From b044f39843def881d0971e39579b44198c095ce5 Mon Sep 17 00:00:00 2001
From: "Alexander A. Klimov" <alexander.klimov@icinga.com>
Date: Fri, 13 Dec 2024 17:07:21 +0100
Subject: [PATCH] JsonRpcConnection#HandleIncomingMessages(): don't block
 #m_IoStrand with #MessageHandler()

---
 lib/remote/jsonrpcconnection.cpp | 82 +++++++++++++++++++-------------
 1 file changed, 48 insertions(+), 34 deletions(-)

diff --git a/lib/remote/jsonrpcconnection.cpp b/lib/remote/jsonrpcconnection.cpp
index c70b82d94e..bcbc29f004 100644
--- a/lib/remote/jsonrpcconnection.cpp
+++ b/lib/remote/jsonrpcconnection.cpp
@@ -13,6 +13,7 @@
 #include "base/logger.hpp"
 #include "base/exception.hpp"
 #include "base/convert.hpp"
+#include "base/shared.hpp"
 #include "base/tlsstream.hpp"
 #include <memory>
 #include <utility>
@@ -66,13 +67,14 @@ void JsonRpcConnection::HandleIncomingMessages(boost::asio::yield_context yc)
 		return ch::duration_cast<ch::milliseconds>(d).count();
 	});
 
+	auto& io (m_IoStrand.context());
+	auto msg (Shared<std::pair<String, AsioConditionVariable>>::Make(String(), io));
+
 	m_Stream->next_layer().SetSeen(&m_Seen);
 
 	while (!m_ShuttingDown) {
-		String jsonString;
-
 		try {
-			jsonString = JsonRpc::ReadMessage(m_Stream, yc, m_Endpoint ? -1 : 1024 * 1024);
+			msg->first = JsonRpc::ReadMessage(m_Stream, yc, m_Endpoint ? -1 : 1024 * 1024);
 		} catch (const std::exception& ex) {
 			Log(m_ShuttingDown ? LogDebug : LogNotice, "JsonRpcConnection")
 				<< "Error while reading JSON-RPC message for identity '" << m_Identity
@@ -83,52 +85,64 @@ void JsonRpcConnection::HandleIncomingMessages(boost::asio::yield_context yc)
 
 		m_Seen = Utility::GetTime();
 		if (m_Endpoint) {
-			m_Endpoint->AddMessageReceived(jsonString.GetLength());
+			m_Endpoint->AddMessageReceived(msg->first.GetLength());
 		}
 
-		String rpcMethod("UNKNOWN");
 		ch::steady_clock::duration cpuBoundDuration(0);
 		auto start (ch::steady_clock::now());
+		CpuBoundWork handleMessage (yc);
 
-		try {
-			CpuBoundWork handleMessage (yc);
+		// Cache the elapsed time to acquire a CPU semaphore used to detect extremely heavy workloads.
+		cpuBoundDuration = ch::steady_clock::now() - start;
 
-			// Cache the elapsed time to acquire a CPU semaphore used to detect extremely heavy workloads.
-			cpuBoundDuration = ch::steady_clock::now() - start;
+		io.post([this, keepAlive = Ptr(this), msg, start, toMilliseconds, cpuBoundDuration] {
+			Defer wakeUp ([this, msg] {
+				m_IoStrand.post([msg] { msg->second.Set(); });
+			});
 
-			Dictionary::Ptr message = JsonRpc::DecodeMessage(jsonString);
-			if (String method = message->Get("method"); !method.IsEmpty()) {
-				rpcMethod = std::move(method);
-			}
+			String rpcMethod ("UNKNOWN");
+
+			try {
+				Dictionary::Ptr message = JsonRpc::DecodeMessage(msg->first);
+				if (String method = message->Get("method"); !method.IsEmpty()) {
+					rpcMethod = std::move(method);
+				}
 
-			MessageHandler(message);
+				MessageHandler(message);
 
-			l_TaskStats.InsertValue(Utility::GetTime(), 1);
+				l_TaskStats.InsertValue(Utility::GetTime(), 1);
 
-			auto total = ch::steady_clock::now() - start;
+				auto total = ch::steady_clock::now() - start;
+				Log msg (total >= ch::seconds(5) ? LogWarning : LogDebug, "JsonRpcConnection");
 
-			Log msg(total >= ch::seconds(5) ? LogWarning : LogDebug, "JsonRpcConnection");
-			msg << "Processed JSON-RPC '" << rpcMethod << "' message for identity '" << m_Identity
-				<< "' (took total " << toMilliseconds(total) << "ms";
+				msg << "Processed JSON-RPC '" << rpcMethod << "' message for identity '" << m_Identity
+					<< "' (took total " << toMilliseconds(total) << "ms";
 
-			if (cpuBoundDuration >= ch::seconds(1)) {
-				msg << ", waited " << toMilliseconds(cpuBoundDuration) << "ms on semaphore";
-			}
-			msg << ").";
-		} catch (const std::exception& ex) {
-			auto total = ch::steady_clock::now() - start;
+				if (cpuBoundDuration >= ch::seconds(1)) {
+					msg << ", waited " << toMilliseconds(cpuBoundDuration) << "ms on semaphore";
+				}
 
-			Log msg(m_ShuttingDown ? LogDebug : LogWarning, "JsonRpcConnection");
-			msg << "Error while processing JSON-RPC '" << rpcMethod << "' message for identity '"
-				<< m_Identity << "' (took total " << toMilliseconds(total) << "ms";
+				msg << ").";
+			} catch (const std::exception& ex) {
+				auto total = ch::steady_clock::now() - start;
+
+				Log msg (m_ShuttingDown ? LogDebug : LogWarning, "JsonRpcConnection");
+
+				msg << "Error while processing JSON-RPC '" << rpcMethod << "' message for identity '"
+					<< m_Identity << "' (took total " << toMilliseconds(total) << "ms";
+
+				if (cpuBoundDuration >= ch::seconds(1)) {
+					msg << ", waited " << toMilliseconds(cpuBoundDuration) << "ms on semaphore";
+				}
 
-			if (cpuBoundDuration >= ch::seconds(1)) {
-				msg << ", waited " << toMilliseconds(cpuBoundDuration) << "ms on semaphore";
+				msg << "): " << DiagnosticInformation(ex);
+
+				Disconnect();
 			}
-			msg << "): " << DiagnosticInformation(ex);
+		});
 
-			break;
-		}
+		msg->second.Wait(yc);
+		msg->second.Clear();
 	}
 
 	Disconnect();
@@ -381,7 +395,7 @@ void JsonRpcConnection::MessageHandler(const Dictionary::Ptr& message)
 		resultMessage->Set("jsonrpc", "2.0");
 		resultMessage->Set("id", message->Get("id"));
 
-		SendMessageInternal(resultMessage);
+		SendMessage(resultMessage);
 	}
 }