# UDP Remote File Transfer Multi-Client/Server
>A project assigned in Dr. Smith's Introduction to Computer Networks class, CPE 464.

# Course Description
> Computer network architectures; communications protocol standards; services provided by the network; historical and current examples presented.

# Program Description
`rcopy.c` is a remote file transfer client that communicates with the file server via UDP. `rcopy.c` will create the output file and write the data packets sent from the server to disk.

The file copy client relies on a self-written "Sliding Window" data structure in the file titled `window.c`. 

Ref: (https://www.baeldung.com/cs/sliding-window-algorithm)

Usage: `rcopy from-filename to-filename window-size buffer-size error-percent remote-machine remote-port`

Where: 
* `from-filename`: is the name of the file to download from the server (server sends this down)
* `to-filename`: is the name of file created by rcopy (rcopy writes to this file)
* `window-size`: is the size of the window in PACKETS (i.e. number of packets in window)
* `buffer-size`: is the number of data bytes (from the file) transmitted in a data packet2
* `error-percent`: is the percent of packets that are in error (floating point number)
* `remote-machine`: is the remote machine running the server
* `remote-port`: is the port number of the server application


`server.c` is a remote file server and is responsible for downloading the requested file to rcopy. This program only terminates unless killed with ctrl-c and will continually process file requests for multiple clients simultaneously.

The server takes two arguments, an error percentage and an optional port number for clients to use. 

Usage:`server error-percent optional-port-number`

Where:
* `error-percent`: is the percent of packets that are in error (floating point number)
* `optional-port-number`: allows the user to specify the port number to be used by the server (If this parameter is not present you should pass a 0 (zero) as the port number to bind().)


Utilize MAKE to build the output files. 

Packet Flags Used: 
* 3 - Data packet
* 5 - RR packet
* 6 - SREJ packet
* 7 - Filename and relevant metadata (rcopy to server) (used for setup)
* 8 - Filename response (good/bad filename) (server to rcopy)
* 9 - EOF packet (server to rcopy)
* 10 - EOF ACK packet (rcopy to server)

Please view the selective_reject_assignment... pdf for more verbose project details.