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When changing so that the client passes its stdout and stderr as well as
stdin up to the server, I forgot one essential point - the tmux server
could now be both the producer and consumer. This happens when tmux is
run inside tmux, as well as when piping tmux commands together.

So, using stdio(3) was a bad idea - if sufficient data was written, this
could block in write(2). When that happened and the server was both
producer and consumer, it deadlocks.

Change to use libevent bufferevents for the client stdin, stdout and
stderr instead. This is trivial enough for output but requires a
callback mechanism to trigger when stdin is finished.

This relies on the underlying polling mechanism for libevent to work
with whatever devices to which the user could redirect stdin, stdout or
stderr, hence the change to use poll(2) over kqueue(2) for tmux.

/* $OpenBSD: cmd-save-buffer.c,v 1.8 2010/07/24 20:11:59 nicm Exp $ */

/*
 * Copyright (c) 2009 Tiago Cunha <me@tiagocunha.org>
 *
 * 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 MIND, 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/types.h>
#include <sys/stat.h>

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

#include "tmux.h"

/*
 * Saves a session paste buffer to a file.
 */

int	cmd_save_buffer_exec(struct cmd *, struct cmd_ctx *);

const struct cmd_entry cmd_save_buffer_entry = {
	"save-buffer", "saveb",
	"[-a] " CMD_BUFFER_SESSION_USAGE " path",
	CMD_ARG1, "a",
	cmd_buffer_init,
	cmd_buffer_parse,
	cmd_save_buffer_exec,
	cmd_buffer_free,
	cmd_buffer_print
};

int
cmd_save_buffer_exec(struct cmd *self, struct cmd_ctx *ctx)
{
	struct cmd_buffer_data	*data = self->data;
	struct session		*s;
	struct paste_buffer	*pb;
	mode_t			 mask;
	FILE			*f;

	if ((s = cmd_find_session(ctx, data->target)) == NULL)
		return (-1);

	if (data->buffer == -1) {
		if ((pb = paste_get_top(&s->buffers)) == NULL) {
			ctx->error(ctx, "no buffers");
			return (-1);
		}
	} else {
		if ((pb = paste_get_index(&s->buffers, data->buffer)) == NULL) {
			ctx->error(ctx, "no buffer %d", data->buffer);
			return (-1);
		}
	}

	if (strcmp(data->arg, "-") == 0) {
		if (ctx->cmdclient == NULL) {
			ctx->error(ctx, "%s: can't write to stdout", data->arg);
			return (-1);
		}
		bufferevent_write(
		    ctx->cmdclient->stdout_event, pb->data, pb->size);
	} else {
		mask = umask(S_IRWXG | S_IRWXO);
		if (cmd_check_flag(data->chflags, 'a'))
			f = fopen(data->arg, "ab");
		else
			f = fopen(data->arg, "wb");
		umask(mask);
		if (f == NULL) {
			ctx->error(ctx, "%s: %s", data->arg, strerror(errno));
			return (-1);
		}
		if (fwrite(pb->data, 1, pb->size, f) != pb->size) {
			ctx->error(ctx, "%s: fwrite error", data->arg);
			fclose(f);
			return (-1);
		}
		fclose(f);
	}

	return (0);
}