CXX-1116 result::insert_one needs to hold on to owned copy of _id ele

Fixes a bug where the return value of
result::insert_one::inserted_id() could contain dangling references.

Author: jrassi

src/mongocxx/result/insert_one.cpp

@@ -14,22 +14,27 @@
 
 #include <mongocxx/result/insert_one.hpp>
 
+#include <bsoncxx/builder/stream/array.hpp>
+
 #include <mongocxx/config/private/prelude.hh>
 
 namespace mongocxx {
 MONGOCXX_INLINE_NAMESPACE_BEGIN
 namespace result {
 
-insert_one::insert_one(result::bulk_write result, bsoncxx::types::value generated_id)
-    : _result(std::move(result)), _generated_id(std::move(generated_id)) {
+insert_one::insert_one(result::bulk_write result, bsoncxx::types::value inserted_id)
+    : _result(std::move(result)),
+      _inserted_id_owned(bsoncxx::builder::stream::array{} << inserted_id
+                                                           << bsoncxx::builder::stream::finalize),
+      _inserted_id(_inserted_id_owned.view()[0].get_value()) {
 }
 
 const result::bulk_write& insert_one::result() const {
     return _result;
 }
 
 const bsoncxx::types::value& insert_one::inserted_id() const {
-    return _generated_id;
+    return _inserted_id;
 }
 
 }  // namespace result

src/mongocxx/result/insert_one.hpp

@@ -14,6 +14,7 @@
 
 #pragma once
 
+#include <bsoncxx/array/value.hpp>
 #include <bsoncxx/types.hpp>
 #include <bsoncxx/types/value.hpp>
 #include <mongocxx/result/bulk_write.hpp>
@@ -28,7 +29,7 @@ namespace result {
 class MONGOCXX_API insert_one {
    public:
     // This constructor is public for testing purposes only
-    insert_one(result::bulk_write result, bsoncxx::types::value generated_id);
+    insert_one(result::bulk_write result, bsoncxx::types::value inserted_id);
 
     ///
     /// Returns the bulk write result for this insert operation.
@@ -40,13 +41,18 @@ class MONGOCXX_API insert_one {
     ///
     /// Gets the _id of the inserted document.
     ///
-    /// @return The value of the _id field for inserted document.
+    /// @return The value of the _id field for the inserted document.
     ///
     const bsoncxx::types::value& inserted_id() const;
 
    private:
     result::bulk_write _result;
-    bsoncxx::types::value _generated_id;
+
+    // Array with a single element, containing the value of the _id field for the inserted document.
+    bsoncxx::array::value _inserted_id_owned;
+
+    // Points into _inserted_id_owned.
+    bsoncxx::types::value _inserted_id;
 };
 
 }  // namespace result

src/mongocxx/test/collection.cpp

@@ -104,6 +104,16 @@ TEST_CASE("CRUD functionality", "[driver::collection]") {
         REQUIRE(i == 1);
     }
 
+    SECTION("insert_one returns correct result object", "[collection]") {
+        stdx::string_view expected_id{"foo"};
+
+        auto result = coll.insert_one(document{} << "_id" << expected_id << finalize);
+        REQUIRE(result);
+        REQUIRE(result->result().inserted_count() == 1);
+        REQUIRE(result->inserted_id().type() == bsoncxx::type::k_utf8);
+        REQUIRE(result->inserted_id().get_utf8().value == expected_id);
+    }
+
     SECTION("insert and read multiple documents", "[collection]") {
         document b1;
         document b2;