#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>	/* For atoi() */
#include <ctype.h>	/* For toupper() */
#include <unistd.h>	/* For read() */
#include <netdb.h>	/* for gethostbyaddr() */

int open_listen(int port)
{
    int fd;
    struct sockaddr_in serverAddr;
    int optVal;

    /* Create TCP socket */
    fd = socket(AF_INET, SOCK_STREAM, 0);
    if(fd < 0) {
	perror("Error creating socket");
	exit(1);
    }

    /* Allows address (port) to be reused */
    optVal = 1;
    if(setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &optVal, sizeof(int)) < 0) {
	perror("Error setting socket option");
	exit(1);
    }

    /* Create address we're going to listen on (given port number - converted
    ** to network byte order & any IP address for this machine */
    serverAddr.sin_family = AF_INET;	
    serverAddr.sin_port = htons(port);
    serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);

    /* Bind address to the socket */
    if(bind(fd, (struct sockaddr*)&serverAddr, sizeof(struct sockaddr_in)) < 0){
	perror("Error binding socket to port");
	exit(1);
    }

    /* Listen on socket - means we're ready to accept connections - 
    ** incoming connection requests will be queued */
    if(listen(fd, SOMAXCONN) < 0) {
	perror("Error listening");
	exit(1);
    }

    return fd;
}

char* capitalise(char* buffer, int len)
{
    int i;

    for(i=0; i<len; i++) {
	buffer[i] = (char)toupper((int)buffer[i]);
    }
    return buffer;
}

void process_connections(int fdServer)
{
    int fd;
    struct sockaddr_in fromAddr;
    int fromAddrSize;
    char buffer[1024];
    ssize_t numBytesRead;
    struct hostent *hp; 

    while(1) {
	fromAddrSize = sizeof(struct sockaddr_in);
	
	/* Accept a connection - block until a connection is ready to
	** be accepted. Get back a new file descriptor to communicate on. */
	fd = accept(fdServer, (struct sockaddr*)&fromAddr,  &fromAddrSize);
	if(fd < 0) {
	    perror("Error accepting connection");
	    exit(1);
	}
     
	/* Work out where the connection came from  & print it out */
	hp = gethostbyaddr((char *)&fromAddr.sin_addr.s_addr,
			    sizeof(fromAddr.sin_addr.s_addr), AF_INET);
	printf("Accepted request from %s (%s), port %d\n", 
		inet_ntoa(fromAddr.sin_addr),
		hp->h_name,
		ntohs(fromAddr.sin_port));

	/* Repeatedly read characters from the connection, convert to 
	** upper case and send them back 
	*/
	while((numBytesRead = read(fd, buffer, 1024)) > 0) {
	    capitalise(buffer, numBytesRead);
	    write(fd, buffer, numBytesRead);
	}
	/* EOF or error */

	if(numBytesRead < 0) {
	    perror("Error reading from socket");
	    exit(1);
	}
	printf("Done\n");
	fflush(stdout);
	close(fd);
    }
}

int main(int argc, char* argv[])
{
    int portnum;
    int fdServer;

    if(argc != 2) {
	fprintf(stderr, "Usage: %s port-num\n", argv[0]);
	exit(1);
    }

    portnum = atoi(argv[1]);
    if(portnum < 1024 || portnum > 65535) {
	fprintf(stderr,  "Invalid port number: %s\n", argv[1]);
	exit(1);
    }

    fdServer = open_listen(portnum);
    process_connections(fdServer);
    return 0;
}