Edit File: ftp.py
# 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()
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