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 

    21 import sys, posix, string

    22 from socket import *

    23 

    24 

    25 BUFSIZE = 1024

    26 

    27 # Default port numbers used by the FTP protocol.

    28 #

    29 FTP_PORT = 21

    30 FTP_DATA_PORT = FTP_PORT - 1

    31 

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

    33 #

    34 FTP_DATA_PORT = FTP_DATA_PORT + 50000

    35 

    36 

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

    38 #

    39 def main():

    40     hostname = sys.argv[1]

    41     control(hostname)

    42 

    43 

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

    45 #

    46 def 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 #

    75 nextport = 0

    76 #

    77 def 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 #

    90 def 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 #

   107 def 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 #

   123 def 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 #

   135 def 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 #

   146 main()