client server code

Client-server communication is carried out between a client program (called rcmd, for "remote command"), and a server (called rcmdd, for "remote command daemon"). The client sends the server a string message that contains an execution_count, time_delay (in seconds) and a Unix command. On receiving message the server executes the command, execution_count times, with the gap between two executions specified by time_delay . For each execution, the server returns the time of execution and the result, which is displayed by the client. In addition, the server prints information on the client request (current time, source IP, command, status) on server console - upon connection (status = "connected") or termination (status = "closed"). The client terminates after printing the time (at server) and the results of the executions of the command on the screen. The server continues serving client requests indefinitely. Part I: Implement an iterative UDP based client-server architecture, in which the server can queue at least five requests. Assume that UDP checksum provides a sufficient level of reliability. Part II: Implement a concurrent server architecture using TCP. Server need to be able to handle a minimum of five requests at a time. Details A client takes five arguments: the name of the server machine, the port number to which it should connect, the execution_count, the time_delay (in seconds) and the command (in that order). It translates the server name to its IP address using the gethostbyname system call, uses the IP address to fill in a sockaddr_in structure, and then opens a socket to the server using the socket and connect system calls. Next, the client sends the command as an ASCII string, using the write system call. Finally, it reads the reply, using the read call, and displays the result on the screen using the write system call. The server takes one argument, which is the port number on which it listens for an incoming command. It fills in a sockaddr_in structure with the port number, with the incoming address field (s_addr) set to INADDR_ANY. The server should display its IP Address / servername for the client to connect to it. The server uses the socket, bind, and listen system calls to create a socket, bind the port number to it, and to listen for a request. On getting the request, server queues it and, then accepts it. It reads the message sent to it, executes the corresponding command using the Unix system call and writes the result to a temporary file. It then opens the file for reading, reads the result, and uses the write call to write the results back to the client. TCP/IP does not provide message boundaries. So, the client does not know how long a result to read from the server. To get around this, the first 10 bytes of the server's message is the length of the reply, in ASCII. For example, if the length of the reply is 15 bytes, the first 10 bytes would be ASCII 5, ASCII 1 and eight 0s (use sprintf call to convert from binary to ASCII). For Part II, the session termination is initiated by the server when it has executed the command execution_times. The session also may be terminated by entering rcend on the client terminal.