pop3-client.c

/* Copyright (c) 2002-2017 Dovecot authors, see the included COPYING file */

#include "pop3-common.h"
#include "array.h"
#include "ioloop.h"
#include "net.h"
#include "iostream.h"
#include "istream.h"
#include "ostream.h"
#include "iostream-rawlog.h"
#include "crc32.h"
#include "str.h"
#include "llist.h"
#include "hostpid.h"
#include "file-dotlock.h"
#include "var-expand.h"
#include "master-service.h"
#include "mail-storage.h"
#include "mail-storage-service.h"
#include "pop3-commands.h"
#include "mail-search-build.h"
#include "mail-namespace.h"

#include <unistd.h>

/* max. length of input command line (spec says 512) */
#define MAX_INBUF_SIZE 2048

/* Disconnect client when it sends too many bad commands in a row */
#define CLIENT_MAX_BAD_COMMANDS 20

/* Disconnect client after idling this many milliseconds */
#define CLIENT_IDLE_TIMEOUT_MSECS (10*60*1000)
/* If client starts idling for this many milliseconds, commit the current
   transaction. This allows the mailbox to become unlocked. */
#define CLIENT_COMMIT_TIMEOUT_MSECS (10*1000)

#define POP3_LOCK_FNAME "dovecot-pop3-session.lock"
#define POP3_SESSION_DOTLOCK_STALE_TIMEOUT_SECS (60*5)

extern struct pop3_client_vfuncs pop3_client_vfuncs;

struct pop3_module_register pop3_module_register = { 0 };

struct client *pop3_clients;
unsigned int pop3_client_count;

static enum mail_sort_type pop3_sort_program[] = {
	MAIL_SORT_POP3_ORDER,
	MAIL_SORT_END
};

static const struct dotlock_settings session_dotlock_set = {
	.timeout = 10,
	.stale_timeout = POP3_SESSION_DOTLOCK_STALE_TIMEOUT_SECS,
	.lock_suffix = "",
	.use_io_notify = TRUE
};

static void client_input(struct client *client);
static int client_output(struct client *client);

static void client_commit_timeout(struct client *client)
{
	if (client->cmd != NULL) {
		/* Can't commit while commands are running */
		return;
	}

	(void)mailbox_transaction_commit(&client->trans);
	client->trans = mailbox_transaction_begin(client->mailbox, 0);
}

static void client_idle_timeout(struct client *client)
{
	if (client->cmd != NULL) {
		client_destroy(client,
			"Disconnected for inactivity in reading our output");
	} else {
		client_send_line(client, "-ERR Disconnected for inactivity.");
		client_destroy(client, "Disconnected for inactivity");
	}
}

static int
pop3_mail_get_size(struct client *client, struct mail *mail, uoff_t *size_r)
{
	int ret;

	if (!client->set->pop3_fast_size_lookups)
		return mail_get_virtual_size(mail, size_r);

	/* first try to get the virtual size */
	mail->lookup_abort = MAIL_LOOKUP_ABORT_READ_MAIL;
	ret = mail_get_virtual_size(mail, size_r);
	mail->lookup_abort = MAIL_LOOKUP_ABORT_NEVER;
	if (ret == 0)
		return 0;

	if (mailbox_get_last_mail_error(mail->box) != MAIL_ERROR_LOOKUP_ABORTED)
		return -1;

	/* virtual size not available with a fast lookup.
	   fallback to trying the physical size */
	mail->lookup_abort = MAIL_LOOKUP_ABORT_READ_MAIL;
	ret = mail_get_physical_size(mail, size_r);
	mail->lookup_abort = MAIL_LOOKUP_ABORT_NEVER;
	if (ret == 0)
		return 0;

	if (mailbox_get_last_mail_error(mail->box) != MAIL_ERROR_LOOKUP_ABORTED)
		return -1;

	/* no way to quickly get the size. fallback to doing a slow virtual
	   size lookup */
	return mail_get_virtual_size(mail, size_r);
}

static void
msgnum_to_seq_map_add(ARRAY_TYPE(uint32_t) *msgnum_to_seq_map,
		      struct client *client, struct mail *mail,
		      unsigned int msgnum)
{
	uint32_t seq;

	if (mail->seq == msgnum+1)
		return;

	if (!array_is_created(msgnum_to_seq_map))
		i_array_init(msgnum_to_seq_map, client->messages_count);

	/* add any messages between this and the previous one that had
	   a POP3 order defined */
	seq = array_count(msgnum_to_seq_map) + 1;
	for (; seq <= msgnum; seq++)
		array_append(msgnum_to_seq_map, &seq, 1);
	array_append(msgnum_to_seq_map, &mail->seq, 1);
}

static int read_mailbox(struct client *client, uint32_t *failed_uid_r)
{
        struct mailbox_status status;
        struct mailbox_transaction_context *t;
	struct mail_search_args *search_args;
	struct mail_search_arg *sarg;
	struct mail_search_context *ctx;
	struct mail *mail;
	uoff_t size;
	ARRAY(uoff_t) message_sizes;
	ARRAY_TYPE(uint32_t) msgnum_to_seq_map = ARRAY_INIT;
	unsigned int msgnum;
	int ret = 1;

	*failed_uid_r = 0;

	mailbox_get_open_status(client->mailbox, STATUS_UIDVALIDITY, &status);
	client->uid_validity = status.uidvalidity;
	client->messages_count = status.messages;

	t = mailbox_transaction_begin(client->mailbox, 0);

	search_args = mail_search_build_init();
	if (client->deleted_kw != NULL) {
		sarg = mail_search_build_add(search_args, SEARCH_KEYWORDS);
		sarg->match_not = TRUE;
		sarg->value.str = p_strdup(search_args->pool,
					   client->set->pop3_deleted_flag);
		i_array_init(&client->all_seqs, 32);
	} else {
		mail_search_build_add_all(search_args);
	}
	mail_search_args_init(search_args, client->mailbox, TRUE, NULL);

	ctx = mailbox_search_init(t, search_args, pop3_sort_program,
				  client->set->pop3_fast_size_lookups ? 0 :
				  MAIL_FETCH_VIRTUAL_SIZE, NULL);
	mail_search_args_unref(&search_args);

	client->last_seen_pop3_msn = 0;
	client->total_size = 0;
	i_array_init(&message_sizes, client->messages_count);

	msgnum = 0;
	while (mailbox_search_next(ctx, &mail)) {
		if (pop3_mail_get_size(client, mail, &size) < 0) {
			ret = mail->expunged ? 0 : -1;
			*failed_uid_r = mail->uid;
			break;
		}
		if (array_is_created(&client->all_seqs))
			seq_range_array_add(&client->all_seqs, mail->seq);
		msgnum_to_seq_map_add(&msgnum_to_seq_map, client, mail, msgnum);

		if ((mail_get_flags(mail) & MAIL_SEEN) != 0)
			client->last_seen_pop3_msn = msgnum + 1;
		client->total_size += size;
		if (client->highest_seq < mail->seq)
			client->highest_seq = mail->seq;

		array_append(&message_sizes, &size, 1);
		msgnum++;
	}

	if (mailbox_search_deinit(&ctx) < 0)
		ret = -1;

	if (ret <= 0) {
		/* commit the transaction instead of rollbacking to make sure
		   we don't lose data (virtual sizes) added to cache file */
		(void)mailbox_transaction_commit(&t);
		array_free(&message_sizes);
		if (array_is_created(&msgnum_to_seq_map))
			array_free(&msgnum_to_seq_map);
		return ret;
	}
	i_assert(msgnum <= client->messages_count);
	client->messages_count = msgnum;

	if (!array_is_created(&client->all_seqs)) {
		i_array_init(&client->all_seqs, 1);
		seq_range_array_add_range(&client->all_seqs, 1, msgnum);
	}

	client->trans = t;
	client->message_sizes =
		buffer_free_without_data(&message_sizes.arr.buffer);
	if (array_is_created(&msgnum_to_seq_map)) {
		client->msgnum_to_seq_map_count =
			array_count(&msgnum_to_seq_map);
		client->msgnum_to_seq_map =
			buffer_free_without_data(&msgnum_to_seq_map.arr.buffer);
	}
	return 1;
}

static int init_pop3_deleted_flag(struct client *client, const char **error_r)
{
	const char *deleted_keywords[2];

	if (client->set->pop3_deleted_flag[0] == '\0')
		return 0;

	deleted_keywords[0] = client->set->pop3_deleted_flag;
	deleted_keywords[1] = NULL;
	if (mailbox_keywords_create(client->mailbox, deleted_keywords,
				    &client->deleted_kw) < 0) {
		*error_r = t_strdup_printf(
			"pop3_deleted_flags: Invalid keyword '%s': %s",
			client->set->pop3_deleted_flag,
			mailbox_get_last_error(client->mailbox, NULL));
		return -1;
	}
	return 0;
}

static int init_mailbox(struct client *client, const char **error_r)
{
	uint32_t failed_uid = 0, last_failed_uid = 0;
	int i, ret = -1;

	for (i = 0;; i++) {
		if (mailbox_sync(client->mailbox,
				 MAILBOX_SYNC_FLAG_FULL_READ) < 0) {
			ret = -1;
			break;
		}

		ret = read_mailbox(client, &failed_uid);
		if (ret > 0)
			return 0;
		if (i == 2)
			break;

		/* well, sync and try again. maybe it works the second time. */
		last_failed_uid = failed_uid;
		failed_uid = 0;
	}

	if (ret < 0) {
		*error_r = mailbox_get_last_error(client->mailbox, NULL);
		client_send_storage_error(client);
	} else {
		if (failed_uid == last_failed_uid && failed_uid != 0) {
			/* failed twice in same message */
			*error_r = t_strdup_printf(
				"Getting size of message UID=%u failed",
				failed_uid);
		} else {
			*error_r = "Can't sync mailbox: "
				"Messages keep getting expunged";
		}
		client_send_line(client, "-ERR [SYS/TEMP] Couldn't sync mailbox.");
	}
	return -1;
}

static enum uidl_keys parse_uidl_keymask(const char *format)
{
	enum uidl_keys mask = 0;

	for (; *format != '\0'; format++) {
		if (format[0] == '%' && format[1] != '\0') {
			switch (var_get_key(++format)) {
			case 'v':
				mask |= UIDL_UIDVALIDITY;
				break;
			case 'u':
				mask |= UIDL_UID;
				break;
			case 'm':
				mask |= UIDL_MD5;
				break;
			case 'f':
				mask |= UIDL_FILE_NAME;
				break;
			case 'g':
				mask |= UIDL_GUID;
				break;
			}
		}
	}
	return mask;
}

static void pop3_lock_session_refresh(struct client *client)
{
	if (file_dotlock_touch(client->session_dotlock) < 0) {
		client_send_line(client,
			"-ERR [SYS/TEMP] Couldn't update POP3 session lock.");
		client_destroy(client, "Couldn't lock POP3 session");
	}
}

static int pop3_lock_session(struct client *client)
{
	const struct mail_storage_settings *mail_set =
		mail_storage_service_user_get_mail_set(client->service_user);
	struct dotlock_settings dotlock_set;
	enum mailbox_list_path_type type;
	const char *dir, *path;
	int ret;

	if (mailbox_list_get_root_path(client->inbox_ns->list,
				       MAILBOX_LIST_PATH_TYPE_INDEX, &dir)) {
		type = MAILBOX_LIST_PATH_TYPE_INDEX;
	} else if (mailbox_list_get_root_path(client->inbox_ns->list,
					      MAILBOX_LIST_PATH_TYPE_DIR, &dir)) {
		type = MAILBOX_LIST_PATH_TYPE_DIR;
	} else {
		i_error("pop3_lock_session: Storage has no root/index directory, "
			"can't create a POP3 session lock file");
		return -1;
	}
	if (mailbox_list_mkdir_root(client->inbox_ns->list, dir, type) < 0) {
		i_error("pop3_lock_session: Couldn't create root directory %s: %s",
			dir, mailbox_list_get_last_error(client->inbox_ns->list, NULL));
		return -1;
	}
	path = t_strdup_printf("%s/"POP3_LOCK_FNAME, dir);

	dotlock_set = session_dotlock_set;
	dotlock_set.use_excl_lock = mail_set->dotlock_use_excl;
	dotlock_set.nfs_flush = mail_set->mail_nfs_storage;

	ret = file_dotlock_create(&dotlock_set, path, 0,
				  &client->session_dotlock);
	if (ret < 0)
		i_error("file_dotlock_create(%s) failed: %m", path);
	else if (ret > 0) {
		client->to_session_dotlock_refresh =
			timeout_add(POP3_SESSION_DOTLOCK_STALE_TIMEOUT_SECS*1000,
				    pop3_lock_session_refresh, client);
	}
	return ret;
}

int client_create(int fd_in, int fd_out, const char *session_id,
		  struct mail_user *user,
		  struct mail_storage_service_user *service_user,
		  const struct pop3_settings *set, struct client **client_r)
{
	struct client *client;
	pool_t pool;
	int ret;

	/* always use nonblocking I/O */
	net_set_nonblock(fd_in, TRUE);
	net_set_nonblock(fd_out, TRUE);

	pool = pool_alloconly_create("pop3 client", 256);
	client = p_new(pool, struct client, 1);
	client->pool = pool;
	client->service_user = service_user;
	client->v = pop3_client_vfuncs;
	client->set = set;
	client->session_id = p_strdup(pool, session_id);
	client->fd_in = fd_in;
	client->fd_out = fd_out;
	client->input = i_stream_create_fd(fd_in, MAX_INBUF_SIZE, FALSE);
	client->output = o_stream_create_fd(fd_out, (size_t)-1, FALSE);
	o_stream_set_no_error_handling(client->output, TRUE);
	o_stream_set_flush_callback(client->output, client_output, client);

	if (set->rawlog_dir[0] != '\0') {
		(void)iostream_rawlog_create(set->rawlog_dir, &client->input,
					     &client->output);
	}

	p_array_init(&client->module_contexts, client->pool, 5);
	client->io = io_add_istream(client->input, client_input, client);
        client->last_input = ioloop_time;
	client->to_idle = timeout_add(CLIENT_IDLE_TIMEOUT_MSECS,
				      client_idle_timeout, client);
	client->to_commit = timeout_add(CLIENT_COMMIT_TIMEOUT_MSECS,
					client_commit_timeout, client);

	client->user = user;

	client->mail_set = mail_user_set_get_storage_set(user);
	client->uidl_keymask =
		parse_uidl_keymask(client->mail_set->pop3_uidl_format);
	if (client->uidl_keymask == 0)
		i_fatal("Invalid pop3_uidl_format");

	if (var_has_key(set->pop3_logout_format, 'u', "uidl_change")) {
		/* logging uidl_change. we need hashes of the UIDLs */
		client->message_uidls_save = TRUE;
	} else if (strcmp(set->pop3_uidl_duplicates, "allow") != 0) {
		/* UIDL duplicates aren't allowed, so we'll need to
		   keep track of them */
		client->message_uidls_save = TRUE;
	}

	pop3_client_count++;
	DLLIST_PREPEND(&pop3_clients, client);

	client->inbox_ns = mail_namespace_find_inbox(user->namespaces);
	i_assert(client->inbox_ns != NULL);

	if (hook_client_created != NULL)
		hook_client_created(&client);

	if (set->pop3_lock_session && (ret = pop3_lock_session(client)) <= 0) {
		client_send_line(client, ret < 0 ?
			"-ERR [SYS/TEMP] Failed to create POP3 session lock." :
			"-ERR [IN-USE] Mailbox is locked by another POP3 session.");
		client_destroy(client, "Couldn't lock POP3 session");
		return -1;
	}

	*client_r = client;
	return 0;

}

int client_init_mailbox(struct client *client, const char **error_r)
{
        enum mailbox_flags flags;
	const char *ident, *errmsg;

	flags = MAILBOX_FLAG_POP3_SESSION;
	if (!client->set->pop3_no_flag_updates)
		flags |= MAILBOX_FLAG_DROP_RECENT;
	client->mailbox = mailbox_alloc(client->inbox_ns->list, "INBOX", flags);
	if (mailbox_open(client->mailbox) < 0) {
		*error_r = t_strdup_printf("Couldn't open INBOX: %s",
			mailbox_get_last_error(client->mailbox, NULL));
		client_send_storage_error(client);
		return -1;
	}

	if (init_pop3_deleted_flag(client, &errmsg) < 0 ||
	    init_mailbox(client, &errmsg) < 0) {
		*error_r = t_strdup_printf("Couldn't init INBOX: %s", errmsg);
		return -1;
	}

	if (!client->set->pop3_no_flag_updates && client->messages_count > 0)
		client->seen_bitmask = i_malloc(MSGS_BITMASK_SIZE(client));

	ident = mail_user_get_anvil_userip_ident(client->user);
	if (ident != NULL) {
		master_service_anvil_send(master_service, t_strconcat(
			"CONNECT\t", my_pid, "\tpop3/", ident, "\n", NULL));
		client->anvil_sent = TRUE;
	}

	pop3_refresh_proctitle();
	return 0;
}

static const char *client_build_uidl_change_string(struct client *client)
{
	uint32_t i, old_hash, new_hash;
	unsigned int old_msg_count, new_msg_count;

	if (client->message_uidls == NULL) {
		/* UIDL command not given */
		return "";
	}

	/* 1..new-1 were probably left to mailbox by previous POP3 session */
	old_msg_count = client->lowest_retr_pop3_msn > 0 ?
		client->lowest_retr_pop3_msn - 1 : client->messages_count;
	for (i = 0, old_hash = 0; i < old_msg_count; i++)
		old_hash ^= crc32_str(client->message_uidls[i]);

	/* assume all except deleted messages were sent to POP3 client */
	if (!client->deleted) {
		for (i = 0, new_hash = 0; i < client->messages_count; i++)
			new_hash ^= crc32_str(client->message_uidls[i]);
	} else {
		for (i = 0, new_hash = 0; i < client->messages_count; i++) {
			if (client->deleted_bitmask[i / CHAR_BIT] &
			    (1 << (i % CHAR_BIT)))
				continue;
			new_hash ^= crc32_str(client->message_uidls[i]);
		}
	}

	new_msg_count = client->messages_count - client->deleted_count;
	if (old_hash == new_hash && old_msg_count == new_msg_count)
		return t_strdup_printf("%u/%08x", old_msg_count, old_hash);
	else {
		return t_strdup_printf("%u/%08x -> %u/%08x",
				       old_msg_count, old_hash,
				       new_msg_count, new_hash);
	}
}

static const char *client_stats(struct client *client)
{
	static struct var_expand_table static_tab[] = {
		{ 'p', NULL, "top_bytes" },
		{ 't', NULL, "top_count" },
		{ 'b', NULL, "retr_bytes" },
		{ 'r', NULL, "retr_count" },
		{ 'd', NULL, "deleted_count" },
		{ 'm', NULL, "message_count" },
		{ 's', NULL, "message_bytes" },
		{ 'i', NULL, "input" },
		{ 'o', NULL, "output" },
		{ 'u', NULL, "uidl_change" },
		{ '\0', NULL, "session" },
		{ 'd', NULL, "deleted_bytes" },
		{ '\0', NULL, NULL }
	};
	struct var_expand_table *tab;
	string_t *str;

	tab = t_malloc(sizeof(static_tab));
	memcpy(tab, static_tab, sizeof(static_tab));

	tab[0].value = dec2str(client->top_bytes);
	tab[1].value = dec2str(client->top_count);
	tab[2].value = dec2str(client->retr_bytes);
	tab[3].value = dec2str(client->retr_count);
	tab[4].value = client->delete_success ?
		dec2str(client->deleted_count) : "0";
	tab[5].value = dec2str(client->messages_count);
	tab[6].value = dec2str(client->total_size);
	tab[7].value = dec2str(client->input->v_offset);
	tab[8].value = dec2str(client->output->offset);
	if (var_has_key(client->set->pop3_logout_format,
			tab[9].key, tab[9].long_key))
		tab[9].value = client_build_uidl_change_string(client);
	else
		tab[9].value = "";
	tab[10].value = client->session_id;
	tab[11].value = client->delete_success ?
		dec2str(client->deleted_size) : "0";

	str = t_str_new(128);
	var_expand(str, client->set->pop3_logout_format, tab);
	return str_c(str);
}

void client_destroy(struct client *client, const char *reason)
{
	client->v.destroy(client, reason);
}

static void client_default_destroy(struct client *client, const char *reason)
{
	if (client->seen_change_count > 0)
		(void)client_update_mails(client);

	if (!client->disconnected) {
		if (reason == NULL) {
			reason = io_stream_get_disconnect_reason(client->input,
								 client->output);
		}
		i_info("%s %s", reason, client_stats(client));
	}

	if (client->cmd != NULL) {
		/* deinitialize command */
		i_stream_close(client->input);
		o_stream_close(client->output);
		client->cmd(client);
		i_assert(client->cmd == NULL);
	}

	if (client->trans != NULL) {
		/* client didn't QUIT, but we still want to save any changes
		   done in this transaction. especially the cached virtual
		   message sizes. */
		(void)mailbox_transaction_commit(&client->trans);
	}
	if (array_is_created(&client->all_seqs))
		array_free(&client->all_seqs);
	if (client->deleted_kw != NULL)
		mailbox_keywords_unref(&client->deleted_kw);
	if (client->mailbox != NULL)
		mailbox_free(&client->mailbox);
	if (client->anvil_sent) {
		master_service_anvil_send(master_service, t_strconcat(
			"DISCONNECT\t", my_pid, "\tpop3/",
			mail_user_get_anvil_userip_ident(client->user),
			"\n", NULL));
	}
	mail_user_unref(&client->user);

	if (client->session_dotlock != NULL)
		file_dotlock_delete(&client->session_dotlock);
	if (client->to_session_dotlock_refresh != NULL)
		timeout_remove(&client->to_session_dotlock_refresh);

	if (client->uidl_pool != NULL)
		pool_unref(&client->uidl_pool);
	i_free(client->message_sizes);
	i_free(client->deleted_bitmask);
	i_free(client->seen_bitmask);
	i_free(client->msgnum_to_seq_map);

	if (client->io != NULL)
		io_remove(&client->io);
	timeout_remove(&client->to_idle);
	if (client->to_commit != NULL)
		timeout_remove(&client->to_commit);

	i_stream_destroy(&client->input);
	o_stream_destroy(&client->output);

	fd_close_maybe_stdio(&client->fd_in, &client->fd_out);
	mail_storage_service_user_unref(&client->service_user);

	pop3_client_count--;
	DLLIST_REMOVE(&pop3_clients, client);
	pool_unref(&client->pool);

	master_service_client_connection_destroyed(master_service);
	pop3_refresh_proctitle();
}

static void client_destroy_timeout(struct client *client)
{
	client_destroy(client, NULL);
}

void client_disconnect(struct client *client, const char *reason)
{
	if (client->disconnected)
		return;

	client->disconnected = TRUE;
	i_info("Disconnected: %s %s", reason, client_stats(client));

	(void)o_stream_flush(client->output);

	i_stream_close(client->input);
	o_stream_close(client->output);

	if (client->to_idle != NULL)
		timeout_remove(&client->to_idle);
	client->to_idle = timeout_add(0, client_destroy_timeout, client);
}

void client_send_line(struct client *client, const char *fmt, ...)
{
	va_list va;
	ssize_t ret;

	if (client->output->closed)
		return;

	va_start(va, fmt);

	T_BEGIN {
		string_t *str;

		str = t_str_new(256);
		str_vprintfa(str, fmt, va);
		str_append(str, "\r\n");

		ret = o_stream_send(client->output,
				    str_data(str), str_len(str));
		i_assert(ret < 0 || (size_t)ret == str_len(str));
	} T_END;
	if (ret >= 0) {
		if (!POP3_CLIENT_OUTPUT_FULL(client))
			client->last_output = ioloop_time;
		else if (client->io != NULL) {
			/* no more input until client has read
			   our output */
			io_remove(&client->io);

			/* If someone happens to flush output, we want to get
			   our IO handler back in flush callback */
			o_stream_set_flush_pending(client->output, TRUE);
		}
	}
	va_end(va);
}

void client_send_storage_error(struct client *client)
{
	const char *errstr;
	enum mail_error error;

	if (mailbox_is_inconsistent(client->mailbox)) {
		client_send_line(client, "-ERR [SYS/TEMP] Mailbox is in inconsistent "
				 "state, please relogin.");
		client_disconnect(client, "Mailbox is in inconsistent state.");
		return;
	}

	errstr = mailbox_get_last_error(client->mailbox, &error);
	switch (error) {
	case MAIL_ERROR_TEMP:
	case MAIL_ERROR_NOQUOTA:
	case MAIL_ERROR_INUSE:
		client_send_line(client, "-ERR [SYS/TEMP] %s", errstr);
		break;
	default:
		client_send_line(client, "-ERR [SYS/PERM] %s", errstr);
		break;
	}
}

bool client_handle_input(struct client *client)
{
	char *line, *args;
	int ret;

	o_stream_cork(client->output);
	while (!client->output->closed &&
	       (line = i_stream_next_line(client->input)) != NULL) {
		args = strchr(line, ' ');
		if (args != NULL)
			*args++ = '\0';

		T_BEGIN {
			ret = client_command_execute(client, line,
						     args != NULL ? args : "");
		} T_END;
		if (ret >= 0) {
			client->bad_counter = 0;
			if (client->cmd != NULL) {
				o_stream_set_flush_pending(client->output,
							   TRUE);
				client->waiting_input = TRUE;
				break;
			}
		} else if (++client->bad_counter > CLIENT_MAX_BAD_COMMANDS) {
			client_send_line(client, "-ERR Too many bad commands.");
			client_disconnect(client, "Too many bad commands.");
		}
	}
	o_stream_uncork(client->output);

	if (client->output->closed) {
		client_destroy(client, NULL);
		return FALSE;
	}
	return TRUE;
}

static void client_input(struct client *client)
{
	if (client->cmd != NULL) {
		/* we're still processing a command. wait until it's
		   finished. */
		io_remove(&client->io);
		client->waiting_input = TRUE;
		return;
	}

	client->waiting_input = FALSE;
	client->last_input = ioloop_time;
	timeout_reset(client->to_idle);
	if (client->to_commit != NULL)
		timeout_reset(client->to_commit);

	switch (i_stream_read(client->input)) {
	case -1:
		/* disconnected */
		client_destroy(client, NULL);
		return;
	case -2:
		/* line too long, kill it */
		client_send_line(client, "-ERR Input line too long.");
		client_destroy(client, "Input line too long");
		return;
	}

	(void)client_handle_input(client);
}

static int client_output(struct client *client)
{
	o_stream_cork(client->output);
	if (o_stream_flush(client->output) < 0) {
		client_destroy(client, NULL);
		return 1;
	}

	client->last_output = ioloop_time;
	timeout_reset(client->to_idle);
	if (client->to_commit != NULL)
		timeout_reset(client->to_commit);

	if (client->cmd != NULL)
		client->cmd(client);

	if (client->cmd == NULL) {
		if (o_stream_get_buffer_used_size(client->output) <
		    POP3_OUTBUF_THROTTLE_SIZE/2 && client->io == NULL &&
		    !client->input->closed) {
			/* enable input again */
			client->io = io_add_istream(client->input, client_input,
						    client);
		}
		if (client->io != NULL && client->waiting_input) {
			if (!client_handle_input(client)) {
				/* client got destroyed */
				return 1;
			}
		}
	}

	o_stream_uncork(client->output);
	if (client->cmd != NULL) {
		/* command not finished yet */
		return 0;
	} else if (client->io == NULL) {
		/* data still in output buffer, get back here to add IO */
		return 0;
	} else {
		return 1;
	}
}

void clients_destroy_all(struct mail_storage_service_ctx *storage_service)
{
	while (pop3_clients != NULL) {
		if (pop3_clients->cmd == NULL) {
			client_send_line(pop3_clients,
				"-ERR [SYS/TEMP] Server shutting down.");
		}
		mail_storage_service_io_activate_user(pop3_clients->service_user);
		client_destroy(pop3_clients, "Server shutting down.");
	}
	mail_storage_service_io_deactivate(storage_service);
}

struct pop3_client_vfuncs pop3_client_vfuncs = {
	client_default_destroy
};