From 205088e23f4b14185a47cb1924ef7f3c8d32bfe9 Mon Sep 17 00:00:00 2001
From: "Alan T. DeKok" <aland@freeradius.org>
Date: Mon, 15 Apr 2024 11:59:50 -0400
Subject: [PATCH] set TCP_NODELAY by default

---
 src/lib/bio/fd.h      |  1 +
 src/lib/bio/fd_open.c | 29 ++++++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/lib/bio/fd.h b/src/lib/bio/fd.h
index aee79b7944..7c695251c4 100644
--- a/src/lib/bio/fd.h
+++ b/src/lib/bio/fd.h
@@ -98,6 +98,7 @@ typedef struct {
 	int		flags;		//!< O_RDONLY, etc.
 
 	bool		async;		//!< is it async
+	bool		tcp_delay;	//!< We do tcp_nodelay by default.
 } fr_bio_fd_config_t;
 
 /** Run-time status of the socket.
diff --git a/src/lib/bio/fd_open.c b/src/lib/bio/fd_open.c
index 1f93fa2f98..aae05ac7a8 100644
--- a/src/lib/bio/fd_open.c
+++ b/src/lib/bio/fd_open.c
@@ -30,21 +30,48 @@
 #include <net/if.h>
 #include <fcntl.h>
 #include <libgen.h>
+#include <netinet/tcp.h>
 
 /** Initialize common datagram information
  *
  */
-static int fr_bio_fd_common_tcp(int fd, UNUSED fr_socket_t const *sock, UNUSED fr_bio_fd_config_t const *cfg)
+static int fr_bio_fd_common_tcp(int fd, UNUSED fr_socket_t const *sock, fr_bio_fd_config_t const *cfg)
 {
 	int on = 1;
 
 #ifdef SO_KEEPALIVE
+	/*
+	 *	TCP keepalives are always a good idea.  Too many people put firewalls between critical
+	 *	systems, and then the firewalls drop live TCP streams.
+	 */
 	if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on)) < 0) {
 		fr_strerror_printf("Failed setting SO_KEEPALIVE: %s", fr_syserror(errno));
 		return -1;
 	}
 #endif
 
+#ifdef TCP_NODELAY
+	/*
+	 *	Add some defines for *BSD, and Solaris systems.
+	 */
+#  if !defined(SOL_TCP) && defined(IPPROTO_TCP)
+#    define SOL_TCP IPPROTO_TCP
+#  endif
+
+	/*
+	 *	Also set TCP_NODELAY, to force the data to be written quickly.
+	 *
+	 *	We buffer full packets in memory before we write them, so there's no reason for the kernel to
+	 *	sit around waiting for more data from us.
+	 */
+	if (!cfg->tcp_delay) {
+		if (setsockopt(fd, SOL_TCP, TCP_NODELAY, &on, sizeof(on)) < 0) {
+			fr_strerror_printf("Failed setting TCP_NODELAY: %s", fr_syserror(errno));
+			return -1;
+		}
+	}
+#endif
+
 	return 0;
 }
 
-- 
2.47.3