Forward feature RPC (#1440)

Fixes #1436 

This is a temporary implementation of the `feature` RPC that will always
return `noPermission` iff `vetoed` is set.
If `vetoed` isn't specified, Clio will always forward the request to
`rippled` instead.

In the future, #1131 will implement a Clio-native `feature` RPC. This
requires specific support from `libxrpl` side and that is not going to
be available till at least 2.2.1, hence the temporary forwarding.

It would be great to review the error message and code so that we pick
the right one from the start.

Co-authored-by: Sergey Kuznetsov <skuznetsov@ripple.com>

tests/unit/CMakeLists.txt

@@ -67,6 +67,7 @@ target_sources(
           rpc/handlers/BookOffersTests.cpp
           rpc/handlers/DefaultProcessorTests.cpp
           rpc/handlers/DepositAuthorizedTests.cpp
+          rpc/handlers/FeatureTests.cpp
           rpc/handlers/GatewayBalancesTests.cpp
           rpc/handlers/GetAggregatePriceTests.cpp
           rpc/handlers/LedgerDataTests.cpp

tests/unit/rpc/ForwardingProxyTests.cpp

@@ -260,6 +260,38 @@ TEST_F(RPCForwardingProxyTest, ShouldForwardReturnsFalseIfAPIVersionIsV2)
     });
 }
 
+TEST_F(RPCForwardingProxyTest, ShouldForwardFeatureWithoutVetoedFlag)
+{
+    auto const apiVersion = 1u;
+    auto const method = "feature";
+    auto const params = json::parse(R"({"feature": "foo"})");
+
+    runSpawn([&](auto yield) {
+        auto const range = backend->fetchLedgerRange();
+        auto const ctx =
+            web::Context(yield, method, apiVersion, params.as_object(), nullptr, tagFactory, *range, CLIENT_IP, true);
+
+        auto const res = proxy.shouldForward(ctx);
+        ASSERT_TRUE(res);
+    });
+}
+
+TEST_F(RPCForwardingProxyTest, ShouldNeverForwardFeatureWithVetoedFlag)
+{
+    auto const apiVersion = 1u;
+    auto const method = "feature";
+    auto const params = json::parse(R"({"vetoed": true, "feature": "foo"})");
+
+    runSpawn([&](auto yield) {
+        auto const range = backend->fetchLedgerRange();
+        auto const ctx =
+            web::Context(yield, method, apiVersion, params.as_object(), nullptr, tagFactory, *range, CLIENT_IP, true);
+
+        auto const res = proxy.shouldForward(ctx);
+        ASSERT_FALSE(res);
+    });
+}
+
 TEST_F(RPCForwardingProxyTest, ShouldNeverForwardSubscribe)
 {
     auto const apiVersion = 1u;

tests/unit/rpc/handlers/FeatureTests.cpp

@@ -0,0 +1,48 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "rpc/Errors.hpp"
+#include "rpc/common/AnyHandler.hpp"
+#include "rpc/common/Types.hpp"
+#include "rpc/handlers/Feature.hpp"
+#include "util/Fixtures.hpp"
+
+#include <boost/json/parse.hpp>
+#include <gtest/gtest.h>
+
+using namespace rpc;
+
+class RPCFeatureHandlerTest : public HandlerBaseTest {};
+
+TEST_F(RPCFeatureHandlerTest, AlwaysNoPermissionForVetoed)
+{
+    runSpawn([](auto yield) {
+        auto const handler = AnyHandler{FeatureHandler{}};
+        auto const output =
+            handler.process(boost::json::parse(R"({"vetoed": true, "feature": "foo"})"), Context{yield});
+
+        ASSERT_FALSE(output);
+
+        auto const err = rpc::makeError(output.result.error());
+        EXPECT_EQ(err.at("error").as_string(), "noPermission");
+        EXPECT_EQ(
+            err.at("error_message").as_string(), "The admin portion of feature API is not available through Clio."
+        );
+    });
+}