fix: Compatible feature response (#1539)

Fixes #1538

src/rpc/handlers/Feature.cpp

@@ -99,7 +99,10 @@ FeatureHandler::process(FeatureHandler::Input input, Context const& ctx) const
     );
 
     return Output{
-        .features = std::move(features), .ledgerHash = ripple::strHex(lgrInfo.hash), .ledgerIndex = lgrInfo.seq
+        .features = std::move(features),
+        .ledgerHash = ripple::strHex(lgrInfo.hash),
+        .ledgerIndex = lgrInfo.seq,
+        .inlineResult = input.feature.has_value()
     };
 }
 
@@ -124,14 +127,20 @@ tag_invoke(boost::json::value_from_tag, boost::json::value& jv, FeatureHandler::
 {
     using boost::json::value_from;
 
+    if (output.inlineResult) {
+        jv = value_from(output.features);
+    } else {
         jv = {
             {JS(features), value_from(output.features)},
-        {JS(ledger_hash), output.ledgerHash},
-        {JS(ledger_index), output.ledgerIndex},
-        {JS(validated), output.validated},
         };
     }
 
+    auto& obj = jv.as_object();
+    obj[JS(ledger_hash)] = output.ledgerHash;
+    obj[JS(ledger_index)] = output.ledgerIndex;
+    obj[JS(validated)] = output.validated;
+}
+
 void
 tag_invoke(boost::json::value_from_tag, boost::json::value& jv, FeatureHandler::Output::Feature const& feature)
 {

src/rpc/handlers/Feature.hpp

@@ -71,6 +71,9 @@ public:
         std::string ledgerHash;
         uint32_t ledgerIndex{};
 
+        // when set to true, output will be inlined in `result` instead of wrapping as `features` inside of `result`.
+        bool inlineResult = false;
+
         // validated should be sent via framework
         bool validated = true;
     };

tests/unit/rpc/handlers/FeatureTests.cpp

@@ -257,13 +257,11 @@ TEST_F(RPCFeatureHandlerTest, SuccessPathViaNameWithSingleSupportedAndEnabledRes
 
     auto const expectedOutput = fmt::format(
         R"({{
-            "features": {{
             "2E2FB9CF8A44EB80F4694D38AADAE9B8B7ADAFD2F092E10068E61C98C4F092B0": 
             {{
                 "name": "fixUniversalNumber", 
                 "enabled": true, 
                 "supported": true
-                }}
             }},
             "ledger_hash": "{}", 
             "ledger_index": {}, 
@@ -311,13 +309,11 @@ TEST_F(RPCFeatureHandlerTest, SuccessPathViaHashWithSingleResult)
 
     auto const expectedOutput = fmt::format(
         R"({{
-            "features": {{
             "2E2FB9CF8A44EB80F4694D38AADAE9B8B7ADAFD2F092E10068E61C98C4F092B0": 
             {{
                 "name": "fixUniversalNumber", 
                 "enabled": true, 
                 "supported": true
-                }}
             }},
             "ledger_hash": "{}", 
             "ledger_index": {},