mbsync/src/drv_maildir.c

// SPDX-FileCopyrightText: 2000-2002 Michael R. Elkins <me@mutt.org>
// SPDX-FileCopyrightText: 2002-2022 Oswald Buddenhagen <ossi@users.sf.net>
// SPDX-FileCopyrightText: 2004 Theodore Y. Ts'o <tytso@mit.edu>
// SPDX-License-Identifier: GPL-2.0-or-later WITH LicenseRef-isync-GPL-exception
/*
 * mbsync - mailbox synchronizer
 */

#define DEBUG_FLAG DEBUG_MAILDIR

#include "driver.h"

#include <ctype.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>
#include <utime.h>

#if !defined(_POSIX_SYNCHRONIZED_IO) || _POSIX_SYNCHRONIZED_IO <= 0
# define fdatasync fsync
#endif

#ifdef USE_DB
#include <db.h>
#endif /* USE_DB */

#define SUB_UNSET      0
#define SUB_VERBATIM   1
#define SUB_MAILDIRPP  2
#define SUB_LEGACY     3

typedef union maildir_store_conf {
	store_conf_t gen;
	struct {
		STORE_CONF
		char *path;
		char *path_sfx;
		char *inbox;
#ifdef USE_DB
		int alt_map;
#endif /* USE_DB */
		char info_delimiter;
		char sub_style;
		char failed;
		char *info_prefix, *info_stop;  /* precalculated from info_delimiter */
	};
} maildir_store_conf_t;

typedef union maildir_message {
	message_t gen;
	struct {
		MESSAGE(union maildir_message)
		char *base;
	};
} maildir_message_t;

typedef union maildir_store {
	store_t gen;
	struct {
		STORE(union maildir_store)
		int uvfd, uvok, is_inbox, fresh[3];
		uint opts, minuid, maxuid, finduid, pairuid, newuid, uidvalidity, nuid;
		uint_array_t excs;
		char *path;  // own
		char *trash;
#ifdef USE_DB
		DB *db;
		char *usedb;
#endif /* USE_DB */
		string_list_t *boxes;  // _list results
		char listed;  // was _list already run with these flags?
		// note that the message counts do _not_ reflect stats from msgs,
		// but mailbox totals. also, don't trust them beyond the initial load.
		int total_msgs, recent_msgs;
		maildir_message_t *msgs;
		maildir_message_t **app_msgs;  // Only for testing find_new()
		wakeup_t lcktmr;

		void (*expunge_callback)( message_t *msg, void *aux );
		void (*bad_callback)( void *aux );
		void *callback_aux;
	};
} maildir_store_t;

#ifdef USE_DB
static DBT key, value; /* no need to be reentrant, and this saves lots of memset()s */
#endif /* USE_DB */
static struct flock lck;

static int MaildirCount;

static uchar
maildir_parse_flags( const char *info_prefix, const char *base )
{
	const char *s;
	uint i;
	uchar flags;

	flags = 0;
	if ((s = strstr( base, info_prefix )))
		for (s += 3, i = 0; i < as(MsgFlags); i++)
			if (strchr( s, MsgFlags[i] ))
				flags |= (1 << i);
	return flags;
}

static int
maildir_ensure_path( maildir_store_conf_t *conf )
{
	if (!conf->path) {
		error( "Maildir error: store '%s' has no Path\n", conf->name );
		conf->failed = FAIL_FINAL;
		return -1;
	}
	return 0;
}

/* Subdirs of INBOX include a leading slash. */
/* Path includes a trailing slash, Inbox does not. */
static char *
maildir_join_path( maildir_store_conf_t *conf, int in_inbox, const char *box )
{
	char *out, *p;
	const char *prefix, *infix;
	uint pl, il, bl, n;
	char c;

	if (in_inbox || conf->sub_style == SUB_MAILDIRPP) {
		prefix = conf->inbox;
		infix = NULL;
		il = 0;
	} else {
		if (maildir_ensure_path( conf ) < 0)
			return NULL;
		prefix = conf->path;
		infix = conf->path_sfx;
		il = strlen( infix ) + 1;
	}
	pl = strlen( prefix );
	for (bl = 0, n = 0; (c = box[bl]); bl++) {
		if (c == '/') {
			if (conf->sub_style == SUB_UNSET) {
				error( "Maildir error: accessing subfolder '%s', but store '%s' does not specify SubFolders style\n",
				       box, conf->name );
				return NULL;
			}
			n++;
		} else if (c == '.' && conf->sub_style == SUB_MAILDIRPP) {
			error( "Maildir error: store '%s', folder '%s': SubFolders style Maildir++ does not support dots in mailbox names\n",
			       conf->name, box );
			return NULL;
		}
	}
	switch (conf->sub_style) {
	case SUB_VERBATIM:
		n = 0;
		break;
	case SUB_MAILDIRPP:
		n = 2;
		break;
	default: /* SUB_LEGACY and SUB_UNSET */
		break;
	}
	out = nfmalloc( pl + il + bl + n + 1 );
	memcpy( out, prefix, pl );
	p = out + pl;
	if (conf->sub_style == SUB_MAILDIRPP) {
		*p++ = '/';
		*p++ = '.';
	} else if (il) {
		*p++ = '/';
		memcpy( p, infix, il - 1 );
		p += il - 1;
	}
	while ((c = *box++)) {
		if (c == '/') {
			switch (conf->sub_style) {
			case SUB_VERBATIM:
				*p++ = c;
				break;
			case SUB_LEGACY:
				*p++ = c;
				FALLTHROUGH
			default: /* SUB_MAILDIRPP */
				*p++ = '.';
				break;
			}
		} else {
			*p++ = c;
		}
	}
	*p = 0;
	return out;
}

static int
maildir_validate_path( maildir_store_conf_t *conf )
{
	struct stat st;

	if (stat( conf->path, &st ) || !S_ISDIR(st.st_mode)) {
		error( "Maildir error: cannot open store '%s'\n", conf->path );
		conf->failed = FAIL_FINAL;
		return -1;
	}
	return 0;
}

static void lcktmr_timeout( void *aux );

static store_t *
maildir_alloc_store( store_conf_t *gconf, const char *label ATTR_UNUSED )
{
	maildir_store_t *ctx;

	ctx = nfzalloc( sizeof(*ctx) );
	ctx->driver = &maildir_driver;
	ctx->gen.conf = gconf;
	ctx->uvfd = -1;
	init_wakeup( &ctx->lcktmr, lcktmr_timeout, ctx );
	return &ctx->gen;
}

static void
maildir_connect_store( store_t *gctx,
                       void (*cb)( int sts, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_store_conf_t *conf = ctx->conf;

	if (conf->path && maildir_validate_path( conf ) < 0) {
		cb( DRV_STORE_BAD, aux );
		return;
	}
	if (conf->trash && !(ctx->trash = maildir_join_path( conf, 0, conf->trash ))) {
		cb( DRV_STORE_BAD, aux );
		return;
	}
	cb( DRV_OK, aux );
}

static void
free_maildir_messages( maildir_message_t *msg )
{
	while (msg) {
		maildir_message_t *tmsg = msg->next;
		free( msg->base );
		free( msg->msgid );
		free( msg );
		msg = tmsg;
	}
}

static void
maildir_cleanup( store_t *gctx )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	free_maildir_messages( ctx->msgs );
#ifdef USE_DB
	if (ctx->db)
		ctx->db->close( ctx->db, 0 );
	free( ctx->usedb );
#endif /* USE_DB */
	free( ctx->path );
	free( ctx->excs.data );
	if (ctx->uvfd >= 0)
		close( ctx->uvfd );
	conf_wakeup( &ctx->lcktmr, -1 );
}

static void
maildir_free_store( store_t *gctx )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	maildir_cleanup( gctx );
	wipe_wakeup( &ctx->lcktmr );
	free( ctx->trash );
	free_string_list( ctx->boxes );
	free( gctx );
}

static void
maildir_cleanup_drv( void )
{
}

static void
maildir_set_callbacks( store_t *gctx, void (*exp_cb)( message_t *, void * ),
                       void (*bad_cb)( void * ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	ctx->expunge_callback = exp_cb;
	ctx->bad_callback = bad_cb;
	ctx->callback_aux = aux;
}

static void
maildir_invoke_bad_callback( maildir_store_t *ctx )
{
	ctx->bad_callback( ctx->callback_aux );
}

static int
maildir_list_maildirpp( maildir_store_t *ctx, int flags, const char *inbox )
{
	DIR *dir;
	struct dirent *de;
	int warned = 0;
	struct stat st;

	if (ctx->listed & LIST_PATH)  // Implies LIST_INBOX
		return 0;

	if (!(ctx->listed & LIST_INBOX))
		add_string_list( &ctx->boxes, "INBOX" );

	char path[_POSIX_PATH_MAX];
	int pathLen = nfsnprintf( path, _POSIX_PATH_MAX, "%s/", inbox );
	if (!(dir = opendir( path ))) {
		if (errno == ENOENT || errno == ENOTDIR)
			return 0;
		sys_error( "Maildir error: cannot list %s", path );
		return -1;
	}
	while ((de = readdir( dir ))) {
		const char *ent = de->d_name;
		if (*ent++ != '.' || !*ent)
			continue;
		char name[_POSIX_PATH_MAX];
		char *effName = name;
		if (*ent == '.') {
			if (ctx->listed & LIST_INBOX)
				continue;
			if (!*++ent)
				continue;
			// The Maildir++ Inbox is technically not under Path (as there is none), so
			// "*" would never match INBOX*, which is rather unintuitive. Matching INBOX*
			// implicitly instead makes it consistent with an IMAP Store with an empty Path.
		} else {
			if (!(flags & (LIST_PATH | LIST_PATH_MAYBE)))
				continue;
			// Explained in maildir_list_recurse().
			if (starts_with( ent, -1, "INBOX", 5 ) && (!ent[5] || ent[5] == '.')) {
				if (!warned) {
					warned = 1;
					path[pathLen] = 0;
					warn( "Maildir warning: ignoring INBOX in %s\n", path );
				}
				continue;
			}
			effName += 6;
		}
		nfsnprintf( path + pathLen, _POSIX_PATH_MAX - pathLen, "%s/cur", de->d_name );
		if (!stat( path, &st ) && S_ISDIR(st.st_mode)) {
			int nl = nfsnprintf( name, _POSIX_PATH_MAX, "INBOX/%s", ent );
			for (int i = 6; i < nl; i++) {
				if (name[i] == '.')
					name[i] = '/';
			}
			add_string_list( &ctx->boxes, effName );
		}
	}
	closedir (dir);

	if (flags & (LIST_PATH | LIST_PATH_MAYBE))
		ctx->listed |= LIST_PATH;
	ctx->listed |= LIST_INBOX;
	return 0;
}

static int maildir_list_inbox( maildir_store_t *ctx );

static int
maildir_list_recurse( maildir_store_t *ctx, int isBox,
                      const char *inbox, uint inboxLen,
                      char *suffix, int suffixLen,
                      char *path, int pathLen, char *name, int nameLen )
{
	DIR *dir;
	int style = ctx->conf->sub_style;
	int pl, nl;
	struct dirent *de;
	struct stat st;

	if (!(dir = opendir( path ))) {
		if (isBox && (errno == ENOENT || errno == ENOTDIR))
			return 0;
		sys_error( "Maildir error: cannot list %s", path );
		return -1;
	}
	if (isBox > 1 && style == SUB_UNSET) {
		error( "Maildir error: found subfolder '%.*s', but store '%s' does not specify SubFolders style\n",
		       nameLen - 1, name, ctx->conf->name );
		closedir( dir );
		return -1;
	}
	if (isBox > 10) {
		// We do the other checks first to avoid confusing error messages for files.
		error( "Maildir error: path %s is too deeply nested. Symlink loop?\n", path );
		closedir( dir );
		return -1;
	}
	while ((de = readdir( dir ))) {
		const char *ent = de->d_name;
		if (ent[0] == '.' && (!ent[1] || (ent[1] == '.' && !ent[2])))
			continue;
		pl = nfsnprintf( path + pathLen, _POSIX_PATH_MAX - pathLen, "%s", ent );
		if (pl == 3 && (!memcmp( ent, "cur", 3 ) || !memcmp( ent, "new", 3 ) || !memcmp( ent, "tmp", 3 )))
			continue;
		if (suffixLen) {
			if (!starts_with( ent, pl, suffix, suffixLen ))
				continue;
			if (pl == suffixLen) {
				error( "Maildir error: empty mailbox name under %s - did you forget the trailing slash?\n", path );
				closedir( dir );
				return -1;
			}
			ent += suffixLen;
		}
		pl += pathLen;
		if (inbox && equals( path, pl, inbox, inboxLen )) {
			// Inbox nested into Path.
			if (maildir_list_inbox( ctx ) < 0) {
				closedir( dir );
				return -1;
			}
		} else {
			if (style == SUB_LEGACY) {
				if (*ent == '.') {
					if (!isBox)
						continue;
					ent++;
				} else {
					if (isBox)
						continue;
				}
			}
			// A folder named "INBOX" would be indistinguishable from the
			// actual INBOX after prefix stripping, so drop it. This applies
			// only to the fully uppercased spelling, as our canonical box
			// names are case-sensitive (unlike IMAP's INBOX).
			if (!nameLen && equals( ent, -1, "INBOX", 5 )) {
				path[pathLen] = 0;
				warn( "Maildir warning: ignoring INBOX in %s\n", path );
				continue;
			}
			nl = nameLen + nfsnprintf( name + nameLen, _POSIX_PATH_MAX - nameLen, "%s", ent );
			path[pl++] = '/';
			nfsnprintf( path + pl, _POSIX_PATH_MAX - pl, "cur" );
			if (!stat( path, &st ) && S_ISDIR(st.st_mode))
				add_string_list( &ctx->boxes, name );
			path[pl] = 0;
			name[nl++] = '/';
			if (maildir_list_recurse( ctx, isBox + 1, inbox, inboxLen, NULL, 0, path, pl, name, nl ) < 0) {
				closedir( dir );
				return -1;
			}
		}
	}
	closedir (dir);
	return 0;
}

static int
maildir_list_inbox( maildir_store_t *ctx )
{
	char path[_POSIX_PATH_MAX], name[_POSIX_PATH_MAX];

	if (ctx->listed & LIST_INBOX)
		return 0;
	ctx->listed |= LIST_INBOX;

	add_string_list( &ctx->boxes, "INBOX" );
	return maildir_list_recurse(
	        ctx, 1, NULL, 0, NULL, 0,
	        path, nfsnprintf( path, _POSIX_PATH_MAX, "%s/", ctx->conf->inbox ),
	        name, nfsnprintf( name, _POSIX_PATH_MAX, "INBOX/" ) );
}

static int
maildir_list_path( maildir_store_t *ctx )
{
	char path[_POSIX_PATH_MAX], name[_POSIX_PATH_MAX];

	if (ctx->listed & LIST_PATH)
		return 0;
	ctx->listed |= LIST_PATH;

	if (maildir_ensure_path( ctx->conf ) < 0)
		return -1;
	const char *inbox = ctx->conf->inbox;
	return maildir_list_recurse(
	        ctx, 0, inbox, strlen( inbox ),
	        ctx->conf->path_sfx, strlen( ctx->conf->path_sfx ),
	        path, nfsnprintf( path, _POSIX_PATH_MAX, "%s/", ctx->conf->path ),
	        name, 0 );
}

static void
maildir_list_store( store_t *gctx, int flags,
                    void (*cb)( int sts, string_list_t *boxes, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_store_conf_t *conf = ctx->conf;

	if (conf->sub_style == SUB_MAILDIRPP
	        ? maildir_list_maildirpp( ctx, flags, conf->inbox ) < 0
	        : ((((flags & LIST_PATH) || ((flags & LIST_PATH_MAYBE) && conf->path))
	            && maildir_list_path( ctx ) < 0) ||
	           ((flags & LIST_INBOX)
	            && maildir_list_inbox( ctx ) < 0))) {
		maildir_invoke_bad_callback( ctx );
		cb( DRV_CANCELED, NULL, aux );
	} else {
		cb( DRV_OK, ctx->boxes, aux );
	}
}

static const char *subdirs[] = { "cur", "new", "tmp" };

typedef struct {
	char *base;
	char *msgid;
	uint size;
	uint uid;
	uchar recent;
	char tuid[TUIDL];
} msg_t;

DEFINE_ARRAY_TYPE(msg_t)

static void
maildir_free_scan( msg_t_array_alloc_t *msglist )
{
	uint i;

	if (msglist->array.data) {
		for (i = 0; i < msglist->array.size; i++) {
			free( msglist->array.data[i].base );
			free( msglist->array.data[i].msgid );
		}
		free( msglist->array.data );
	}
}

#define _24_HOURS (3600 * 24)

static int
maildir_clear_tmp( char *buf, int bufsz, int bl )
{
	DIR *dirp;
	struct dirent *entry;
	time_t now;
	struct stat st;

	memcpy( buf + bl, "tmp/", 5 );
	bl += 4;
	if (!(dirp = opendir( buf ))) {
		sys_error( "Maildir error: cannot list %s", buf );
		return DRV_BOX_BAD;
	}
	time( &now );
	while ((entry = readdir( dirp ))) {
		nfsnprintf( buf + bl, bufsz - bl, "%s", entry->d_name );
		if (stat( buf, &st )) {
			if (errno != ENOENT)
				sys_error( "Maildir error: cannot access %s", buf );
		} else if (S_ISREG(st.st_mode) && now - st.st_ctime >= _24_HOURS) {
			/* This should happen infrequently enough that it won't be
			 * bothersome to the user to display when it occurs.
			 */
			notice( "Maildir notice: removing stale file %s\n", buf );
			if (unlink( buf ) && errno != ENOENT)
				sys_error( "Maildir error: cannot remove %s", buf );
		}
	}
	closedir( dirp );
	return DRV_OK;
}

static int
maildir_validate( const char *box, int create, maildir_store_t *ctx )
{
	int i, bl, ret;
	struct stat st;
	char buf[_POSIX_PATH_MAX];

	bl = nfsnprintf( buf, sizeof(buf) - 4, "%s/", box );
	if (stat( buf, &st )) {
		if (errno != ENOENT) {
			sys_error( "Maildir error: cannot access mailbox '%s'", buf );
			return DRV_BOX_BAD;
		}
		if (!create)
			return DRV_BOX_BAD;
		if (mkdir_p( buf, bl - 1 )) {
			sys_error( "Maildir error: cannot create mailbox '%s'", buf );
			ctx->conf->failed = FAIL_FINAL;
			maildir_invoke_bad_callback( ctx );
			return DRV_CANCELED;
		}
	} else if (!S_ISDIR(st.st_mode)) {
	  notdir:
		error( "Maildir error: '%s' is no valid mailbox\n", buf );
		return DRV_BOX_BAD;
	}
	for (i = 0; i < 3; i++) {
		memcpy( buf + bl, subdirs[i], 4 );
		if (stat( buf, &st )) {
			/* We always create new/ and tmp/ if they are missing. cur/ is the presence indicator. */
			if (!i && !create)
				return DRV_BOX_BAD;
			if (mkdir( buf, 0700 )) {
				sys_error( "Maildir error: cannot create directory %s", buf );
				return DRV_BOX_BAD;
			}
			ctx->fresh[i] = 1;
		} else if (!S_ISDIR(st.st_mode)) {
			goto notdir;
		} else {
			if (i == 2) {
				if ((ret = maildir_clear_tmp( buf, sizeof(buf), bl )) != DRV_OK)
					return ret;
			}
		}
	}
	return DRV_OK;
}

#ifdef USE_DB
static void
make_key( const char *info_stop, DBT *tkey, const char *name )
{
	char *u = strpbrk( name, info_stop );
DIAG_PUSH
DIAG_DISABLE("-Wcast-qual")  // C has no const_cast<> ...
	tkey->data = (char *)name;
DIAG_POP
	tkey->size = u ? (size_t)(u - name) : strlen( name );
}
#endif /* USE_DB */

static int
maildir_store_uidval( maildir_store_t *ctx )
{
	int n;
#ifdef USE_DB
	int ret;
	uint uv[2];
#endif
	char buf[128];

#ifdef USE_DB
	if (ctx->db) {
		key.data = (void *)"UIDVALIDITY";
		key.size = 11;
		uv[0] = ctx->uidvalidity;
		uv[1] = ctx->nuid;
		value.data = uv;
		value.size = sizeof(uv);
		if ((ret = ctx->db->put( ctx->db, NULL, &key, &value, 0 ))) {
			ctx->db->err( ctx->db, ret, "Maildir error: db->put()" );
			return DRV_BOX_BAD;
		}
		if ((ret = ctx->db->sync( ctx->db, 0 ))) {
			ctx->db->err( ctx->db, ret, "Maildir error: db->sync()" );
			return DRV_BOX_BAD;
		}
	} else
#endif /* USE_DB */
	{
		n = sprintf( buf, "%u\n%u\n", ctx->uidvalidity, ctx->nuid );
		lseek( ctx->uvfd, 0, SEEK_SET );
		if (write( ctx->uvfd, buf, (uint)n ) != n || ftruncate( ctx->uvfd, n ) || (UseFSync && fdatasync( ctx->uvfd ))) {
			error( "Maildir error: cannot write UIDVALIDITY in %s\n", ctx->path );
			return DRV_BOX_BAD;
		}
	}
	conf_wakeup( &ctx->lcktmr, 2000 );
	return DRV_OK;
}

static int
maildir_init_uidval( maildir_store_t *ctx )
{
	ctx->uidvalidity = (uint)time( NULL );
	ctx->nuid = 0;
	ctx->uvok = 0;
#ifdef USE_DB
	if (ctx->db) {
		u_int32_t count;
		ctx->db->truncate( ctx->db, NULL, &count, 0 );
	}
#endif /* USE_DB */
	return maildir_store_uidval( ctx );
}

static int
maildir_init_uidval_new( maildir_store_t *ctx )
{
	notice( "Maildir notice: no UIDVALIDITY in %s, creating new.\n", ctx->path );
	return maildir_init_uidval( ctx );
}

static int
maildir_uidval_lock( maildir_store_t *ctx )
{
	int n;
#ifdef USE_DB
	int ret;
	struct stat st;
#endif
	char buf[128];

	if (pending_wakeup( &ctx->lcktmr )) {
		/* The unlock timer is active, so we are obviously already locked. */
		return DRV_OK;
	}
	/* This (theoretically) works over NFS. Let's hope nobody else did
	   the same in the opposite order, as we'd deadlock then. */
#if SEEK_SET != 0
	lck.l_whence = SEEK_SET;
#endif
	lck.l_type = F_WRLCK;
	if (fcntl( ctx->uvfd, F_SETLKW, &lck )) {
		error( "Maildir error: cannot fcntl lock UIDVALIDITY in %s.\n", ctx->path );
		return DRV_BOX_BAD;
	}

#ifdef USE_DB
	if (ctx->usedb) {
		if (fstat( ctx->uvfd, &st )) {
			sys_error( "Maildir error: cannot fstat UID database in %s", ctx->path );
			return DRV_BOX_BAD;
		}
		if (db_create( &ctx->db, NULL, 0 )) {
			fputs( "Maildir error: db_create() failed\n", stderr );
			return DRV_BOX_BAD;
		}
		if ((ret = (ctx->db->open)( ctx->db, NULL, ctx->usedb, NULL, DB_HASH,
		                            st.st_size ? 0 : DB_CREATE | DB_TRUNCATE, 0 ))) {
			ctx->db->err( ctx->db, ret, "Maildir error: db->open(%s)", ctx->usedb );
			return DRV_BOX_BAD;
		}
		key.data = (void *)"UIDVALIDITY";
		key.size = 11;
		if ((ret = ctx->db->get( ctx->db, NULL, &key, &value, 0 ))) {
			if (ret != DB_NOTFOUND) {
				ctx->db->err( ctx->db, ret, "Maildir error: db->get()" );
				return DRV_BOX_BAD;
			}
			return maildir_init_uidval_new( ctx );
		}
		ctx->uidvalidity = ((uint *)value.data)[0];
		ctx->nuid = ((uint *)value.data)[1];
	} else
#endif
	{
		lseek( ctx->uvfd, 0, SEEK_SET );
		if ((n = read( ctx->uvfd, buf, sizeof(buf) - 1 )) <= 0 ||
			(buf[n] = 0, sscanf( buf, "%u\n%u", &ctx->uidvalidity, &ctx->nuid ) != 2)) {
#if 1
			/* In a generic driver, resetting the UID validity would be the right thing.
			 * But this would mess up the sync state completely. So better bail out and
			 * give the user a chance to fix the mailbox. */
			if (n) {
				error( "Maildir error: cannot read UIDVALIDITY in %s.\n", ctx->path );
				return DRV_BOX_BAD;
			}
#endif
			return maildir_init_uidval_new( ctx );
		}
	}
	ctx->uvok = 1;
	conf_wakeup( &ctx->lcktmr, 2000 );
	return DRV_OK;
}

static void
maildir_uidval_unlock( maildir_store_t *ctx )
{
#ifdef USE_DB
	if (ctx->db) {
		ctx->db->close( ctx->db, 0 );
		ctx->db = NULL;
	}
#endif /* USE_DB */
	lck.l_type = F_UNLCK;
	fcntl( ctx->uvfd, F_SETLK, &lck );
}

static void
lcktmr_timeout( void *aux )
{
	maildir_uidval_unlock( (maildir_store_t *)aux );
}

static int
maildir_obtain_uid( maildir_store_t *ctx, uint *uid )
{
	int ret;

	if ((ret = maildir_uidval_lock( ctx )) != DRV_OK)
		return ret;
	*uid = ++ctx->nuid;
	return maildir_store_uidval( ctx );
}

#ifdef USE_DB
static int
maildir_set_uid( maildir_store_t *ctx, const char *name, uint *uid )
{
	int ret;

	if ((ret = maildir_uidval_lock( ctx )) != DRV_OK)
		return ret;
	*uid = ++ctx->nuid;

	make_key( ctx->conf->info_stop, &key, name );
	value.data = uid;
	value.size = sizeof(*uid);
	if ((ret = ctx->db->put( ctx->db, NULL, &key, &value, 0 ))) {
		ctx->db->err( ctx->db, ret, "Maildir error: db->put()" );
		return DRV_BOX_BAD;
	}
	return maildir_store_uidval( ctx );
}
#endif

static int
maildir_compare( const void *l, const void *r )
{
	const msg_t *lm = (const msg_t *)l, *rm = (const msg_t *)r;
	char *ldot, *rdot, *ldot2, *rdot2, *lseq, *rseq;
	uint llen, rlen;
	int ret;

	if (lm->uid != rm->uid)  // Can't subtract, the result might not fit into signed int.
		return lm->uid > rm->uid ? 1 : -1;

	/* No UID, so sort by arrival date. We should not do this, but we rely
	   on the suggested unique file name scheme - we have no choice. */
	/* The first field are always the seconds. Alphabetical sort should be
	   faster than numeric. */
	if (!(ldot = strchr( lm->base, '.' )) || !(rdot = strchr( rm->base, '.' )))
		goto stronly; /* Should never happen ... */
	llen = (uint)(ldot - lm->base), rlen = (uint)(rdot - rm->base);
	/* The shorter number is smaller. Really. This won't trigger with any
	   mail created after Sep 9 2001 anyway. */
	if ((ret = (int)llen - (int)rlen))
		return ret;
	if ((ret = memcmp( lm->base, rm->base, llen )))
		return ret;

	ldot++, rdot++;

	if ((llen = strtoul( ldot, &ldot2, 10 ))) {
		if (!(rlen = strtoul( rdot, &rdot2, 10 )))
			goto stronly; /* Comparing apples to oranges ... */
		/* Classical PID specs */
		if ((ret = (int)llen - (int)rlen)) {
		  retpid:
			/* Handle PID wraparound. This works only on systems
			   where PIDs are not reused too fast */
			if (ret > 20000 || ret < -20000)
				ret = -ret;
			return ret;
		}
		return (*ldot2 != '_' ? 0 : atoi( ldot2 + 1 )) -
		       (*rdot2 != '_' ? 0 : atoi( rdot2 + 1 ));
	}

	if (!(ldot2 = strchr( ldot, '.' )) || !(rdot2 = strchr( rdot, '.' )))
		goto stronly; /* Should never happen ... */
	llen = (uint)(ldot2 - ldot), rlen = (uint)(rdot2 - rdot);

	if (((lseq = memchr( ldot, '#', llen )) && (rseq = memchr( rdot, '#', rlen ))) ||
	    ((lseq = memchr( ldot, 'M', llen )) && (rseq = memchr( rdot, 'M', rlen ))))
		return atoi( lseq + 1 ) - atoi( rseq + 1 );

	if ((lseq = memchr( ldot, 'P', llen )) && (rseq = memchr( rdot, 'P', rlen ))) {
		if ((ret = atoi( lseq + 1 ) - atoi( rseq + 1 )))
			goto retpid;
		if ((lseq = memchr( ldot, 'Q', llen )) && (rseq = memchr( rdot, 'Q', rlen )))
			return atoi( lseq + 1 ) - atoi( rseq + 1 );
	}

  stronly:
	/* Fall-back, so the sort order is defined at all */
	return strcmp( lm->base, rm->base );
}

static int
maildir_scan( maildir_store_t *ctx, msg_t_array_alloc_t *msglist )
{
	maildir_store_conf_t *conf = ctx->conf;
	DIR *d;
	FILE *f;
	struct dirent *e;
	const char *u, *ru;
#ifdef USE_DB
	DB *tdb;
	DBC *dbc;
#endif /* USE_DB */
	msg_t *entry;
	uint i;
	int bl, fnl, ret;
	uint uid;
	time_t now, stamps[2];
	struct stat st;
	char buf[_POSIX_PATH_MAX], nbuf[_POSIX_PATH_MAX];

  again:
	ARRAY_INIT( msglist );
	ctx->total_msgs = ctx->recent_msgs = 0;
	if (ctx->uvok || ctx->maxuid == UINT_MAX) {
#ifdef USE_DB
		if (ctx->usedb) {
			if (db_create( &tdb, NULL, 0 )) {
				fputs( "Maildir error: db_create() failed\n", stderr );
				return DRV_BOX_BAD;
			}
			if ((tdb->open)( tdb, NULL, NULL, NULL, DB_HASH, DB_CREATE, 0 )) {
				fputs( "Maildir error: tdb->open() failed\n", stderr );
			  bork:
				tdb->close( tdb, 0 );
				return DRV_BOX_BAD;
			}
		}
#endif /* USE_DB */
		bl = nfsnprintf( buf, sizeof(buf) - 4, "%s/", ctx->path );
	  restat:
		now = time( NULL );
		for (i = 0; i < 2; i++) {
			memcpy( buf + bl, subdirs[i], 4 );
			if (stat( buf, &st )) {
				sys_error( "Maildir error: cannot stat %s", buf );
				goto dfail;
			}
			if (st.st_mtime == now && !(DFlags & ZERODELAY) && !ctx->fresh[i]) {
				/* If the modification happened during this second, we wouldn't be able to
				 * tell if there were further modifications during this second. So wait.
				 * This has the nice side effect that we wait for "batches" of changes to
				 * complete. On the downside, it can potentially block indefinitely. */
				notice( "Maildir notice: sleeping due to recent directory modification.\n" );
				sleep( 1 ); /* FIXME: should make this async */
				goto restat;
			}
			stamps[i] = st.st_mtime;
		}
		for (i = 0; i < 2; i++) {
			memcpy( buf + bl, subdirs[i], 4 );
			if (!(d = opendir( buf ))) {
				sys_error( "Maildir error: cannot list %s", buf );
			  rfail:
				maildir_free_scan( msglist );
			  dfail:
#ifdef USE_DB
				if (ctx->usedb)
					tdb->close( tdb, 0 );
#endif /* USE_DB */
				return DRV_BOX_BAD;
			}
			while ((e = readdir( d ))) {
				if (*e->d_name == '.')
					continue;
				ctx->total_msgs++;
				ctx->recent_msgs += i;
#ifdef USE_DB
				if (ctx->usedb) {
					if (maildir_uidval_lock( ctx ) != DRV_OK)
						goto mbork;
					make_key( conf->info_stop, &key, e->d_name );
					if ((ret = ctx->db->get( ctx->db, NULL, &key, &value, 0 ))) {
						if (ret != DB_NOTFOUND) {
							ctx->db->err( ctx->db, ret, "Maildir error: db->get()" );
						  mbork:
							maildir_free_scan( msglist );
							closedir( d );
							goto bork;
						}
						uid = UINT_MAX;
					} else {
						value.size = 0;
						if ((ret = tdb->put( tdb, NULL, &key, &value, 0 ))) {
							tdb->err( tdb, ret, "Maildir error: tdb->put()" );
							goto mbork;
						}
						uid = *(uint *)value.data;
					}
				} else
#endif /* USE_DB */
				{
					uid = (ctx->uvok && (u = strstr( e->d_name, ",U=" ))) ? strtoul( u + 3, NULL, 10 ) : 0;
					if (!uid)
						uid = UINT_MAX;
				}
				if (uid <= ctx->maxuid) {
					if (uid < ctx->minuid && !find_uint_array( ctx->excs, uid ))
						continue;
					entry = msg_t_array_append( msglist );
					entry->base = nfstrdup( e->d_name );
					entry->msgid = NULL;
					entry->uid = uid;
					entry->recent = (uchar)i;
					entry->size = 0;
					entry->tuid[0] = 0;
				}
			}
			closedir( d );
		}
		for (i = 0; i < 2; i++) {
			memcpy( buf + bl, subdirs[i], 4 );
			if (stat( buf, &st )) {
				sys_error( "Maildir error: cannot re-stat %s", buf );
				goto rfail;
			}
			if (st.st_mtime != stamps[i]) {
				/* Somebody messed with the mailbox since we started listing it. */
#ifdef USE_DB
				if (ctx->usedb)
					tdb->close( tdb, 0 );
#endif /* USE_DB */
				maildir_free_scan( msglist );
				goto again;
			}
		}
#ifdef USE_DB
		if (ctx->usedb) {
			if (maildir_uidval_lock( ctx ) != DRV_OK) {
			} else if ((ret = ctx->db->cursor( ctx->db, NULL, &dbc, 0 ))) {
				ctx->db->err( ctx->db, ret, "Maildir error: db->cursor()" );
			} else {
				for (;;) {
					if ((ret = dbc->c_get( dbc, &key, &value, DB_NEXT ))) {
						if (ret != DB_NOTFOUND)
							ctx->db->err( ctx->db, ret, "Maildir error: db->c_get()" );
						break;
					}
					if (!equals( key.data, (int)key.size, "UIDVALIDITY", 11 ) &&
					    (ret = tdb->get( tdb, NULL, &key, &value, 0 ))) {
						if (ret != DB_NOTFOUND) {
							tdb->err( tdb, ret, "Maildir error: tdb->get()" );
							break;
						}
						if ((ret = dbc->c_del( dbc, 0 ))) {
							ctx->db->err( ctx->db, ret, "Maildir error: db->c_del()" );
							break;
						}
					}
				}
				dbc->c_close( dbc );
			}
			tdb->close( tdb, 0 );
		}
#endif /* USE_DB */
		qsort( msglist->array.data, msglist->array.size, sizeof(msg_t), maildir_compare );
		for (uid = i = 0; i < msglist->array.size; i++) {
			entry = &msglist->array.data[i];
			if (entry->uid != UINT_MAX) {
				if (uid == entry->uid) {
#if 1
					/* See comment in maildir_uidval_lock() why this is fatal. */
					error( "Maildir error: duplicate UID %u in %s.\n", uid, ctx->path );
					maildir_free_scan( msglist );
					return DRV_BOX_BAD;
#else
					notice( "Maildir notice: duplicate UID in %s; changing UIDVALIDITY.\n", ctx->path );
					if ((ret = maildir_init_uid( ctx )) != DRV_OK) {
						maildir_free_scan( msglist );
						return ret;
					}
					maildir_free_scan( msglist );
					goto again;
#endif
				}
				uid = entry->uid;
				if (uid > ctx->nuid) {
					/* In principle, we could just warn and top up nuid. However, getting into this
					 * situation might indicate some serious trouble, so let's not make it worse. */
					error( "Maildir error: UID %u is beyond highest assigned UID %u in %s.\n",
					       uid, ctx->nuid, ctx->path );
					maildir_free_scan( msglist );
					return DRV_BOX_BAD;
				}
				fnl = 0;
#ifdef USE_DB
			} else if (ctx->usedb) {
				if ((ret = maildir_set_uid( ctx, entry->base, &uid )) != DRV_OK) {
					maildir_free_scan( msglist );
					return ret;
				}
				entry->uid = uid;
				fnl = 0;
#endif /* USE_DB */
			} else {
				if ((ret = maildir_obtain_uid( ctx, &uid )) != DRV_OK) {
					maildir_free_scan( msglist );
					return ret;
				}
				entry->uid = uid;
				if ((u = strstr( entry->base, ",U=" )))
					for (ru = u + 3; isdigit( (uchar)*ru ); ru++);
				else
					u = ru = strchr( entry->base, conf->info_delimiter );
				fnl = (u ?
					nfsnprintf( buf + bl, _POSIX_PATH_MAX - bl, "%s/%.*s,U=%u%s", subdirs[entry->recent], (int)(u - entry->base), entry->base, uid, ru ) :
					nfsnprintf( buf + bl, _POSIX_PATH_MAX - bl, "%s/%s,U=%u", subdirs[entry->recent], entry->base, uid ))
					- 4;
				memcpy( nbuf, buf, (size_t)(bl + 4) );
				nfsnprintf( nbuf + bl + 4, _POSIX_PATH_MAX - bl - 4, "%s", entry->base );
				if (rename( nbuf, buf )) {
					if (errno != ENOENT) {
						sys_error( "Maildir error: cannot rename %s to %s", nbuf, buf );
					  fail:
						maildir_free_scan( msglist );
						return DRV_BOX_BAD;
					}
				  retry:
					maildir_free_scan( msglist );
					goto again;
				}
				free( entry->base );
				entry->base = nfstrndup( buf + bl + 4, (size_t)fnl );
			}
			int want_size = ((ctx->opts & OPEN_OLD_SIZE) && uid <= ctx->newuid) ||
			                ((ctx->opts & OPEN_NEW_SIZE) && uid > ctx->newuid);
			int want_tuid = ((ctx->opts & OPEN_FIND) && uid >= ctx->finduid);
			int want_msgid = ((ctx->opts & OPEN_PAIRED_IDS) && uid <= ctx->pairuid);
			if (!want_size && !want_tuid && !want_msgid)
				continue;
			if (!fnl)
				nfsnprintf( buf + bl, _POSIX_PATH_MAX - bl, "%s/%s", subdirs[entry->recent], entry->base );
			if (want_size) {
				if (stat( buf, &st )) {
					if (errno != ENOENT) {
						sys_error( "Maildir error: cannot stat %s", buf );
						goto fail;
					}
					goto retry;
				}
				// The clipped value is good enough for MaxSize comparisons.
				entry->size = st.st_size > UINT_MAX ? UINT_MAX : (uint)st.st_size;
			}
			if (want_tuid || want_msgid) {
				if (!(f = fopen( buf, "r" ))) {
					if (errno != ENOENT) {
						sys_error( "Maildir error: cannot open %s", buf );
						goto fail;
					}
					goto retry;
				}
				int off, in_msgid = 0;
				char lnbuf[1000];  // Says RFC2822
				while ((want_tuid || want_msgid) && fgets( lnbuf, sizeof(lnbuf), f )) {
					int bufl = strlen( lnbuf );
					if (bufl && lnbuf[bufl - 1] == '\n')
						--bufl;
					if (bufl && lnbuf[bufl - 1] == '\r')
						--bufl;
					if (!bufl)
						break;
					if (want_tuid && starts_with( lnbuf, bufl, "X-TUID: ", 8 )) {
						if (bufl < 8 + TUIDL) {
							error( "Maildir error: malformed X-TUID header in %s\n", buf );
							continue;
						}
						memcpy( entry->tuid, lnbuf + 8, TUIDL );
						want_tuid = 0;
						in_msgid = 0;
						continue;
					}
					if (want_msgid && starts_with_upper( lnbuf, bufl, "MESSAGE-ID:", 11 )) {
						off = 11;
					} else if (in_msgid) {
						if (!isspace( lnbuf[0] )) {
							in_msgid = 0;
							continue;
						}
						off = 1;
					} else {
						continue;
					}
					while (off < bufl && isspace( lnbuf[off] ))
						off++;
					if (off == bufl) {
						in_msgid = 1;
						continue;
					}
					entry->msgid = nfstrndup( lnbuf + off, (size_t)(bufl - off) );
					want_msgid = 0;
					in_msgid = 0;
				}
				fclose( f );
			}
		}
		ctx->uvok = 1;
	}
	return DRV_OK;
}

static void
maildir_init_msg( maildir_store_t *ctx, maildir_message_t *msg, msg_t *entry )
{
	msg->base = entry->base;
	entry->base = NULL; /* prevent deletion */
	msg->msgid = entry->msgid;
	entry->msgid = NULL; /* prevent deletion */
	msg->size = entry->size;
	memcpy( msg->tuid, entry->tuid, TUIDL );
	if (entry->recent)
		msg->status |= M_RECENT;
	if (ctx->opts & OPEN_FLAGS) {
		msg->status |= M_FLAGS;
		msg->flags = maildir_parse_flags( ctx->conf->info_prefix, msg->base );
	} else {
		msg->flags = 0;
	}
}

static void
maildir_app_msg( maildir_store_t *ctx, maildir_message_t ***msgapp, msg_t *entry )
{
	maildir_message_t *msg = nfmalloc( sizeof(*msg) );
	msg->next = **msgapp;
	**msgapp = msg;
	*msgapp = &msg->next;
	msg->uid = entry->uid;
	msg->status = 0;
	msg->srec = NULL;
	maildir_init_msg( ctx, msg, entry );
}

static int
maildir_select_box( store_t *gctx, const char *name )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_store_conf_t *conf = ctx->conf;

	maildir_cleanup( gctx );
	ctx->msgs = NULL;
	ctx->app_msgs = &ctx->msgs;
	ctx->excs.data = NULL;
	ctx->uvfd = -1;
#ifdef USE_DB
	ctx->db = NULL;
	ctx->usedb = NULL;
#endif /* USE_DB */
	ctx->fresh[0] = ctx->fresh[1] = 0;
	if (starts_with( name, -1, "INBOX", 5 ) && (!name[5] || name[5] == '/')) {
		if (!name[5]) {
			ctx->path = nfstrdup( conf->inbox );
			ctx->is_inbox = 1;
		} else {
			ctx->path = maildir_join_path( conf, 1, name + 5 );
			ctx->is_inbox = 0;
		}
	} else {
		if (!(ctx->path = maildir_join_path( conf, 0, name )))
		    return DRV_STORE_BAD;
		ctx->is_inbox = 0;
	}
	return ctx->path ? DRV_OK : DRV_BOX_BAD;
}

static const char *
maildir_get_box_path( store_t *gctx )
{
	return ((maildir_store_t *)gctx)->path;
}

static void
maildir_open_box( store_t *gctx,
                  void (*cb)( int sts, uint uidvalidity, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	int ret;
	char uvpath[_POSIX_PATH_MAX];

	if ((ret = maildir_validate( ctx->path, ctx->is_inbox, ctx )) != DRV_OK)
		goto bail;

	nfsnprintf( uvpath, sizeof(uvpath), "%s/.uidvalidity", ctx->path );
#ifndef USE_DB
	if ((ctx->uvfd = open( uvpath, O_RDWR | O_CREAT, 0600 )) < 0) {
		sys_error( "Maildir error: cannot write %s", uvpath );
		cb( DRV_BOX_BAD, UIDVAL_BAD, aux );
		return;
	}
#else
	ctx->usedb = NULL;
	if ((ctx->uvfd = open( uvpath, O_RDWR, 0600 )) < 0) {
		nfsnprintf( uvpath, sizeof(uvpath), "%s/.isyncuidmap.db", ctx->path );
		if ((ctx->uvfd = open( uvpath, O_RDWR, 0600 )) < 0) {
			if (ctx->conf->alt_map) {
				if ((ctx->uvfd = open( uvpath, O_RDWR | O_CREAT, 0600 )) >= 0)
					goto dbok;
			} else {
				nfsnprintf( uvpath, sizeof(uvpath), "%s/.uidvalidity", ctx->path );
				if ((ctx->uvfd = open( uvpath, O_RDWR | O_CREAT, 0600 )) >= 0)
					goto fnok;
			}
			sys_error( "Maildir error: cannot write %s", uvpath );
			cb( DRV_BOX_BAD, UIDVAL_BAD, aux );
			return;
		} else {
		  dbok:
			ctx->usedb = nfstrdup( uvpath );
		}
	}
  fnok:
#endif /* USE_DB */
	ret = maildir_uidval_lock( ctx );

  bail:
	cb( ret, ctx->uidvalidity, aux );
}

static uint
maildir_get_uidnext( store_t *gctx )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	return ctx->nuid;
}

static xint
maildir_get_supported_flags( store_t *gctx ATTR_UNUSED )
{
	return 255;
}

static void
maildir_create_box( store_t *gctx,
                    void (*cb)( int sts, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	cb( maildir_validate( ctx->path, 1, ctx ), aux );
}

static int
maildir_confirm_box_empty( store_t *gctx )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	msg_t_array_alloc_t msglist;

	ctx->excs.size = ctx->minuid = ctx->maxuid = ctx->finduid = 0;

	if (maildir_scan( ctx, &msglist ) != DRV_OK)
		return DRV_BOX_BAD;
	maildir_free_scan( &msglist );
	return ctx->total_msgs ? DRV_BOX_BAD : DRV_OK;
}

static void
maildir_delete_box( store_t *gctx,
                    void (*cb)( int sts, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	int i, bl, ret = DRV_OK;
	struct stat st;
	char buf[_POSIX_PATH_MAX];

	bl = nfsnprintf( buf, sizeof(buf) - 4, "%s/", ctx->path );
	if (stat( buf, &st )) {
		if (errno != ENOENT) {
			sys_error( "Maildir error: cannot access mailbox '%s'", ctx->path );
			ret = DRV_BOX_BAD;
		}
	} else if (!S_ISDIR(st.st_mode)) {
		error( "Maildir error: '%s' is no valid mailbox\n", ctx->path );
		ret = DRV_BOX_BAD;
	} else if ((ret = maildir_clear_tmp( buf, sizeof(buf), bl )) == DRV_OK) {
		nfsnprintf( buf + bl, _POSIX_PATH_MAX - bl, ".uidvalidity" );
		if (unlink( buf ) && errno != ENOENT)
			goto badrm;
#ifdef USE_DB
		nfsnprintf( buf + bl, _POSIX_PATH_MAX - bl, ".isyncuidmap.db" );
		if (unlink( buf ) && errno != ENOENT)
			goto badrm;
#endif
		/* We delete cur/ last, as it is the indicator for a present mailbox.
		 * That way an interrupted operation can be resumed. */
		for (i = 3; --i >= 0; ) {
			memcpy( buf + bl, subdirs[i], 4 );
			if (rmdir( buf ) && errno != ENOENT) {
			  badrm:
				sys_error( "Maildir error: cannot remove '%s'", buf );
				ret = DRV_BOX_BAD;
				break;
			}
		}
	}
	cb( ret, aux );
}

static int
maildir_finish_delete_box( store_t *gctx )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	/* Subfolders are not deleted; the deleted folder is only "stripped of its mailboxness".
	 * Consequently, the rmdir may legitimately fail. This behavior follows the IMAP spec. */
	if (rmdir( ctx->path ) && errno != ENOENT && errno != ENOTEMPTY) {
		sys_error( "Maildir warning: cannot remove '%s'", ctx->path );
		return DRV_BOX_BAD;
	}
	return DRV_OK;
}

static uint
maildir_prepare_load_box( store_t *gctx, uint opts )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	if (opts & OPEN_SETFLAGS)
		opts |= OPEN_PAIRED;
	if (opts & OPEN_EXPUNGE)
		opts |= OPEN_PAIRED | OPEN_OLD | OPEN_NEW | OPEN_FLAGS | OPEN_UID_EXPUNGE;
	ctx->opts = opts;
	return opts;
}

static void
maildir_load_box( store_t *gctx, uint minuid, uint maxuid, uint finduid, uint pairuid, uint newuid, uint_array_t excs,
                  void (*cb)( int sts, message_t *msgs, int total_msgs, int recent_msgs, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_message_t **msgapp;
	msg_t_array_alloc_t msglist;
	uint i;

	ctx->minuid = minuid;
	ctx->maxuid = maxuid;
	ctx->finduid = finduid;
	ctx->pairuid = pairuid;
	ctx->newuid = newuid;
	ARRAY_SQUEEZE( &excs );
	ctx->excs = excs;

	assert( !ctx->msgs );
	if (maildir_scan( ctx, &msglist ) != DRV_OK) {
		cb( DRV_BOX_BAD, NULL, 0, 0, aux );
		return;
	}
	msgapp = &ctx->msgs;
	for (i = 0; i < msglist.array.size; i++)
		maildir_app_msg( ctx, &msgapp, msglist.array.data + i );
	ctx->app_msgs = msgapp;
	maildir_free_scan( &msglist );

	cb( DRV_OK, &ctx->msgs->gen, ctx->total_msgs, ctx->recent_msgs, aux );
}

static int
maildir_rescan( maildir_store_t *ctx )
{
	maildir_message_t **msgapp, *msg;
	msg_t_array_alloc_t msglist;
	uint i;

	ctx->fresh[0] = ctx->fresh[1] = 0;
	if (maildir_scan( ctx, &msglist ) != DRV_OK)
		return DRV_BOX_BAD;
	debug( "Maildir processing rescan of %s:\n", ctx->path );
	for (msgapp = &ctx->msgs, i = 0; (msg = *msgapp) || i < msglist.array.size; ) {
		if (!msg) {
			debug( "  adding new message %u\n", msglist.array.data[i].uid );
			maildir_app_msg( ctx, &msgapp, msglist.array.data + i );
			i++;
		} else if (i >= msglist.array.size) {
			debug( "  purging deleted message %u\n", msg->uid );
			msg->status = M_DEAD;
			ctx->expunge_callback( &msg->gen, ctx->callback_aux );
			msgapp = &msg->next;
		} else if (msglist.array.data[i].uid < msg->uid) {
			/* this should not happen, actually */
			debug( "  adding new message %u\n", msglist.array.data[i].uid );
			maildir_app_msg( ctx, &msgapp, msglist.array.data + i );
			i++;
		} else if (msglist.array.data[i].uid > msg->uid) {
			debug( "  purging deleted message %u\n", msg->uid );
			msg->status = M_DEAD;
			ctx->expunge_callback( &msg->gen, ctx->callback_aux );
			msgapp = &msg->next;
		} else {
			debug( "  updating message %u\n", msg->uid );
			msg->status &= ~(M_FLAGS | M_RECENT);
			free( msg->base );
			free( msg->msgid );
			maildir_init_msg( ctx, msg, msglist.array.data + i );
			i++, msgapp = &msg->next;
		}
	}
	maildir_free_scan( &msglist );
	return DRV_OK;
}

static int ATTR_PRINTFLIKE(3, 0)
maildir_again( maildir_store_t *ctx, maildir_message_t *msg, const char *err, ... )
{
	int ret;

	if (errno != ENOENT) {
		va_list va;
		va_start( va, err );
		vsys_error( err, va );
		va_end( va );
		return DRV_BOX_BAD;
	}
	if ((ret = maildir_rescan( ctx )) != DRV_OK)
		return ret;
	return (msg->status & M_DEAD) ? DRV_MSG_BAD : DRV_OK;
}

static void
maildir_fetch_msg( store_t *gctx, message_t *gmsg, msg_data_t *data, int minimal ATTR_UNUSED,
                   void (*cb)( int sts, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_message_t *msg = (maildir_message_t *)gmsg;
	int fd, ret;
	struct stat st;
	char buf[_POSIX_PATH_MAX];

	for (;;) {
		nfsnprintf( buf, sizeof(buf), "%s/%s/%s", ctx->path, subdirs[gmsg->status & M_RECENT], msg->base );
		if ((fd = open( buf, O_RDONLY )) >= 0)
			break;
		if ((ret = maildir_again( ctx, msg, "Cannot open %s", buf )) != DRV_OK) {
			cb( ret, aux );
			return;
		}
	}
	fstat( fd, &st );
	if (st.st_size > INT_MAX) {
		error( "Maildir error: %s is too big\n", buf );
		goto mbad;
	}
	data->len = st.st_size;
	if (data->date == -1)
		data->date = st.st_mtime;
	data->data = nfmalloc( data->len );
	if (read( fd, data->data, data->len ) != data->len) {
		sys_error( "Maildir error: cannot read %s", buf );
	  mbad:
		close( fd );
		cb( DRV_MSG_BAD, aux );
		return;
	}
	close( fd );
	if (!(gmsg->status & M_FLAGS))
		data->flags = maildir_parse_flags( ctx->conf->info_prefix, msg->base );
	cb( DRV_OK, aux );
}

static int
maildir_make_flags( char info_delimiter, uchar flags, char *buf )
{
	int i, d;

	buf[0] = info_delimiter;
	buf[1] = '2';
	buf[2] = ',';
	for (d = 3, i = 0; i < (int)as(MsgFlags); i++)
		if (flags & (1 << i))
			buf[d++] = MsgFlags[i];
	buf[d] = 0;
	return d;
}

static void
maildir_store_msg( store_t *gctx, msg_data_t *data, int to_trash,
                   void (*cb)( int sts, uint uid, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	const char *box;
	int ret, fd, bl;
	uint uid;
	char buf[_POSIX_PATH_MAX], nbuf[_POSIX_PATH_MAX], fbuf[as(MsgFlags) + 3], base[128];

	bl = nfsnprintf( base, sizeof(base), "%lld.%d_%d.%s", (long long)time( NULL ), Pid, ++MaildirCount, Hostname );
	if (!to_trash) {
#ifdef USE_DB
		if (ctx->usedb) {
			if ((ret = maildir_set_uid( ctx, base, &uid )) != DRV_OK) {
				free( data->data );
				cb( ret, 0, aux );
				return;
			}
		} else
#endif /* USE_DB */
		{
			if ((ret = maildir_obtain_uid( ctx, &uid )) != DRV_OK) {
				free( data->data );
				cb( ret, 0, aux );
				return;
			}
			nfsnprintf( base + bl, (int)sizeof(base) - bl, ",U=%u", uid );
		}
		box = ctx->path;
	} else {
		uid = 0;
		box = ctx->trash;
	}

	maildir_make_flags( ctx->conf->info_delimiter, data->flags, fbuf );
	nfsnprintf( buf, sizeof(buf), "%s/tmp/%s%s", box, base, fbuf );
	if ((fd = open( buf, O_WRONLY | O_CREAT | O_EXCL, 0600 )) < 0) {
		if (errno != ENOENT || !to_trash) {
			sys_error( "Maildir error: cannot create %s", buf );
			free( data->data );
			cb( DRV_BOX_BAD, 0, aux );
			return;
		}
		if ((ret = maildir_validate( box, 1, ctx )) != DRV_OK) {
			free( data->data );
			cb( ret, 0, aux );
			return;
		}
		if ((fd = open( buf, O_WRONLY | O_CREAT | O_EXCL, 0600 )) < 0) {
			sys_error( "Maildir error: cannot create %s", buf );
			free( data->data );
			cb( DRV_BOX_BAD, 0, aux );
			return;
		}
	}
	ret = write( fd, data->data, data->len );
	free( data->data );
	if (ret != (int)data->len || (UseFSync && (ret = fsync( fd )))) {
		if (ret < 0)
			sys_error( "Maildir error: cannot write %s", buf );
		else
			error( "Maildir error: cannot write %s. Disk full?\n", buf );
		close( fd );
		cb( DRV_BOX_BAD, 0, aux );
		return;
	}
	if (close( fd ) < 0) {
		/* Quota exceeded may cause this. */
		sys_error( "Maildir error: cannot write %s", buf );
		cb( DRV_BOX_BAD, 0, aux );
		return;
	}

	if (data->date) {
		/* Set atime and mtime according to INTERNALDATE or mtime of source message */
		struct utimbuf utimebuf;
		utimebuf.actime = utimebuf.modtime = data->date;
		if (utime( buf, &utimebuf ) < 0) {
			sys_error( "Maildir error: cannot set times for %s", buf );
			cb( DRV_BOX_BAD, 0, aux );
			return;
		}
	}

	/* Moving seen messages to cur/ is strictly speaking incorrect, but makes mutt happy. */
	nfsnprintf( nbuf, sizeof(nbuf), "%s/%s/%s%s", box, subdirs[!(data->flags & F_SEEN)], base, fbuf );
	if (rename( buf, nbuf )) {
		sys_error( "Maildir error: cannot rename %s to %s", buf, nbuf );
		cb( DRV_BOX_BAD, 0, aux );
		return;
	}
	if (DFlags & FAKEDUMBSTORE)
		uid = 0;
	cb( DRV_OK, uid, aux );
}

static void
maildir_find_new_msgs( store_t *gctx, uint newuid,
                       void (*cb)( int sts, message_t *msgs, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;

	assert( DFlags & FAKEDUMBSTORE );
	ctx->opts |= OPEN_FIND;
	ctx->finduid = newuid;
	int ret = maildir_rescan( ctx );
	cb( ret, &(*ctx->app_msgs)->gen, aux );
}

static void
maildir_set_msg_flags( store_t *gctx, message_t *gmsg, uint uid ATTR_UNUSED, int add, int del,
                       void (*cb)( int sts, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_store_conf_t *conf = ctx->conf;
	maildir_message_t *msg = (maildir_message_t *)gmsg;
	char *s, *p;
	uint i;
	int j, ret, ol, fl, bbl, bl, tl;
	char buf[_POSIX_PATH_MAX], nbuf[_POSIX_PATH_MAX];

	bbl = nfsnprintf( buf, sizeof(buf), "%s/", ctx->path );
	memcpy( nbuf, ctx->path, (size_t)bbl - 1 );
	memcpy( nbuf + bbl - 1, "/cur/", 5 );
	for (;;) {
		bl = bbl + nfsnprintf( buf + bbl, _POSIX_PATH_MAX - bbl, "%s/", subdirs[gmsg->status & M_RECENT] );
		ol = strlen( msg->base );
		if (_POSIX_PATH_MAX - bl < ol + 3 + (int)as(MsgFlags))
			oob();
		memcpy( buf + bl, msg->base, (size_t)ol + 1 );
		memcpy( nbuf + bl, msg->base, (size_t)ol + 1 );
		if ((s = strstr( nbuf + bl, conf->info_prefix ))) {
			s += 3;
			fl = ol - (s - (nbuf + bl));
			for (i = 0; i < as(MsgFlags); i++) {
				if ((p = strchr( s, MsgFlags[i] ))) {
					if (del & (1 << i)) {
						memmove( p, p + 1, (size_t)fl - (size_t)(p - s) );
						fl--;
					}
				} else if (add & (1 << i)) {
					for (j = 0; j < fl && MsgFlags[i] > s[j]; j++);
					fl++;
					memmove( s + j + 1, s + j, (size_t)(fl - j) );
					s[j] = MsgFlags[i];
				}
			}
			tl = ol + 3 + fl;
		} else {
			tl = ol + maildir_make_flags( conf->info_delimiter, (uchar)add, nbuf + bl + ol );
		}
		if (!rename( buf, nbuf ))
			break;
		if ((ret = maildir_again( ctx, msg, "Maildir error: cannot rename %s to %s", buf, nbuf )) != DRV_OK) {
			cb( ret, aux );
			return;
		}
	}
	free( msg->base );
	msg->base = nfstrndup( nbuf + bl, (size_t)tl );
	msg->flags |= add;
	msg->flags &= ~del;
	gmsg->status &= ~M_RECENT;

	cb( DRV_OK, aux );
}

#ifdef USE_DB
static int
maildir_purge_msg( maildir_store_t *ctx, const char *name )
{
	int ret;

	if ((ret = maildir_uidval_lock( ctx )) != DRV_OK)
		return ret;
	make_key( ctx->conf->info_stop, &key, name );
	if ((ret = ctx->db->del( ctx->db, NULL, &key, 0 ))) {
		ctx->db->err( ctx->db, ret, "Maildir error: db->del()" );
		return DRV_BOX_BAD;
	}
	return DRV_OK;
}
#endif /* USE_DB */

static void
maildir_trash_msg( store_t *gctx, message_t *gmsg,
                   void (*cb)( int sts, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_message_t *msg = (maildir_message_t *)gmsg;
	char *s;
	int ret;
	struct stat st;
	char buf[_POSIX_PATH_MAX], nbuf[_POSIX_PATH_MAX];

	for (;;) {
		nfsnprintf( buf, sizeof(buf), "%s/%s/%s", ctx->path, subdirs[gmsg->status & M_RECENT], msg->base );
		s = strstr( msg->base, ctx->conf->info_prefix );
		nfsnprintf( nbuf, sizeof(nbuf), "%s/%s/%lld.%d_%d.%s%s", ctx->trash,
		            subdirs[gmsg->status & M_RECENT], (long long)time( NULL ), Pid, ++MaildirCount, Hostname, s ? s : "" );
		if (!rename( buf, nbuf ))
			break;
		if (!stat( buf, &st )) {
			if ((ret = maildir_validate( ctx->trash, 1, ctx )) != DRV_OK) {
				cb( ret, aux );
				return;
			}
			if (!rename( buf, nbuf ))
				break;
			if (errno != ENOENT) {
				sys_error( "Maildir error: cannot move %s to %s", buf, nbuf );
				cb( DRV_BOX_BAD, aux );
				return;
			}
		}
		if ((ret = maildir_again( ctx, msg, "Maildir error: cannot move %s to %s", buf, nbuf )) != DRV_OK) {
			cb( ret, aux );
			return;
		}
	}
	gmsg->status |= M_DEAD;
	ctx->total_msgs--;
	ctx->expunge_callback( gmsg, ctx->callback_aux );

#ifdef USE_DB
	if (ctx->usedb) {
		cb( maildir_purge_msg( ctx, msg->base ), aux );
		return;
	}
#endif /* USE_DB */
	cb( DRV_OK, aux );
}

static void
maildir_close_box( store_t *gctx,
                   void (*cb)( int sts, int reported, void *aux ), void *aux )
{
	maildir_store_t *ctx = (maildir_store_t *)gctx;
	maildir_message_t *msg;
	int basel, retry, ret;
	char buf[_POSIX_PATH_MAX];

	for (;;) {
		retry = 0;
		basel = nfsnprintf( buf, sizeof(buf), "%s/", ctx->path );
		for (msg = ctx->msgs; msg; msg = msg->next) {
			if (!(msg->status & M_DEAD) && (msg->status & M_EXPUNGE)) {
				nfsnprintf( buf + basel, _POSIX_PATH_MAX - basel, "%s/%s", subdirs[msg->status & M_RECENT], msg->base );
				if (unlink( buf )) {
					if (errno == ENOENT)
						retry = 1;
					else
						sys_error( "Maildir error: cannot remove %s", buf );
				} else {
					msg->status |= M_DEAD;
					ctx->total_msgs--;
					ctx->expunge_callback( &msg->gen, ctx->callback_aux );
#ifdef USE_DB
					if (ctx->db && (ret = maildir_purge_msg( ctx, msg->base )) != DRV_OK) {
						cb( ret, 1, aux );
						return;
					}
#endif /* USE_DB */
				}
			}
		}
		if (!retry) {
			cb( DRV_OK, 1, aux );
			return;
		}
		if ((ret = maildir_rescan( ctx )) != DRV_OK) {
			cb( ret, 1, aux );
			return;
		}
	}
}

static void
maildir_cancel_cmds( store_t *gctx ATTR_UNUSED,
                     void (*cb)( void *aux ), void *aux )
{
	cb( aux );
}

static uint
maildir_get_memory_usage( store_t *gctx ATTR_UNUSED )
{
	return 0;
}

static int
maildir_get_fail_state( store_conf_t *gconf )
{
	return ((maildir_store_conf_t *)gconf)->failed;
}

static int
maildir_parse_store( conffile_t *cfg, store_conf_t **storep )
{
	maildir_store_conf_t *store;

	if (strcasecmp( "MaildirStore", cfg->cmd ))
		return 0;
	store = nfzalloc( sizeof(*store) );
	store->info_delimiter = FieldDelimiter;
	store->driver = &maildir_driver;
	store->name = nfstrdup( cfg->val );

	while (getcline( cfg ) && cfg->cmd) {
		if (!strcasecmp( "Inbox", cfg->cmd )) {
			store->inbox = expand_strdup( cfg->val, cfg );
		} else if (!strcasecmp( "Path", cfg->cmd )) {
			store->path = expand_strdup( cfg->val, cfg );
		} else if (!strcasecmp( "AltMap", cfg->cmd )) {
#ifdef USE_DB
			store->alt_map = parse_bool( cfg );
#else
			if (parse_bool( cfg )) {
				error( "Error: AltMap=true is not supported by this build.\n" );
				cfg->err = 1;
			}
#endif /* USE_DB */
		} else if (!strcasecmp( "InfoDelimiter", cfg->cmd )) {
			if (strlen( cfg->val ) != 1) {
				error( "%s:%d: Info delimiter must be exactly one character long\n", cfg->file, cfg->line );
				cfg->err = 1;
				continue;
			}
			store->info_delimiter = cfg->val[0];
			if (!ispunct( store->info_delimiter )) {
				error( "%s:%d: Info delimiter must be a punctuation character\n", cfg->file, cfg->line );
				cfg->err = 1;
				continue;
			}
		} else if (!strcasecmp( "SubFolders", cfg->cmd )) {
			if (!strcasecmp( "Verbatim", cfg->val )) {
				store->sub_style = SUB_VERBATIM;
			} else if (!strcasecmp( "Maildir++", cfg->val )) {
				store->sub_style = SUB_MAILDIRPP;
			} else if (!strcasecmp( "Legacy", cfg->val )) {
				store->sub_style = SUB_LEGACY;
			} else {
				error( "%s:%d: Unrecognized SubFolders style\n", cfg->file, cfg->line );
				cfg->err = 1;
			}
		} else {
			parse_generic_store( &store->gen, cfg, "MaildirStore" );
		}
	}
	if (!store->inbox)
		store->inbox = expand_strdup( "~/Maildir", NULL );
	if (store->path) {
		if (store->sub_style == SUB_MAILDIRPP) {
			error( "Maildir store '%s': Setting Path is incompatible with 'SubFolders Maildir++'\n", store->name );
			cfg->err = 1;
		} else {
			uint inboxLen = strlen( store->inbox );
			if (starts_with( store->path, -1, store->inbox, inboxLen ) && store->path[inboxLen] == '/') {
				error( "Maildir store '%s': Path cannot be nested under Inbox\n", store->name );
				cfg->err = 1;
			} else {
				char *s = strrchr( store->path, '/' );
				assert( s );  // due to expand_strdup()
				store->path_sfx = s + 1;
				*s = 0;
			}
		}
	}
	nfasprintf( &store->info_prefix, "%c2,", store->info_delimiter );
	nfasprintf( &store->info_stop, "%c,", store->info_delimiter );
	*storep = &store->gen;
	return 1;
}

static uint
maildir_get_caps( store_t *gctx ATTR_UNUSED )
{
	return 0; /* XXX DRV_CRLF? */
}

struct driver maildir_driver = {
	maildir_get_caps,
	maildir_parse_store,
	maildir_cleanup_drv,
	maildir_alloc_store,
	maildir_set_callbacks,
	maildir_connect_store,
	maildir_free_store,
	maildir_free_store, /* _cancel_, but it's the same */
	maildir_list_store,
	maildir_select_box,
	maildir_get_box_path,
	maildir_create_box,
	maildir_open_box,
	maildir_get_uidnext,
	maildir_get_supported_flags,
	maildir_confirm_box_empty,
	maildir_delete_box,
	maildir_finish_delete_box,
	maildir_prepare_load_box,
	maildir_load_box,
	maildir_fetch_msg,
	maildir_store_msg,
	maildir_find_new_msgs,
	maildir_set_msg_flags,
	maildir_trash_msg,
	maildir_close_box,
	maildir_cancel_cmds,
	maildir_get_memory_usage,
	maildir_get_fail_state,
};