build-aux/mktempd

   1 #!/bin/sh
   2 # Create a temporary directory, much like mktemp -d does.
   3
   4 # Copyright (C) 2007-2020 Free Software Foundation, Inc.
   5
   6 # This program is free software: you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation, either version 3 of the License, or
   9 # (at your option) any later version.
  10
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 # GNU General Public License for more details.
  15
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
  18
  19 # Written by Jim Meyering.
  20
  21 # Usage: mktempd /tmp phoey.XXXXXXXXXX
  22
  23 # First, try to use the mktemp program.
  24 # Failing that, we'll roll our own mktemp-like function:
  25 #  - try to get random bytes from /dev/urandom
  26 #  - failing that, generate output from a combination of quickly-varying
  27 #      sources and gzip.  Ignore non-varying gzip header, and extract
  28 #      "random" bits from there.
  29 #  - given those bits, map to file-name bytes using tr, and try to create
  30 #      the desired directory.
  31 #  - make only $MAX_TRIES attempts
  32
  33 ME=`basename "$0"`
  34 die() { echo >&2 "$ME: $@"; exit 1; }
  35
  36 MAX_TRIES=4
  37
  38 rand_bytes()
  39 {
  40   n=$1
  41
  42   chars=abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
  43
  44   dev_rand=/dev/urandom
  45   if test -r "$dev_rand"; then
  46     # Note: 256-length($chars) == 194; 3 copies of $chars is 186 + 8 = 194.
  47     dd ibs=$n count=1 if="$dev_rand" 2>/dev/null \
  48       | tr -c $chars 01234567$chars$chars$chars
  49     return
  50   fi
  51
  52   cmds='date; date +%N; free; who -a; w; ps auxww; ps -ef'
  53   data=` (eval "$cmds") 2>&1 | gzip `
  54
  55   n_plus_50=`expr $n + 50`
  56
  57   # Ensure that $data has length at least 50+$n
  58   while :; do
  59     len=`echo "$data"|wc -c`
  60     test $n_plus_50 -le $len && break;
  61     data=` (echo "$data"; eval "$cmds") 2>&1 | gzip `
  62   done
  63
  64   echo "$data" \
  65     | dd bs=1 skip=50 count=$n 2>/dev/null \
  66     | tr -c $chars 01234567$chars$chars$chars
  67 }
  68
  69 mktempd()
  70 {
  71   case $# in
  72   2);;
  73   *) die "Usage: $ME DIR TEMPLATE";;
  74   esac
  75
  76   destdir=$1
  77   template=$2
  78
  79   # Disallow any trailing slash on specified destdir:
  80   # it would subvert the post-mktemp "case"-based destdir test.
  81   case $destdir in
  82   /) ;;
  83   */) die "invalid destination dir: remove trailing slash(es)";;
  84   esac
  85
  86   case $template in
  87   *XXXX) ;;
  88   *) die "invalid template: $template (must have a suffix of at least 4 X's)";;
  89   esac
  90
  91   fail=0
  92
  93   # First, try to use mktemp.
  94   d=`env -u TMPDIR mktemp -d -t -p "$destdir" "$template" 2>/dev/null` \
  95     || fail=1
  96
  97   # The resulting name must be in the specified directory.
  98   case $d in "$destdir"*);; *) fail=1;; esac
  99
 100   # It must have created the directory.
 101   test -d "$d" || fail=1
 102
 103   # It must have 0700 permissions.  Handle sticky "S" bits.
 104   perms=`ls -dgo "$d" 2>/dev/null|tr S -` || fail=1
 105   case $perms in drwx------*) ;; *) fail=1;; esac
 106
 107   test $fail = 0 && {
 108     echo "$d"
 109     return
 110   }
 111
 112   # If we reach this point, we'll have to create a directory manually.
 113
 114   # Get a copy of the template without its suffix of X's.
 115   base_template=`echo "$template"|sed 's/XX*$//'`
 116
 117   # Calculate how many X's we've just removed.
 118   template_length=`echo "$template" | wc -c`
 119   nx=`echo "$base_template" | wc -c`
 120   nx=`expr $template_length - $nx`
 121
 122   err=
 123   i=1
 124   while :; do
 125     X=`rand_bytes $nx`
 126     candidate_dir="$destdir/$base_template$X"
 127     err=`mkdir -m 0700 "$candidate_dir" 2>&1` \
 128       && { echo "$candidate_dir"; return; }
 129     test $MAX_TRIES -le $i && break;
 130     i=`expr $i + 1`
 131   done
 132   die "$err"
 133 }
 134
 135 mktempd "$@"