首页 > > 详细

COMP3331作业代做、代写Computer Networks作业、代做Java,C++,Python编程语言作业代写留学生 Statistics统计、回归

COMP3331/9331 Computer Networks and Applications
Assignment for Term 3, 2019
Version 1.0
Due: 11:59am (noon) Friday, 22 November 2019 (Week 10)
1. Change Log
Version 1.0 released on 7th October 2019.
2. Goal and learning objectives
Instant messaging applications such as WhatsApp, WeChat, Facebook Messenger, etc. are widely
used with millions of subscribers participating in them globally. In this assignment, you will have the
opportunity to implement your own version of an instant messaging application. In addition to basic
messaging functionality, you will also implement many additional services that are available in many
of the aforementioned applications. Your application is based on a client server model consisting of
one server and multiple messaging clients. The clients communicate with the server using TCP. The
server is mainly used to authenticate the clients and direct the messages (online or offline) between
clients. Besides, the server also has to support certain additional functions (presence notification,
blacklisting, timeout, etc.). You should also implement functionality that allows clients to send peerto-peer
messages to each other that bypass the server.
2.1 Learning Objectives
On completing this assignment, you will gain sufficient expertise in the following skills:
1. Detailed understanding of how instant messaging services work.
2. Expertise in socket programming.
3. Insights into designing an application layer protocol.
3. Assignment Specification
The base specification of the assignment is worth 20 marks. The specification is structured in two
parts. The first part covers the basic interactions between the clients and server and includes
functionality for clients to communicate with each other through the server. The second part asks you
implement additional functionality whereby two users can exchange messages with each other
directly (i.e. bypassing the server) in a peer-to-peer fashion. This first part is self-contained (Sections
3.1-3.3) and is worth 15 marks. Implementing peer-to-peer messaging (Section 3.4) is worth 5
marks. CSE students are expected to implement both functionalities. Non-CSE students are only
required to implement the first part (i.e. no peer-to-peer messaging). The marking guidelines are thus
different for the two groups and are indicated in Section 7.
Updates to the assignment, including any corrections and clarifications, will be posted on the
subject website. Please make sure that you check the subject website regularly for updates.
2
The assignment includes 2 major modules, the server program and the client program. The server
program will be run first followed by multiple instances of the client program (Each instance supports
one client). They will be run from the terminals on the same and/or different hosts.
There is an extension component (outlined in Section 3.5) that is worth 4 marks. Note that the bonus
marks may not be proportional to the amount of extra work that you will have to do. They are there
to encourage you to go beyond the standard assignment. The bonus marks can be used to make up
for lost marks in the lab exercises but NOT for any of the exams (mid-session and final).
3.1. Server
The server has the following responsibilities -
User Authentication - When a new client requests for a connection, the server should prompt the
user to input the username and password and authenticate the user. The valid username and password
combinations will be stored in a file called credentials.txt which will be in the same directory as the
server program. An example credentials.txt file is provided on the assignment page. Username and
passwords are case-sensitive. We may use a different file for testing so DO NOT hardcode this
information in your program. You may assume that each username and password will be on a separate
line and that there will be one white space between the two. If the credentials are correct, the client
is considered to be logged in (i.e. online) and a welcome message is displayed. When all messaging
is done, a user should be able to logout from the server.
On entering invalid credentials, the user is prompted to retry. After 3 consecutive failed attempts, the
user is blocked for a duration of block_duration seconds (block_duration is a command line argument
supplied to the server) and cannot login during this duration (even from another IP address). While a
user is online, if someone uses the same username/password to log in (even from another IP address),
then this new login attempt is denied.
Timeout - The server should keep track of all online users. If the server does not receive any
commands from a user for a period of timeout seconds (timeout is a command line argument supplied
to the server), then the server should automatically log this user out. Note that, to be considered active,
a user must actively issue a command. The receipt of a message does not count.
Presence Broadcasts - The server should notify the presence/absence of other users logged into the
server, i.e. send a broadcast notification to all online users when a user logs in and logs out.
List of online users - The server should provide a list of users that are currently online in response
to such a query from a user.
Online history – The sever should provide a list of users that logged in for a user specified time in
the past (e.g. users who logged in within the past 15 minutes).
Message Forwarding - The server should forward each instant message to the correct recipient
assuming they are online.
Offline Messaging - When the recipient of a message is not logged in (i.e. is offline), the message
will be saved by the server. When the recipient logs in next, the server will send all the unread
messages stored for that user (timestamps are not required).
Message Broadcast – The server should allow a user to broadcast a message to all online users.
Offline messaging is not required for broadcast messages.
3
Blacklisting - The server should allow a user to block / unblock any other user. For example, if user
A has blocked user B, B can no longer send messages to A i.e. the server should intercept such
messages and inform B that the message cannot be forwarded. Blocked users also do not get presence
notifications i.e. B will not be informed each time A logs in or logs out.
3.2. Client
The client has the following responsibilities -
Authentication - The client should provide a login prompt to enable the user to authenticate with the
server.
Message - The client should allow the user to send a message to any other user and display messages
sent by other users. The client should also allow the user to send a broadcast message to all online
users.
Notifications - The client should display presence notifications sent by the server about users logging
in and out from the server.
Find users online - The client should provide a way for the user to obtain a list of all the users
currently online from the server.
Find online history – The client should provide a way for the user to obtain a list of all users who
had logged in within a user specified time period.
Blacklist – The client should allow a user to block a user from sending any further messages. The
client should also allow a user to unblock a user that was earlier blocked.
3.3 Commands supported by the client
After a user is logged in, the client should support all the commands shown in the table below. For
the following, assume that commands were run by user A.
Command Description
message Send to through the server. If the user is
online then deliver the message immediately, else store the
message for offline delivery. If has blocked A, then a
message to that effect should be displayed for A. If the is
not present in the credentials file (i.e. invalid user) or is self (A)
then an appropriate error message should be displayed. The
used in our tests will be a few words at most.
broadcast Send to all online users except A and those users who
have blocked A. Inform A that message could not be sent to some
recipients.
whoelse This should display the names of all users that are currently
online excluding A. Users can be displayed in any order.
whoelsesince

联系我们
  • QQ:99515681
  • 邮箱:99515681@qq.com
  • 工作时间:8:00-23:00
  • 微信:codinghelp
热点文章
程序代写更多图片

联系我们 - QQ: 99515681 微信:codinghelp
© 2014 www.7daixie.com
程序代写网!