[PATCH/RFC db/text-delta 0/4] vcs-svn: avoid hangs for corrupt deltas

Hi,

As promised, here's a quick series to stop a too-greedy delta from causing svn-fe deadlock. It took longer than I thought it would, mostly because I started too late.

If I remember correctly, this first showed up as a theoretical possibility when chatting with Ram and later showed up in practice due to a bug in a test script or something like that. I don't remember the details but luckily it is not hard to make up a delta exhibiting the problem. See the test script in patch 4 for details.

After review, I'd like to push this to the main svn-fe branch and ask Junio to pull it so text delta support can be rolled out. There's just no reason not to, except for the obvious ones:

 - less pleasant raw UI for svn-fe
 - losing support for non-git fast-import backends that don't
   support cat-blob yet

Waiting for those would be to put the cart before the horse (how can people experiment with making something better if they haven't experienced what we have now?). Review of the pending patches at

 git://repo.or.cz/git/jrn.git svn-fe-next

to find missed details or other things that would be nice to get taken care of toward that end would be very welcome.

As for this series: hopefully it's simple but it's perfectly possible I got something terribly wrong. Thoughts welcome, as always.

Thanks to David and Ram for some useful discussions on irc, including those that led to these patches.

Jonathan Nieder (4):
  test-svn-fe: split off "test-svn-fe -d" into a separate function
  vcs-svn: cap number of bytes read from sliding view
  vcs-svn: guard against overflow when computing preimage length
  vcs-svn: avoid hangs from corrupt deltas