World's Shortest P2P App: 15 Lines

World's Shortest P2P App: 15 Lines: "'The New Scientist has an article about TinyP2P, the world's smallest P2P app. It's 15 lines of Python code brought to us by Edward Felten, CS Professor at Princeton and outspoken supporter of the digital rights the Slashdot community holds so dear. He wrote the program as a proof-of-concept that P2P apps are really easy to write, don't have to be complicated, and thus banning them (a la the INDUCE Act) is pointless and silly.'"

# tinyp2p.py 1.0 (documentation at http://freedom-to-tinker.com/tinyp2p.html)

import sys, os, SimpleXMLRPCServer, xmlrpclib, re, hmac # (C) 2004, E.W. Felten

ar,pw,res = (sys.argv,lambda u:hmac.new(sys.argv[1],u).hexdigest(),re.search)

pxy,xs = (xmlrpclib.ServerProxy,SimpleXMLRPCServer.SimpleXMLRPCServer)

def ls(p=""):return filter(lambda n:(p=="")or res(p,n),os.listdir(os.getcwd()))

if ar[2]!="client": # license: http://creativecommons.org/licenses/by-nc-sa/2.0

  myU,prs,srv = ("http://"+ar[3]+":"+ar[4], ar[5:],lambda x:x.serve_forever())

  def pr(x=[]): return ([(y in prs) or prs.append(y) for y in x] or 1) and prs

  def c(n): return ((lambda f: (f.read(), f.close()))(file(n)))[0]

  f=lambda p,n,a:(p==pw(myU))and(((n==0)and pr(a))or((n==1)and [ls(a)])or c(a))

  def aug(u): return ((u==myU) and pr()) or pr(pxy(u).f(pw(u),0,pr([myU])))

  pr() and [aug(s) for s in aug(pr()[0])]

  (lambda sv:sv.register_function(f,"f") or srv(sv))(xs((ar[3],int(ar[4]))))

for url in pxy(ar[3]).f(pw(ar[3]),0,[]):

  for fn in filter(lambda n:not n in ls(), (pxy(url).f(pw(url),1,ar[4]))[0]):

    (lambda fi:fi.write(pxy(url).f(pw(url),2,fn)) or fi.close())(file(fn,"wc"))