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# IVLE - Informatics Virtual Learning Environment
# Copyright (C) 2007-2008 The University of Melbourne
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
# Module: Chat
# Author: Thomas Conway
# Date: 5/2/2008
try:
import json
except ImportError:
import simplejson as json
import cStringIO
import hashlib
import sys
import os
import socket
import traceback
SOCKETTIMEOUT = 60
BLOCKSIZE = 1024
class Terminate(Exception):
"""Exception thrown when server is to be shut down. It will attempt to
send the final_response to the client and then exits"""
def __init__(self, final_response=None):
self.final_response = final_response
def __str__(self):
return repr(self.final_response)
class ProtocolError(Exception):
"""Exception thrown when client violates the the chat protocol"""
pass
def start_server(port, magic, daemon_mode, handler, initializer = None):
# Attempt to open the socket.
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('', port))
s.listen(1)
# Excellent! It worked. Let's turn ourself into a daemon,
# then get on with the job of being a python interpreter.
if daemon_mode:
if os.fork(): # launch child and...
os._exit(0) # kill off parent
os.setsid()
if os.fork(): # launch child and...
os._exit(0) # kill off parent again.
os.umask(077)
try:
MAXFD = os.sysconf("SC_OPEN_MAX")
except:
MAXFD = 256
# Close all file descriptors, except the socket.
for i in xrange(MAXFD):
if i == s.fileno():
continue
try:
os.close(i)
except OSError:
pass
si = os.open(os.devnull, os.O_RDONLY)
os.dup2(si, sys.stdin.fileno())
so = os.open(os.devnull, os.O_WRONLY)
os.dup2(so, sys.stdout.fileno())
se = os.open(os.devnull, os.O_WRONLY)
os.dup2(se, sys.stderr.fileno())
if initializer:
initializer()
while True:
(conn, addr) = s.accept()
conn.settimeout(SOCKETTIMEOUT)
try:
# Grab the input and try to decode
inp = recv_netstring(conn)
try:
content = decode(inp, magic)
except ProtocolError:
conn.close()
continue
response = handler(content)
send_netstring(conn, json.dumps(response))
conn.close()
except Terminate, t:
# Try and send final response and then terminate
if t.final_response:
send_netstring(conn, json.dumps(t.final_response))
conn.close()
sys.exit(0)
except Exception:
# Make a JSON object full of exceptional goodness
tb_dump = cStringIO.StringIO()
e_type, e_val, e_tb = sys.exc_info()
traceback.print_tb(e_tb, file=tb_dump)
json_exc = {
"type": e_type.__name__,
"value": str(e_val),
"traceback": tb_dump.getvalue()
}
send_netstring(conn, json.dumps(json_exc))
conn.close()
def chat(host, port, msg, magic, decode = True):
sok = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sok.connect((host, port))
sok.settimeout(SOCKETTIMEOUT)
out = encode(msg, magic)
send_netstring(sok, out)
inp = recv_netstring(sok)
sok.close()
if decode:
return json.loads(inp)
else:
return inp
def encode(message, magic):
"""Converts a message into a JSON serialisation and uses a magic
string to attach a HMAC digest.
"""
# XXX: Any reason that we double encode?
content = json.dumps(message)
digest = hashlib.md5(content + magic).hexdigest()
env = {'digest':digest,'content':content}
return json.dumps(env)
def decode(message, magic):
"""Takes a message with an attached HMAC digest and validates the message.
"""
msg = json.loads(message)
# Check that the message is valid
digest = hashlib.md5(msg['content'] + magic).hexdigest()
if msg['digest'] != digest:
raise ProtocolError("HMAC digest is invalid")
content = json.loads(msg['content'])
return content
def send_netstring(sok, data):
""" Sends a netstring to a socket
"""
netstring = "%d:%s,"%(len(data),data)
sok.sendall(netstring)
def recv_netstring(sok):
""" Attempts to recieve a Netstring from a socket.
Throws a ProtocolError if the received data violates the Netstring
protocol.
"""
# Decode netstring
size_buffer = []
c = sok.recv(1)
while c != ':':
# Limit the Netstring to less than 10^10 bytes (~1GB).
if len(size_buffer) >= 10:
raise ProtocolError(
"Could not read Netstring size in first 9 bytes: '%s'"%(
''.join(size_buffer)))
size_buffer.append(c)
c = sok.recv(1)
try:
# Message should be length plus ',' terminator
recv_expected = int(''.join(size_buffer)) + 1
except ValueError, e:
raise ProtocolError("Could not decode Netstring size as int: '%s'"%(
''.join(size_buffer)))
# Read data
buf = []
recv_data = sok.recv(min(recv_expected, BLOCKSIZE))
recv_size = len(recv_data)
while recv_size < recv_expected:
buf.append(recv_data)
recv_data = sok.recv(min(recv_expected-recv_size, 1024))
recv_size = recv_size + len(recv_data)
assert(recv_size == recv_expected)
# Did we receive the correct amount?
if recv_data[-1] != ',':
raise ProtocolError("Netstring did not end with ','")
buf.append(recv_data[:-1])
return ''.join(buf)
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