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146 lines
3.5 KiB
Python
Executable file
146 lines
3.5 KiB
Python
Executable file
# A simple FTP client.
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#
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# The information to write this program was gathered from RFC 959,
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# but this is not a complete implementation! Yet it shows how a simple
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# FTP client can be built, and you are welcome to extend it to suit
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# it to your needs...
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#
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# How it works (assuming you've read the RFC):
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#
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# User commands are passed uninterpreted to the server. However, the
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# user never needs to send a PORT command. Rather, the client opens a
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# port right away and sends the appropriate PORT command to the server.
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# When a response code 150 is received, this port is used to receive
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# the data (which is written to stdout in this version), and when the
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# data is exhausted, a new port is opened and a corresponding PORT
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# command sent. In order to avoid errors when reusing ports quickly
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# (and because there is no s.getsockname() method in Python yet) we
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# cycle through a number of ports in the 50000 range.
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import sys, posix, string
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from socket import *
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BUFSIZE = 1024
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# Default port numbers used by the FTP protocol.
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#
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FTP_PORT = 21
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FTP_DATA_PORT = FTP_PORT - 1
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# Change the data port to something not needing root permissions.
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#
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FTP_DATA_PORT = FTP_DATA_PORT + 50000
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# Main program (called at the end of this file).
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#
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def main():
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hostname = sys.argv[1]
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control(hostname)
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# Control process (user interface and user protocol interpreter).
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#
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def control(hostname):
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#
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# Create control connection
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#
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s = socket(AF_INET, SOCK_STREAM)
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s.connect(hostname, FTP_PORT)
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f = s.makefile('r') # Reading the replies is easier from a file...
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#
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# Control loop
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#
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r = None
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while 1:
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code = getreply(f)
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if code in ('221', 'EOF'): break
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if code == '150':
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getdata(r)
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code = getreply(f)
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r = None
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if not r:
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r = newdataport(s, f)
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cmd = getcommand()
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if not cmd: break
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s.send(cmd + '\r\n')
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# Create a new data port and send a PORT command to the server for it.
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# (Cycle through a number of ports to avoid problems with reusing
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# a port within a short time.)
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#
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nextport = 0
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#
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def newdataport(s, f):
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global nextport
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port = nextport + FTP_DATA_PORT
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nextport = (nextport+1) % 16
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r = socket(AF_INET, SOCK_STREAM)
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r.bind(gethostbyname(gethostname()), port)
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r.listen(1)
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sendportcmd(s, f, port)
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return r
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# Send an appropriate port command.
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#
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def sendportcmd(s, f, port):
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hostname = gethostname()
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hostaddr = gethostbyname(hostname)
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hbytes = string.splitfields(hostaddr, '.')
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pbytes = [`port/256`, `port%256`]
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bytes = hbytes + pbytes
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cmd = 'PORT ' + string.joinfields(bytes, ',')
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s.send(cmd + '\r\n')
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code = getreply(f)
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# Process an ftp reply and return the 3-digit reply code (as a string).
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# The reply should be a line of text starting with a 3-digit number.
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# If the 4th char is '-', it is a multi-line reply and is
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# terminate by a line starting with the same 3-digit number.
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# Any text while receiving the reply is echoed to the file.
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#
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def getreply(f):
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line = f.readline()
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if not line: return 'EOF'
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print line,
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code = line[:3]
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if line[3:4] == '-':
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while 1:
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line = f.readline()
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if not line: break # Really an error
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print line,
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if line[:3] == code and line[3:4] != '-': break
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return code
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# Get the data from the data connection.
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#
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def getdata(r):
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print '(accepting data connection)'
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conn, host = r.accept()
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print '(data connection accepted)'
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while 1:
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data = conn.recv(BUFSIZE)
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if not data: break
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sys.stdout.write(data)
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print '(end of data connection)'
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# Get a command from the user.
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#
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def getcommand():
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try:
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while 1:
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line = raw_input('ftp.py> ')
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if line: return line
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except EOFError:
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return ''
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# Call the main program.
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#
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main()
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