[utils] enhance YAML emission with recursive handling

src/utils/yaml_node_utils.cpp

@@ -58,7 +58,57 @@ std::string mp::utils::emit_yaml(const YAML::Node& node)
 {
     YAML::Emitter emitter;
     emitter.SetIndent(2);
-    emitter << node;
+
+    // Helper function to handle nodes recursively
+    std::function<void(const YAML::Node&)> emit_node;
+    emit_node = [&emitter, &emit_node](const YAML::Node& n) {
+        switch (n.Type())
+        {
+        case YAML::NodeType::Map:
+        {
+            emitter << YAML::BeginMap;
+            for (const auto& kv : n)
+            {
+                emitter << YAML::Key;
+                emit_node(kv.first);
+                emitter << YAML::Value;
+                emit_node(kv.second);
+            }
+            emitter << YAML::EndMap;
+            break;
+        }
+        case YAML::NodeType::Sequence:
+        {
+            emitter << YAML::BeginSeq;
+            for (const auto& v : n)
+            {
+                emit_node(v);
+            }
+            emitter << YAML::EndSeq;
+            break;
+        }
+        default:
+        {
+            // Special handling for strings that look like octal numbers (e.g. "0755")
+            if (n.IsScalar())
+            {
+                const std::string value = n.Scalar();
+                // If the node is a scalar string that looks like an octal number, emit
+                // it explicitly as a string to prevent YAML from interpreting it as an octal value.
+                if (value.length() >= 2 && value[0] == '0' &&
+                    std::all_of(value.begin() + 1, value.end(), ::isdigit))
+                {
+                    emitter << YAML::LocalTag("str") << value;
+                    break;
+                }
+            }
+            emitter << n;
+        }
+        }
+    };
+
+    emit_node(node);
+
     if (!emitter.good())
         throw std::runtime_error{fmt::format("Failed to emit YAML: {}", emitter.GetLastError())};
 

tests/test_yaml_node_utils.cpp

@@ -164,3 +164,25 @@ cloud-name: multipass)";
     EXPECT_EQ(meta_data_node["local-hostname"].as<std::string>(), "vm1");
     EXPECT_EQ(meta_data_node["cloud-name"].as<std::string>(), "multipass");
 }
+
+TEST(UtilsTests, emitYamlWithOctalString)
+{
+    YAML::Node node;
+    node["permissions"] = "0755";
+    node["another_permission"] = "0644";
+    node["not_octal"] = "0abc";
+    node["regular_string"] = "hello";
+
+    const std::string result = mpu::emit_yaml(node);
+
+    // The octal strings should be tagged as strings to preserve their format
+    EXPECT_TRUE(result.find("permissions: !str \"0755\"") != std::string::npos ||
+                result.find("permissions: !str 0755") != std::string::npos);
+    EXPECT_TRUE(result.find("another_permission: !str \"0644\"") != std::string::npos ||
+                result.find("another_permission: !str 0644") != std::string::npos);
+    // Non-octal strings should not be tagged
+    EXPECT_TRUE(result.find("not_octal: 0abc") != std::string::npos ||
+                result.find("not_octal: \"0abc\"") != std::string::npos);
+    EXPECT_TRUE(result.find("regular_string: hello") != std::string::npos ||
+                result.find("regular_string: \"hello\"") != std::string::npos);
+}