[PATCH] archive: flush deflate stream until Z_STREAM_END

From: Justin Tobler <jltobler@gmail.com>
Date: Aug 2, 2025, 22:08 UTC
Message-ID: <20250802220803.95137-1-jltobler@gmail.com>

In `archive-zip.c:write_zip_entry()` when using a stream as input for deflating a file, the call to `git_deflate()` with Z_FINISH always expects Z_STREAM_END to be returned. Per zlib documentation[1]:

        If the parameter flush is set to Z_FINISH, pending input is
        processed, pending output is flushed and deflate returns with
        Z_STREAM_END if there was enough output space. If deflate
        returns with Z_OK or Z_BUF_ERROR, this function must be called
        again with Z_FINISH and more output space (updated avail_out)
        but no more input data, until it returns with Z_STREAM_END or an
        error. After deflate has returned Z_STREAM_END, the only
        possible operations on the stream are deflateReset or
        deflateEnd.

In scenarios where the output buffer is not large enough to write all the compressed data, it is perfectly valid for the underlying `deflate()` to return Z_OK. Thus, expecting a single pass of `deflate()` here to always return Z_STREAM_END is a bug. Update the code to flush the deflate stream until Z_STREAM_END is returned.

[1]: https://zlib.net/manual.html

Helped-by: Toon Claes <toon@iotcl.com>
Signed-off-by: Justin Tobler <jltobler@gmail.com>
---

Greetings,

At GitLab, we received a report of a user getting the following error when generating a zip archive of their repository via git-archive(1):

        fatal: deflate error (0)

I've so far only been able to reproduce this issue in the chromium.git repository with a specific file:

        git clone --depth=1 https://github.com/chromium/chromium.git
        cd chromium
        git -c core.bigFileThreshold=1 archive -o foo.zip --format=zip HEAD -- \
                ui/events/ozone/evdev/touch_filter/palm_model/onedevice_train_palm_detection_filter_inference.cc

In the above example, `core.bigFileThreshold` is set to a low value to cause more files to use a stream as input while being deflated. This is the codepath that produces the specific error.

I've tested the patch against this specific file, and it fixes the issue, but I'm uncertain how to reproduce and test this issue more generically. I'm open to suggestions if anyone has some ideas :)

Thanks, -Justin

---
 archive-zip.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/archive-zip.c b/archive-zip.c
index df8866d5bae..29e7c9f5e3f 100644
--- a/archive-zip.c
+++ b/archive-zip.c
@@ -492,14 +492,22 @@ static int write_zip_entry(struct archiver_args *args,
 
 		zstream.next_in = buf;
 		zstream.avail_in = 0;
-		result = git_deflate(&zstream, Z_FINISH);
-		if (result != Z_STREAM_END)
-			die("deflate error (%d)", result);
+
+		do {
+			result = git_deflate(&zstream, Z_FINISH);
+			if (result != Z_OK && result != Z_STREAM_END)
+				die("deflate error (%d)", result);
+
+			out_len = zstream.next_out - compressed;
+			if (out_len > 0) {
+				write_or_die(1, compressed, out_len);
+				compressed_size += out_len;
+				zstream.next_out = compressed;
+				zstream.avail_out = sizeof(compressed);
+			}
+		} while (result != Z_STREAM_END);
 
 		git_deflate_end(&zstream);
-		out_len = zstream.next_out - compressed;
-		write_or_die(1, compressed, out_len);
-		compressed_size += out_len;
 		zip_offset += compressed_size;
 
 		write_zip_data_desc(size, compressed_size, crc);

-- 
2.50.1.214.ga30f80fde9