Re: [PATCH v7 1/5] unpack-objects.c: add dry_run mode for get_data()

From: Han Xin <redacted>

In dry_run mode, "get_data()" is used to verify the inflation of data,
and the returned buffer will not be used at all and will be freed
immediately. Even in dry_run mode, it is dangerous to allocate a
full-size buffer for a large blob object. Therefore, only allocate a
low memory footprint when calling "get_data()" in dry_run mode.

Suggested-by: Jiang Xin <redacted>
Signed-off-by: Han Xin <redacted>
---
 builtin/unpack-objects.c            | 23 +++++++++---
 t/t5590-unpack-non-delta-objects.sh | 57 +++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 6 deletions(-)
 create mode 100755 t/t5590-unpack-non-delta-objects.sh

diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index 4a9466295b..9104eb48da 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c

@@ -96,15 +96,21 @@ static void use(int bytes)
 	display_throughput(progress, consumed_bytes);
 }
 
-static void *get_data(unsigned long size)
+static void *get_data(size_t size, int dry_run)
 {
 	git_zstream stream;
-	void *buf = xmallocz(size);
+	size_t bufsize;
+	void *buf;
 
 	memset(&stream, 0, sizeof(stream));
+	if (dry_run && size > 8192)
+		bufsize = 8192;
+	else
+		bufsize = size;
+	buf = xmallocz(bufsize);

diff --git a/t/t5590-unpack-non-delta-objects.sh b/t/t5590-unpack-non-delta-objects.sh
new file mode 100755
index 0000000000..48c4fb1ba3
--- /dev/null
+++ b/t/t5590-unpack-non-delta-objects.sh

@@ -0,0 +1,57 @@
+#!/bin/sh
+#
+# Copyright (c) 2021 Han Xin
+#
+
+test_description='Test unpack-objects with non-delta objects'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+prepare_dest () {
+	test_when_finished "rm -rf dest.git" &&
+	git init --bare dest.git
+}
+
+test_expect_success "setup repo with big blobs (1.5 MB)" '
+	test-tool genrandom foo 1500000 >big-blob &&
+	test_commit --append foo big-blob &&
+	test-tool genrandom bar 1500000 >big-blob &&
+	test_commit --append bar big-blob &&
+	(
+		cd .git &&
+		find objects/?? -type f | sort
+	) >expect &&
+	PACK=$(echo main | git pack-objects --revs test)
+'
+
+test_expect_success 'setup env: GIT_ALLOC_LIMIT to 1MB' '
+	GIT_ALLOC_LIMIT=1m &&
+	export GIT_ALLOC_LIMIT
+'
+
+test_expect_success 'fail to unpack-objects: cannot allocate' '
+	prepare_dest &&
+	test_must_fail git -C dest.git unpack-objects <test-$PACK.pack 2>err &&
+	grep "fatal: attempting to allocate" err &&
+	(
+		cd dest.git &&
+		find objects/?? -type f | sort
+	) >actual &&
+	test_file_not_empty actual &&
+	! test_cmp expect actual
+'
+
+test_expect_success 'unpack-objects dry-run' '
+	prepare_dest &&
+	git -C dest.git unpack-objects -n <test-$PACK.pack &&
+	(
+		cd dest.git &&
+		find objects/ -type f
+	) >actual &&
+	test_must_be_empty actual
+'
+
+test_done