Assignment 3 - Chat Server
You are tasked with creating a chat server that will serve multiple clients and
hold multiple channels.
The server will receive messages sent from clients and relay the messages to
other clients.
Server
Your server needs to acquire information for itself. It needs to know what port it
is listening to, which database it is reading from and manages a large number of
concurrent connections. The server should try to utilise non-blocking IO and/or
processes to allow for asynchronous communication. Consider using the select
module and/or multiple processes for the server.
Any implementation that can only serve one client at a time will not be accepted.
Your server will be lauched in the following way.
python server.py
Protocol
You need to implement the following protocol on the server. A message protocol
is a set of agreed procedures between parties. In this case, these protocols specify
the different type of messages that will be communicated between the client and
the server.
The client and server are aware of the types of messages they can send to and
receive from each other. Any messages that lie outside of the specified protocols
can safely be ignored.
Message Format
The message format is string in UTF-8 encoding. This character set supports
languages other than English, e.g. CJK characters, which can also be sent as
valid messages and usernames. However, protocol commands such as CONNECT
and REGISTER are required to exist in their specified form.
Messages
• LOGIN :USERNAME :PASSWORD
1
Your server will receive this message upon connection from a client. Your server
will process the username and password by checking if the user exists and the
password matches.
• REGISTER :USERNAME :PASSWORD
The client will be able to send the REGISTER message to register their own
username and password. The server will hold the username and password in a
database. The password should be hashed and not stored in plain text.
Since this is only version 0.1 of our protocol, we will only communicate using
plain text sockets.
• JOIN :CHANNEL
The JOIN message is sent to the server to indicate a channel that a user would
like to join. If the channel exists, the user is able to join the channel and be able
to send messages to others in that channel. If the channel does not exist or the
user attempt to re-join a joined channel, the user will receive a reply indicating
the error.
• CREATE :CHANNEL
A user is able to create a channel with a given name. If the channel already
exists, the channel will not be created and the user will receive a reply indicating
the error.
• SAY :CHANNEL :MESSAGE
This allows the user to send a message to a channel. Assume the user has joined
the channel, the server will receive this message and send it to the other users
in the same channel. If the user has not jointed the channel, then the user will
receive a reply indicating the error.
Once a user sends a SAY message, the user should receive a RECV of that message.
• RECV :USER :CHANNEL :MESSAGE
The client will receive this message, this occurs when a user sends a message
to the server via SAY, the server will send a RECV message detailing the user
who sent it, channel it was sent to and the message that was sent.
• CHANNELS
2
This command does not require the client to be logged in. It returns a list of
all the channels.
• RESULT :TYPE :MSG [:MORE. . . ]
This is a generic response from the server to the client. The result can contain
different types such as:
• JOIN
• CREATE
• LOGIN
• REGISTER
• CHANNELS
Each type will have a message or more to confirm if the message was successful
or invalid. Given the different types, this will impact the message(s) that can
be sent.
Result Types
As discussed in the previous section, the result message can contain different
types and messages. We will need to ensure that any message we send, the
client can receive confirmation from it.
• RESULT JOIN :CHANNEL :CONFIRMATION
The server will send the JOIN RESULT, alongside the channel and if the operation
was successful. If the operation is successful, the :CONFIRMATION would
be represented as “1”. If the operation was unsuccessful, the :CONFIRMATION
would be represented as “0”.
• RESULT CREATE :CHANNEL :CONFIRMATION
Similar to the JOIN RESULT, the message will contain the channel name that
was requested and confirmation string of either “1” or “0” to indiciate if the operation
was successful or not. The :CONFIRMATION component will indicate
“1” on success or “0” if the operation was unsuccessful.
• RESULT (LOGIN | REGISTER) :CONFIRMATION
Given the username and password to be sent to the server, the server will
respond with confirmation if the login or registration was successful. Similar to
JOIN and CREATE RESULT types, the confirmation part will be represented
as either “1” or “0” for determining success.
3
• RESULT CHANNELS [CHANNEL-NAME,. . . ]
Unlike the other result types, this result does not provide a confirmation since
it should always work. The result will contain a list of channel names.
Testing and Client
You are required to write your own test cases for this assignment. This includes
writing your own client and ensuring that your program can output code
coverage information.
Extension - Federation
If you have passed all compliance test cases for the chat server, you can implement
the federation extension within your chat server application. This extension
enables cross-server communication. That is, to allow multiple servers to
cooperate to allow users of different servers to message each other.
This means there will be an extension to the protocol itself. This is to ensure
that we do not encounter identifier clashing of users and channels. The extension
should not break any existing compatibility with your compliant chat server.
How does federation work?
Federation will allow your users to participate in discussions and subscribe to
channels on other servers. However your server will need to have a configuration
mode that will specify what servers it will cooperate with.
• Federating with other servers
One server is able to federate with other servers when given a file that contains
servers it can contact to federate with.
The file will be in the following format:
Example:
192.168.1.1:4400
168.172.3.23:2344
4
The server will attempt to send the following message to other servers:
• FEDERATE-OUT
The server that receives this message will add the connecting server to its own
internal list, and then send back a confirmation with the message: FEDERATECONFIRM
The following special commands need to be implemented.
• FEDCHANNELS [CHANNEL-NAME,. . . ]
Upon confirmation of federation of a server, servers will need to provide a channel
list to others. This is to ensure that other servers can list channels that are
not hosted by them but are available to their users.
• FEDNEW :CHANNEL-NAME
When a new channel is created, the server will need to send this message to all
connected federation servers to inform that a new channel has been created and
to update their current channel list.
• FEDJOIN :USER :CHANNEL
The server that the user belongs to, will request to join the channel on another
server, this message originates from the user’s connected federated server.
• FEDSAY :USER :CHANNEL :MESSAGE
This message originates from the user’s server and is directed to the channel on
a federated server. The federated server will receive this message and send the
message to all users subscribed to that channel.
• FEDRECV :TOUSER :FROMUSER :CHANNEL :MESSAGE
When updates are made to a federated channel, subscribers to that channel may
exist on a different federated server. The message is directed at the :TOUSER
server.
• FEDRESULT :USER :TYPE :MSG [:MORE. . . ]
This is a response message that will inform the user requesting a previously
mentioned federation message if their request succeeded or failed. This result is
just the federation version of RESULT.
5
End To End Interaction
From the client application perspective, the client’s will only implement utilise
the standard chat client protocol and will not implement the federation protocol.
The federation protocol is between servers, not clients.
Here is an example of a user from SERVER1 joining a channel on SERVER2.
Lets assume SERVER1 and SERVER2 have federated. Assuming the channel
exists, the interaction is as followed.
client sends LOGIN bob password to server1.com
client sends JOIN helloworld:server2.com to server1.com
server1 receives JOIN helloworld:server2.com from client
server1 sends FEDJOIN [email protected] helloworld to server2.com
server2 receives FEDJOIN [email protected] helloworld from server1.com
server2 adds [email protected] to helloworld channel
server2 sends FEDRESULT bob JOIN helloworld:server2.com 1 to server1.com
server1 sends RESULT JOIN helloworld:server2.com 1 to client
client receives RESULT message from server1
After successful confirmation, the client is able to send messages to users on the
helloworld channel on server2.
Distinguishing users and rooms
Federated users and rooms need to be distinguised from their local server counterparts.
The best way to do this, is to ensure that any user or channel is identifiable
by their local-server identifier and their host identifier that the server
knows it by.
Federated users will appear with hostname after their identifier.
Example:
[email protected]
Channels will be identifable similarly, however, instead of using the @ symbol,
they will be distinguished by the colon symbol :
secretchat:myhost.com
Note that a valid hostname or IP address should not contain @ and : as defined.
6
Restrictions - What would warrant serious deduction
You will need to ensure that you do not break any of the following restrictions
when writing your solution. If one or more of the following restrictions are
broken, you will receive 0 for your assessment mark.
• Code that explicitly targets a test case
This is known as ‘hard-coding’ and it subverts assessment itself by explicitly
writing code to handle a particular test case.
Marking Criteria
Your program must be submitted using git to Ed. We will only mark your final
submission that has been committed to Ed. Your program will need to satisfy
the following criteria to receive marks for each area.
• Automatic Test Cases - Compliance (16%)
Your program will be ran against automatic test cases to check if your server
is compliant with the outlined protocol and behaves as expected. These will
include public, private and hidden test cases.
• Your Test Cases (4%)
You will need to supply test cases that shows that you have tested your solution
completely and present it in a easily digestable form. Aim to have multiple tests
for each feature of your application.
Your test cases resolution must be presented in JSON format, otherwise your
test cases will not be marked. Utilising netcat or write your own client to test
your server.
• Extension (6%) - (6 bonus marks available)
You will need to implement this extension completely to achieve all marks. You
are only eligible for the extension only if you have passed all public compliance
test cases. You will need to implement your own set of test cases to show that
your extension works.
