/*	$OpenBSD: smtp.c,v 1.60 2009/08/06 16:46:57 gilles Exp $	*/

/*
 * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
 * Copyright (c) 2008 Pierre-Yves Ritschard <pyr@openbsd.org>
 * Copyright (c) 2009 Jacek Masiulaniec <jacekm@dobremiasto.net>
 *
 * 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/types.h>
#include <sys/queue.h>
#include <sys/tree.h>
#include <sys/param.h>
#include <sys/socket.h>

#include <ctype.h>
#include <event.h>
#include <netdb.h>
#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include "smtpd.h"

__dead void	smtp_shutdown(void);
void		smtp_sig_handler(int, short, void *);
void		smtp_dispatch_parent(int, short, void *);
void		smtp_dispatch_mfa(int, short, void *);
void		smtp_dispatch_lka(int, short, void *);
void		smtp_dispatch_queue(int, short, void *);
void		smtp_dispatch_control(int, short, void *);
void		smtp_dispatch_runner(int, short, void *);
void		smtp_setup_events(struct smtpd *);
void		smtp_disable_events(struct smtpd *);
void		smtp_pause(struct smtpd *);
void		smtp_resume(struct smtpd *);
void		smtp_accept(int, short, void *);
void		session_auth_pickup(struct session *, char *, size_t);
struct session *session_lookup(struct smtpd *, u_int64_t);

void
smtp_sig_handler(int sig, short event, void *p)
{
	switch (sig) {
	case SIGINT:
	case SIGTERM:
		smtp_shutdown();
		break;
	default:
		fatalx("smtp_sig_handler: unexpected signal");
	}
}

void
smtp_dispatch_parent(int sig, short event, void *p)
{
	struct smtpd		*env = p;
	struct imsgev		*iev;
	struct imsgbuf		*ibuf;
	struct imsg		 imsg;
	ssize_t			 n;

	iev = env->sc_ievs[PROC_PARENT];
	ibuf = &iev->ibuf;


	if (event & EV_READ) {
		if ((n = imsg_read(ibuf)) == -1)
			fatal("imsg_read_error");
		if (n == 0) {
			/* this pipe is dead, so remove the event handler */
			event_del(&iev->ev);
			event_loopexit(NULL);
			return;
		}
	}

	if (event & EV_WRITE) {
		if (msgbuf_write(&ibuf->w) == -1)
			fatal("msgbuf_write");
	}

	for (;;) {
		if ((n = imsg_get(ibuf, &imsg)) == -1)
			fatalx("smtp_dispatch_parent: imsg_get error");
		if (n == 0)
			break;

		switch (imsg.hdr.type) {
		case IMSG_CONF_RELOAD: {
			struct session *s;

			/* reloading may invalidate various pointers our
			 * sessions rely upon, we better tell clients we
			 * want them to retry.
			 */
			SPLAY_FOREACH(s, sessiontree, &env->sc_sessions) {
				s->s_l = NULL;
				s->s_msg.status |= S_MESSAGE_TEMPFAILURE;
			}
			if (env->sc_listeners)
				smtp_disable_events(env);
			imsg_compose_event(iev, IMSG_PARENT_SEND_CONFIG, 0, 0, -1,
			    NULL, 0);
			break;
		}
		case IMSG_CONF_START:
			if (env->sc_flags & SMTPD_CONFIGURING)
				break;
			env->sc_flags |= SMTPD_CONFIGURING;

			if ((env->sc_listeners = calloc(1, sizeof(*env->sc_listeners))) == NULL)
				fatal("smtp_dispatch_parent: calloc");
			if ((env->sc_ssl = calloc(1, sizeof(*env->sc_ssl))) == NULL)
				fatal("smtp_dispatch_parent: calloc");
			TAILQ_INIT(env->sc_listeners);
			break;
		case IMSG_CONF_SSL: {
			struct ssl	*s;
			struct ssl	*x_ssl;

			if (!(env->sc_flags & SMTPD_CONFIGURING))
				break;

			if ((s = calloc(1, sizeof(*s))) == NULL)
				fatal(NULL);
			x_ssl = imsg.data;
			(void)strlcpy(s->ssl_name, x_ssl->ssl_name,
			    sizeof(s->ssl_name));
			s->ssl_cert_len = x_ssl->ssl_cert_len;
			if ((s->ssl_cert =
			    strdup((char *)imsg.data + sizeof(*s))) == NULL)
				fatal(NULL);
			s->ssl_key_len = x_ssl->ssl_key_len;
			if ((s->ssl_key = strdup((char *)imsg.data +
			    (sizeof(*s) + s->ssl_cert_len))) == NULL)
				fatal(NULL);

			SPLAY_INSERT(ssltree, env->sc_ssl, s);
			break;
		}
		case IMSG_CONF_LISTENER: {
			struct listener	*l;
			struct ssl	 key;

			if (!(env->sc_flags & SMTPD_CONFIGURING))
				break;

			if ((l = calloc(1, sizeof(*l))) == NULL)
				fatal(NULL);
			memcpy(l, imsg.data, sizeof(*l));

			if ((l->fd = imsg.fd) == -1)
				fatal("cannot get fd");

			(void)strlcpy(key.ssl_name, l->ssl_cert_name,
			    sizeof(key.ssl_name));

			if (l->flags & F_SSL)
				if ((l->ssl = SPLAY_FIND(ssltree,
				    env->sc_ssl, &key)) == NULL)
					fatal("parent and smtp desynchronized");

			TAILQ_INSERT_TAIL(env->sc_listeners, l, entry);
			break;
		}
		case IMSG_CONF_END:
			if (!(env->sc_flags & SMTPD_CONFIGURING))
				break;
			smtp_setup_events(env);
			env->sc_flags &= ~SMTPD_CONFIGURING;
			break;
		case IMSG_PARENT_AUTHENTICATE: {
			struct auth	*reply = imsg.data;
			struct session	*s;

			log_debug("smtp_dispatch_parent: got auth reply");

			IMSG_SIZE_CHECK(reply);

			if ((s = session_lookup(env, reply->id)) == NULL)
				break;

			if (reply->success) {
				s->s_flags |= F_AUTHENTICATED;
				s->s_msg.flags |= F_MESSAGE_AUTHENTICATED;
			} else {
				s->s_flags &= ~F_AUTHENTICATED;
				s->s_msg.flags &= ~F_MESSAGE_AUTHENTICATED;
			}

			session_pickup(s, NULL);
			break;
		}
		default:
			log_warnx("smtp_dispatch_parent: got imsg %d",
			    imsg.hdr.type);
			fatalx("smtp_dispatch_parent: unexpected imsg");
		}
		imsg_free(&imsg);
	}
	imsg_event_add(iev);
}

void
smtp_dispatch_mfa(int sig, short event, void *p)
{
	struct smtpd		*env = p;
	struct imsgev		*iev;
	struct imsgbuf		*ibuf;
	struct imsg		 imsg;
	ssize_t			 n;

	iev = env->sc_ievs[PROC_MFA];
	ibuf = &iev->ibuf;

	if (event & EV_READ) {
		if ((n = imsg_read(ibuf)) == -1)
			fatal("imsg_read_error");
		if (n == 0) {
			/* this pipe is dead, so remove the event handler */
			event_del(&iev->ev);
			event_loopexit(NULL);
			return;
		}
	}

	if (event & EV_WRITE) {
		if (msgbuf_write(&ibuf->w) == -1)
			fatal("msgbuf_write");
	}

	for (;;) {
		if ((n = imsg_get(ibuf, &imsg)) == -1)
			fatalx("smtp_dispatch_mfa: imsg_get error");
		if (n == 0)
			break;

		switch (imsg.hdr.type) {
		case IMSG_MFA_MAIL:
		case IMSG_MFA_RCPT: {
			struct submit_status	*ss = imsg.data;
			struct session		*s;

			log_debug("smtp_dispatch_mfa: mfa handled return path");

			IMSG_SIZE_CHECK(ss);

			if ((s = session_lookup(env, ss->id)) == NULL)
				break;

			session_pickup(s, ss);
			break;
		}
		default:
			log_warnx("smtp_dispatch_mfa: got imsg %d",
			    imsg.hdr.type);
			fatalx("smtp_dispatch_mfa: unexpected imsg");
		}
		imsg_free(&imsg);
	}
	imsg_event_add(iev);
}

void
smtp_dispatch_lka(int sig, short event, void *p)
{
	struct smtpd		*env = p;
	struct imsgev		*iev;
	struct imsgbuf		*ibuf;
	struct imsg		 imsg;
	ssize_t			 n;

	iev = env->sc_ievs[PROC_LKA];
	ibuf = &iev->ibuf;

	if (event & EV_READ) {
		if ((n = imsg_read(ibuf)) == -1)
			fatal("imsg_read_error");
		if (n == 0) {
			/* this pipe is dead, so remove the event handler */
			event_del(&iev->ev);
			event_loopexit(NULL);
			return;
		}
	}

	if (event & EV_WRITE) {
		if (msgbuf_write(&ibuf->w) == -1)
			fatal("msgbuf_write");
	}

	for (;;) {
		if ((n = imsg_get(ibuf, &imsg)) == -1)
			fatalx("smtp_dispatch_lka: imsg_get error");
		if (n == 0)
			break;

		switch (imsg.hdr.type) {
		case IMSG_DNS_PTR: {
			struct dns		*reply = imsg.data;
			struct session		*s;
			struct session		 key;

			IMSG_SIZE_CHECK(reply);

			key.s_id = reply->id;

			s = SPLAY_FIND(sessiontree, &env->sc_sessions, &key);
			if (s == NULL)
				fatal("smtp_dispatch_lka: session is gone");

			strlcpy(s->s_hostname,
			    reply->error ? "<unknown>" : reply->host,
			    sizeof(s->s_hostname));

			strlcpy(s->s_msg.session_hostname, s->s_hostname,
			    sizeof(s->s_msg.session_hostname));

			session_init(s->s_l, s);

			break;
		}
		default:
			log_warnx("smtp_dispatch_lka: got imsg %d",
			    imsg.hdr.type);
			fatalx("smtp_dispatch_lka: unexpected imsg");
		}
		imsg_free(&imsg);
	}
	imsg_event_add(iev);
}

void
smtp_dispatch_queue(int sig, short event, void *p)
{
	struct smtpd		*env = p;
	struct imsgev		*iev;
	struct imsgbuf		*ibuf;
	struct imsg		 imsg;
	ssize_t			 n;

	iev = env->sc_ievs[PROC_QUEUE];
	ibuf = &iev->ibuf;

	if (event & EV_READ) {
		if ((n = imsg_read(ibuf)) == -1)
			fatal("imsg_read_error");
		if (n == 0) {
			/* this pipe is dead, so remove the event handler */
			event_del(&iev->ev);
			event_loopexit(NULL);
			return;
		}
	}

	if (event & EV_WRITE) {
		if (msgbuf_write(&ibuf->w) == -1)
			fatal("msgbuf_write");
	}

	for (;;) {
		if ((n = imsg_get(ibuf, &imsg)) == -1)
			fatalx("smtp_dispatch_queue: imsg_get error");
		if (n == 0)
			break;

		switch (imsg.hdr.type) {
		case IMSG_QUEUE_CREATE_MESSAGE: {
			struct submit_status	*ss = imsg.data;
			struct session		*s;

			log_debug("smtp_dispatch_queue: queue handled message creation");

			IMSG_SIZE_CHECK(ss);

			if ((s = session_lookup(env, ss->id)) == NULL)
				break;

			(void)strlcpy(s->s_msg.message_id, ss->u.msgid,
			    sizeof(s->s_msg.message_id));
			session_pickup(s, ss);
			break;
		}
		case IMSG_QUEUE_MESSAGE_FILE: {
			struct submit_status	*ss = imsg.data;
			struct session		*s;
			int			 fd;

			log_debug("smtp_dispatch_queue: queue handled message creation");

			IMSG_SIZE_CHECK(ss);

			fd = imsg.fd;

			if ((s = session_lookup(env, ss->id)) == NULL) {
				close(fd);
				break;
			}

			if ((s->datafp = fdopen(fd, "w")) == NULL) {
				/* queue may have experienced tempfail. */
				if (ss->code != 421)
					fatal("smtp_dispatch_queue: fdopen");
				close(fd);
			}

			session_pickup(s, ss);
			break;
		}
		case IMSG_QUEUE_TEMPFAIL: {
			struct submit_status	*ss = imsg.data;
			struct session		*s;
			struct session		 key;

			log_debug("smtp_dispatch_queue: tempfail in queue");

			IMSG_SIZE_CHECK(ss);

			key.s_id = ss->id;
			s = SPLAY_FIND(sessiontree, &env->sc_sessions, &key);
			if (s == NULL)
				fatalx("smtp_dispatch_queue: session is gone");

			if (s->s_flags & F_WRITEONLY) {
				/*
				 * Session is write-only, can't destroy it.
				 */
				s->s_msg.status |= S_MESSAGE_TEMPFAILURE;
			} else
				fatalx("smtp_dispatch_queue: corrupt session");
			break;
		}

		case IMSG_QUEUE_COMMIT_ENVELOPES:
		case IMSG_QUEUE_COMMIT_MESSAGE: {
			struct submit_status	*ss = imsg.data;
			struct session		*s;

			log_debug("smtp_dispatch_queue: queue acknowledged message submission");

			IMSG_SIZE_CHECK(ss);

			if ((s = session_lookup(env, ss->id)) == NULL)
				break;

			session_pickup(s, ss);
			break;
		}
		default:
			log_warnx("smtp_dispatch_queue: got imsg %d",
			    imsg.hdr.type);
			fatalx("smtp_dispatch_queue: unexpected imsg");
		}
		imsg_free(&imsg);
	}
	imsg_event_add(iev);
}

void
smtp_dispatch_control(int sig, short event, void *p)
{
	struct smtpd		*env = p;
	struct imsgev		*iev;
	struct imsgbuf		*ibuf;
	struct imsg		 imsg;
	ssize_t			 n;

	iev = env->sc_ievs[PROC_CONTROL];
	ibuf = &iev->ibuf;

	if (event & EV_READ) {
		if ((n = imsg_read(ibuf)) == -1)
			fatal("imsg_read_error");
		if (n == 0) {
			/* this pipe is dead, so remove the event handler */
			event_del(&iev->ev);
			event_loopexit(NULL);
			return;
		}
	}

	if (event & EV_WRITE) {
		if (msgbuf_write(&ibuf->w) == -1)
			fatal("msgbuf_write");
	}

	for (;;) {
		if ((n = imsg_get(ibuf, &imsg)) == -1)
			fatalx("smtp_dispatch_control: imsg_get error");
		if (n == 0)
			break;

		switch (imsg.hdr.type) {
		case IMSG_SMTP_ENQUEUE: {
			static struct listener	 l;
			struct addrinfo		 hints, *res;
			struct session		*s;
			int			 fd[2];

			bzero(&l, sizeof(l));
			l.env = env;

			if (env->stats->smtp.sessions_active >=
			    env->sc_maxconn) {
				log_warnx("denying local connection, too many"
				    " sessions active");
				imsg_compose_event(iev, IMSG_SMTP_ENQUEUE, 0, 0, -1,
				    imsg.data, sizeof(int));
				break;
			}

			if (socketpair(
			    AF_UNIX, SOCK_STREAM, PF_UNSPEC, fd) == -1)
				fatal("socketpair");

			if ((s = calloc(1, sizeof(*s))) == NULL)
				fatal(NULL);

			s->s_id = queue_generate_id();
			s->s_fd = fd[0];
			s->s_env = env;
			s->s_l = &l;
			s->s_msg.flags |= F_MESSAGE_ENQUEUED;

			bzero(&hints, sizeof(hints));
			hints.ai_family = PF_UNSPEC;
			hints.ai_flags = AI_NUMERICHOST;

			if (getaddrinfo("::1", NULL, &hints, &res) != 0)
				fatal("getaddrinfo");

			memcpy(&s->s_ss, res->ai_addr, res->ai_addrlen);

			env->stats->smtp.sessions++;
			env->stats->smtp.sessions_active++;

			strlcpy(s->s_hostname, "localhost",
			    sizeof(s->s_hostname));
			strlcpy(s->s_msg.session_hostname, s->s_hostname,
			    sizeof(s->s_msg.session_hostname));

			SPLAY_INSERT(sessiontree, &s->s_env->sc_sessions, s);

			session_init(s->s_l, s);

			imsg_compose_event(iev, IMSG_SMTP_ENQUEUE, 0, 0, fd[1],
			    imsg.data, sizeof(int));
			break;
		}
		case IMSG_SMTP_PAUSE:
			smtp_pause(env);
			break;
		case IMSG_SMTP_RESUME:
			smtp_resume(env);
			break;
		default:
			log_warnx("smtp_dispatch_control: got imsg %d",
			    imsg.hdr.type);
			fatalx("smtp_dispatch_control: unexpected imsg");
		}
		imsg_free(&imsg);
	}
	imsg_event_add(iev);
}

void
smtp_dispatch_runner(int sig, short event, void *p)
{
	struct smtpd		*env = p;
	struct imsgev		*iev;
	struct imsgbuf		*ibuf;
	struct imsg		 imsg;
	ssize_t			 n;

	iev = env->sc_ievs[PROC_RUNNER];
	ibuf = &iev->ibuf;

	if (event & EV_READ) {
		if ((n = imsg_read(ibuf)) == -1)
			fatal("imsg_read_error");
		if (n == 0) {
			/* this pipe is dead, so remove the event handler */
			event_del(&iev->ev);
			event_loopexit(NULL);
			return;
		}
	}

	if (event & EV_WRITE) {
		if (msgbuf_write(&ibuf->w) == -1)
			fatal("msgbuf_write");
	}

	for (;;) {
		if ((n = imsg_get(ibuf, &imsg)) == -1)
			fatalx("smtp_dispatch_runner: imsg_get error");
		if (n == 0)
			break;

		switch (imsg.hdr.type) {
		case IMSG_SMTP_ENQUEUE: {
			static struct listener	 l;
			struct addrinfo		 hints, *res;
			struct session		*s;
			int			 fd[2];

			bzero(&l, sizeof(l));
			l.env = env;

			if (env->stats->smtp.sessions_active >=
			    env->sc_maxconn) {
				log_warnx("denying internal connection, too many"
				    " sessions active");
				imsg_compose_event(iev, IMSG_SMTP_ENQUEUE, 0, 0, -1,
				    imsg.data, sizeof(struct message));
				break;
			}

			if (socketpair(
			    AF_UNIX, SOCK_STREAM, PF_UNSPEC, fd) == -1)
				fatal("socketpair");

			if ((s = calloc(1, sizeof(*s))) == NULL)
				fatal(NULL);

			s->s_id = queue_generate_id();
			s->s_fd = fd[0];
			s->s_env = env;
			s->s_l = &l;
			s->s_msg.flags |= F_MESSAGE_ENQUEUED|F_MESSAGE_BOUNCE;

			bzero(&hints, sizeof(hints));
			hints.ai_family = PF_UNSPEC;
			hints.ai_flags = AI_NUMERICHOST;

			if (getaddrinfo("::1", NULL, &hints, &res) != 0)
				fatal("getaddrinfo");

			memcpy(&s->s_ss, res->ai_addr, res->ai_addrlen);

			env->stats->smtp.sessions++;
			env->stats->smtp.sessions_active++;

			strlcpy(s->s_hostname, "localhost",
			    sizeof(s->s_hostname));
			strlcpy(s->s_msg.session_hostname, s->s_hostname,
			    sizeof(s->s_msg.session_hostname));

			SPLAY_INSERT(sessiontree, &s->s_env->sc_sessions, s);

			session_init(s->s_l, s);

			imsg_compose_event(iev, IMSG_SMTP_ENQUEUE, 0, 0, fd[1],
			    imsg.data, sizeof(struct message));
			break;
		}
		default:
			log_warnx("smtp_dispatch_runner: got imsg %d",
			    imsg.hdr.type);
			fatalx("smtp_dispatch_runner: unexpected imsg");
		}
		imsg_free(&imsg);
	}
	imsg_event_add(iev);
}

void
smtp_shutdown(void)
{
	log_info("smtp server exiting");
	_exit(0);
}

pid_t
smtp(struct smtpd *env)
{
	pid_t		 pid;
	struct passwd	*pw;

	struct event	 ev_sigint;
	struct event	 ev_sigterm;

	struct peer peers[] = {
		{ PROC_PARENT,	smtp_dispatch_parent },
		{ PROC_MFA,	smtp_dispatch_mfa },
		{ PROC_QUEUE,	smtp_dispatch_queue },
		{ PROC_LKA,	smtp_dispatch_lka },
		{ PROC_CONTROL,	smtp_dispatch_control },
		{ PROC_RUNNER,	smtp_dispatch_runner }
	};

	switch (pid = fork()) {
	case -1:
		fatal("smtp: cannot fork");
	case 0:
		break;
	default:
		return (pid);
	}

	ssl_init();
	purge_config(env, PURGE_EVERYTHING);

	pw = env->sc_pw;

#ifndef DEBUG
	if (chroot(pw->pw_dir) == -1)
		fatal("smtp: chroot");
	if (chdir("/") == -1)
		fatal("smtp: chdir(\"/\")");
#else
#warning disabling privilege revocation and chroot in DEBUG MODE
#endif

	smtpd_process = PROC_SMTP;
	setproctitle("%s", env->sc_title[smtpd_process]);

#ifndef DEBUG
	if (setgroups(1, &pw->pw_gid) ||
	    setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) ||
	    setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid))
		fatal("smtp: cannot drop privileges");
#endif

	event_init();

	signal_set(&ev_sigint, SIGINT, smtp_sig_handler, env);
	signal_set(&ev_sigterm, SIGTERM, smtp_sig_handler, env);
	signal_add(&ev_sigint, NULL);
	signal_add(&ev_sigterm, NULL);
	signal(SIGPIPE, SIG_IGN);
	signal(SIGHUP, SIG_IGN);

	config_pipes(env, peers, nitems(peers));
	config_peers(env, peers, nitems(peers));

	event_dispatch();
	smtp_shutdown();

	return (0);
}

void
smtp_setup_events(struct smtpd *env)
{
	struct listener *l;

	TAILQ_FOREACH(l, env->sc_listeners, entry) {
		log_debug("smtp_setup_events: listen on %s port %d flags 0x%01x"
		    " cert \"%s\"", ss_to_text(&l->ss), ntohs(l->port),
		    l->flags, l->ssl_cert_name);

		session_socket_blockmode(l->fd, BM_NONBLOCK);
		if (listen(l->fd, SMTPD_BACKLOG) == -1)
			fatal("listen");
		l->env = env;
		event_set(&l->ev, l->fd, EV_READ, smtp_accept, l);
		event_add(&l->ev, NULL);
		ssl_setup(env, l);
	}
}

void
smtp_disable_events(struct smtpd *env)
{
	struct listener	*l;

	log_debug("smtp_disable_events: closing listening sockets");
	while ((l = TAILQ_FIRST(env->sc_listeners)) != NULL) {
		TAILQ_REMOVE(env->sc_listeners, l, entry);
		event_del(&l->ev);
		close(l->fd);
		free(l);
	}
	free(env->sc_listeners);
	env->sc_listeners = NULL;
}

void
smtp_pause(struct smtpd *env)
{
	struct listener *l;

	log_debug("smtp_pause: pausing listening sockets");
	env->sc_opts |= SMTPD_SMTP_PAUSED;

	TAILQ_FOREACH(l, env->sc_listeners, entry)
		event_del(&l->ev);
}

void
smtp_resume(struct smtpd *env)
{
	struct listener *l;

	log_debug("smtp_resume: resuming listening sockets");
	env->sc_opts &= ~SMTPD_SMTP_PAUSED;

	TAILQ_FOREACH(l, env->sc_listeners, entry)
		event_add(&l->ev, NULL);
}

void
smtp_accept(int fd, short event, void *p)
{
	int			 s_fd;
	struct sockaddr_storage	 ss;
	struct listener		*l = p;
	struct session		*s;
	socklen_t		 len;

	log_debug("smtp_accept: incoming client on listener: %p", l);
	len = sizeof(struct sockaddr_storage);
	if ((s_fd = accept(l->fd, (struct sockaddr *)&ss, &len)) == -1) {
		event_del(&l->ev);
		return;
	}

	log_debug("smtp_accept: accepted client on listener: %p", l);
	if ((s = calloc(1, sizeof(*s))) == NULL)
		fatal(NULL);
	len = sizeof(s->s_ss);

	s->s_id = queue_generate_id();
	s->s_fd = s_fd;
	s->s_env = l->env;
	s->s_l = l;

	(void)memcpy(&s->s_ss, &ss, sizeof(s->s_ss));

	event_add(&l->ev, NULL);

	s->s_env->stats->smtp.sessions++;
	s->s_env->stats->smtp.sessions_active++;

	if (s->s_env->stats->smtp.sessions_active == s->s_env->sc_maxconn)
		event_del(&l->ev);

	dns_query_ptr(l->env, &s->s_ss, s->s_id);

	SPLAY_INSERT(sessiontree, &s->s_env->sc_sessions, s);
}

/*
 * Helper function for handling IMSG replies.
 */
struct session *
session_lookup(struct smtpd *env, u_int64_t id)
{
	struct session	 key;
	struct session	*s;

	key.s_id = id;
	s = SPLAY_FIND(sessiontree, &env->sc_sessions, &key);
	if (s == NULL)
		fatalx("session_lookup: session is gone");

	if (!(s->s_flags & F_WRITEONLY))
		fatalx("session_lookup: corrupt session");
	s->s_flags &= ~F_WRITEONLY;

	if (s->s_flags & F_QUIT) {
		session_destroy(s);
		s = NULL;
	}

	return (s);
}