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sync with kristaps up to Sun Feb 17 2019

339cf5998c0c022623cd68de50722b6c14543952 Push "error trail" further into code.

baf58ce5fe1bc6ce431b3b0ac8264b83ae8c7d02 Document all arguments.  Add
  common -av usage.  Remove bits about not supporting anything but
  files/dirs.

821a811a8c80e52fb56b241fc65a16cae1b4fb2c Disambiguate as prodded by deraadt@

6c4475b8f226e9031ec0ec1b3f14f7d347132c87 Add -h to usage string

4d344ae6156873b44c95de0c1ed629e637c2d7ab Clarify error message
  language, use service name instead of port, specify that the socket is
  SOCK_STREAM.  From deraadt@.  Tweaked for lowercase messages.

f3ec049e76257fc96bcdc872f1d3b967b98f3eb6 In consideration to benno@'s
  comments, let the mktemp functions propogate an errno handled by the
  caller.  Also keep the original line lengths.  While in mktemp.c, make
  some defines into an enum.

e116c2bd00e634b56e4276120135915ceaa31cf2 Put the FSM of the sender
  into its own function.  Put dry_run ack and end of phase ack into the
  send buffer too, further reducing the possibility of deadlock.

c7745aa4c7394ca89d841f8ee76782256d694340 Make the sender write loop be
  fully non-blocking.  This frees us of deadlocking the protocol because
  the sender will always be able to pull down data.

93c7b4843e80aeac2ec6ae6ffc395df4deaf4a31 Remove "yoda" notation to be
  more in tune with OpenBSD.  Most found by deraadt@.

/*	$Id: server.c,v 1.6 2019/02/18 21:34:54 benno Exp $ */
/*
 * Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include <sys/stat.h>

#include <assert.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

static int
fcntl_nonblock(struct sess *sess, int fd)
{
	int	 fl;

	if ((fl = fcntl(fd, F_GETFL, 0)) == -1)
		ERR(sess, "fcntl: F_GETFL");
	else if (fcntl(fd, F_SETFL, fl|O_NONBLOCK) == -1)
		ERR(sess, "fcntl: F_SETFL");
	else
		return 1;

	return 0;
}

/*
 * The server (remote) side of the system.
 * This parses the arguments given it by the remote shell then moves
 * into receiver or sender mode depending upon those arguments.
 *
 * Pledges: unveil rpath, cpath, wpath, stdio, fattr.
 *
 * Pledges (dry-run): -cpath, -wpath, -fattr.
 * Pledges (!preserve_times): -fattr.
 */
int
rsync_server(const struct opts *opts, size_t argc, char *argv[])
{
	struct sess	 sess;
	int		 fdin = STDIN_FILENO,
			 fdout = STDOUT_FILENO, c = 0;

	memset(&sess, 0, sizeof(struct sess));
	sess.opts = opts;

	/* Begin by making descriptors non-blocking. */

	if (!fcntl_nonblock(&sess, fdin) ||
	     !fcntl_nonblock(&sess, fdout)) {
		ERRX1(&sess, "fcntl_nonblock");
		goto out;
	}

	/* Standard rsync preamble, server side. */

	sess.lver = RSYNC_PROTOCOL;
	sess.seed = arc4random();

	if (!io_read_int(&sess, fdin, &sess.rver)) {
		ERRX1(&sess, "io_read_int");
		goto out;
	} else if (!io_write_int(&sess, fdout, sess.lver)) {
		ERRX1(&sess, "io_write_int");
		goto out;
	} else if (!io_write_int(&sess, fdout, sess.seed)) {
		ERRX1(&sess, "io_write_int");
		goto out;
	}

	sess.mplex_writes = 1;

	if (sess.rver < sess.lver) {
		ERRX(&sess, "remote protocol is older "
			"than our own (%" PRId32 " < %" PRId32 "): "
			"this is not supported",
			sess.rver, sess.lver);
		goto out;
	}

	LOG2(&sess, "server detected client version %" PRId32
		", server version %" PRId32 ", seed %" PRId32,
		sess.rver, sess.lver, sess.seed);

	if (sess.opts->sender) {
		LOG2(&sess, "server starting sender");

		/*
		 * At this time, I always get a period as the first
		 * argument of the command line.
		 * Let's make it a requirement until I figure out when
		 * that differs.
		 * rsync [flags] "." <source> <...>
		 */

		if (strcmp(argv[0], ".")) {
			ERRX(&sess, "first argument must "
				"be a standalone period");
			goto out;
		}
		argv++;
		argc--;
		if (argc == 0) {
			ERRX(&sess, "must have arguments");
			goto out;
		}

		if (!rsync_sender(&sess, fdin, fdout, argc, argv)) {
			ERRX1(&sess, "rsync_sender");
			goto out;
		}
	} else {
		LOG2(&sess, "server starting receiver");

		/*
		 * I don't understand why this calling convention
		 * exists, but we must adhere to it.
		 * rsync [flags] "." <destination>
		 */

		if (argc != 2) {
			ERRX(&sess, "server receiver mode "
				"requires two argument");
			goto out;
		} else if (strcmp(argv[0], ".")) {
			ERRX(&sess, "first argument must "
				"be a standalone period");
			goto out;
		}

		if (!rsync_receiver(&sess, fdin, fdout, argv[1])) {
			ERRX1(&sess, "rsync_receiver");
			goto out;
		}
	}

#if 0
	/* Probably the EOF. */
	if (io_read_check(&sess, fdin))
		WARNX(&sess, "data remains in read pipe");
#endif

	c = 1;
out:
	return c;
}