传说中只用了十五行Python语句的P2P客户端/服务端 [转]

#zz from http://www.exonsoft.com/~kochin/TinyP2P/tinyp2p.html  
# tinyp2p.py 1.0 (documentation at http://freedom-to-tinker.com/tinyp2p.html)  
# (C) 2004, E.W. Felten  
# license: http://creativecommons.org/licenses/by-nc-sa/2.0  
  
  
# Annotated by Kochin Chang, Jan. 2005  
  
  
# Usage:  
#   Server - python tinyp2p.py password server hostname  portnum [otherurl]  
#   Client - python tinyp2p.py password client serverurl pattern  
#                   ar[0]      ar[1]    ar[2]  ar[3]     ar[4]   ar[5]  
  
  
import sys, os, SimpleXMLRPCServer, xmlrpclib, re, hmac   
# Import libraries used in the program.  
# sys : system variables and functions.  
# os : portable OS dependent functionalities.  
# SimpleXMLRPCServer : basic XML-RPC server framework.  
# xmlrpclib : XML-RPC client support.  
# re : regular expression support.  
# hmac : RFC 2104 Keyed-Hashing Message Authentication.  
  
  
ar,pw,res = (sys.argv,lambda u:hmac.new(sys.argv[1],u).hexdigest(),re.search)  
# A multiple assignment.  
# ar <- sys.argv : the argument list.  
# pw <- lambda u:hmac.new(sys.argv[1],u).hexdigest() :  
#   a function makes an HMAC digest from a URL.  
#   INPUT: a string, u, which is a URL here.  
#   OUTPUT: a hexdecimal HMAC digest.  
#   DESCRIPTION:  
#     1. Creates a HMAC object from the URL using network's password,  
#        sys.argv[1], as the key.  
#     2. Returns a hexdecimal digest of the HMAC object.  
# res <- re.search : alias for the regular expression search function.  
  
pxy,xs = (xmlrpclib.ServerProxy,SimpleXMLRPCServer.SimpleXMLRPCServer)  
# A multiple assignment.  
# pxy <- xmlrpclib.ServerProxy : alias for the ServerProxy class.  
# xs <- SimpleXMLRPCServer.SimpleXMLRPCServer : alias for the SimpleXMLRPCServer class.  
  
def ls(p=""):return filter(lambda n:(p=="")or res(p,n),os.listdir(os.getcwd()))  
# a function lists directory entries.  
# INPUT: a string, p, which is a regular expression pattern.  
# OUTPUT: a list of directory entries matched the pattern.  
# DESCRIPTION:  
#   1. Creates a function using lambda expression that takes a pathname as its  
#      parameter. The function returns true if the pattern is empty or the  
#      pathname matches the pattern.  
#   2. Finds out what is the current working directory.  
#   3. Retrieves a list of directory entries of current working directory.  
#   4. Filters the list using the lambda function defined.  
  
if ar[2]!="client":  
# Running in server mode...  
    
  myU,prs,srv = ("http://"+ar[3]+":"+ar[4], ar[5:],lambda x:x.serve_forever())  
  # A multiple assignment.  
  # myU <- "http://"+ar[3]+":"+ar[4] : server's own URL.  
  # prs <- ar[5:] : URL's of other servers in the network.  
  # srv <- lambda x:x.serve_forever() :  
  #   a function to start a SimpleXMLRPCServer.  
  #   INPUT: a SimpleXMLRPCServer object, x.  
  #   OUTPUT: (none)  
  #   DESCRIPTION:  
  #     Calls the server's serve_forever() method to start handling request.  
    
  def pr(x=[]): return ([(y in prs) or prs.append(y) for y in x] or 1) and prs  
  # a function returns the server list.  
  # INPUT: a list, x, of servers' URLs to be added to the server list.  
  # OUTPUT: the updated server list.  
  # DESCRIPTION:  
  #   1. For each URL in x, checks whether it's already in the server list.  
  #      If it's not in the list, appends in onto the list.  
  #   2. Returns the updated server list.  
    
  def c(n): return ((lambda f: (f.read(), f.close()))(file(n)))[0]  
  # a function returns content of the specified file.  
  # INPUT: a string, n, which is a filename.  
  # OUTPUT: the content of the file in a string.  
  # DESCRIPTION:  
  #   1. Creates a function using lambda expression that takes a file object, f,  
  #      as its parameter. The function reads the content of the file, then  
  #      closes it. The results of the read and close are put into a tuple, and  
  #      the tuple is returned.  
  #   2. Creates a file object with the filename. Passes it to the lambda  
  #      function.  
  #   3. Retrieves and returns the first item returned from the lambda function.  
    
  f=lambda p,n,a:(p==pw(myU))and(((n==0)and pr(a))or((n==1)and [ls(a)])or c(a))  
  #   a request handling function, depending on the mode, returns server list,  
  #   directory entries, or content of a file.  
  #   INPUT: a string, p, which is a hexdecimal HMAC digest.  
  #          a mode number, n.  
  #          if n is 0, a is a list of servers to be added to server list.  
  #          if n is 1, a is a pattern string.  
  #          if n is anything else, a is a filename.  
  #   OUTPUT: if n is 0, returns the server list.  
  #           if n is 1, returns directory entries match the pattern.  
  #           if n is anything else, returns content of the file.  
  #   DESCRIPTION:  
  #     1. Verifies the password by comparing the HMAC digest received and the  
  #        one created itself. Continues only when they match.  
  #     2. If n is 0, calls pr() to add list, a, and returns the result.  
  #        If n is 1, calls ls() to list entries match pattern a, and returns  
  #        the result enclosed in a list.  
  #        If n is any other value, retreives and return content of the file  
  #        with filename specified in a.  
    
  def aug(u): return ((u==myU) and pr()) or pr(pxy(u).f(pw(u),0,pr([myU])))  
  # a function augments the network.  
  # INPUT: a string, u, which is a URL.  
  # OUTPUT: a list of URL's of servers in the network.  
  # DESCRIPTION:  
  #   1. If the URL, u, equals to my own URL, just returns the server list.  
  #   2. Otherwise, creates a ServerProxy object for server u. Then calls its  
  #      request handling function f with a HMAC digest, mode 0, and server  
  #      list with myself added.  
  #   3. Calls pr() with the result returned from server u to add them to my  
  #      own list.  
  #   4. Returns the new list.  
    
  pr() and [aug(s) for s in aug(pr()[0])]  
  # 1. Checks the server list is not empty.  
  # 2. Takes the first server on the list. Asks that server to augment its  
  #    server list with my URL.  
  # 3. For each server on the returned list, asks it to add this server to its  
  #    list.  
    
  (lambda sv:sv.register_function(f,"f") or srv(sv))(xs((ar[3],int(ar[4]))))  
  # Starts request processing.  
  # 1. Defines a function with lambda expression that takes a SimpleXMLRPCServer  
  #    object, registers request handling function, f, and starts the server.  
  # 2. Creates a SimpleXMLRPCServer object using hostname (ar[3]) and portnum  
  #    (ar[4]). Then feeds the object to the lambda function.  
    
# Running in client mode...  
for url in pxy(ar[3]).f(pw(ar[3]),0,[]):  
# 1. Create a ServerProxy object using the serverurl (ar[3]).  
# 2. Calls the remote server and retrieves a server list.  
# 3. For each URL on the list, do the following:  
  
  for fn in filter(lambda n:not n in ls(), (pxy(url).f(pw(url),1,ar[4]))[0]):  
  # 1. Create a ServerProxy object using the URL.  
  # 2. Calls the remote server to return a list of filenames matching the  
  #    pattern (ar[4]).  
  # 3. For each filename doesn't exist locally, do the following:  
    
    (lambda fi:fi.write(pxy(url).f(pw(url),2,fn)) or fi.close())(file(fn,"wc"))  
    # 1. Define a lambda function that takes a file object, calls remote server  
    #    for the file content, then closes the file.  
    # 2. Create a file object in write and binary mode with the filename. (I  
    #    think the mode "wc" should be "wb".)  
    # 3. Passes the file object to the lambda function.