/*-*- 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                              │
│                                                                              │
│ This program is free software; you can redistribute it and/or modify         │
│ it under the terms of the GNU General Public License as published by         │
│ the Free Software Foundation; version 2 of the License.                      │
│                                                                              │
│ This program is distributed in the hope that it will be useful, but          │
│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
│ General Public License for more details.                                     │
│                                                                              │
│ You should have received a copy of the GNU General Public License            │
│ along with this program; if not, write to the Free Software                  │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
│ 02110-1301 USA                                                               │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/bits/popcnt.h"
#include "libc/mem/mem.h"
#include "libc/stdio/stdio.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/errfuns.h"

/**
 * Opens buffer as stream.
 *
 * @param buf becomes owned by this function, and is allocated if NULL
 * @return new stream or NULL w/ errno
 */
FILE *fmemopen(void *buf, size_t size, const char *mode) {
  FILE *f;
  char *p;
  unsigned flags;

  if (size && size > 0x7ffff000) {
    einval();
    return NULL;
  }

  if (!(f = calloc(1, sizeof(FILE)))) {
    return NULL;
  }

  if (!buf) {
    if (!size) size = BUFSIZ;
    if (!(buf = calloc(1, size))) {
      free(f);
      return NULL;
    }
  } else {
    f->nofree = true;
  }

  f->fd = -1;
  f->buf = buf;
  f->size = size;
  f->end = size;
  f->iomode = fopenflags(mode);

  if (f->iomode & O_APPEND) {
    if ((p = memchr(buf, '\0', size))) {
      f->beg = p - (char *)buf;
    } else {
      f->beg = f->end;
    }
  }

  return f;
}