reftable/block: check deflateInit() return value

block_writer_init() allocates a z_stream and calls deflateInit()
to prepare it for compressing log records. The return value of
deflateInit() is silently discarded. If zlib initialization fails
(e.g., Z_MEM_ERROR when the system is under memory pressure), the
z_stream is left in an undefined state.

Subsequent deflate() calls in block_writer_finish() then operate
on this uninitialized stream. Current zlib/zlib-ng versions handle
such a stream gracefully, by returning `Z_STREAM_ERROR`, so in
practice it would likely not result in catastrophic error.

The function already uses REFTABLE_ZLIB_ERROR for deflate() failures
later in the code path, so returning the same error code for
deflateInit() failure is consistent.

Pointed out by Coverity.

Assisted-by: Claude Opus 4.6
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions