reftable: ensure that obj_id_len is >= 2 on writing

hanwen · gitster · commit b4007fcc6fe0 · 2022-02-23T13:36:26.000-08:00
When writing the same hash many times, we might decide to use a
length-1 object ID prefix for the ObjectID =&gt; ref table, which is out
of spec.

Signed-off-by: Han-Wen Nienhuys &lt;hanwen@google.com&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/reftable/readwrite_test.c b/reftable/readwrite_test.c
@@ -667,6 +667,42 @@ static void test_write_empty_table(void)
 	strbuf_release(&buf);
 }
 
+static void test_write_object_id_min_length(void)
+{
+	struct reftable_write_options opts = {
+		.block_size = 75,
+	};
+	struct strbuf buf = STRBUF_INIT;
+	struct reftable_writer *w =
+		reftable_new_writer(&strbuf_add_void, &buf, &opts);
+	uint8_t hash[GIT_SHA1_RAWSZ] = {42};
+	struct reftable_ref_record ref = {
+		.update_index = 1,
+		.value_type = REFTABLE_REF_VAL1,
+		.value.val1 = hash,
+	};
+	int err;
+	int i;
+
+	reftable_writer_set_limits(w, 1, 1);
+
+	/* Write the same hash in many refs. If there is only 1 hash, the
+	 * disambiguating prefix is length 0 */
+	for (i = 0; i < 256; i++) {
+		char name[256];
+		snprintf(name, sizeof(name), "ref%05d", i);
+		ref.refname = name;
+		err = reftable_writer_add_ref(w, &ref);
+		EXPECT_ERR(err);
+	}
+
+	err = reftable_writer_close(w);
+	EXPECT_ERR(err);
+	EXPECT(writer_stats(w)->object_id_len == 2);
+	reftable_writer_free(w);
+	strbuf_release(&buf);
+}
+
 static void test_write_empty_key(void)
 {
 	struct reftable_write_options opts = { 0 };
@@ -772,5 +808,6 @@ int readwrite_test_main(int argc, const char *argv[])
 	RUN_TEST(test_write_empty_key);
 	RUN_TEST(test_write_empty_table);
 	RUN_TEST(test_log_overflow);
+	RUN_TEST(test_write_object_id_min_length);
 	return 0;
 }
diff --git a/reftable/writer.c b/reftable/writer.c
@@ -515,7 +515,9 @@ static void object_record_free(void *void_arg, void *key)
 static int writer_dump_object_index(struct reftable_writer *w)
 {
 	struct write_record_arg closure = { .w = w };
-	struct common_prefix_arg common = { NULL };
+	struct common_prefix_arg common = {
+		.max = 1,		/* obj_id_len should be >= 2. */
+	};
 	if (w->obj_index_tree) {
 		infix_walk(w->obj_index_tree, &update_common, &common);
 	}

Original file line number	Diff line number	Diff line change
`@@ -515,7 +515,9 @@ static void object_record_free(void void_arg, void key)`
`515`	`515`	`static int writer_dump_object_index(struct reftable_writer *w)`
`516`	`516`	`{`
`517`	`517`	`struct write_record_arg closure = { .w = w };`
`518`		`- struct common_prefix_arg common = { NULL };`
	`518`	`+ struct common_prefix_arg common = {`
	`519`	`+ .max = 1, /* obj_id_len should be >= 2. */`
	`520`	`+ };`
`519`	`521`	`if (w->obj_index_tree) {`
`520`	`522`	`infix_walk(w->obj_index_tree, &update_common, &common);`
`521`	`523`	`}`