Reset string array size when allocation fails in init (ros2#593) (ros2#597)

(cherry picked from commit bf78574)

Signed-off-by: leoca <leo.camus23@gmail.com>
Co-authored-by: Leo Camus <leo.camus23@gmail.com>

Author: mergify[bot]

src/string_array.c

@@ -57,6 +57,7 @@ rcutils_string_array_init(
   string_array->data = allocator->zero_allocate(size, sizeof(char *), allocator->state);
   if (NULL == string_array->data && 0 != size) {
     RCUTILS_SET_ERROR_MSG("failed to allocate string array");
+    string_array->size = 0;
     return RCUTILS_RET_BAD_ALLOC;
   }
   string_array->allocator = *allocator;

test/test_string_array.cpp

@@ -73,6 +73,18 @@ TEST(test_string_array, boot_string_array) {
   ASSERT_EQ(RCUTILS_RET_OK, rcutils_string_array_fini(&sa4));
 }
 
+TEST(test_string_array, init_alloc_failure_leaves_array_empty) {
+  auto failing_allocator = get_failing_allocator();
+
+  rcutils_string_array_t sa = rcutils_get_zero_initialized_string_array();
+  EXPECT_EQ(RCUTILS_RET_BAD_ALLOC, rcutils_string_array_init(&sa, 3, &failing_allocator));
+  rcutils_reset_error();
+  // Nothing was allocated, so the array must not advertise entries that cannot be read.
+  EXPECT_EQ(nullptr, sa.data);
+  EXPECT_EQ(0u, sa.size);
+  EXPECT_EQ(RCUTILS_RET_OK, rcutils_string_array_fini(&sa));
+}
+
 TEST(test_string_array, string_array_cmp) {
   auto allocator = rcutils_get_default_allocator();
   rcutils_ret_t ret = RCUTILS_RET_OK;