A very basic HTTP file server in 13 lines of python. Assumes all requests are GETs, and it vulnerable to directory traversal (Run it in ~ and localhost:8080/../../ will ls root), so don't use it online. Will correctly list files in directories.

fileserver.py

import sys, os, socket
s = socket.socket()
s.bind((sys.argv[1], int(sys.argv[2])))
s.listen(5)
try:
	while True:
		conn, addr = s.accept()
		path = os.path.join(os.getcwd(), "./"+conn.recv(4096).split("\n")[0].split(" ")[1])
		conn.send((open(path).read() if os.path.isfile(path) else reduce(lambda x,s:x+"\n"+s+("/" if os.path.isdir(s) else ""),sorted(os.listdir(path)),"Directory "+path+" ls")) if os.path.exists(path) else '404: '+path)
		conn.close()
finally:
	s.close()

prettyversion.py

#!/bin/env python
#pretty version
import sys, os, socket
s = socket.socket() #set up out socket
s.bind((sys.argv[1], int(sys.argv[2]))) #bind (I usually pass in localhost 8080, you will need root for a port < 1000)
s.listen(5) #start listening, drop all connection if we have > 5 waiting connections
try:
	while True: #listen loop
		conn, addr = s.accept() #block for a connection
		request = conn.recv(4096) #read up to 4 kb, I figure no get request should be more than this
		first_line = request.split("\n")[0] #get the GET <path> HTTP/1.1 line, this should be "\r\n" but it doesn't make a difference for this
		requested_file = first_line.split(" ")[1] #the the <path> part
		path = os.path.join(os.getcwd(), "./" + requested_file) #join to current directory. THIS DOES NOT PROTECT AGAINST DIRECTORY TRAVERSAL!!
		if os.path.exists(path): #checks to see is we have a file, obviously
			if os.path.isfile(path):
				conn.send(open(path).read()) #read that file. Seems to fail on very large files.
			else:
				conn.send("Directory " + path + " ls\n") #send the header
				for p in sorted(os.listdir(path)): #sort, does not put directories first like most file servers
					if os.path.isdir(p):
						conn.send(p + "/\n") #append a forward slash
					else:
						conn.send(p + "\n")
		else:
			conn.send("404: " + path) #meh
		conn.close() #we're done here
finally:
	s.close() #close the socket, freeing the port so we can relaunch on it