passt/doc/platform-requirements/recv-zero.c

// SPDX-License-Identifier: GPL-2.0-or-later

/* recv-zero.c
 *
 * Verify that we're able to discard datagrams by recv()ing into a zero-length
 * buffer.
 *
 * Copyright Red Hat
 * Author: David Gibson <david@gibson.dropbear.id.au>
 */

#include <arpa/inet.h>
#include <errno.h>
#include <net/if.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "common.h"

#define DSTPORT	13257U

/* 127.0.0.1:DSTPORT */
static const struct sockaddr_in lo_dst = SOCKADDR_INIT(INADDR_LOOPBACK, DSTPORT);

static void test_discard(void)
{
	long token1, token2;
	int recv_s, send_s;
	ssize_t rc;

	token1 = random();
	token2 = random();

	recv_s = sock_reuseaddr();
	if (bind(recv_s, (struct sockaddr *)&lo_dst, sizeof(lo_dst)) < 0)
		die("bind(): %s\n", strerror(errno));

	send_s = sock_reuseaddr();
	if (connect(send_s, (struct sockaddr *)&lo_dst, sizeof(lo_dst)) < 0)
		die("connect(): %s\n", strerror(errno));

	send_token(send_s, token1);
	send_token(send_s, token2);

	/* cppcheck-suppress nullPointer */
	rc = recv(recv_s, NULL, 0, MSG_DONTWAIT);
	if (rc < 0)
		die("discarding recv(): %s\n", strerror(errno));
	
	recv_token(recv_s, token2);

	/* cppcheck-suppress nullPointer */
	rc = recv(recv_s, NULL, 0, MSG_DONTWAIT);
	if (rc < 0 && errno != EAGAIN)
		die("redundant discarding recv(): %s\n", strerror(errno));
	if (rc >= 0)
		die("Unexpected receive: rc=%zd\n", rc);
}

int main(int argc, char *argv[])
{
	(void)argc;
	(void)argv;

	test_discard();

	printf("Discarding datagrams with a 0-length recv() seems to work\n");

	exit(0);
}