#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>

externint    errno;

int    errexit(constchar *format, ...);

u_short    portbase = 0;        /* port base, for non-root servers    */int
passivesock(constchar *service, constchar *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);
    elseif ( (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;
}