t/lib-pack.sh

   1 #!/bin/sh
   2 #
   3 # Support routines for hand-crafting weird or malicious packs.
   4 #
   5 # You can make a complete pack like:
   6 #
   7 #   pack_header 2 >foo.pack &&
   8 #   pack_obj e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 >>foo.pack &&
   9 #   pack_obj e68fe8129b546b101aee9510c5328e7f21ca1d18 >>foo.pack &&
  10 #   pack_trailer foo.pack
  11
  12 # Print the big-endian 4-byte octal representation of $1
  13 uint32_octal () {
  14         n=$1
  15         printf '\%o' $(($n / 16777216)); n=$((n % 16777216))
  16         printf '\%o' $(($n /    65536)); n=$((n %    65536))
  17         printf '\%o' $(($n /      256)); n=$((n %      256))
  18         printf '\%o' $(($n           ));
  19 }
  20
  21 # Print the big-endian 4-byte binary representation of $1
  22 uint32_binary () {
  23         printf "$(uint32_octal "$1")"
  24 }
  25
  26 # Print a pack header, version 2, for a pack with $1 objects
  27 pack_header () {
  28         printf 'PACK' &&
  29         printf '\0\0\0\2' &&
  30         uint32_binary "$1"
  31 }
  32
  33 # Print the pack data for object $1, as a delta against object $2 (or as a full
  34 # object if $2 is missing or empty). The output is suitable for including
  35 # directly in the packfile, and represents the entirety of the object entry.
  36 # Doing this on the fly (especially picking your deltas) is quite tricky, so we
  37 # have hardcoded some well-known objects. See the case statements below for the
  38 # complete list.
  39 pack_obj () {
  40         case "$1" in
  41         # empty blob
  42         e69de29bb2d1d6434b8b29ae775ad8c2e48c5391)
  43                 case "$2" in
  44                 '')
  45                         printf '\060\170\234\003\0\0\0\0\1'
  46                         return
  47                         ;;
  48                 esac
  49                 ;;
  50
  51         # blob containing "\7\76"
  52         e68fe8129b546b101aee9510c5328e7f21ca1d18)
  53                 case "$2" in
  54                 '')
  55                         printf '\062\170\234\143\267\3\0\0\116\0\106'
  56                         return
  57                         ;;
  58                 esac
  59                 ;;
  60         esac
  61
  62         echo >&2 "BUG: don't know how to print $1${2:+ (from $2)}"
  63         return 1
  64 }
  65
  66 # Compute and append pack trailer to "$1"
  67 pack_trailer () {
  68         test-sha1 -b <"$1" >trailer.tmp &&
  69         cat trailer.tmp >>"$1" &&
  70         rm -f trailer.tmp
  71 }
  72
  73 # Remove any existing packs to make sure that
  74 # whatever we index next will be the pack that we
  75 # actually use.
  76 clear_packs () {
  77         rm -f .git/objects/pack/*
  78 }