~azzar1/unity/add-show-desktop-key

# 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

import cjson

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, cjson.encode(response))

            conn.close()

        except Terminate, t:

            # Try and send final response and then terminate

            if t.final_response:

                send_netstring(conn, cjson.encode(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, cjson.encode(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)

    json = encode(msg, magic)

    send_netstring(sok, json)

    inp = recv_netstring(sok)

    sok.close()

    if decode:

        return cjson.decode(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 = cjson.encode(message)

    digest = hashlib.md5(content + magic).hexdigest()

    env = {'digest':digest,'content':content}

    json = cjson.encode(env)

    return json

def decode(message, magic):

    """Takes a message with an attached HMAC digest and validates the message.

    """

    msg = cjson.decode(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 = cjson.decode(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)