rpc: JSON-RPC 2.0 should not respond to "notifications"

For JSON-RPC 2.0 requests we need to distinguish between
a missing "id" field and "id":null. This is accomplished
by making the JSONRPCRequest id property a
std::optional<UniValue> with a default value of
UniValue::VNULL.

A side-effect of this change for non-2.0 requests is that request which do not
specify an "id" field will no longer return "id": null in the response.

3 files changed, 12 insertions, 5 deletions

diff --git a/src/rpc/protocol.h b/src/rpc/protocol.h
index 75e42e4c88..83a9010681 100644
--- a/src/rpc/protocol.h
+++ b/src/rpc/protocol.h
@@ -10,6 +10,7 @@
 enum HTTPStatusCode
 {
     HTTP_OK                    = 200,
+    HTTP_NO_CONTENT            = 204,
     HTTP_BAD_REQUEST           = 400,
     HTTP_UNAUTHORIZED          = 401,
     HTTP_FORBIDDEN             = 403,
diff --git a/src/rpc/request.cpp b/src/rpc/request.cpp
index b5bf1e5ffa..ca424b4953 100644
--- a/src/rpc/request.cpp
+++ b/src/rpc/request.cpp
@@ -37,7 +37,7 @@ UniValue JSONRPCRequestObj(const std::string& strMethod, const UniValue& params,
     return request;
 }
 
-UniValue JSONRPCReplyObj(UniValue result, UniValue error, UniValue id, JSONRPCVersion jsonrpc_version)
+UniValue JSONRPCReplyObj(UniValue result, UniValue error, std::optional<UniValue> id, JSONRPCVersion jsonrpc_version)
 {
     UniValue reply(UniValue::VOBJ);
     // Add JSON-RPC version number field in v2 only.
@@ -52,7 +52,7 @@ UniValue JSONRPCReplyObj(UniValue result, UniValue error, UniValue id, JSONRPCVe
         if (jsonrpc_version == JSONRPCVersion::V1_LEGACY) reply.pushKV("result", NullUniValue);
         reply.pushKV("error", std::move(error));
     }
-    reply.pushKV("id", std::move(id));
+    if (id.has_value()) reply.pushKV("id", std::move(id.value()));
     return reply;
 }
 
@@ -172,7 +172,11 @@ void JSONRPCRequest::parse(const UniValue& valRequest)
     const UniValue& request = valRequest.get_obj();
 
     // Parse id now so errors from here on will have the id
-    id = request.find_value("id");
+    if (request.exists("id")) {
+        id = request.find_value("id");
+    } else {
+        id = std::nullopt;
+    }
 
     // Check for JSON-RPC 2.0 (default 1.1)
     m_json_version = JSONRPCVersion::V1_LEGACY;
diff --git a/src/rpc/request.h b/src/rpc/request.h
index a7c9af2216..e47f90af86 100644
--- a/src/rpc/request.h
+++ b/src/rpc/request.h
@@ -7,6 +7,7 @@
 #define BITCOIN_RPC_REQUEST_H
 
 #include <any>
+#include <optional>
 #include <string>
 
 #include <univalue.h>
@@ -17,7 +18,7 @@ enum class JSONRPCVersion {
 };
 
 UniValue JSONRPCRequestObj(const std::string& strMethod, const UniValue& params, const UniValue& id);
-UniValue JSONRPCReplyObj(UniValue result, UniValue error, UniValue id, JSONRPCVersion jsonrpc_version);
+UniValue JSONRPCReplyObj(UniValue result, UniValue error, std::optional<UniValue> id, JSONRPCVersion jsonrpc_version);
 UniValue JSONRPCError(int code, const std::string& message);
 
 /** Generate a new RPC authentication cookie and write it to disk */
@@ -32,7 +33,7 @@ std::vector<UniValue> JSONRPCProcessBatchReply(const UniValue& in);
 class JSONRPCRequest
 {
 public:
-    UniValue id;
+    std::optional<UniValue> id = UniValue::VNULL;
     std::string strMethod;
     UniValue params;
     enum Mode { EXECUTE, GET_HELP, GET_ARGS } mode = EXECUTE;
@@ -43,6 +44,7 @@ public:
     JSONRPCVersion m_json_version = JSONRPCVersion::V1_LEGACY;
 
     void parse(const UniValue& valRequest);
+    [[nodiscard]] bool IsNotification() const { return !id.has_value() && m_json_version == JSONRPCVersion::V2; };
 };
 
 #endif // BITCOIN_RPC_REQUEST_H