cosmopolitan/libc/calls/getdomainname.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/calls/syscall_support-sysv.internal.h"
#include "libc/dce.h"
#include "libc/intrin/strace.internal.h"
#include "libc/macros.internal.h"
#include "libc/nt/enum/computernameformat.h"
#include "libc/str/str.h"
#include "libc/sysv/errfuns.h"

#define KERN_DOMAINNAME 22

/**
 * Returns domain of current host.
 *
 * For example, if the fully-qualified hostname is "host.domain.example"
 * then this SHOULD return "domain.example" however, it might not be the
 * case; it depends on how the host machine is configured.
 *
 * The nul / mutation semantics are tricky. Here is some safe copypasta:
 *
 *     char domain[254];
 *     if (getdomainname(domain, sizeof(domain))) {
 *       strcpy(domain, "(none)");
 *     }
 *
 * On Linux this is the same as `/proc/sys/kernel/domainname`. However,
 * we turn the weird `"(none)"` string into empty string.
 *
 * @param name receives output name, which is guaranteed to be complete
 *     and have a nul-terminator if this function return zero
 * @param len is size of `name` consider using `DNS_NAME_MAX + 1` (254)
 * @raise EINVAL if `len` is negative
 * @raise EFAULT if `name` is an invalid address
 * @raise ENAMETOOLONG if the underlying system call succeeded, but the
 *     returned hostname had a length equal to or greater than `len` in
 *     which case this error is raised and the buffer is modified, with
 *     as many bytes of hostname as possible excluding a nul-terminator
 * @return 0 on success, or -1 w/ errno
 */
int getdomainname(char *name, size_t len) {
  int rc;
  if (len < 0) {
    rc = einval();
  } else if (!len) {
    rc = 0;
  } else if (!name) {
    rc = efault();
  } else if (IsLinux()) {
    rc = getdomainname_linux(name, len);
  } else if (IsBsd()) {
    rc = gethostname_bsd(name, len, KERN_DOMAINNAME);
  } else if (IsWindows()) {
    rc = gethostname_nt(name, len, kNtComputerNamePhysicalDnsDomain);
  } else {
    rc = enosys();
  }
  if (!rc && len && !strcmp(name, "(none)")) {
    name[0] = 0;
  }
  STRACE("getdomainname([%#.*s], %'zu) → %d% m", (int)len, name, len, rc);
  return rc;
}