Develop the client and server components of a text chat application, consisting of one chat server and multiple chat clients over TCP connections.

2.1 Sockets

Used TCP Sockets. Used the select() system call only for handling multiple socket connections.

2.2 Running my program

This program will take 2 command line parameters: The first parameter (s/c) indicates whether your program instance should run as a server or a client. The second parameter (number) is the port number on which your process will listen for incoming connections. In the rest of the document, this port is referred to as the listening port.

E.g., if your executable is named chat_app: To run as a server listening on port 4322 ./chat_app s 4322 To run as a client listening on port 4322 ./chat_app c 4322

The chat application follows a typical client-server model, whereby we will have one server instance and two or more client instances. Given that we will be testing on the five dedicated servers listed before, you can assume that at most four clients will be online at any given time. The clients, when launched, log in to the server, identify themselves, and obtain the list of other clients that are connected to the server. Clients can either send a unicast message to any one of the other clients or a broadcast a message to all the other clients. Note that the clients maintain an active connection only with the server and not with any other clients. Consequently, all messages exchanged between the clients must flow through the server. Clients never exchange messages directly with each other. The server exists to facilitate the exchange of messages between the clients. The server can exchange control messages with the clients. Among other things, it maintains a list of all clients that are connected to it, and their related information (IP address, port number, etc.).

When launched (either as server or client), your application should work like a UNIX shell accepting specific commands (described below), in addition to performing network operations required for the chat application to work. You will need to use the select() system call which will allow you to provide a user interface and perform network functions at the same time (simultaneously).

Your application should accept commands only when they are inputted:In UPPER CASE. Having exactly the same syntax as described below.

5.1. SHELL Command Output [IMPORTANT]

The first line of output of all the commands should declare whether it was successfully executed or it failed. If the command was successful, use the following format string: (“[%s:SUCCESS]\n”, command_str) //where command_str is the command inputted without its arguments If the command failed with error, use the following format string: (“[%s:ERROR]\n”, command_str) //where command_str is the command inputted without its arguments

If the command is successful, it should immediately be followed by its real output (if any) as described in the sections below. Extra output lines in the log file between the success message and output will cause test cases to fail. The last line of the output of all the commands (whether success or failure) should use the following format string: (“[%s:END]\n”, command_str) //where command_str is the command inputted without its arguments For events, printing format/requirements will be the same as for commands. Each of the event’s description tells the value of the command_str you should use for it.

5.2 Server/Client SHELL Command Description

This set of commands should work irrespective of whether the application is started as a server or a client.

AUTHOR

Print a statement using the following format string: (“I, %s, have read and understood the course academic integrity policy.\n”, your_ubit_name) Your submission will not be graded if the AUTHOR command fails to work.

IP

Print the IP address of this process. Note that this should not be the localhost address (127.0.0.1), but the external IP address. Use the following format string: (“IP:%s\n”, ip_addr) //where ip_addr is a null-terminated char array storing IP Example Code Snippet To generate the required output for this command, you would need the following lines in your code: //Successful cse4589_print_and_log(“[%s:SUCCESS]\n”, command_str); cse4589_print_and_log(“IP:%s\n”, ip_addr); cse4589_print_and_log(“[%s:END]\n”, command_str); //Error cse4589_print_and_log(“[%s:ERROR]\n”, command_str); cse4589_print_and_log(“[%s:END]\n”, command_str); Here, command_str and ip_str are char arrays containing “IP” and some valid IP address like “xxx.xx.xx.xx”, respectively. Any extra output in between the SUCCESS/ERROR and END output will cause the test cases to fail.

PORT

Print the port number this process is listening on. Use the following format string: (“PORT:%d\n”, port)

LIST

Display a numbered list of all the currently logged-in clients. The output should display the hostname, IP address, and the listening port numbers, sorted by their listening port numbers, in increasing order. E.g.,

                      1   stones.cse.buffalo.edu          128.205.36.46     4545
                      2   embankment.cse.buffalo.edu      128.205.36.35     5000
                      3   highgate.cse.buffalo.edu        128.205.36.33     5499
                      4   euston.cse.buffalo.edu          128.205.36.34     5701

Use the following format string: /*The following printf will print out one host. Repeat this printf statement to

• print all hosts
• list_id: integer item number
• hostname: null-terminated char array containing fully qualified hostname
• ip_addr: null-terminated char array storing IP
• port_num: integer storing listening port num */ ("%-5d%-35s%-20s%-8d\n", list_id, hostname, ip_addr, port_num) Notes: LIST output should contain all the currently logged-in clients, including the client that executed the command. The server should NOT be included in the output.)

5.3 Server SHELL Command/Event Description

This set of commands should work only when the application is started as a server.

STATISTICS

Display a numbered list of all the clients that have ever logged-in to the server (but have never executed the EXIT command) and statistics about each one. The output should display the hostname, #messages-sent, #messages-received, and the current status: logged-in/logged-out depending on whether the client is currently logged-in or not, sorted by their listening port numbers, in increasing order. E.g.,

                      1     stones.cse.buffalo.edu          4       0       logged-in
                      2     embankment.cse.buffalo.edu      3       67      logged-out
                      3     highgate.cse.buffalo.edu        7       14      logged-in
                      4     euston.cse.buffalo.edu          11      23      logged-in

Use the following format string: /*The following printf will print out one host. Repeat this printf statement to

• print all hosts
• list_id: integer item number
• hostname: null-terminated char array containing fully qualified hostname
• num_msg_sent: integer number of messages sent by the client
• num_msg_rcv: integer number of messages received by the client */
• status: null-terminated char array containing logged-in or logged-out ("%-5d%-35s%-8d%-8d%-8s\n", list_id, hostname, num_msg_sent, num_msg_rcv, status)

Exceptions to be handled Invalid IP address Valid but incorrect/non-existent IP address

**[EVENT]: Message Relayed

All messages exchanged between clients pass through (are relayed by) the server. In the event of relay of a message from a client with ip address: addressed to another client with ip address: , print/log the message using the following format string: ("msg from:%s, to:%s\n[msg]:%s\n", from-client-ip, to-client-ip, msg) In case of a broadcast message, will be 255.255.255.255 For the purposes of printing/logging, use command_str: RELAYED

5.4 Client SHELL Command/Event Description

This set of commands should work only when the application is started as a client.

LOGIN

This command is used by a client to login to the server located at ip address: listening on port: . The LOGIN command takes 2 arguments. The first argument is the IP address of the server and the second argument is the listening port of the server.On successful registration, the server responds with:

1. List of all currently logged-in clients. The client should store this list for later display and use.

A client should not accept any other command, except LOGIN, EXIT, IP, PORT, and AUTHOR, or receive packets, unless it is successfully logged-in to the server.

The LOGIN SUCCESS/ERROR message should be printed after all the event related output (triggered by the buffered messages).

Exceptions to be handled : Invalid IP address/port number (e.g., 127.abc is an invalid IP; 43f is an invalid port). You can assume that a valid IP/port will always be the actual IP/listening port of the server.

REFRESH

Get an updated list of currently logged-in clients from the server.

SEND [client-ip] [msg]

Send message: to client with ip address: . can have a maximum length of 256 bytes and will consist of valid ASCII characters.

Exceptions to be handled Invalid IP address. Valid IP address which does not exist in the local copy of the list of logged-in clients (This list may be outdated. Do not update it as a result of this check).

BROADCAST [msg]

Send message: to all logged-in clients. can have a maximum length of 256 bytes and will consist of valid ASCII characters.

This should be a server-assisted broadcast. The sending client should send only one message to the server, indicating it is a broadcast. The server then forwards/relays this message to all the currently logged-in clients and stores/buffers the message for the others. Notes : The client that executes BROADCAST should not receive the same message back.

LOGOUT

Logout from the server. However, your application should not exit and continue to accept LOGIN, EXIT, IP, PORT, and AUTHOR commands. In general, on LOGOUT all state related to this client is maintained on both the client and the server. Notes : LOGOUT does NOT reset the statistic counters (see STATISTICS command ).

EXIT

Logout from the server (if logged-in) and terminate the application with exit code 0. This should delete all the state for this client on the server. You can assume that an EXITed client will never start again.

[EVENT]: Message Received

In the event of receipt of a message from a client with ip address: , print/log the message using the following format string: ("msg from:%s\n[msg]:%s\n", client-ip, msg) Note that here is the IP address of the original sender, not of the relaying server. For the purposes of printing/logging, use command_str: RECEIVED