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================================================================

    README file for Assignment 3 - FTP Protocol

     Names and roll numbers:	Gowthami Gudipati(11012312) and Tanya Goyal(11012340)
     Department:	Mathematics & Computing 
 
================================================================

HOW TO USE THE FTP PROTOCOL
===========================
1. Copy all the files in one directory.

2. On the terminal:
	~$ cd <path-to-main-directory>
	~$ make
	
	At server side:
	~$ cd <path-to-server-directory>
	~$ ./server <port number>
	
	--> The server should start listening for connections on the specified port.
	
	At client side:
	~$ cd <path-to-client-directory>
	~$ ./client <IP address of server> <port number>

3. Use the following commands:

	ftp>put <filename> 		(to upload a file named filename to the server) 
	ftp>get <filename> 		(to download a file named filename from the server)
	ftp>ls 					(to list the files under the present directory of the server) 
	ftp>cd <directory> 		(to change the present working directory of the server)
	ftp>pwd 				(to display the present working directory of the server)
	ftp>!ls 				(to list the files under the present directory of the client) 
	ftp>!cd <directory> 	(to change the present directory of the client) 
	ftp>!pwd 				(to display the present working directory of the client) 
	ftp>quit 				(to quit from ftp session at the client and return to Unix prompt) 


EXIT 
====
* You can exit the server by simply using Ctrl + C on the server terminal.
* You can close the client by typing "quit" on the client terminal.

LIMITATIONS
===========
* Only the above mentioned commands are implemented.
* A maximum of 8 clients can connect to the server at one time.
* There should be no spaces in the directory name to which you want to change the working directory to (because cd <directory> is implemented using chdir(<directory>) which does not allow white spaces)
* The get command rewrites the file if it already exists in the client working directory. Similarly, the put command rewrites the file if it already exists in the server working directory.

FEATURES
========
* Accepts any of the above mentioned commands. Otherwise, responds back with a "An invalid FTP command" error.
* Parses the command and prints the appropriate output on the terminal.
* End of file in case of get and put commands is implemented by telling the appropriate process(server/client) the size(or number of blocks) of the file.
* Works in connection-oriented and concurrent-server mode.

IMPLEMENTATION DETAILS
=======================
1. server.cpp is the file that implements the server side of the FTP protocol as follows:
 	
	*  Creates a Socket and binds it to a port(specified as cmd-line argument)
	*  Starts listening on the socket.
	*  Accepts connections from the client.
	*  Receives FTP command from the client.
	*  Parses the FTP command and checks for errors & unsupported commands. If Error in request, sends the error to client.
	*  All commands are shell commands. They are converted to valid format and executed (by the client/ server as requested).
	*  In case of get command, checks for the appropriate file and sends it to the client over a data connection(data port is generated by the server) in blocks.
	*  In case of put command, receives the file over a data connection(data port is generated by the server) in blocks from the client. 
	*  In case of ls command, we use popen("ls","r") and send the list of files over a data connection(data port is generated by the server) in blocks (because the list of files can be huge).  
	*  In case of cd <directory> command, we use chdir(<directory>) to change the working directory of the server.
	*  In case of pwd command, we use _getcwd if it is a Windows machine or getcwd otherwise to get the path to current working directory of server and send it to the client.
	*  Closes the connection with client if it receives a "quit" command from the client.
	*  Waits for new connections and repeats the above process.

2. client.cpp is the file that implements the client side of the FTP protocol as follows:

	*  Creates a Socket and connects to the server via the IP address of the server and port(specified as cmd-line arguments)
	*  Parses the FTP command and checks for errors & unsupported commands. If Error in request, prints the error.
	*  All commands are shell commands. They are converted to valid format and executed (by the client/ server as requested).
	*  In case of get command, receives the file over a data connection(data port is generated by the server) in blocks from the server. 
	*  In case of put command, checks for the appropriate file and sends it to the server over a data connection(data port is generated by the server) in blocks.
	*  In case of ls command, we receive the list of files over a data connection(again, data port is generated by the server) in blocks (because the list of files can be huge). 
	*  In case of !ls command, we use system("ls") to print the list of files under the client working directory.
	*  In case of !cd <directory> command, we use chdir(<directory>) to change the working directory of the client.
	*  In case of !pwd command, we use _getcwd if it is a Windows machine or getcwd otherwise to get the path to current working directory of client. 
	*  Returns to Unix prompt at the client if it receives a "quit" command.


SAMPLE TEST
============
1) Initializing the connection:
	Server Side:								Client Side:
	~$./server 2000								
	Server running...waiting for connections.				~$./client 127.0.0.1 2000
	Received request...							ftp>
	Child created for dealing with client requests				
	
2) ls
	Client Side:								Server Side:
	ftp>ls									String received from client: ls
	sample
	server
	server.cpp
	server.o

3) !ls
	Client Side:								Server Side:
	ftp>!ls									String received from client: !ls
	client	client.cpp  client.o  temp

4) put 
	Client Side:								Server Side:
	ftp>put temp								String received from client: put temp
	File upload done.							Filename given is: temp
										File download done.
	
5) get
	Client Side:								Server Side:
	ftp>get sample								String received from client: get sample
	File download done.							Filename given is: sample
										File upload done.
6) pwd
	Client Side:								Server Side:
	ftp>pwd									String received from client: pwd
	/home/goyal/ftp/Server							

7) !pwd
	Client Side:								Server Side:
	ftp>!pwd								String received from client: !pwd	
	/home/goyal/ftp/Client	

6) cd
	Client Side:								Server Side:
	ftp>cd ../Client							String received from client: cd ../Client
	Path given is: ../Client						Path given is: ../Client

7) !cd
	Client Side:								Server Side:
	ftp>!cd ../Server							String received from client: !cd ../Server
	Path given is: ../Server						Path given is: ../Server

8) quit
	Client Side:								Server Side:
	ftp>quit								String received from client: quit
										The client has quit