alok-upadhyay / guptsshclient Goto Github PK

This was done as a part of one of the assignments for my Computer Networks course.

Author : Alok Upadhyay.

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HOW TO COMPILE:
:Server:
$ make

:Client:
$ make 

:Usage:

:Fire up the server from server dir:
$ ./guptSSHServer

:Fire up the client from client dir: 
$ ./guptSSHClient <username>@<server-ip>

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HOW TO USE:

* Run the server binary first on the server machine.

* Then run the client compiled binary in the client machine, and please do remember to give the server IP as the commandline argument.

* You can close the session by using the 'bye' command. The server will close the running connection, and come into the waitingForClient mode.

* Limitations: The server doesn't cater to more than one client at a time. However, it can serve multiple clients at different times, after the preceding client has gone.
 
* Limitations: There is some race-condition happening due to which sometimes the prompt 'guptSSH:~> ' doesnot appear on the client side, even the banner is appearing. To sort this out do Ctrl+C on the client side, the server will go into waiting state again, run the client again. In one or two times the prompt will appear and you may run your commands. 

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ABOUT THE CODE:

# I have used inband data transfer, i.e., the control-messages/prompts as well as the file data are sent through the same connection on server port 2222.

# There are two source files, namely SSH_server.c and SSH_client.c, for the corresponding functions in the system.

# I have also included the compiled binaries of my source files, namely SSHServer.out and SSHClient.out, which you can use to directly test the code.

# The SSH_server.c is the one responsible for majority of the actions which are conducted by this SSH ( I have named it as guptSSH :P ).

# The SSH_client.c is the file which is basically responsible for printing the server messages/prompts on the user console etc. And also creating the local copies of files when doing the 'get <file>' .


# SSH_server.c has its work divided into many sub-routines mainly :

	void setupServerPrimaries();		=== responsible for creating the socket and other misc. data structures.

	void serveClients();			=== is the routine responsible for idle waiting for client connection requests. Happens everytime a user leaves, as the server then starts to wait for the next coming client.

	void closeSocket();			=== is the separate function to separate the connection closing logic.

	void executeCommand(char *);		=== is the routine which is responsible for executing the command recieved from client on the server.

	void transferFile(char *);		=== is the separate function which sends file to the client (when 'get' command is used by the user). I have used the sendfile() function found in the sys/sendfile.h library for sending files.

	void writeToFile(char *, char *);	=== is the separate function invoked when the user sends the 'put' command. It is responsible for creating a local copy of the file and writing the data recieved into it.



# It may be noted that all of the prompts and the response messages which are shown on the client side are generated at ther server-side and only displayed on the client side. While the server side keeps displaying the info which may be useful for the server-admin.



# While SSH_client.c is less complex since it has very few responsibilities in comparison.

	int main(int argc, char **argv) 	=== the main function here retains certain important functionalites like creating the socket sock, connecting witht the given server ip in argv[1].

	void writeToFile(char *, char *);	=== is the separate function invoked when the user sends the 'put' command. It is responsible for creating a local copy of the file and writing the data recieved into it.

	void transferFile(char *);		=== is the separate function which sends file to the client (when 'get' command is used by the user). I have used the sendfile() function found in the sys/sendfile.h library for sending files.



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