t/lib-pack.sh

   1 # Support routines for hand-crafting weird or malicious packs.
   2 #
   3 # You can make a complete pack like:
   4 #
   5 #   pack_header 2 >foo.pack &&
   6 #   pack_obj e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 >>foo.pack &&
   7 #   pack_obj e68fe8129b546b101aee9510c5328e7f21ca1d18 >>foo.pack &&
   8 #   pack_trailer foo.pack
   9
  10 # Print the big-endian 4-byte octal representation of $1
  11 uint32_octal () {
  12         n=$1
  13         printf '\\%o' $(($n / 16777216)); n=$((n % 16777216))
  14         printf '\\%o' $(($n /    65536)); n=$((n %    65536))
  15         printf '\\%o' $(($n /      256)); n=$((n %      256))
  16         printf '\\%o' $(($n           ));
  17 }
  18
  19 # Print the big-endian 4-byte binary representation of $1
  20 uint32_binary () {
  21         printf "$(uint32_octal "$1")"
  22 }
  23
  24 # Print a pack header, version 2, for a pack with $1 objects
  25 pack_header () {
  26         printf 'PACK' &&
  27         printf '\0\0\0\2' &&
  28         uint32_binary "$1"
  29 }
  30
  31 # Print the pack data for object $1, as a delta against object $2 (or as a full
  32 # object if $2 is missing or empty). The output is suitable for including
  33 # directly in the packfile, and represents the entirety of the object entry.
  34 # Doing this on the fly (especially picking your deltas) is quite tricky, so we
  35 # have hardcoded some well-known objects. See the case statements below for the
  36 # complete list.
  37 pack_obj () {
  38         case "$1" in
  39         # empty blob
  40         e69de29bb2d1d6434b8b29ae775ad8c2e48c5391)
  41                 case "$2" in
  42                 '')
  43                         printf '\060\170\234\003\0\0\0\0\1'
  44                         return
  45                         ;;
  46                 esac
  47                 ;;
  48
  49         # blob containing "\7\76"
  50         e68fe8129b546b101aee9510c5328e7f21ca1d18)
  51                 case "$2" in
  52                 '')
  53                         printf '\062\170\234\143\267\3\0\0\116\0\106'
  54                         return
  55                         ;;
  56                 01d7713666f4de822776c7622c10f1b07de280dc)
  57                         printf '\165\1\327\161\66\146\364\336\202\47\166' &&
  58                         printf '\307\142\54\20\361\260\175\342\200\334\170' &&
  59                         printf '\234\143\142\142\142\267\003\0\0\151\0\114'
  60                         return
  61                         ;;
  62                 esac
  63                 ;;
  64
  65         # blob containing "\7\0"
  66         01d7713666f4de822776c7622c10f1b07de280dc)
  67                 case "$2" in
  68                 '')
  69                         printf '\062\170\234\143\147\0\0\0\20\0\10'
  70                         return
  71                         ;;
  72                 e68fe8129b546b101aee9510c5328e7f21ca1d18)
  73                         printf '\165\346\217\350\22\233\124\153\20\32\356' &&
  74                         printf '\225\20\305\62\216\177\41\312\35\30\170\234' &&
  75                         printf '\143\142\142\142\147\0\0\0\53\0\16'
  76                         return
  77                         ;;
  78                 esac
  79                 ;;
  80         esac
  81
  82         # If it's not a delta, we can convince pack-objects to generate a pack
  83         # with just our entry, and then strip off the header (12 bytes) and
  84         # trailer (20 bytes).
  85         if test -z "$2"
  86         then
  87                 echo "$1" | git pack-objects --stdout >pack_obj.tmp &&
  88                 size=$(wc -c <pack_obj.tmp) &&
  89                 dd if=pack_obj.tmp bs=1 count=$((size - 20 - 12)) skip=12 &&
  90                 rm -f pack_obj.tmp
  91                 return
  92         fi
  93
  94         echo >&2 "BUG: don't know how to print $1${2:+ (from $2)}"
  95         return 1
  96 }
  97
  98 # Compute and append pack trailer to "$1"
  99 pack_trailer () {
 100         test-sha1 -b <"$1" >trailer.tmp &&
 101         cat trailer.tmp >>"$1" &&
 102         rm -f trailer.tmp
 103 }
 104
 105 # Remove any existing packs to make sure that
 106 # whatever we index next will be the pack that we
 107 # actually use.
 108 clear_packs () {
 109         rm -f .git/objects/pack/*
 110 }