/*
	File 		: tcp_uppercase_echo_server.c
	Programmer	: Nasif Ekiz
	Date		:
	Description	: This is the server side of a TCP client/server application
	where the client sends a message to the server and server responds with an
	modified echo message where the incomming message is converted to all uppercase
	message.  
*/

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/un.h>

#define STRING_SIZE 1024
#define SERV_TCP_PORT 6500

int main(void) {
	
	int sock_server;		// socket identifier of server's listening socket			
	int sock_connection;		// socket identifier of server's data send/recv socket 			
	
	struct sockaddr_in server_addr;	// address structure to keep server's IPv4 address info
	unsigned int server_addr_len;	// length of the server's address structure
	unsigned short server_port;	// server application port number

	struct sockaddr_in client_addr; // address structure to keep client's IPv4 address info
	unsigned int client_addr_len;	// length of the client's address structure
	
	char sentence[STRING_SIZE];		// message received from client
	char modifiedSentence[STRING_SIZE];	// modified message send to client
	unsigned int msg_len;			// message length
	int bytes_sent, bytes_recd;		// number of bytes sent and received
	unsigned int i;				// loop variable

	/* 
	 	open a socket
	 	AF_INET 	: IPv4 protocol
		SOCK_STREAM	: stream socket
		IPPROTO_TCP	: TCP transport protocol
	*/ 	
	if ((sock_server = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
		perror("Server : can't open stream socket");
		exit(1);
	}	
	
	// initialize server address information 
	memset(&server_addr, 0, sizeof(server_addr));
	server_addr.sin_family = AF_INET;
	server_addr.sin_addr.s_addr = htonl(INADDR_ANY); 	/* in the case of multiple interfaces
								accept connection on any host interface */
	server_port = SERV_TCP_PORT;				// server application port number
	server_addr.sin_port = htons(server_port);		// convert port number from host byte
								// order to network byte order and assign to
								// server's port number 

	// bind the socket to the local server port
	if (bind(sock_server, (struct sockaddr *) &server_addr, sizeof(server_addr)) < 0) {
		perror("Server : can't bind to local address");
		close(sock_server);
		exit(1);
	}	

	// listen for incomming requests from clients
	if (listen(sock_server, 50) < 0) {
		perror("Server : error on listen");
		close(sock_server);
		exit(1);
	}
		
	printf("I am here to listen ... on port %hu\n\n", SERV_TCP_PORT);
	
	client_addr_len = sizeof(client_addr);	// length of client address structure
	
	// wait for incomming connection requests in an indefinite loop
	for(;;) {

		/* The accept function blocks the server until a connection request comes from 
		   a client    
		*/
		sock_connection = accept(sock_server, (struct sockaddr *) &client_addr, &client_addr_len);
		
		if (sock_connection < 0) {
			perror("Server : accept() error\n");
			close(sock_server);
			exit(1);
		}

		// receive the message
		bytes_recd = recv(sock_connection, sentence, STRING_SIZE, 0);

		// message read successfully
		if (bytes_recd > 0) {
			
			// print the received message 
			printf("Received Sentence is : \n");
			printf("%s", sentence);
			printf("\nwith length %d\n\n", bytes_recd);

			// prepare the message to send 
			msg_len = bytes_recd;
			
			// convert incomming message to all uppercase characters
			for(i=0; i < msg_len; i++) {
				modifiedSentence[i] = toupper(sentence[i]);
			}

			// send modified message to client
			bytes_sent = send(sock_connection, modifiedSentence, msg_len, 0);
		}

		// close the socket 
		close(sock_connection);	
	}
}