[PATCH v6 5/6] http: permit unlinking partial packs on Windows

On Windows, an open file must permit FILE_SHARE_DELETE before another
process can unlink it. MinGW's non-append O_RDWR open enables that
sharing mode only for an existing file; adding O_CREAT falls back to
_wopen(), which cannot set it.

First try opening the partial pack without O_CREAT. If it does not
exist, create it exclusively, close that descriptor, and retry through
the existing-file path. A racing creator retries after EEXIST.

This ensures that every retained descriptor permits another downloader
to unlink the staging path. Add an unlink-while-indexing test that does
not require FIFOs and can therefore run on MinGW.

Signed-off-by: Ted Nyman <[email protected]>
---
 http.c                     | 17 ++++++++++++++++-
 t/t5550-http-fetch-dumb.sh | 21 +++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/http.c b/http.c
index ad07ef3549..a0d399b274 100644
--- a/http.c
+++ b/http.c
@@ -2746,7 +2746,22 @@ struct http_pack_request *new_direct_http_pack_request(
 
 	odb_pack_name(the_repository, &preq->tmpfile, packed_git_hash, "pack");
 	strbuf_addstr(&preq->tmpfile, ".temp");
-	fd = open(preq->tmpfile.buf, O_RDWR | O_CREAT, 0666);
+	/*
+	 * MinGW's non-append O_RDWR open grants FILE_SHARE_DELETE only for an
+	 * existing file; reopen a newly created file so others may unlink it.
+	 */
+	for (;;) {
+		fd = open(preq->tmpfile.buf, O_RDWR);
+		if (fd >= 0 || errno != ENOENT)
+			break;
+		fd = open(preq->tmpfile.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
+		if (fd >= 0) {
+			close(fd);
+			continue;
+		}
+		if (errno != EEXIST)
+			break;
+	}
 	if (fd < 0) {
 		error_errno("unable to open local file %s for pack",
 			    preq->tmpfile.buf);
diff --git a/t/t5550-http-fetch-dumb.sh b/t/t5550-http-fetch-dumb.sh
index 86b9d87ef5..b5758f1c9c 100755
--- a/t/t5550-http-fetch-dumb.sh
+++ b/t/t5550-http-fetch-dumb.sh
@@ -328,6 +328,27 @@ test_expect_success 'http-fetch --packfile resumes a partial download' '
 	git -C packfileclient-resume cat-file -e "$HASH"
 '
 
+test_expect_success 'http-fetch --packfile permits unlink while indexing' '
+	git init packfileclient-unlink &&
+	p=$(cd "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git &&
+		ls objects/pack/pack-*.pack) &&
+	tmpfile="packfileclient-unlink/.git/objects/pack/pack-$ARBITRARY.pack.temp" &&
+	write_script git-unlink-index-pack <<-\EOF &&
+	test -f "$GIT_TEST_PACK_TEMP" || exit 1
+	rm "$GIT_TEST_PACK_TEMP" || exit 1
+	exec git index-pack "$@"
+	EOF
+	test_when_finished "rm -f git-unlink-index-pack" &&
+	PATH="$TRASH_DIRECTORY:$PATH" \
+	GIT_TEST_PACK_TEMP="$TRASH_DIRECTORY/$tmpfile" \
+	git -C packfileclient-unlink http-fetch --packfile="$ARBITRARY" \
+		--index-pack-arg=unlink-index-pack \
+		--index-pack-arg=--stdin --index-pack-arg=--keep \
+		"$HTTPD_URL/dumb/repo_pack.git/$p" >out &&
+	test_path_is_missing "$tmpfile" &&
+	git -C packfileclient-unlink cat-file -e "$HASH"
+'
+
 test_expect_success PERL,PIPE 'concurrent http-fetch --packfile cannot corrupt an overlapping download' '
 	git init packfileclient-overlap &&
 	blob=$(test-tool genrandom pack-overlap 2m |
-- 
2.55.0.openai.131.g83a728de1eb6