From fa7c02e9f5e53afba2f867fc3b77ec8a59d62528 Mon Sep 17 00:00:00 2001
From: Ian Craggs <icraggs@gmail.com>
Date: Thu, 12 Feb 2026 15:17:43 +0000
Subject: [PATCH] Set TCP_NODELAY by default, CMake option to not use it #530

---
 CMakeLists.txt | 5 +++++
 src/Socket.c   | 9 +++++++++
 2 files changed, 14 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4b8d15f8..d244484c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -64,6 +64,7 @@ option(PAHO_ENABLE_TESTING "Build tests and run" TRUE)
 option(PAHO_ENABLE_CPACK "Enable CPack" TRUE)
 option(PAHO_HIGH_PERFORMANCE "Disable tracing and heap tracking" FALSE)
 option(PAHO_USE_SELECT "Revert to select system call instead of poll" FALSE)
+option(PAHO_NO_TCP_NODELAY "Don't disable Nagle's algorithm on TCP sockets" FALSE)
 
 if(NOT WIN32)
     option(PAHO_WITH_UNIX_SOCKETS "Flag that defines whether to enable Unix-domain sockets" FALSE)
@@ -85,6 +86,10 @@ if(PAHO_WITH_LIBUUID)
   add_definitions(-DUSE_LIBUUID=1)
 endif()
 
+if(PAHO_NO_TCP_NODELAY)
+  add_definitions(-DNO_TCP_NODELAY=1)
+endif()
+
 if(NOT PAHO_BUILD_SHARED AND NOT PAHO_BUILD_STATIC)
   message(FATAL_ERROR "You must set either PAHO_BUILD_SHARED, PAHO_BUILD_STATIC, or both")
 endif()
diff --git a/src/Socket.c b/src/Socket.c
index 4909c6ab..d2ebfdab 100644
--- a/src/Socket.c
+++ b/src/Socket.c
@@ -1462,6 +1462,15 @@ int Socket_new(const char* addr, size_t addr_len, int port, SOCKET* sock)
 			if (setsockopt(*sock, SOL_SOCKET, SO_NOSIGPIPE, (void*)&opt, sizeof(opt)) != 0)
 				Log(LOG_ERROR, -1, "Could not set SO_NOSIGPIPE for socket %d", *sock);
 #endif
+#if !defined(NO_TCP_NODELAY)
+			{
+				int opt = 1;
+				socklen_t opt_size = sizeof(opt);
+				
+				if (setsockopt(*sock, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt)) != 0)
+					Log(LOG_ERROR, -1, "Could not set TCP_NODELAY for socket %d", *sock);
+			}
+#endif
 /*#define SMALL_TCP_BUFFER_TESTING
   This section sets the TCP send buffer to a small amount to provoke TCPSOCKET_INTERRUPTED
 	return codes from send, for testing only!