commit 7653854d27087b49787a7c31b5cc4cffb5eeaf8a
author Youssef Elghareeb <ghareeb@google.com> Fri Jul 07 18:00:07 2023 +0200
committer Youssef Elghareeb <ghareeb@google.com> Tue Jul 11 14:45:48 2023 +0200
tree 070ce2cdd315f8bb1fc7f7f2c6f38705e9647672
parent e2f9d5b559db36f1689b3e0c5ac9ef8221cdbe56

Fail 'Get Diff' requests for file sizes that exceed 50Mb

We add a new DiffValidator extension point with one implementation that
checks the file size and fails the diff if the file size or size delta
exceeded 50Mb.

The validation is performed in PatchScriptFactory after the file diff is
computed through DiffOperations. This codepath is executed on the 'Get
Diff' request path, but not on 'List Files'.

The validation is done after the diff computation and not before it for
two reasons:
1) 'List Files' and 'Get Diff' both use the exact same logic in
   DiffOperations. This was designed that way because some of the fields
   that we return with the 'List Files' response require performing the
   file diff (e.g. lines_inserted/deleted). If we fail the request
   before the diff computation, this will mean that both 'List Files'
   and 'Get Diff' will be affected. We don't want to do that so that
   existing changes with large file sizes can continue to load and show
   the files in the web UI, but only expanding diffs to fail.  Though
   this can be solved with some refactoring of the code to separate both
   code paths and only fail 'Get Diff' requests "before" the diff
   computation, doing that will duplicate the code that's already
   encapsulated and executed inside the diff cache (reading the tree,
   getting file size).

2) Doing the validation after the diff computation is still beneficial,
   since we'll fail and skip the remaining code that formats the entire
   two sides of the diff (requires loading the file). Also we fail
   instead of returning a response of very large size. Note that the
   diff computation in DiffOperations only returns the list of edits
   (start/end lines and positions at both sides as integers).

Google-Bug-Id: b/288895561
Release-Notes: Fail 'Get Diff' requests for file sizes that exceed 50Mb
Change-Id: I174b58239b67abc8891f5b1c914dca86e10cdb93