From 861274c9f8cf2a5c00ded9580ea91b22def683f7 Mon Sep 17 00:00:00 2001
From: Gleb Smirnoff <glebius@FreeBSD.org>
Date: Thu, 1 Feb 2024 13:37:26 -0800
Subject: [PATCH] tests/netinet: add a demo of TCP implied connect

The TCP implied connect is an artifact left after T/TCP.  To my surprise
it still works, hence the existence of this test.  Please read this email
first:

https://lists.freebsd.org/pipermail/freebsd-net/2010-August/026311.html

An interesting fact that this test takes 220 - 240 milliseconds to
execute on my Threadripper PRO.  Flipping the '#if 0' to '#if 1' in the
test, thus bringing it back to normal connect(2), would speed the test up
a hundred times and I guess all this time is fork+exec of the test.
---
 tests/sys/netinet/Makefile              |  1 +
 tests/sys/netinet/tcp_implied_connect.c | 81 +++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 tests/sys/netinet/tcp_implied_connect.c

diff --git a/tests/sys/netinet/Makefile b/tests/sys/netinet/Makefile
index 434aadc87f46..b86457c2d723 100644
--- a/tests/sys/netinet/Makefile
+++ b/tests/sys/netinet/Makefile
@@ -11,6 +11,7 @@ ATF_TESTS_C=	ip_reass_test \
 		so_reuseport_lb_test \
 		socket_afinet \
 		tcp_connect_port_test \
+		tcp_implied_connect \
 		tcp_md5_getsockopt
 
 ATF_TESTS_SH=	arp \
diff --git a/tests/sys/netinet/tcp_implied_connect.c b/tests/sys/netinet/tcp_implied_connect.c
new file mode 100644
index 000000000000..2961626d5e5b
--- /dev/null
+++ b/tests/sys/netinet/tcp_implied_connect.c
@@ -0,0 +1,81 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2024 Gleb Smirnoff <glebius@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+
+#include <atf-c.h>
+
+static struct sockaddr_in sin = {
+	.sin_family = AF_INET,
+	.sin_len = sizeof(sin),
+};
+
+static const char buf[] = "hello";
+static char repl[sizeof(buf)];
+
+ATF_TC_WITHOUT_HEAD(tcp_implied_connect);
+ATF_TC_BODY(tcp_implied_connect, tc)
+{
+	socklen_t len;
+	int s, c, a;
+
+	ATF_REQUIRE(s = socket(PF_INET, SOCK_STREAM, 0));
+	ATF_REQUIRE(c = socket(PF_INET, SOCK_STREAM, 0));
+
+	ATF_REQUIRE(bind(s, (struct sockaddr *)&sin, sizeof(sin)) == 0);
+	len = sizeof(sin);
+	ATF_REQUIRE(getsockname(s, (struct sockaddr *)&sin, &len) == 0);
+	ATF_REQUIRE(listen(s, -1) == 0);
+#if 0
+	/*
+	 * The disabled code is that you would normally do.
+	 */
+	ATF_REQUIRE(connect(c, (struct sockaddr *)&sin, sizeof(sin)) == 0);
+	ATF_REQUIRE(send(c, &buf, sizeof(buf), 0) == sizeof(buf));
+#else
+	/*
+	 * And this is implied connect.
+	 */
+	ATF_REQUIRE(sendto(c, &buf, sizeof(buf), 0, (struct sockaddr *)&sin,
+	    sizeof(sin)) == sizeof(buf));
+#endif
+
+	ATF_REQUIRE((a = accept(s, NULL, NULL)) != 1);
+	ATF_REQUIRE(recv(a, &repl, sizeof(repl), 0) == sizeof(buf));
+	ATF_REQUIRE(strcmp(buf, repl) == 0);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, tcp_implied_connect);
+
+	return (atf_no_error());
+}