From ca46c321915798818d6716fb5c2be9f538f2e722 Mon Sep 17 00:00:00 2001
From: David Härdeman <david@hardeman.nu>
Date: Thu, 11 Jun 2020 12:29:43 +0200
Subject: Add some socket options to minecraft protocol sockets

---
 idle.c   |  2 ++
 main.h   |  5 +++--
 proxy.c  |  2 ++
 rcon.c   |  2 ++
 server.c | 21 +++++++++++++++++++--
 utils.c  | 27 +++++++++++++++++++++++++++
 utils.h  |  2 ++
 7 files changed, 57 insertions(+), 4 deletions(-)

diff --git a/idle.c b/idle.c
index 3fddf79..8f2530a 100644
--- a/idle.c
+++ b/idle.c
@@ -361,6 +361,8 @@ again:
                 goto again;
         }
 
+	socket_set_gaming_options(cfg, sfd);
+
         uring_task_set_fd(&idle->idlecheck, sfd);
         uring_connect(cfg, &idle->idlecheck, &idle->remote, idle_check_remote_connected);
 }
diff --git a/main.h b/main.h
index d0cb41b..578c8d7 100644
--- a/main.h
+++ b/main.h
@@ -3,6 +3,9 @@
 
 #include <sys/socket.h>
 #include <netinet/ip.h>
+
+struct cfg;
+
 #include "utils.h"
 
 extern bool exiting;
@@ -18,8 +21,6 @@ void die(const char *fmt, ...);
 
 #define perrordie(msg) die("%s: %m\n", msg)
 
-struct cfg;
-
 struct uring_task;
 
 /* To save typing in all the function definitions below */
diff --git a/proxy.c b/proxy.c
index 9fda0c5..6b724f2 100644
--- a/proxy.c
+++ b/proxy.c
@@ -236,6 +236,8 @@ again:
 		goto again;
 	}
 
+	socket_set_gaming_options(cfg, sfd);
+
 	proxy->sfd = sfd;
 	uring_task_set_fd(&proxy->servertask, sfd);
 	uring_connect(cfg, &proxy->servertask, &proxy->server, proxy_server_connected);
diff --git a/rcon.c b/rcon.c
index a1fd90f..4229527 100644
--- a/rcon.c
+++ b/rcon.c
@@ -372,6 +372,8 @@ again:
                 goto again;
         }
 
+	socket_set_gaming_options(cfg, sfd);
+
         uring_task_set_fd(&rcon->task, sfd);
         uring_connect(cfg, &rcon->task, &rcon->rcon, rcon_connected);
 }
diff --git a/server.c b/server.c
index 0298491..3cc2398 100644
--- a/server.c
+++ b/server.c
@@ -10,6 +10,9 @@
 #include <poll.h>
 #include <errno.h>
 #include <sched.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
 
 #include "main.h"
 #include "uring.h"
@@ -212,7 +215,7 @@ static bool
 server_local_open(struct cfg *cfg, struct server *scfg, struct server_local *local)
 {
 	int sfd;
-	int enable = 1;
+	int option;
 	int r;
 
 	sfd = socket(local->addr.storage.ss_family, SOCK_STREAM | SOCK_CLOEXEC, 0);
@@ -221,11 +224,25 @@ server_local_open(struct cfg *cfg, struct server *scfg, struct server_local *loc
 		goto out;
 	}
 
-	if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) < 0) {
+	option = true;
+	if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &option, sizeof(option)) < 0) {
 		perror("setsockopt");
 		goto out;
 	}
 
+	/* The MC protocol expects the client to send data first */
+	/* FIXME: could make this configurable */
+	option = true;
+	if (setsockopt(sfd, IPPROTO_TCP, TCP_DEFER_ACCEPT, &option, sizeof(option)) < 0)
+		perror("setsockopt");
+
+	/* FIXME: could make this configurable */
+	option = true;
+	if (setsockopt(sfd, IPPROTO_IP, IP_FREEBIND, &option, sizeof(option)) < 0)
+		perror("setsockopt");
+
+	socket_set_gaming_options(cfg, sfd);
+
 	r = bind(sfd, (struct sockaddr *)&local->addr.storage, local->addr.addrlen);
 	if (r < 0) {
 		perror("bind");
diff --git a/utils.c b/utils.c
index 39f91f1..93bc0b8 100644
--- a/utils.c
+++ b/utils.c
@@ -8,6 +8,9 @@
 #include <dirent.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
 
 #include "main.h"
 #include "utils.h"
@@ -155,6 +158,30 @@ debug_resource_usage()
 	}
 }
 
+void
+socket_set_gaming_options(struct cfg *cfg, int sfd)
+{
+	int option;
+
+	if (sfd <= 0)
+		return;
+
+	/* FIXME: could make this configurable */
+	option = true;
+	if (setsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, &option, sizeof(option)) < 0)
+		perror("setsockopt");
+
+	/* Doubtful if it has much effect, but can't hurt */
+	option = IPTOS_LOWDELAY;
+	if (setsockopt(sfd, IPPROTO_IP, IP_TOS, &option, sizeof(option)) < 0)
+		perror("setsockopt");
+
+	/* Nagle's algorithm is a poor fit for gaming */
+	option = true;
+	if (setsockopt(sfd, IPPROTO_TCP, TCP_NODELAY, &option, sizeof(option)) < 0)
+		perror("setsockopt");
+}
+
 uint16_t sockaddr_port(struct sockaddr_in46 *addr)
 {
 	switch (addr->storage.ss_family) {
diff --git a/utils.h b/utils.h
index 52a1078..8f8a153 100644
--- a/utils.h
+++ b/utils.h
@@ -104,6 +104,8 @@ struct sockaddr_in46 {
 	struct list_head list;
 };
 
+void socket_set_gaming_options(struct cfg *cfg, int sfd);
+
 uint16_t sockaddr_port(struct sockaddr_in46 *addr);
 
 char *sockaddr_to_str(struct sockaddr_in46 *addr, char *buf, size_t buflen);
-- 
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