Add ping handler (#503)

Fix #506

src/rpc/common/Concepts.h

@@ -49,12 +49,21 @@ concept Requirement = requires(T a) {
  */
 // clang-format off
 template <typename T>
-concept Handler = requires(T a, typename T::Input in, typename T::Output out) {
+concept HandlerWithInput = requires(T a, typename T::Input in, typename T::Output out) {
     { a.spec() } -> std::same_as<RpcSpecConstRef>;
-    { a.process(in) } -> std::same_as<HandlerReturnType<decltype(out)>>;
-} 
-&& boost::json::has_value_from<typename T::Output>::value
-&& boost::json::has_value_to<typename T::Input>::value;
+    { a.process(in) } -> std::same_as<HandlerReturnType<decltype(out)>>;}
+    && boost::json::has_value_to<typename T::Input>::value;
+
+template <typename T>
+concept HandlerWithoutInput = requires(T a, typename T::Output out) {
+    { a.process() } -> std::same_as<HandlerReturnType<decltype(out)>>;};
+
+template <typename T>
+concept Handler = 
+(HandlerWithInput<T>
+||
+HandlerWithoutInput<T>)
+&& boost::json::has_value_from<typename T::Output>::value;
 // clang-format on
 
 }  // namespace RPCng

src/rpc/common/Types.h

@@ -53,4 +53,14 @@ struct FieldSpec;
 
 using RpcSpecConstRef = RpcSpec const&;
 
+struct VoidOutput
+{
+};
+
+inline void
+tag_invoke(boost::json::value_from_tag, boost::json::value& jv, VoidOutput)
+{
+    jv = boost::json::object{};
+}
+
 }  // namespace RPCng

src/rpc/common/impl/Processors.h

@@ -24,6 +24,9 @@
 
 namespace RPCng::detail {
 
+template <typename>
+static constexpr bool unsupported_handler_v = false;
+
 template <Handler HandlerType>
 struct DefaultProcessor final
 {
@@ -33,19 +36,35 @@ struct DefaultProcessor final
     {
         using boost::json::value_from;
         using boost::json::value_to;
+        if constexpr (HandlerWithInput<HandlerType>)
+        {
+            // first we run validation
+            auto const spec = handler.spec();
+            if (auto const ret = spec.validate(value); not ret)
+                return Error{ret.error()};  // forward Status
 
-        // first we run validation
-        auto const spec = handler.spec();
-        if (auto const ret = spec.validate(value); not ret)
-            return Error{ret.error()};  // forward Status
+            auto const inData = value_to<typename HandlerType::Input>(value);
 
-        auto const inData = value_to<typename HandlerType::Input>(value);
-
-        // real handler is given expected Input, not json
-        if (auto const ret = handler.process(inData); not ret)
-            return Error{ret.error()};  // forward Status
+            // real handler is given expected Input, not json
+            if (auto const ret = handler.process(inData); not ret)
+                return Error{ret.error()};  // forward Status
+            else
+                return value_from(ret.value());
+        }
+        else if constexpr (HandlerWithoutInput<HandlerType>)
+        {
+            // no input to pass, ignore the value
+            if (auto const ret = handler.process(); not ret)
+                return Error{ret.error()};  // forward Status
+            else
+                return value_from(ret.value());
+        }
         else
-            return value_from(ret.value());
+        {
+            // when concept HandlerWithInput and HandlerWithoutInput not cover
+            // all Handler case
+            static_assert(unsupported_handler_v<HandlerType>);
+        }
     }
 };
 

src/rpc/ngHandlers/Ping.h

@@ -0,0 +1,38 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, 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.
+*/
+//==============================================================================
+
+#pragma once
+
+#include <rpc/common/Types.h>
+
+namespace RPCng {
+
+class PingHandler
+{
+public:
+    using Output = VoidOutput;
+    using Result = HandlerReturnType<Output>;
+
+    Result
+    process() const
+    {
+        return Output{};
+    }
+};
+}  // namespace RPCng