pop3-migration-plugin.c

/* Copyright (c) 2007-2016 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "array.h"
#include "istream.h"
#include "istream-header-filter.h"
#include "sha1.h"
#include "message-size.h"
#include "message-header-parser.h"
#include "mail-namespace.h"
#include "mail-search-build.h"
#include "mail-storage-private.h"
#include "pop3-migration-plugin.h"

#define POP3_MIGRATION_CONTEXT(obj) \
	MODULE_CONTEXT(obj, pop3_migration_storage_module)
#define POP3_MIGRATION_MAIL_CONTEXT(obj) \
	MODULE_CONTEXT(obj, pop3_migration_mail_module)

struct pop3_uidl_map {
	uint32_t pop3_seq;
	uint32_t imap_uid;

	/* UIDL */
	const char *pop3_uidl;
	/* LIST size */
	uoff_t size;
	/* sha1(TOP 0) - set only when needed */
	unsigned char hdr_sha1[SHA1_RESULTLEN];
	unsigned int hdr_sha1_set:1;
};

struct imap_msg_map {
	uint32_t uid, pop3_seq;
	uoff_t psize;
	const char *pop3_uidl;

	/* sha1(header) - set only when needed */
	unsigned char hdr_sha1[SHA1_RESULTLEN];
	unsigned int hdr_sha1_set:1;
};

struct pop3_migration_mail_storage {
	union mail_storage_module_context module_ctx;

	const char *pop3_box_vname;
	ARRAY(struct pop3_uidl_map) pop3_uidl_map;

	unsigned int all_mailboxes:1;
	unsigned int pop3_all_hdr_sha1_set:1;
	unsigned int ignore_missing_uidls:1;
	unsigned int skip_size_check:1;
};

struct pop3_migration_mailbox {
	union mailbox_module_context module_ctx;

	ARRAY(struct imap_msg_map) imap_msg_map;
	unsigned int first_unfound_idx;

	unsigned int uidl_synced:1;
	unsigned int uidl_sync_failed:1;
	unsigned int uidl_ordered:1;
};

/* NOTE: these headers must be sorted */
static const char *hdr_hash_skip_headers[] = {
	"Content-Length",
	"Return-Path", /* Yahoo IMAP has Return-Path, Yahoo POP3 doesn't */
	"Status",
	"X-IMAP",
	"X-IMAPbase",
	"X-Keywords",
	"X-Message-Flag",
	"X-Status",
	"X-UID",
	"X-UIDL"
};
const char *pop3_migration_plugin_version = DOVECOT_ABI_VERSION;

static MODULE_CONTEXT_DEFINE_INIT(pop3_migration_storage_module,
				  &mail_storage_module_register);
static MODULE_CONTEXT_DEFINE_INIT(pop3_migration_mail_module,
				  &mail_module_register);

static int imap_msg_map_uid_cmp(const struct imap_msg_map *map1,
				const struct imap_msg_map *map2)
{
	if (map1->uid < map2->uid)
		return -1;
	if (map1->uid > map2->uid)
		return 1;
	return 0;
}

static int pop3_uidl_map_pop3_seq_cmp(const struct pop3_uidl_map *map1,
				      const struct pop3_uidl_map *map2)
{
	if (map1->pop3_seq < map2->pop3_seq)
		return -1;
	if (map1->pop3_seq > map2->pop3_seq)
		return 1;
	return 0;
}

static int pop3_uidl_map_hdr_cmp(const struct pop3_uidl_map *map1,
				 const struct pop3_uidl_map *map2)
{
	return memcmp(map1->hdr_sha1, map2->hdr_sha1, sizeof(map1->hdr_sha1));
}

static int imap_msg_map_hdr_cmp(const struct imap_msg_map *map1,
				const struct imap_msg_map *map2)
{
	return memcmp(map1->hdr_sha1, map2->hdr_sha1, sizeof(map1->hdr_sha1));
}

struct pop3_hdr_context {
	bool have_eoh;
	bool stop;
};

static void
pop3_header_filter_callback(struct header_filter_istream *input ATTR_UNUSED,
			    struct message_header_line *hdr,
			    bool *matched, struct pop3_hdr_context *ctx)
{
	if (hdr == NULL)
		return;
	if (hdr->eoh) {
		ctx->have_eoh = TRUE;
		if (ctx->stop) {
			/* matched is handled differently for eoh by
			 istream-header-filter. a design bug I guess.. */
			*matched = FALSE;
		}
	} else {
		if (strspn(hdr->name, "\r") == hdr->name_len) {
			/* CR+CR+LF - some servers stop the header processing
			 here while others don't. To make sure they can be
			 matched correctly we want to stop here entirely. */
			ctx->stop = TRUE;
		}
		if (ctx->stop)
			*matched = TRUE;
	}
}

int pop3_migration_get_hdr_sha1(uint32_t mail_seq, struct istream *input,
				uoff_t hdr_size,
				unsigned char sha1_r[SHA1_RESULTLEN],
				bool *have_eoh_r)
{
	struct istream *input2;
	const unsigned char *data, *p;
	size_t size, idx;
	struct sha1_ctxt sha1_ctx;
	struct pop3_hdr_context hdr_ctx;

	memset(&hdr_ctx, 0, sizeof(hdr_ctx));
	input2 = i_stream_create_limit(input, hdr_size);
	/* hide headers that might change or be different in IMAP vs. POP3 */
	input = i_stream_create_header_filter(input2,
				HEADER_FILTER_EXCLUDE | HEADER_FILTER_NO_CR,
				hdr_hash_skip_headers,
				N_ELEMENTS(hdr_hash_skip_headers),
				pop3_header_filter_callback, &hdr_ctx);
	i_stream_unref(&input2);

	sha1_init(&sha1_ctx);
	while (i_stream_read_data(input, &data, &size, 0) > 0) {
		/* if there are NULs in header, replace them with 0x80
		   character. This is done by at least Dovecot IMAP and also
		   POP3 with outlook-no-nuls workaround. */
		while ((p = memchr(data, '\0', size)) != NULL) {
			idx = p - data;
			sha1_loop(&sha1_ctx, data, idx);
			sha1_loop(&sha1_ctx, "\x80", 1);
			i_assert(size > idx);
			data += idx + 1;
			size -= idx + 1;
		}
		sha1_loop(&sha1_ctx, data, size);
		i_stream_skip(input, size);
	}
	if (input->stream_errno != 0) {
		i_error("pop3_migration: Failed to read header for msg %u: %s",
			mail_seq, i_stream_get_error(input));
		i_stream_unref(&input);
		return -1;
	}
	sha1_result(&sha1_ctx, sha1_r);
	i_stream_unref(&input);

	*have_eoh_r = hdr_ctx.have_eoh;
	return 0;
}

static int
get_hdr_sha1(struct mail *mail, unsigned char sha1_r[SHA1_RESULTLEN])
{
	struct istream *input;
	struct message_size hdr_size;
	bool have_eoh;

	if (mail_get_hdr_stream(mail, &hdr_size, &input) < 0) {
		i_error("pop3_migration: Failed to get header for msg %u: %s",
			mail->seq, mailbox_get_last_error(mail->box, NULL));
		return -1;
	}
	if (pop3_migration_get_hdr_sha1(mail->seq, input,
					hdr_size.physical_size,
					sha1_r, &have_eoh) < 0)
		return -1;
	if (have_eoh)
		return 0;

	/* The empty "end of headers" line is missing. Either this means that
	   the headers ended unexpectedly (which is ok) or that the remote
	   server is buggy. Some servers have problems with

	   1) header line continuations that contain only whitespace and
	   2) headers that have no ":". The header gets truncated when such
	   line is reached.

	   At least Oracle IMS IMAP FETCH BODY[HEADER] handles 1) by not
	   returning the whitespace line and 2) by returning the line but
	   truncating the rest. POP3 TOP instead returns the entire header.
	   This causes the IMAP and POP3 hashes not to match.

	   If there's LF+CR+CR+LF in the middle of headers, Courier IMAP's
	   FETCH BODY[HEADER] stops after that, but Courier POP3's TOP doesn't.

	   So we'll try to avoid this by falling back to full FETCH BODY[]
	   (and/or RETR) and we'll parse the header ourself from it. This
	   should work around any similar bugs in all IMAP/POP3 servers. */
	if (mail_get_stream(mail, &hdr_size, NULL, &input) < 0) {
		i_error("pop3_migration: Failed to get body for msg %u: %s",
			mail->seq, mailbox_get_last_error(mail->box, NULL));
		return -1;
	}
	return pop3_migration_get_hdr_sha1(mail->seq, input,
					   hdr_size.physical_size,
					   sha1_r, &have_eoh);

}

static struct mailbox *pop3_mailbox_alloc(struct mail_storage *storage)
{
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(storage);
	struct mail_namespace *ns;

	ns = mail_namespace_find(storage->user->namespaces,
				 mstorage->pop3_box_vname);
	i_assert(ns != NULL);
	return mailbox_alloc(ns->list, mstorage->pop3_box_vname,
			     MAILBOX_FLAG_READONLY | MAILBOX_FLAG_POP3_SESSION);
}

static int pop3_map_read(struct mail_storage *storage, struct mailbox *pop3_box)
{
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(storage);
	struct mailbox_transaction_context *t;
	struct mail_search_args *search_args;
	struct mail_search_context *ctx;
	struct mail *mail;
	struct pop3_uidl_map *map;
	const char *uidl;
	uoff_t size = (uoff_t)-1;
	int ret = 0;

	if (array_is_created(&mstorage->pop3_uidl_map)) {
		/* already read these, just reset the imap_uids */
		array_foreach_modifiable(&mstorage->pop3_uidl_map, map)
			map->imap_uid = 0;
		return 0;
	}
	i_array_init(&mstorage->pop3_uidl_map, 128);

	if (mailbox_sync(pop3_box, 0) < 0) {
		i_error("pop3_migration: Couldn't sync mailbox %s: %s",
			pop3_box->vname, mailbox_get_last_error(pop3_box, NULL));
		return -1;
	}

	t = mailbox_transaction_begin(pop3_box, 0);
	search_args = mail_search_build_init();
	mail_search_build_add_all(search_args);
	ctx = mailbox_search_init(t, search_args, NULL,
				  mstorage->skip_size_check ? 0 :
				  MAIL_FETCH_PHYSICAL_SIZE, NULL);
	mail_search_args_unref(&search_args);

	while (mailbox_search_next(ctx, &mail)) {
		/* get the size with LIST instead of RETR */
		mail->lookup_abort = MAIL_LOOKUP_ABORT_READ_MAIL;

		if (mstorage->skip_size_check)
			;
		else if (mail_get_physical_size(mail, &size) < 0) {
			i_error("pop3_migration: Failed to get size for msg %u: %s",
				mail->seq,
				mailbox_get_last_error(pop3_box, NULL));
			ret = -1;
			break;
		}
		if (mail_get_special(mail, MAIL_FETCH_UIDL_BACKEND, &uidl) < 0) {
			i_error("pop3_migration: Failed to get UIDL for msg %u: %s",
				mail->seq,
				mailbox_get_last_error(pop3_box, NULL));
			ret = -1;
			break;
		}
		if (*uidl == '\0') {
			i_warning("pop3_migration: UIDL for msg %u is empty",
				  mail->seq);
			continue;
		}

		map = array_append_space(&mstorage->pop3_uidl_map);
		map->pop3_seq = mail->seq;
		map->pop3_uidl = p_strdup(storage->pool, uidl);
		map->size = size;
	}

	if (mailbox_search_deinit(&ctx) < 0) {
		i_error("pop3_migration: Failed to search all POP3 mails: %s",
			mailbox_get_last_error(pop3_box, NULL));
		ret = -1;
	}
	(void)mailbox_transaction_commit(&t);
	return ret;
}

static int
pop3_map_read_hdr_hashes(struct mail_storage *storage, struct mailbox *pop3_box,
			 unsigned first_seq)
{
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(storage);
        struct mailbox_transaction_context *t;
	struct mail_search_args *search_args;
	struct mail_search_context *ctx;
	struct mail *mail;
	struct pop3_uidl_map *map;
	int ret = 0;

	if (mstorage->pop3_all_hdr_sha1_set)
		return 0;
	if (mstorage->all_mailboxes) {
		/* we may be matching against multiple mailboxes.
		   read all the hashes only once. */
		first_seq = 1;
	}

	t = mailbox_transaction_begin(pop3_box, 0);
	search_args = mail_search_build_init();
	mail_search_build_add_seqset(search_args, first_seq,
				     array_count(&mstorage->pop3_uidl_map)+1);
	ctx = mailbox_search_init(t, search_args, NULL,
				  MAIL_FETCH_STREAM_HEADER, NULL);
	mail_search_args_unref(&search_args);

	while (mailbox_search_next(ctx, &mail)) {
		map = array_idx_modifiable(&mstorage->pop3_uidl_map,
					   mail->seq-1);

		if (get_hdr_sha1(mail, map->hdr_sha1) < 0)
			ret = -1;
		else
			map->hdr_sha1_set = TRUE;
	}

	if (mailbox_search_deinit(&ctx) < 0) {
		i_error("pop3_migration: Failed to search all POP3 mail hashes: %s",
			mailbox_get_last_error(pop3_box, NULL));
		ret = -1;
	}
	(void)mailbox_transaction_commit(&t);
	if (ret == 0 && first_seq == 1)
		mstorage->pop3_all_hdr_sha1_set = TRUE;
	return ret;
}

static int imap_map_read(struct mailbox *box)
{
	struct pop3_migration_mailbox *mbox = POP3_MIGRATION_CONTEXT(box);
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(box->storage);
	struct mailbox_status status;
        struct mailbox_transaction_context *t;
	struct mail_search_args *search_args;
	struct mail_search_context *ctx;
	struct mail *mail;
	struct imap_msg_map *map;
	uoff_t psize = (uoff_t)-1;
	int ret = 0;

	mailbox_get_open_status(box, STATUS_MESSAGES, &status);

	i_assert(!array_is_created(&mbox->imap_msg_map));
	p_array_init(&mbox->imap_msg_map, box->pool, status.messages);

	t = mailbox_transaction_begin(box, 0);
	search_args = mail_search_build_init();
	mail_search_build_add_all(search_args);
	ctx = mailbox_search_init(t, search_args, NULL,
				  mstorage->skip_size_check ? 0 :
				  MAIL_FETCH_PHYSICAL_SIZE, NULL);
	mail_search_args_unref(&search_args);

	while (mailbox_search_next(ctx, &mail)) {
		if (mstorage->skip_size_check)
			;
		else if (mail_get_physical_size(mail, &psize) < 0) {
			i_error("pop3_migration: Failed to get psize for imap uid %u: %s",
				mail->uid,
				mailbox_get_last_error(box, NULL));
			ret = -1;
			break;
		}

		map = array_append_space(&mbox->imap_msg_map);
		map->uid = mail->uid;
		map->psize = psize;
	}

	if (mailbox_search_deinit(&ctx) < 0) {
		i_error("pop3_migration: Failed to search all IMAP mails: %s",
			mailbox_get_last_error(box, NULL));
		ret = -1;
	}
	(void)mailbox_transaction_commit(&t);
	return ret;
}

static int imap_map_read_hdr_hashes(struct mailbox *box)
{
	struct pop3_migration_mailbox *mbox = POP3_MIGRATION_CONTEXT(box);
        struct mailbox_transaction_context *t;
	struct mail_search_args *search_args;
	struct mail_search_context *ctx;
	struct mail *mail;
	struct imap_msg_map *map;
	int ret = 0;

	t = mailbox_transaction_begin(box, 0);
	search_args = mail_search_build_init();
	mail_search_build_add_seqset(search_args, mbox->first_unfound_idx+1,
				     array_count(&mbox->imap_msg_map)+1);
	ctx = mailbox_search_init(t, search_args, NULL,
				  MAIL_FETCH_STREAM_HEADER, NULL);
	mail_search_args_unref(&search_args);

	while (mailbox_search_next(ctx, &mail)) {
		map = array_idx_modifiable(&mbox->imap_msg_map, mail->seq-1);

		if (get_hdr_sha1(mail, map->hdr_sha1) < 0)
			ret = -1;
		else
			map->hdr_sha1_set = TRUE;
	}

	if (mailbox_search_deinit(&ctx) < 0) {
		i_error("pop3_migration: Failed to search all IMAP mail hashes: %s",
			mailbox_get_last_error(box, NULL));
		ret = -1;
	}
	(void)mailbox_transaction_commit(&t);
	return ret;
}

static bool pop3_uidl_assign_by_size(struct mailbox *box)
{
	struct pop3_migration_mailbox *mbox = POP3_MIGRATION_CONTEXT(box);
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(box->storage);
	struct pop3_uidl_map *pop3_map;
	struct imap_msg_map *imap_map;
	unsigned int i, pop3_count, imap_count, count;

	pop3_map = array_get_modifiable(&mstorage->pop3_uidl_map, &pop3_count);
	imap_map = array_get_modifiable(&mbox->imap_msg_map, &imap_count);
	count = I_MIN(pop3_count, imap_count);

	/* see if we can match the messages using sizes */
	for (i = 0; i < count; i++) {
		if (pop3_map[i].size != imap_map[i].psize)
			break;
		if (i+1 < count && pop3_map[i].size == pop3_map[i+1].size) {
			/* two messages with same size, don't trust them */
			break;
		}

		pop3_map[i].imap_uid = imap_map[i].uid;
		imap_map[i].pop3_uidl = pop3_map[i].pop3_uidl;
		imap_map[i].pop3_seq = pop3_map[i].pop3_seq;
	}
	mbox->first_unfound_idx = i;
	if (box->storage->user->mail_debug)
		i_debug("pop3_migration: %u/%u mails matched by size", i, count);
	return i == count;
}

static int
pop3_uidl_assign_by_hdr_hash(struct mailbox *box, struct mailbox *pop3_box)
{
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(box->storage);
	struct pop3_migration_mailbox *mbox = POP3_MIGRATION_CONTEXT(box);
	struct pop3_uidl_map *pop3_map;
	struct imap_msg_map *imap_map;
	unsigned int pop3_idx, imap_idx, pop3_count, imap_count;
	unsigned int first_seq, missing_uids_count;
	uint32_t first_missing_idx = (uint32_t)-1;
	int ret;

	first_seq = mbox->first_unfound_idx+1;
	if (pop3_map_read_hdr_hashes(box->storage, pop3_box, first_seq) < 0 ||
	    imap_map_read_hdr_hashes(box) < 0)
		return -1;

	array_sort(&mstorage->pop3_uidl_map, pop3_uidl_map_hdr_cmp);
	array_sort(&mbox->imap_msg_map, imap_msg_map_hdr_cmp);

	pop3_map = array_get_modifiable(&mstorage->pop3_uidl_map, &pop3_count);
	imap_map = array_get_modifiable(&mbox->imap_msg_map, &imap_count);

	pop3_idx = imap_idx = 0;
	while (pop3_idx < pop3_count && imap_idx < imap_count) {
		if (!pop3_map[pop3_idx].hdr_sha1_set ||
		    pop3_map[pop3_idx].imap_uid != 0) {
			pop3_idx++;
			continue;
		}
		if (!imap_map[imap_idx].hdr_sha1_set ||
		    imap_map[imap_idx].pop3_uidl != NULL) {
			imap_idx++;
			continue;
		}
		ret = memcmp(pop3_map[pop3_idx].hdr_sha1,
			     imap_map[imap_idx].hdr_sha1,
			     sizeof(pop3_map[pop3_idx].hdr_sha1));
		if (ret < 0)
			pop3_idx++;
		else if (ret > 0)
			imap_idx++;
		else {
			pop3_map[pop3_idx].imap_uid = imap_map[imap_idx].uid;
			imap_map[imap_idx].pop3_uidl =
				pop3_map[pop3_idx].pop3_uidl;
			imap_map[imap_idx].pop3_seq =
				pop3_map[pop3_idx].pop3_seq;
		}
	}
	missing_uids_count = 0;
	for (pop3_idx = 0; pop3_idx < pop3_count; pop3_idx++) {
		if (pop3_map[pop3_idx].imap_uid == 0) {
			if (first_missing_idx == (uint32_t)-1)
				first_missing_idx = pop3_map[pop3_idx].pop3_seq;
			missing_uids_count++;
		}
	}
	if (missing_uids_count > 0 && !mstorage->all_mailboxes) {
		if (!mstorage->ignore_missing_uidls) {
			i_error("pop3_migration: %u POP3 messages have no "
				"matching IMAP messages (set "
				"pop3_migration_ignore_missing_uidls=yes "
				"to continue anyway)", missing_uids_count);
			return -1;
		}
		i_warning("pop3_migration: %u POP3 messages have no "
			  "matching IMAP messages (first POP3 msg %u UIDL %s)",
			  missing_uids_count,
			  pop3_map[first_missing_idx].pop3_seq,
			  pop3_map[first_missing_idx].pop3_uidl);
	} else if (box->storage->user->mail_debug) {
		i_debug("pop3_migration: %u mails matched by headers", pop3_count);
	}
	array_sort(&mstorage->pop3_uidl_map, pop3_uidl_map_pop3_seq_cmp);
	array_sort(&mbox->imap_msg_map, imap_msg_map_uid_cmp);
	return 0;
}

static int pop3_migration_uidl_sync(struct mailbox *box)
{
	struct pop3_migration_mailbox *mbox = POP3_MIGRATION_CONTEXT(box);
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(box->storage);
	struct mailbox *pop3_box;
	const struct pop3_uidl_map *pop3_map;
	unsigned int i, count;
	uint32_t prev_uid;

	if (mbox->uidl_synced)
		return 0;

	pop3_box = pop3_mailbox_alloc(box->storage);
	/* the POP3 server isn't connected to yet. handle all IMAP traffic
	   first before connecting, so POP3 server won't disconnect us due to
	   idling. */
	if (imap_map_read(box) < 0 ||
	    pop3_map_read(box->storage, pop3_box) < 0) {
		mailbox_free(&pop3_box);
		return -1;
	}

	if (!pop3_uidl_assign_by_size(box)) {
		/* everything wasn't assigned, figure out the rest with
		   header hashes */
		if (pop3_uidl_assign_by_hdr_hash(box, pop3_box) < 0) {
			mailbox_free(&pop3_box);
			return -1;
		}
	}

	/* see if the POP3 UIDL order is the same as IMAP UID order */
	mbox->uidl_ordered = TRUE;
	pop3_map = array_get(&mstorage->pop3_uidl_map, &count);
	prev_uid = 0;
	for (i = 0; i < count; i++) {
		if (pop3_map[i].imap_uid == 0)
			continue;

		if (prev_uid > pop3_map[i].imap_uid) {
			mbox->uidl_ordered = FALSE;
			break;
		}
		prev_uid = pop3_map[i].imap_uid;
	}

	mbox->uidl_synced = TRUE;
	mailbox_free(&pop3_box);
	return 0;
}

static int
pop3_migration_get_special(struct mail *_mail, enum mail_fetch_field field,
			   const char **value_r)
{
	struct mail_private *mail = (struct mail_private *)_mail;
	union mail_module_context *mmail = POP3_MIGRATION_MAIL_CONTEXT(mail);
	struct pop3_migration_mailbox *mbox = POP3_MIGRATION_CONTEXT(_mail->box);
	struct imap_msg_map map_key, *map;

	if (field == MAIL_FETCH_UIDL_BACKEND ||
	    field == MAIL_FETCH_POP3_ORDER) {
		if (mbox->uidl_sync_failed ||
		    pop3_migration_uidl_sync(_mail->box) < 0) {
			mbox->uidl_sync_failed = TRUE;
			mail_storage_set_error(_mail->box->storage,
					       MAIL_ERROR_TEMP,
					       "POP3 UIDLs couldn't be synced");
			return -1;
		}

		memset(&map_key, 0, sizeof(map_key));
		map_key.uid = _mail->uid;
		map = array_bsearch(&mbox->imap_msg_map, &map_key,
				    imap_msg_map_uid_cmp);
		if (map != NULL && map->pop3_uidl != NULL) {
			if (field == MAIL_FETCH_UIDL_BACKEND)
				*value_r = map->pop3_uidl;
			else
				*value_r = t_strdup_printf("%u", map->pop3_seq);
			return 0;
		}
		/* not found from POP3 server, fallback to default */
	}
	return mmail->super.get_special(_mail, field, value_r);
}

static void pop3_migration_mail_allocated(struct mail *_mail)
{
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(_mail->box->storage);
	struct mail_private *mail = (struct mail_private *)_mail;
	struct mail_vfuncs *v = mail->vlast;
	union mail_module_context *mmail;
	struct mail_namespace *ns;

	if (mstorage == NULL ||
	    (!mstorage->all_mailboxes && !_mail->box->inbox_user)) {
		/* assigns UIDLs only for INBOX */
		return;
	}

	ns = mail_namespace_find(_mail->box->storage->user->namespaces,
				 mstorage->pop3_box_vname);
	if (ns == mailbox_get_namespace(_mail->box)) {
		/* we're accessing the pop3-migration namespace itself */
		return;
	}

	mmail = p_new(mail->pool, union mail_module_context, 1);
	mmail->super = *v;
	mail->vlast = &mmail->super;

	v->get_special = pop3_migration_get_special;
	MODULE_CONTEXT_SET_SELF(mail, pop3_migration_mail_module, mmail);
}

static void pop3_migration_mailbox_allocated(struct mailbox *box)
{
	struct mailbox_vfuncs *v = box->vlast;
	struct pop3_migration_mailbox *mbox;

	mbox = p_new(box->pool, struct pop3_migration_mailbox, 1);
	mbox->module_ctx.super = *v;
	box->vlast = &mbox->module_ctx.super;

	MODULE_CONTEXT_SET(box, pop3_migration_storage_module, mbox);
}

static void pop3_migration_mail_storage_destroy(struct mail_storage *storage)
{
	struct pop3_migration_mail_storage *mstorage =
		POP3_MIGRATION_CONTEXT(storage);

	if (array_is_created(&mstorage->pop3_uidl_map))
		array_free(&mstorage->pop3_uidl_map);

	mstorage->module_ctx.super.destroy(storage);
}

static void pop3_migration_mail_storage_created(struct mail_storage *storage)
{
	struct pop3_migration_mail_storage *mstorage;
	struct mail_storage_vfuncs *v = storage->vlast;
	const char *pop3_box_vname;

	pop3_box_vname = mail_user_plugin_getenv(storage->user,
						 "pop3_migration_mailbox");
	if (pop3_box_vname == NULL) {
		if (storage->user->mail_debug)
			i_debug("pop3_migration: No pop3_migration_mailbox setting - disabled");
		return;
	}

	mstorage = p_new(storage->pool, struct pop3_migration_mail_storage, 1);
	mstorage->module_ctx.super = *v;
	storage->vlast = &mstorage->module_ctx.super;
	v->destroy = pop3_migration_mail_storage_destroy;

	mstorage->pop3_box_vname = p_strdup(storage->pool, pop3_box_vname);
	mstorage->all_mailboxes =
		mail_user_plugin_getenv(storage->user,
					"pop3_migration_all_mailboxes") != NULL;
	mstorage->ignore_missing_uidls =
		mail_user_plugin_getenv(storage->user,
			"pop3_migration_ignore_missing_uidls") != NULL;
	mstorage->skip_size_check =
		mail_user_plugin_getenv(storage->user,
			"pop3_migration_skip_size_check") != NULL;

	MODULE_CONTEXT_SET(storage, pop3_migration_storage_module, mstorage);
}

static struct mail_storage_hooks pop3_migration_mail_storage_hooks = {
	.mail_allocated = pop3_migration_mail_allocated,
	.mailbox_allocated = pop3_migration_mailbox_allocated,
	.mail_storage_created = pop3_migration_mail_storage_created
};

void pop3_migration_plugin_init(struct module *module)
{
	mail_storage_hooks_add(module, &pop3_migration_mail_storage_hooks);
}

void pop3_migration_plugin_deinit(void)
{
	mail_storage_hooks_remove(&pop3_migration_mail_storage_hooks);
}