TCPServer-ex2.c

/*
NAME:        TCPServer 
SYNOPSIS:    TCPServer [port]

DESCRIPTION:  The program creates a TCP socket in the inet 
              listen for connections from TCPClients, 
              accept clients into private sockets, and 
              fork an echo process to ``serve'' the client.
              If [port] is not specified, the program uses any available port.

*/
#include <stdio.h>
/* socket(), bind(), recv, send */
#include <sys/types.h>
#include <sys/socket.h> /* sockaddr_in */
#include <netinet/in.h> /* inet_addr() */
#include <arpa/inet.h>
#include <netdb.h> /* struct hostent */
#include <string.h> /* memset() */
#include <unistd.h> /* close() */
#include <stdlib.h> /* exit() */

#define MAXHOSTNAME 80
void reusePort(int sock);
void EchoServe(int psd, struct sockaddr_in from);


int main(int argc, char **argv ) {
    int   sd, psd;
    struct   sockaddr_in server;
    struct  hostent *hp, *gethostbyname();
    struct  servent *sp;
    struct sockaddr_in from;
    int fromlen;
    int length;
    char ThisHost[80];
    int pn;
    int childpid;
    
    sp = getservbyname("echo", "tcp");
    /* get TCPServer1 Host information, NAME and INET ADDRESS */

    gethostname(ThisHost, MAXHOSTNAME);
    /* OR strcpy(ThisHost,"localhost"); */
    
    printf("----TCP/Server running at host NAME: %s\n", ThisHost);
    if  ( (hp = gethostbyname(ThisHost)) == NULL ) {
      fprintf(stderr, "Can't find host %s\n", argv[1]);
      exit(-1);
    }
    bcopy ( hp->h_addr, &(server.sin_addr), hp->h_length);
    printf("    (TCP/Server INET ADDRESS is: %s )\n", inet_ntoa(server.sin_addr));

    
    
    /** Construct name of socket */
    server.sin_family = AF_INET;
    /* OR server.sin_family = hp->h_addrtype; */
    
    server.sin_addr.s_addr = inet_addr("127.0.0.1");
    if (argc == 1)
        server.sin_port = htons(0);  
    else  {
        pn = htons(atoi(argv[1])); 
        server.sin_port =  pn;
    }
    /*OR    server.sin_port = sp->s_port; */
    
    /** Create socket on which to send  and receive */
    
    sd = socket (AF_INET,SOCK_STREAM,IPPROTO_TCP); 
    /* OR sd = socket (hp->h_addrtype,SOCK_STREAM,0); */
    if (sd<0) {
	perror("opening stream socket");
	exit(-1);
    }
    /** this allow the server to re-start quickly instead of fully wait
	for TIME_WAIT which can be as large as 2 minutes */
    reusePort(sd);
    if ( bind( sd, (struct sockaddr *) &server, sizeof(server) ) < 0 ) {
	close(sd);
	perror("binding name to stream socket");
	exit(-1);
  }
    
    /** get port information and  prints it out */
    length = sizeof(server);
    if ( getsockname (sd, (struct sockaddr *)&server,&length) ) {
	perror("getting socket name");
	exit(0);
    }
    printf("Server Port is: %d\n", ntohs(server.sin_port));
    
    /** accept TCP connections from clients and fork a process to serve each */
    listen(sd,4);
    fromlen = sizeof(from);
    for(;;){
	psd  = accept(sd, (struct sockaddr *)&from, &fromlen);
	childpid = fork();
	if ( childpid == 0) {
	    close (sd);
	    EchoServe(psd, from);
	}
	else{
	    printf("My new child pid is %d\n", childpid);
	    close(psd);
	}
    }
}

void EchoServe(int psd, struct sockaddr_in from) {
    char buf[512];
    int rc;
    struct  hostent *hp, *gethostbyname();
    
    printf("Serving %s:%d\n", inet_ntoa(from.sin_addr),
	   ntohs(from.sin_port));
    if ((hp = gethostbyaddr((char *)&from.sin_addr.s_addr,
			    sizeof(from.sin_addr.s_addr),AF_INET)) == NULL)
	fprintf(stderr, "Can't find host %s\n", inet_ntoa(from.sin_addr));
    else
	printf("(Name is : %s)\n", hp->h_name);
    
    /**  get data from  clients and send it back */
    for(;;){
	printf("\n...server is waiting...\n");
	if( (rc=recv(psd, buf, sizeof(buf), 0)) < 0){
	    perror("receiving stream  message");
	    exit(-1);
	}
	if (rc > 0){
	    buf[rc]='\0';
	    printf("Received: %s\n", buf);
	    printf("From TCP/Client: %s:%d\n", inet_ntoa(from.sin_addr),
		   ntohs(from.sin_port));
	    printf("(Name is : %s)\n", hp->h_name);
	    if (send(psd, buf, rc, 0) <0 )
		perror("sending stream message");
	}
	else {
	    printf("TCP/Client: %s:%d\n", inet_ntoa(from.sin_addr),
		   ntohs(from.sin_port));
	    printf("(Name is : %s)\n", hp->h_name);
	    printf("Disconnected..\n");
	    close (psd);
	    exit(0);
	}
    }
}
void reusePort(int s)
{
    int one=1;
    
    if ( setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *) &one,sizeof(one)) == -1 )
	{
	    printf("error in setsockopt,SO_REUSEPORT \n");
	    exit(-1);
	}
}