TFTP server

My implementation of TFTP server only handles read requests (RRQ).
Server will return error on write requests (WRQ).

I based my solution on an example UDP server provided by Marcel Kyas.

The program takes as arguments the port number to listen on and the
path to the directory to share.

USAGE
    tftpd [port] [path]

When the program receives RRQ from anyone it finds the requested 
file and starts transfering it, 512 bytes at a time.  If the 
requested file does not exist or the filename contains a path then 
the server will send the appropriate error message to client.

After the program sends a packet it waits for an ACK for 100 ms.
If it does not receive ACK in that time it sends the same packet 
again.  It resends it up to five times or until it receives ACK.
If it doesn't receive ACK it will stop the transfer and terminate 
the connection.

If the size of the data payload is less than 512 bytes then the 
whole file has been transmitted.  The smaller size of the last 
packet marks the end of the transmission.

If an error is received from the client then the connection will be
terminated.  If it receives unknown or illegal packet it will send
an error message and terminate the connection.

Warning! This implementation is unsafe and should not be opened to
or accessed from a wide area network.

Notice: This implementation is ment for educational purposes only.