/* passivesock.c - passivesock */
 
#include <sys/types.h>
#include <sys/socket.h>
 
#include <netinet/in.h>
 
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
 
extern int errno;
 
int errexit(const char *format, ...);
 
u_short portbase = 0; /* port base, for non-root servers */
 
/*------------------------------------------------------------------------
 * passivesock - allocate & bind a server socket using TCP or UDP
 *------------------------------------------------------------------------
 */
int
passivesock(const char *service, const char *transport, int qlen)
/*
 * Arguments:
 * service - service associated with the desired port
 * transport - transport protocol to use ("tcp" or "udp")
 * qlen - maximum server request queue length
 */
{
 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(&sin, 0, sizeof(sin));
 sin.sin_family = AF_INET;
 sin.sin_addr.s_addr = INADDR_ANY;
 
 /* Map service name to port number */
 if ( pse = getservbyname(service, transport) )
 sin.sin_port = htons(ntohs((u_short)pse->s_port)
 + portbase);
 else if ( (sin.sin_port = htons((u_short)atoi(service))) == 0 )
 errexit("can't get \"%s\" service entry\n", service);
 
 /* Map protocol name to protocol number */
 if ( (ppe = getprotobyname(transport)) == 0)
 errexit("can't get \"%s\" protocol entry\n", transport);
 
 /* Use protocol to choose a socket type */
 if (strcmp(transport, "udp") == 0)
 type = SOCK_DGRAM;
 else
 type = SOCK_STREAM;
 
 /* Allocate a socket */
 s = socket(PF_INET, type, ppe->p_proto);
 if (s < 0)
 errexit("can't create socket: %s\n", strerror(errno));
 
 /* Bind the socket */
 if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
 errexit("can't bind to %s port: %s\n", service,
 strerror(errno));
 if (type == SOCK_STREAM && listen(s, qlen) < 0)
 errexit("can't listen on %s port: %s\n", service,
 strerror(errno));
 return s;
}