get_hostname.c

[詳解]

/*++
/* NAME
/*  get_hostname 3
/* SUMMARY
/*  network name lookup
/* SYNOPSIS
/*  #include <get_hostname.h>
/*
/*  const char *get_hostname()
/* DESCRIPTION
/*  get_hostname() returns the local hostname as obtained
/*  via gethostname() or its moral equivalent. This routine
/*  goes to great length to avoid dependencies on any network
/*  services.
/* DIAGNOSTICS
/*  Fatal errors: no hostname, invalid hostname.
/* SEE ALSO
/*  valid_hostname(3)
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <sys/param.h>
#include <string.h>
#include <unistd.h>

#if (MAXHOSTNAMELEN < 256)
#undef MAXHOSTNAMELEN
#define MAXHOSTNAMELEN  256
#endif

/* Utility library. */

#include "mymalloc.h"
#include "msg.h"
#include "valid_hostname.h"
#include "get_hostname.h"

/* Local stuff. */

static char *my_host_name;

/* get_hostname - look up my host name */

const char *get_hostname(void)
{
    char    namebuf[MAXHOSTNAMELEN + 1];

    /*
     * The gethostname() call is not (or not yet) in ANSI or POSIX, but it is
     * part of the socket interface library. We avoid the more politically-
     * correct uname() routine because that has no portable way of dealing
     * with long (FQDN) hostnames.
     * 
     * DO NOT CALL GETHOSTBYNAME FROM THIS FUNCTION. IT BREAKS MAILDIR DELIVERY
     * AND OTHER THINGS WHEN THE MACHINE NAME IS NOT FOUND IN /ETC/HOSTS OR
     * CAUSES PROCESSES TO HANG WHEN THE NETWORK IS DISCONNECTED.
     * 
     * POSTFIX NO LONGER NEEDS A FULLY QUALIFIED HOSTNAME. INSTEAD POSTFIX WILL
     * USE A DEFAULT DOMAIN NAME "LOCALDOMAIN".
     */
    if (my_host_name == 0) {
    /* DO NOT CALL GETHOSTBYNAME FROM THIS FUNCTION */
    if (gethostname(namebuf, sizeof(namebuf)) < 0)
        msg_fatal("gethostname: %m");
    namebuf[MAXHOSTNAMELEN] = 0;
    /* DO NOT CALL GETHOSTBYNAME FROM THIS FUNCTION */
    if (valid_hostname(namebuf, DO_GRIPE) == 0)
        msg_fatal("unable to use my own hostname");
    /* DO NOT CALL GETHOSTBYNAME FROM THIS FUNCTION */
    my_host_name = mystrdup(namebuf);
    }
    return (my_host_name);
}