Functionality of your program

When launched, your process should work like a UNIX shell. It should accept incoming connections and at the same time provide a user interface that will offer the following command options: (Note that specific examples are used for clarity.)

1. HELP Display information about the available user interface options.

2. MYIP Display the IP address of this process. Note: The IP should not be your "lo" address (127.0.0.1). It should be the actual IP of the server.

3. MYPORT Display the port on which this process is listening for incoming connections.

4. REGISTER <port_no>: This command is used by the client to register itself with the server and to get the IP and listening port numbers of all the peers currently registered with the server. The first task of every client is to register itself with the server by sending the server a TCP message containing its listening port number. The server should maintain a list of the IP address and the listening ports of all the registered clients. Let's call this list as "Server-IP-List". Whenever a new client registers or a registered client exits, the server should update its Server-IP-List appropriately and then send this updated list to all the registered clients. Client should always listen to such updates from the server and update their own local copy of the available peers. Any such update which is received by the client should be displayed by the client. The REGISTER 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.

Note: The REGISTER command works only on the client and should not work on the server.

5. CONNECT : This command establishes a new TCP connection to the specified at the specified < port no>. The can either be an IP address or a hostname. (e.g., CONNECT euston.cse.buffalo.edu 3456 or CONNECT 192.168.45.55 3456). The specified IP address should be a valid IP address and listed in the Server-IP-List sent to the client by the server. Any attempt to connect to an invalid IP/hostname or an IP/hostname not listed by the server in its Server-IP-List should be rejected and suitable error message should be displayed. Success or failure in connections between two peers should be indicated by both the peers using suitable messages. Self-connections and duplicate connections should be flagged with suitable error messages. Every client can maintain up-to 3 connections with its peers. Any request for more than 3 connections should be rejected. However, every client should always maintain a constant connection with the server.

6. LIST Display a numbered list of all the connections this process is part of. This numbered list will include connections initiated by this process and connections initiated by other processes. The output should display the hostname, IP address and the listening port of all the peers the process is connected to. Also, this should include the server details. E.g., id: Hostname IP address Port No. 1: timberalake.cse.buffalo.edu 192.168.21.20 4545 2: embankment.cse.buffalo.edu 192.168.21.21 5454 3: highgate.cse.buffalo.edu 192.168.21.22 5000 4: euston.cse.buffalo.edu 192.168.21.22 5000

Note: The connection id 1 should always be your server running on timberlake.cse.buffalo.edu. The remaining connections should be the peers who you are connected to.

7. TERMINATE This command will terminate the connection listed under the specified number when LIST is used to display all connections. E.g., TERMINATE 2. In this example, the connection with embankment should end. An error message is displayed if a valid connection does not exist as number 2. If a remote machine terminates one of your connections, you should also display a message.

8. EXIT Close all connections and terminate this process. When a client exits, the server de-registers the client and sends the updated "Server-IP-List" to all the clients. Clients on receiving the updated list from the server should display the updated list. 

9. UPLOAD For example, UPLOAD 3 /local/a.txt. This will upload the file a.txt which is located in /local/ to the host on the connection that is designated by number 3 when LIST is used. An error message is displayed if the file was inaccessible or if 3 does not represent a valid connection. The remote machine will automatically accept the file and save it under the original name in the same directory where your program is. When the upload is complete this process will display a message indicating so. Also, the remote machine will display a message in its user interface indicating that a file (called a.txt) has been downloaded. When an upload is occurring, the user interface of the uploading process will remain unavailable until the upload is complete. Upon completion, a message is displayed. If the upload fails for some reason, an error message should be displayed. When an upload is occurring, a message should be displayed on the remote machine when the upload begins. If the upload fails for some reason, an error message should be displayed on the remote machine. At the end of each successful upload, you will print the rate at which the Transmitter (Sender/Uploader) uploaded the file. Similarly, you will also print at the receiver, the rate at which the file was received. We will call these as Tx Rate and Rx Rate. Tx rate is the amount of data (in Bits) transferred from the Tx end, divided by the time taken by Tx to read and send the complete file in chunks of Packet Size bytes each. The Rx rate is defined similarly (in Bits/sec) as the total file size received (in bits) divided by the time taken to receive the file over the socket and write it. For example, if a file was uploaded from embankment to euston, the format for printing this information is: At Tx end: Tx (embankment ): embankment -> euston, File Size: x Bytes, Time Taken: y seconds, Tx Rate: z bits/second. At Rx end: Rx (euston): embankment -> euston, File Size: a Bytes, Time Taken: b seconds, Rx Rate: c bits/second.

NOTE: You should read the file in chunks of packet size-byte buffers and send those buffers using the send socket call, instead of reading the whole file at once. You can use UNIX utility function gettimeofday to know the time taken for receiving and sending the file at the two ends. Make sure to appropriately call this function in your program to account only for the time taken for uploading (reading and sending) and downloading (receiving and writing) the file. After printing this information, flush the standard output using fflush, to immediately print this information.

NOTE: UPLOAD command on a server should display an error message. No files should be uploaded to the server. Any such attempt should display suitable error messages.

10. DOWNLOAD <connection id 1> <connection id 2> <connection id 3> This will download a file from each host specified in the command. Please note that the total number of hosts may be 1, 2 or 3. The hosts will be part of the list of hosts displayed by the LIST command. E.g., if a command DOWNLOAD 2 file1 3 file2 4 file3 is entered to a process running on the server UNDERGROUND, then the process running on UNDERGROUND receives this command, it will  request file1 from embankment, file2 from highgate and file3 euston. The local machine will automatically accept the file and save it in the same directory where your program is under the original name. When the download is complete this process will display a message indicating so. Also, the remote machine will display a message in its user interface indicating that a file (e.g. a.txt, b.txt or c.txt) has been downloaded along with the hostname of the host from which the file was downloaded. Upon completion, a message is displayed. If the download fails for some reason, an error message should be displayed. When a download is occurring, a message should be displayed on the local machine. If the download fails for some reason, an error message should be displayed on the remote machine.

Similarly as what UPLOAD requires, at the end of each successful download, you will print Rx rate at which the Receiver downloaded those files and the Tx rates at which each Sender sent those files.

NOTE: Both notifications and data sending should use TCP connections.

NOTE: DOWNLOAD command on a server should display an error message. No files should be downloaded from the server.

11. CREATOR Display your (the students) full name, your UBIT name and UB email address.