/* Simple program to demonstrate a UDP-based server.
 * Loops forever. Receives a word from a client. 
 * Sends back the length of that word to the client.
 * 
 * Compile using "cc -o wordlen-server wordlen-server.c"
 * 
 * Written by Carey Williamson, February 2022.
 */
 
/* Include files */
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

/* Manifest constants */
#define MAX_LENGTH 40
#define PORT 44101

/* Verbose debugging */
/* #define DEBUG 1 */

/* Main program */
int main()
  {
    struct sockaddr_in si_server, si_client;
    struct sockaddr *server, *client;
    int s, i, len;
    char messagein[MAX_LENGTH], messageout[MAX_LENGTH];
    int bytesin, bytesout;

    s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if( s < 0)
      {
	printf("wordlen-server: socket() call failed!\n");
	return -1;
      }
    memset((char *) &si_server, 0, sizeof(si_server));
    si_server.sin_family = AF_INET;
    si_server.sin_port = htons(PORT);
    si_server.sin_addr.s_addr = htonl(INADDR_ANY);
    server = (struct sockaddr *) &si_server;
    client = (struct sockaddr *) &si_client;
    len=sizeof(si_server);

    if( bind(s, server, sizeof(si_server)) < 0 )
      {
	printf("wordlen-server: bind() to port %d failed!\n", PORT);
	return -1;
      }
    printf("Welcome! I am the UDP-based word length server!!\n");
    printf("server now listening on UDP port %d...\n", PORT);
	
    /* big loop, looking for incoming messages from clients */
    for( ; ; )
      {
	/* clear out message buffers to be safe */
	bzero(messagein, MAX_LENGTH);
	bzero(messageout, MAX_LENGTH);

	/* see what comes in from a client, if anything */
	bytesin = recvfrom(s, messagein, MAX_LENGTH, 0, client, &len);
	if( bytesin < 0 )
	  {
	    printf("wordlen-server: recvfrom() failed!\n");
	    return -1;
	  }
#ifdef DEBUG
	else printf("Word length server received %d bytes from a client\n", bytesin);
#endif

	printf("  server received \"%s\" from IP %s port %d\n",
	       messagein, inet_ntoa(si_client.sin_addr), ntohs(si_client.sin_port));

#ifdef DEBUG
	printf("server thinks that word has %d characters...\n", strlen(messagein));
#endif
	/* create the outgoing message (as an ASCII string) */
	sprintf(messageout, "%d", strlen(messagein));

#ifdef DEBUG
	printf("Server sending back the message: \"%s\"\n", messageout);
#endif

	/* send the result message back to the client */
	bytesout = sendto(s, messageout, strlen(messageout), 0, client, len);		
	if( bytesout < 0 )
	  printf("wordlen-server: sendto() failed!\n");
#ifdef DEBUG
	else printf("Word length server sent %d bytes back to that client\n", bytesout);
#endif
      }

    close(s);
    return 0;
  }