Saturday, November 27, 2010

Finger protocol notes

finger protocol using netcat:

nc 79
[return] - prints info about everyone
[username] - returns plan and stuff for username

RFC 742 - NAME/FINGER Protocol
RFC 1288 - The Finger User Information Protocol

A finger client written in Python:

import socket

def finger(node):
    # Separate out username and domain
    elements = node.split('@')
    if len(elements) == 1:
        user, host = '', elements[0]
    elif len(elements) == 2:
        user, host = elements
        return '' # Input was not in a useful format
    # Contact host
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.settimeout(5) # we get bored after N seconds
    print 'host by name'
    print "address info"
    socket.getaddrinfo(host, 79)
    print 'start connect:', host
    s.connect((host, 79))
    print 'connect finished'

    #print socket.getaddrinfo(host, 79)
    #s.create_connection((host, 79), timeout = 10.0)
    #s = socket.create_connection((host, 79), timeout = 5)
    s.send(user + "\r\n")
    result = ''
    while True:
        data = s.recv(1024)
        if len(data) == 0: break
        result += data
    # print result
    return result

print finger('')
print finger('')
print 'Finished'

It has a basic problem: it connects via the standard socket connect() command. Unfortunately, on both Linux and Windows, there is no way to set a timeout. This makes it inconvenient to use if you have the host wrong. connect() will eventually time out, but the delay is quite long, and you have no control over it. This makes the python code tedious to use.

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