/*
 * Copyright (c) 2018, Oracle America, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - 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.
 * - Neither the name of "Oracle America, Inc." nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT HOLDER 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/types.h>
#include <sys/socket.h>
#include <sys/time.h>

#include <netdb.h>
#include <netinet/in.h>

#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#include <rpc/rpc.h>

#include "reentrant.h"
#include "rpc_com.h"

extern pthread_mutex_t port_lock;

/*
 * Dynamic port range as defined in RFC 6335 Section 6.
 * This range avoids all IANA-assigned service port
 * numbers.
 */
enum {
	LOWPORT		= 49152,
	ENDPORT		= 65534,
	NPORTS		= ENDPORT - LOWPORT + 1,
};

/*
 * Bind a socket to a dynamically-assigned IP port.
 *
 * @fd is an open but unbound socket.
 *
 * On each call, a port number is chosen at random from
 * within the dynamic/private port range, even if the
 * caller has CAP_NET_ADMIN_BIND.
 *
 * Returns 0 on success, -1 on failure. errno may be
 * set to a non-determinant value.
 *
 * This function is re-entrant.
 */
int __binddynport(int fd)
{
	struct sockaddr_storage ss;
#ifdef INET6
	struct sockaddr_in6 *sin6;
#endif
	struct sockaddr_in *sin;
	static unsigned int seed;
	in_port_t port, *portp;
	struct sockaddr *sap;
	socklen_t salen;
	int i, res;

	if (__rpc_sockisbound(fd))
		return 0;

	res = -1;
	sap = (struct sockaddr *)(void *)&ss;
	salen = sizeof(ss);
	memset(sap, 0, salen);

	mutex_lock(&port_lock);

	if (getsockname(fd, sap, &salen) == -1)
		goto out;

	switch (ss.ss_family) {
	case AF_INET:
		sin = (struct sockaddr_in *)(void *)&ss;
		portp = &sin->sin_port;
		salen = sizeof(struct sockaddr_in);
		break;
#ifdef INET6
	case AF_INET6:
		sin6 = (struct sockaddr_in6 *)(void *)&ss;
		portp = &sin6->sin6_port;
		salen = sizeof(struct sockaddr_in6);
		break;
#endif
	default:
		goto out;
	}

	if (!seed) {
		struct timeval tv;

		gettimeofday(&tv, NULL);
		seed = tv.tv_usec * getpid();
	}
	port = (rand_r(&seed) % NPORTS) + LOWPORT;
	for (i = 0; i < NPORTS; ++i) {
		*portp = htons(port++);
		res = bind(fd, sap, salen);
		if (res >= 0) {
			res = 0;
			break;
		}
		if (errno != EADDRINUSE)
			break;
		if (port > ENDPORT)
			port = LOWPORT;
	}

out:
	mutex_unlock(&port_lock);
	return res;
}