/* 
 * Based on example source code from 
 * "TCP/IP Sockets in C: Practical Guide for Programmers" 
 * by Michael J. Donahoo and Kenneth L. Calvert.
 */

#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define MAXPENDING 5    /* Maximum outstanding connection requests */
#define RCVBUFSIZE 32   /* Size of receive buffer */

int main(int argc, char *argv[])
{
    int servSock;                    /* Socket descriptor for server */
    int clntSock;                    /* Socket descriptor for client */
    struct sockaddr_in ServAddr;     /* Local address */
    struct sockaddr_in ClntAddr;     /* Client address */
    unsigned short ServPort;         /* Server port */
    unsigned int clntLen;            /* Length of client address data structure */
    char echoBuffer[RCVBUFSIZE];     /* Buffer for echo string */
    int recvMsgSize;                 /* Size of received message */

    if (argc != 2)     /* Test for correct number of arguments */
    {
        fprintf(stderr, "Usage:  %s <Server Port>\n", argv[0]);
        exit(1);
    }

    ServPort = atoi(argv[1]);  /* First arg:  local port */

    /* Create socket for incoming connections */
    if ((servSock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
        printf("socket() failed");
	exit(-1);
    }
      
    /* Construct local address structure */
    memset(&ServAddr, 0, sizeof(ServAddr));   /* Zero out structure */
    ServAddr.sin_family = AF_INET;                /* Internet address family */
    ServAddr.sin_addr.s_addr = htonl(INADDR_ANY); /* Any incoming interface */
    ServAddr.sin_port = htons(ServPort);      /* Local port */

    /* Bind to the local address */
    if (bind(servSock, (struct sockaddr *) &ServAddr, sizeof(ServAddr)) < 0) {
        printf("bind() failed");
	exit(-1);
    }

    /* Mark the socket so it will listen for incoming connections */
    if (listen(servSock, MAXPENDING) < 0) {
        printf("listen() failed");
	exit(-1);
    }

    for (;;) { /* Run forever */
        /* Set the size of the in-out parameter */
        clntLen = sizeof(ClntAddr);

        /* Wait for a client to connect */
        if ((clntSock = accept(servSock, (struct sockaddr *) &ClntAddr, 
                               &clntLen)) < 0) {
            printf("accept() failed");
	    exit(-1);
	}

        /* clntSock is connected to a client! */

        printf("Handling client %s\n", inet_ntoa(ClntAddr.sin_addr));

        /* Receive message from client */
        if ((recvMsgSize = recv(clntSock, echoBuffer, RCVBUFSIZE, 0)) < 0) {
             printf("recv() failed");
	     exit(-1);
	}

	/* Send received string and receive again until end of transmission */
	while (recvMsgSize > 0) {    /* zero indicates end of transmission */
				     /* Echo message back to client */
	     if (send(clntSock, echoBuffer, recvMsgSize, 0) != recvMsgSize) {
	          printf("send() failed");
		  exit(-1);
	     }

	     /* See if there is more data to receive */
	     if ((recvMsgSize = recv(clntSock, echoBuffer, RCVBUFSIZE, 0)) < 0) {
		  printf("recv() failed");
		  exit(-1);
             }	
	}

	close(clntSock);    /* Close client socket */
    }
    /* NOT REACHED */
}