From 8d74cc631c73c6124cd0c4e85b09d3e77fb79bda Mon Sep 17 00:00:00 2001
From: Julian Brost <julian.brost@icinga.com>
Date: Mon, 14 Jul 2025 13:37:36 +0200
Subject: [PATCH] Log: don't construct std::ostringstream for no-op messages

This commit removes the existing m_IsNoOp bool and instead wraps the m_Buffer
std::ostringstream into std::optional. Functionally, this is pretty much the
same, with the exception that std::ostringstream is no longer constructed for
messages that will be discarded later.
---
 lib/base/logger.cpp | 18 +++++++++++-------
 lib/base/logger.hpp | 12 ++++++++----
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/lib/base/logger.cpp b/lib/base/logger.cpp
index b3be523a8..f28a19bbd 100644
--- a/lib/base/logger.cpp
+++ b/lib/base/logger.cpp
@@ -247,21 +247,25 @@ void Logger::UpdateMinLogSeverity()
 Log::Log(LogSeverity severity, String facility, const String& message)
 	: Log(severity, std::move(facility))
 {
-	if (!m_IsNoOp) {
-		m_Buffer << message;
-	}
+	*this << message;
 }
 
 Log::Log(LogSeverity severity, String facility)
-	: m_Severity(severity), m_Facility(std::move(facility)), m_IsNoOp(severity < Logger::GetMinLogSeverity())
-{ }
+{
+	// Only fully initialize the object if it's actually going to be logged.
+	if (severity >= Logger::GetMinLogSeverity()) {
+		m_Severity = severity;
+		m_Facility = std::move(facility);
+		m_Buffer.emplace();
+	}
+}
 
 /**
  * Writes the message to the application's log.
  */
 Log::~Log()
 {
-	if (m_IsNoOp) {
+	if (!m_Buffer) {
 		return;
 	}
 
@@ -271,7 +275,7 @@ Log::~Log()
 	entry.Facility = m_Facility;
 
 	{
-		auto msg (m_Buffer.str());
+		auto msg (m_Buffer->str());
 		msg.erase(msg.find_last_not_of("\n") + 1u);
 
 		entry.Message = std::move(msg);
diff --git a/lib/base/logger.hpp b/lib/base/logger.hpp
index 0437ebf39..d7f30bcee 100644
--- a/lib/base/logger.hpp
+++ b/lib/base/logger.hpp
@@ -6,6 +6,7 @@
 #include "base/atomic.hpp"
 #include "base/i2-base.hpp"
 #include "base/logger-ti.hpp"
+#include <optional>
 #include <set>
 #include <sstream>
 
@@ -121,8 +122,8 @@ public:
 	template<typename T>
 	Log& operator<<(T&& val)
 	{
-		if (!m_IsNoOp) {
-			m_Buffer << std::forward<T>(val);
+		if (m_Buffer) {
+			*m_Buffer << std::forward<T>(val);
 		}
 
 		return *this;
@@ -131,8 +132,11 @@ public:
 private:
 	LogSeverity m_Severity;
 	String m_Facility;
-	std::ostringstream m_Buffer;
-	bool m_IsNoOp;
+	/**
+	 * Stream for incrementally generating the log message. If the message will be discarded as it's level currently
+	 * isn't logged, it will be empty as the stream doesn't need to be initialized in this case.
+	 */
+	std::optional<std::ostringstream> m_Buffer;
 };
 
 extern template Log& Log::operator<<(const Value&);