Bug#128818: partial patches - server application

[Anthony Towns <aj@azure.humbug.org.au>]

Andreas Barth wrote:
> with ideas and code (and a lot more) from Anthony, I was able to put
> together the server part for partial patches in a way that it seems to
> me that it might be included in dak. The resulting files are available
> from
>  deb http://merkel.debian.org/~aba/debian sid main contrib non-free
> (or any other combination of suites and components you like)

So here's a script to make use of them:

---
#!/bin/sh

file="$1"
index="$2"
patchurl="${3%/}"
patch=$(tempfile)

sizeof () {
 wc -c "$1" | sed 's/^ *//;s/ .*//'
}

c_sha1=""
c_size="-1"
cur_sha1 () {
  if [ "$c_sha1" = "" ]; then
    c_sha1=$(sha1sum < "$file")
  fi
  echo $c_sha1
}
cur_size () {
  c2_size=$(sizeof "$file")
  if [ $c2_size != $c_size ]; then
    c_size=$c2_size
    c_sha1=""
  fi
  echo $c_size
}

patch_sha1_size () {
  sed -n '/^SHA1-Patches:/,/^[^ ]/'"s/^ \([^ ]*\)  *\([^ ]*\) $1\$/\1 
\2/p" "$index"
}

sed -n '/^SHA1-History:/,/^[^ ]/s/^ / /p' "$index" |
  while read n_sha1 n_size n_patch; do
    echo "try: $n_patch"
    if [ $(cur_size) = "$n_size" ]; then
      if true || [ $(cur_sha1) = "$n_sha1" ]; then
        curl -s "$patchurl/$n_patch.diff.gz" | zcat > $patch
        p_size=$(sizeof $patch)
        p_sha1=$(sha1sum < $patch)

        if [ "$p_sha1 $p_size" = "$(patch_sha1_size $n_patch)" ]; then
          echo "applying patch $n_patch"
          (cat $patch; echo "wq") | ed "$file" >/dev/null
          c_size=0
        fi
      fi
    fi
  done

rm -f "$patch"
---

If the script's installed in /usr/local/bin/untiffani, usage is 
something like:

---
  url=http://merkel.debian.org/~aba/debian
  tmp=$(tempfile) || exit
  cd /var/lib/apt/lists
  for p in *_Packages; do
    path=${p##*_dists_}
    if [ "$path" = "$p" ]; then continue; fi
    path=$(echo ${path%_Packages} | tr _ /)
    >"$tmp"
    url2="${url}/dists/${path}/diff"
    url2=$(echo "$url2" | sed 's/testing/sarge/;s/unstable/sid/')
    wget -q -o "$tmp" "${url2}/Index"
    if [ -s "$tmp" ]; then
      cp "$p" "${p.bak}"
      /usr/local/bin/untiffani "$p" "$tmp" "${url2}"
    fi
  done
  rm -f "$tmp"

  apt-get update
---

It's uh, rather untested. If you try it and it actually works (or you 
fix it so it works), might be worth posting a followup if nobody else 
has already.

For comparison, today's update of unstable/main/i386/Packages.bz2 goes 
from downloading the full 2.5MB to downloading a 2kB Index file, and a 
15kB patch.

Note that the ~aba url is only updated about now every day, and if it 
and your mirror are out of sync, you'll likely end up unhappy.

Cheers,
aj