[PATCH v2 12/12] git-zlib: widen `git_deflate_bound()` to `size_t`

From: Johannes Schindelin <[email protected]>

All four `unsigned long`/`int`/`ssize_t` receivers across archive-zip,
diff, http-push and t/helper/test-pack-deltas were widened to `size_t`
in the prior commits, and remote-curl and fast-import were already
there. With every caller prepared, both the parameter and the return
type can now move without introducing any silent narrowing.

For inputs above zlib's `uLong` range (i.e. >4 GiB on platforms where
`uLong` is 32-bit, notably 64-bit Windows), defer to zlib's stored-block
formula (the same fallback it would itself use, see
https://github.com/madler/zlib/blob/v1.3.2/deflate.c#L832-L928 keeping
in mind that for large sizes, the `storelen` would be relevant, also
compare with https://github.com/madler/zlib/issues/549 for a fuller
story) plus the worst-case wrapper overhead. The existing path through
`deflateBound()` is unchanged for inputs that fit.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <[email protected]>
---
 git-zlib.c | 16 ++++++++++++++--
 git-zlib.h |  2 +-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/git-zlib.c b/git-zlib.c
index d21adb3bf5..ebbbcc6d1a 100644
--- a/git-zlib.c
+++ b/git-zlib.c
@@ -167,9 +167,21 @@ int git_inflate(git_zstream *strm, int flush)
 	return status;
 }
 
-unsigned long git_deflate_bound(git_zstream *strm, unsigned long size)
+size_t git_deflate_bound(git_zstream *strm, size_t size)
 {
-	return deflateBound(&strm->z, size);
+#if SIZE_MAX > ULONG_MAX
+	if (size > maximum_unsigned_value_of_type(uLong))
+		/*
+		 * deflateBound() takes uLong, which is 32-bit on
+		 * Windows. For inputs above that range, return zlib's
+		 * stored-block formula (the conservative path it would
+		 * itself use for an unknown stream state) plus the
+		 * worst-case wrapper overhead.
+		 */
+		return size + (size >> 5) + (size >> 7) + (size >> 11)
+			+ 7 + 18;
+#endif
+	return deflateBound(&strm->z, (uLong)size);
 }
 
 void git_deflate_init(git_zstream *strm, int level)
diff --git a/git-zlib.h b/git-zlib.h
index 0b24b15bd0..9248d11ca9 100644
--- a/git-zlib.h
+++ b/git-zlib.h
@@ -25,6 +25,6 @@ void git_deflate_end(git_zstream *);
 int git_deflate_abort(git_zstream *);
 int git_deflate_end_gently(git_zstream *);
 int git_deflate(git_zstream *, int flush);
-unsigned long git_deflate_bound(git_zstream *, unsigned long);
+size_t git_deflate_bound(git_zstream *, size_t);
 
 #endif /* GIT_ZLIB_H */
-- 
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