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()
147