.recv(BUFSIZE)
129        if not data: break
130        sys.stdout.write(data)
131    print '(end of data connection)'
132
133# Get a command from the user.
134#
135def getcommand():
136    try:
137        while 1:
138            line = raw_input('ftp.py> ')
139            if line: return line
140    except EOFError:
141        return ''
142
143
144# Call the main program.
145#
146main()