/*
   File		: sctp_server_send_receive_echo_messages_from_one_stream.c
   Programmer	: Nasif Ekiz
   Date		: 9/27/2006
   Description	: This is a SCTP server application which accepts association requests from clients. Basicly, 
	   	  it gets a message from a client and echoes the incomming message to the client back. 

		  This program is a SCTP one-to-many style application.
*/

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/sctp.h>

#define BUFFSIZE 8192
#define SERV_PORT 7000
                                                                               
int main (int argc, char **argv)  {

	int sock_fd, msg_flags;			// socket identifier, message flags
	char readbuf[BUFFSIZE];			// receive message buffer
	struct sockaddr_in servaddr, cliaddr; 	// server and client address structures to keep IPv4 address
	struct sctp_sndrcvinfo sri;		// sctp_sndrcvinfo structure used to set default 
						// parameters for the association 
	struct sctp_event_subscribe evnts;	/* this structure is used to enable/disable 
						   various SCTP notifications
						   0 - unsubscribe, 1 - subscribe */

	int stream_increment = 1;		// this integer variable is used to determine weather to 
						// send messages from incomming stream or next stream 
	socklen_t len;				
	size_t rd_sz;	
	size_t sd_sz;

	// checks if an argument is passed for stream_increment if so use this value for stream_increment
	if (argc == 2)
		stream_increment = atoi(argv[1]);

	// open a socket
	// AF_INET - IPv4 protocol
	// SOCK_SEQPACKET - sequenced packet socket
	// IPPROTO_SCTP - SCTP transport protocol 
	sock_fd = socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
	
	// check for errors 
	if (sock_fd < 0) {
		perror("Server can't open socket!");
		exit(1);
	}
	
	// clear server address structure
	memset(&servaddr, 0, sizeof(servaddr)); 
	
	// set server address information 
	servaddr.sin_family = AF_INET;		      // IPv4 protocol	
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY); // in the case of multiple interfaces accept 
						      // connection on any host interface
	servaddr.sin_port = htons(SERV_PORT);	      // set server's application port number 
	
	// assign a local protocol address (IP + port number) to socket 
	if ((bind(sock_fd, (struct sockaddr *) &servaddr, sizeof(servaddr))) < 0 ) {
		perror("Server can't bind to local address!");
		exit(1);
	}

	// clear sctp_event_subscribe structure	
	memset(&evnts, 0, sizeof(evnts));

	// enable sctp_sndrcvinfo to come with each sctp_recvmsg function
	evnts.sctp_data_io_event = 1;

	// set the options for the socket 
	// SCTP_EVENTS option allows a caller to fetch, enable/disable various SCTP notifications
	if ((setsockopt(sock_fd, IPPROTO_SCTP, SCTP_EVENTS, &evnts, sizeof(evnts))) < 0 ) {
		perror("Error in setsockopt!");
		exit(1);
	} 

	/* listen for incomming client requests
	   the second parameter specifies the maximum number of connections the kernel should 
	   queue for the socket */
	if ((listen(sock_fd, 1024)) < 0) {
		perror("Server can't listen for incomming connection requests!");
		exit(1);
	}
	
	for( ; ; ) {
		len = sizeof(struct sockaddr_in);	// length of client address structure

		// read a message from one of the clients
		rd_sz = sctp_recvmsg(sock_fd, readbuf, sizeof(readbuf), (struct sockaddr *) &cliaddr, 
				     &len,  &sri, &msg_flags);
	
		// error in reading data
		if (rd_sz < 0) {
			perror("Error in sctp_recvmsg while reading data!");
			exit(1);
		}

		// if stream_increment argument is presented then send the echo message from the next stream
		if(stream_increment) {

			// sinfo_stream specifies the default stream that messages will be sent
			sri.sinfo_stream++;

			// default value for number of opened streams in an association is 10
			if (sri.sinfo_stream >= 10) {
				sri.sinfo_stream = 0;
			}
		}

		// send an echo message to the client that sent the last message  
		sd_sz = sctp_sendmsg(sock_fd, readbuf, rd_sz, (struct sockaddr *) &cliaddr, len, 
					sri.sinfo_ppid, sri.sinfo_flags, sri.sinfo_stream, 0, 0);
		
		// error in sending data
		if (sd_sz < 0) {
			perror("Error in sctp_sendmsg while sending data!");
			exit(1);
		}
		
	}
}