/* TCP-based server example of socket programming.    */
/* CPSC 441 test server with simple commands.         */
/*                                                    */
/* Usage: cc -o testserver testserver.c               */
/*        ./testserver                                */
/*                                                    */
/* Written by Carey Williamson        August 25, 2021 */

/* Include files for C socket programming and stuff */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <signal.h>
#include <string.h>
#include <arpa/inet.h>

/* Global manifest constants */
#define MAX_MESSAGE_LENGTH 100
#define SERVERPORTNUM 44101

/* Optional verbose debugging output */
#define DEBUG 1

/* Global variable */
int childsockfd;

/* This is a signal handler to do graceful exit if needed */
void catcher( int sig )
  {
    close(childsockfd);
    exit(0);
  }

/* Main program for server */
int main()
  {
    struct sockaddr_in server, client;
    static struct sigaction act;
    char messagein[MAX_MESSAGE_LENGTH];
    char messageout[MAX_MESSAGE_LENGTH];
    int parentsockfd, c, pid, conns;

    /* Set up a signal handler to catch any unusual termination conditions. */
    act.sa_handler = catcher;
    sigfillset(&(act.sa_mask));
    sigaction(SIGPIPE, &act, NULL);

    /* Initialize server sockaddr structure */
    memset(&server, 0, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_port = htons(SERVERPORTNUM);
    server.sin_addr.s_addr = htonl(INADDR_ANY);

    /* set up the transport-level end point to use TCP */
    if( (parentsockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1 )
      {
	fprintf(stderr, "testserver: socket() call failed!\n");
	exit(1);
      }

    /* bind a specific address and port to the end point */
    if( bind(parentsockfd, (struct sockaddr *)&server, sizeof(struct sockaddr_in) ) == -1 )
      {
	fprintf(stderr, "testserver: bind() call failed!\n");
	exit(1);
      }

    /* start listening for incoming connections from clients */
    if( listen(parentsockfd, 5) == -1 )
      {
	fprintf(stderr, "testserver: listen() call failed!\n");
	exit(1);
      }

    /* initialize message strings just to be safe (null-terminated) */
    bzero(messagein, MAX_MESSAGE_LENGTH);
    bzero(messageout, MAX_MESSAGE_LENGTH);

    fprintf(stderr, "Welcome! I am the CPSC 441 test server for L01!!\n");
    fprintf(stderr, "Server listening on TCP port %d...\n\n", SERVERPORTNUM);

    conns = 0;
    c = sizeof(struct sockaddr_in);
    
    /* Main loop: server loops forever listening for requests */
    for( ; ; )
      {
	/* accept a connection */
	if( (childsockfd = accept(parentsockfd, (struct sockaddr *)&client, (socklen_t *) &c)) == -1 )
	  {
	    fprintf(stderr, "testserver: accept() call failed!\n");
	    exit(1);
	  }

	/* increment server's counter variable */
	conns++;
	
	/* try to create a child process to deal with this new client */
	pid = fork();

	/* use process id (pid) returned by fork to decide what to do next */
	if( pid < 0 )
	  {
	    fprintf(stderr, "testserver: fork() call failed!\n");
	    exit(1);
	  }
	else if( pid == 0 )
	  {
	    /* this is the child process doing this part */

	    /* don't need the parent listener socket that was inherited */
	    close(parentsockfd);

	    /* obtain the message from this client */
	    int bytes;
	    int done = 0;
	    while( !done )
	      {
		bytes = recv(childsockfd, messagein, MAX_MESSAGE_LENGTH, 0);
#ifdef DEBUG
		/* print out the received message */
		printf("Child process received %d bytes with command: <%s>\n",
		       bytes, messagein);
#endif
	
		/* create the outgoing message based on command */
		if( strncmp(messagein, "HELLO", 5) == 0 )
		  sprintf(messageout, "Hello to you as well!\n");
		else if( strncmp(messagein, "COUNT", 5) == 0 )
		  sprintf(messageout, "You are client #%d since I was started.\n", conns);
		else if( strncmp(messagein, "HELP", 4) == 0 )
		  sprintf(messageout, "Supported commands:\n  HELLO\n  INFO\n  COUNT\n  HELP\n  BYE\n", conns);
		else if( strncmp(messagein, "INFO", 4) == 0 )
		  sprintf(messageout,
			  "Your transport-level endpoint is IP %s port %d\n",
			  inet_ntoa(client.sin_addr), ntohs(client.sin_port));
		else if( strncmp(messagein, "BYE", 3) == 0 )
		  {
		    sprintf(messageout, "Goodbye! See you next time.\n");
		    done = 1;
		  }
		else sprintf(messageout, "Unrecognized command. Sorry!\n");

#ifdef DEBUG
		printf("Child about to send message: %s\n", messageout);
#endif

		/* send the result message back to the client */
		if( send(childsockfd, messageout, strlen(messageout), 0) < 0)
		  {
		    fprintf(stderr, "Send failed on connection %d\n", conns);
		  }

		/* clear out message strings again to be safe */
		bzero(messagein, MAX_MESSAGE_LENGTH);
		bzero(messageout, MAX_MESSAGE_LENGTH);
	      }

	    /* when client is no longer sending information to us, */
	    /* the socket can be closed and the child process terminated */
	    fprintf(stderr, "Shutting down child process for conn %d\n", conns);
	    close(childsockfd);
	    exit(0);
	  } /* end of then part for child */
	else
	  {
	    /* the parent process is the one doing this part */
	    fprintf(stderr, "Created child process %d to handle that client\n", pid);
	    fprintf(stderr, "Parent going back to job of listening...\n\n");

	    /* parent doesn't need the childsockfd */
	    close(childsockfd);
	  }
      }
  }