gnulib/build-aux/mktempd

#!/bin/sh
# Create a temporary directory, much like mktemp -d does.

# Copyright (C) 2007-2020 Free Software Foundation, Inc.

# 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, either version 3 of the License, or
# (at your option) any later version.

# 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, see <https://www.gnu.org/licenses/>.

# Written by Jim Meyering.

# Usage: mktempd /tmp phoey.XXXXXXXXXX

# First, try to use the mktemp program.
# Failing that, we'll roll our own mktemp-like function:
#  - try to get random bytes from /dev/urandom
#  - failing that, generate output from a combination of quickly-varying
#      sources and gzip.  Ignore non-varying gzip header, and extract
#      "random" bits from there.
#  - given those bits, map to file-name bytes using tr, and try to create
#      the desired directory.
#  - make only $MAX_TRIES attempts

ME=`basename "$0"`
die() { echo >&2 "$ME: $@"; exit 1; }

MAX_TRIES=4

rand_bytes()
{
  n=$1

  chars=abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789

  dev_rand=/dev/urandom
  if test -r "$dev_rand"; then
    # Note: 256-length($chars) == 194; 3 copies of $chars is 186 + 8 = 194.
    dd ibs=$n count=1 if="$dev_rand" 2>/dev/null \
      | tr -c $chars 01234567$chars$chars$chars
    return
  fi

  cmds='date; date +%N; free; who -a; w; ps auxww; ps -ef'
  data=` (eval "$cmds") 2>&1 | gzip `

  n_plus_50=`expr $n + 50`

  # Ensure that $data has length at least 50+$n
  while :; do
    len=`echo "$data"|wc -c`
    test $n_plus_50 -le $len && break;
    data=` (echo "$data"; eval "$cmds") 2>&1 | gzip `
  done

  echo "$data" \
    | dd bs=1 skip=50 count=$n 2>/dev/null \
    | tr -c $chars 01234567$chars$chars$chars
}

mktempd()
{
  case $# in
  2);;
  *) die "Usage: $ME DIR TEMPLATE";;
  esac

  destdir=$1
  template=$2

  # Disallow any trailing slash on specified destdir:
  # it would subvert the post-mktemp "case"-based destdir test.
  case $destdir in
  /) ;;
  */) die "invalid destination dir: remove trailing slash(es)";;
  esac

  case $template in
  *XXXX) ;;
  *) die "invalid template: $template (must have a suffix of at least 4 X's)";;
  esac

  fail=0

  # First, try to use mktemp.
  d=`env -u TMPDIR mktemp -d -t -p "$destdir" "$template" 2>/dev/null` \
    || fail=1

  # The resulting name must be in the specified directory.
  case $d in "$destdir"*);; *) fail=1;; esac

  # It must have created the directory.
  test -d "$d" || fail=1

  # It must have 0700 permissions.  Handle sticky "S" bits.
  perms=`ls -dgo "$d" 2>/dev/null|tr S -` || fail=1
  case $perms in drwx------*) ;; *) fail=1;; esac

  test $fail = 0 && {
    echo "$d"
    return
  }

  # If we reach this point, we'll have to create a directory manually.

  # Get a copy of the template without its suffix of X's.
  base_template=`echo "$template"|sed 's/XX*$//'`

  # Calculate how many X's we've just removed.
  template_length=`echo "$template" | wc -c`
  nx=`echo "$base_template" | wc -c`
  nx=`expr $template_length - $nx`

  err=
  i=1
  while :; do
    X=`rand_bytes $nx`
    candidate_dir="$destdir/$base_template$X"
    err=`mkdir -m 0700 "$candidate_dir" 2>&1` \
      && { echo "$candidate_dir"; return; }
    test $MAX_TRIES -le $i && break;
    i=`expr $i + 1`
  done
  die "$err"
}

mktempd "$@"