[PATCH] cache: flush stdio before restoring FDs

[Konstantin Ryabitsev]

Hi, all:

As far as I can tell, the fix for this is still not in any released 
version of cgit, so the rawdiff cache truncation bug is still present in 
the latest release (as I just found out because EPEL's cgit has the 
unpatched version of the package).

Best,
-K

On Mon, Apr 24, 2017 at 07:52:40PM +0100, John Keeping wrote:
>As described in commit 2efb59e (ui-patch: Flush stdout after outputting
>data, 2014-06-11), we need to ensure that stdout is flushed before
>restoring the file descriptor when writing to the cache.  It turns out
>that it's not just ui-patch that is affected by this but also raw diff
>which writes to stdout internally.
>
>Let's avoid risking more places doing this by ensuring that stdout is
>flushed after writing in fill_slot().
>
>Signed-off-by: John Keeping <john at keeping.me.uk>
>---
>On Mon, Apr 24, 2017 at 11:54:40AM -0400, Konstantin Ryabitsev wrote:
>> Very reminiscent of a fix for ui-patch.c that fixed patch truncation [1]
>> there's a similar problem with cached rawdiff output. E.g.:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/rawdiff/?id=v4.11-rc7&id2=v4.11-rc8
>>
>> You will notice that the output is truncated (if it isn't just reload to
>> get the cached version).
>>
>> I would love a speedy fix, as we're trying to use this in place of
>> publishing pre-generated patches.
>
>I guess it's the same problem we fixed before for ui-patch, so here's a
>patch to move the fix into the common path for all pages.
>
> cache.c    | 6 ++++++
> ui-patch.c | 2 --
> 2 files changed, 6 insertions(+), 2 deletions(-)
>
>diff --git a/cache.c b/cache.c
>index 6736a01..2ccdc4e 100644
>--- a/cache.c
>+++ b/cache.c
>@@ -224,6 +224,12 @@ static int fill_slot(struct cache_slot *slot)
> 	/* Generate cache content */
> 	slot->fn();
>
>+	/* Make sure any buffered data is flushed to the file */
>+	if (fflush(stdout)) {
>+		close(tmp);
>+		return errno;
>+	}
>+
> 	/* update stat info */
> 	if (fstat(slot->lock_fd, &slot->cache_st)) {
> 		close(tmp);
>diff --git a/ui-patch.c b/ui-patch.c
>index 047e2f9..6745b69 100644
>--- a/ui-patch.c
>+++ b/ui-patch.c
>@@ -92,6 +92,4 @@ void cgit_print_patch(const char *new_rev, const char *old_rev,
> 		log_tree_commit(&rev, commit);
> 		printf("-- \ncgit %s\n\n", cgit_version);
> 	}
>-
>-	fflush(stdout);
> }