passivesock.c

/* passivesock.c - passivesock */

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <netinet/in.h>

#include <netdb.h>


static u_short	portbase = 37000;    /* port base, for non-root servers	*/

/*------------------------------------------------------------------------
 * passivesock - allocate & bind a server socket using TCP or UDP
 *------------------------------------------------------------------------
 */

int
passivesock( 
	char	*service,   /* service associated with the desired port	*/
	char	*protocol,  /* name of protocol to use ("tcp" or "udp")	*/
	int	qlen,	    /* max length of the server request queue	*/
	int	*rport )
{
	struct servent	*pse;	/* pointer to service information entry	*/
	struct protoent *ppe;	/* pointer to protocol information entry*/
	struct sockaddr_in sin;	/* an Internet endpoint address		*/
	int	s, type;	/* socket descriptor and socket type	*/

	memset((char *)&sin, 0, sizeof(sin));
	sin.sin_family = AF_INET;
	sin.sin_addr.s_addr = INADDR_ANY;

    /* Map service name to port number */
	if ( *rport )
	{
		/*	If a 1 is in this field, choose a free port */
		sin.sin_port = htons((u_short) 0);
	}
	else
	{
		if ( pse = getservbyname(service, protocol) )
			sin.sin_port = htons(ntohs((u_short)pse->s_port)
				+ portbase);
		else if ( (sin.sin_port = htons((u_short)atoi(service))) == 0 )
		{
			fprintf( stderr, "can't get \"%s\" service entry\n", service);
			exit(-1);
		}
	}

    /* Map protocol name to protocol number */
	if ( (ppe = getprotobyname(protocol)) == 0)
	{
		fprintf( stderr, "can't get \"%s\" protocol entry\n", protocol);
		exit(-1);
	}

    /* Use protocol to choose a socket type */
	if (strcmp(protocol, "udp") == 0)
		type = SOCK_DGRAM;
	else
		type = SOCK_STREAM;

    /* Allocate a socket */
	s = socket(PF_INET, type, ppe->p_proto);
	if (s < 0)
	{
		fprintf( stderr, "can't create socket: %s\n", strerror(errno));
		exit(-1);
	}

    /* Bind the socket */
	if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
	{
		fprintf( stderr, "can't bind to %s port: %s\n", service, strerror(errno));
		exit(-1);
	}
	if (type == SOCK_STREAM && listen(s, qlen) < 0)
	{
		fprintf( stderr, "can't listen on %s port: %s\n", service, strerror(errno));
		exit(-1);
	}

	if ( *rport )
	{
		int	len;

		/* return the selected port in rport */
		len = sizeof(sin);
		if ( getsockname( s, (struct sockaddr *)&sin, &len ) )
		{
			fprintf(  stderr, "chatd: cannot getsockname: %s\n", strerror(errno) );
			exit(-1);
		}
		*rport = ntohs(sin.sin_port);	

	}
	return s;
}